Pontiac Street Performance
Home | Profile | Register | Active Topics | Members | Search | FAQ
Username:
Password:
Save Password

 All Forums
 Pontiac Performance
 Restoration & Performance Forum
 Cam experience
 New Topic  Reply to Topic
 Printer Friendly
Previous Page
Author Previous Topic Topic Next Topic
Page: of 2

cortcomp
Coyote

USA
5335 Posts

Posted - 25 Feb 2015 :  11:21:20 AM  Show Profile  Visit cortcomp's Homepage  Reply with Quote
I am pretty disappointing that Carter Cryogenics had this statement right on the front page:

"However, we will only freeze inanimate objects... Nothing that is alive or was once alive!"

Well Ted and Walt, Fry, and Han looks like i won't be seeing the year 3000 with you guys.
Go to Top of Page

Cliff R
Cochise

USA
535 Posts

Posted - 25 Feb 2015 :  1:58:47 PM  Show Profile  Visit Cliff R's Homepage  Reply with Quote
"Steve, the Voodoo lobes have the same closing velocity as stock GM. They are quiet. Harold split the duration on them as 57.5% on the opening side, and 42.5% on the closing side. Or there about. They open fast, and close slow."

Good info Steve. The importance of this is two fold, less noise, and the valve springs don't get "stupid" at high rpm's. We've seen a number of Comp XE engines on the dyno that very ABRUPTLY stopped making power, and one of them was just two days ago by a shop that builds a LOT of Stock and Super Stock Race engines. They had ZERO experience with Pontiac engines, and XE cams, but engine power went completely "flat" at 4800rpm's on the 455 they were dynoing. They had 02 sensors in it, and it was not fuel delivery related. I've had several other engine builders see the same thing with those cams. Jim Weise over on the Buick Board calls it "lifter crash". Basically the harmonics produced by the ultra quick seating velocities causes the springs to lose their ability to control valve motion.

Harold was a lot smarter than most when it comes to this topic, and that's why he kept with lobe profiles at or close to stock for closing velocity.....FWIW.....Cliff

If you can read this, thank a teacher. If you can read this in English, thank a Veteran.
Go to Top of Page

Steve C.
Crazy Horse

1672 Posts

Posted - 25 Feb 2015 :  5:31:02 PM  Show Profile  Reply with Quote
From Crane....

Always run enough seat pressure to control the valve action as it returns to the seat. Heavier valves require more seat pressure. Strong, lightweight valves require less seat pressure. When in doubt, run slightly more seat pressure . . . not less.

Did you hear the one about Comp Cams 995 valve springs that typically.... Oh never mind :)

Don't get me started on another rant about inadequate spring pressure :)

Go to Top of Page

Cliff R
Cochise

USA
535 Posts

Posted - 26 Feb 2015 :  07:20:28 AM  Show Profile  Visit Cliff R's Homepage  Reply with Quote
Steve, this particular problem goes beyond just seat pressure, and as the weight of the parts involved are a BIG player in this deal.

We ran into one customer who made GREAT power with an XE274 cam in a 455 build with 240cfm iron heads and 10 to 1 compression a few years back.

He did several things that ended up working very well for that engine.

He had the heads HEAVILY ported in the bowls and opened up the seats to 45 degrees, not 30.

He used really light weight parts, retainers, and rockers arms.

He put a LOT of spring on it, up near 400lbs on the seat open pressure, nearly as I can remember.

He was nicely rewarded with just over 1hp/cid and peak power up near 5500rpms, just like we see with larger cams on wide LSA's doing the same thing with 30 degrees seats and less spring pressure, and not quite as much port flow, etc.

The vast majority of the XE cammed 455's I've seen on the dyno have some sort of high rpm valve train instability issues, and power ENDS abruptly up near 4800-5200rpms. I've witnessed this in person, so not regurgitating old information here.

I've seen quite a few dyno sheets showing the same thing, and scores of complaints to our shop from folks using those cams in Pontiac builds.

So I have become the official "Comp Cams XE cam basher", because I simply tell the truth, and don't put my head in the sand and hide from this sort of thing.....FWIW....Cliff

If you can read this, thank a teacher. If you can read this in English, thank a Veteran.
Go to Top of Page

Steve C.
Crazy Horse

1672 Posts

Posted - 26 Feb 2015 :  08:35:33 AM  Show Profile  Reply with Quote
Stated- "In conclusion, I feel the XE cams regardless of rocker arm require a stronger valve spring than expected to control the lifter. Unfortunately the sharp drop off many people report with the XE cams could be directly related to either a geometry issue or the need for more rate in the valve spring."


I've been touting this situation for quite some time, often to deaf ears. And it also can apply to other lobes as well, not specific to XE grinds and other similar valve springs. All too often the Comp Tech people, and depending on which work cubicle the call gets routed to, just regurgitate their standard recommendation and its taken as gospel. And then you hear the crap.... BUT we shouldn't HAVE TO run big spring pressure on our cams !

Within a tech article about cam comparisons on a SBC the cam they choose for the base cam was the infamous Comp 284XE hyd flat tappet cam that won't rev up in a "Pontiac".
But in the specific application the cam went to 6200 peak rpm with no issues. That said, it is important to note the valvetrain components they used.

Used were Comp Pro Magnum roller rocker arms, valvesprings with 153 lb seat pressure and with titanium retainers on the springs. Note the lighter retainers make a big difference in how well the spring controls the valve by reducing the weight of the spring/retainer package. Again, Please keep in mind this was all revolving around a small block Chevy valvetrain weight, even though the particular heads in use on this specific combination had longer, thus heavier valves, it's valvetrain weight might have been lighter than a typical Pontiac but not by much if at all. But I personally do not know that for a fact. And the valvetrain weight is a big factor. Remember today within our hobby more Pontiac engines are using aftermarket cylinder heads with longer and bigger diameter valves.... more mass (weight).

This makes me question why Comp Cams will almost always suggest the 995 spring to control a Pontiac valvetrain weight with that cam ! And they do it as a commonplace. It makes me also want to ask what springs were in use with the these lifter crashing cammed Pontiac motors that don't rev up

Edited by - Steve C. on 26 Feb 2015 08:52:32 AM
Go to Top of Page

Steve C.
Crazy Horse

1672 Posts

Posted - 26 Feb 2015 :  09:26:29 AM  Show Profile  Reply with Quote
Spring Surge - Catastrophe or Not?

If you search the internet for "valve spring surge", you will find several sites with the same explanation, i.e. same exact words and in some cases the same misspelled words. Some of these sites belong to major performance camshaft companies. Here is the popular explanation of spring surge:

"The factor which causes unpredictable valve spring behavior at high reciprocating frequencies. It's caused by the inertia effect of the individual coils of the valve spring. At certain critical engine speeds, the vibrations caused by the cam movement excite the natural frequency characteristics of the valve spring and this surge effect substantially reduces the available static spring load. In other words, these inertia forces oppose the valve spring tension at critical speeds."

This explanation is grossly misleading. First of all, there is nothing unpredictable or mysterious about the spring's behavior. Secondly, the spring is always vibrating at its natural frequency, not just at critical engine speeds. The spring force oscillates about the static force, sometimes greater and sometimes less. The force does not always oppose the valve spring tension. In the 1930's spring surge was thought to be the dominate cause of cam and lifter separation, i.e. valve toss or valve float. Since the early 1950's it has been known that the other components of the valve train are more important, i.e. pushrods stiffness, etc. Study our page on Valve Train Dynamics for a better understanding of this subject.

Here are some cool videos of vibrating valve springs. The spring with few coils has a much higher natural frequency than the one with many coils. For many years it has been known that only high natural frequency springs (low mass) should be used for automotive valve trains (see Turkish (1946)).

http://www.tildentechnologies.com/Cams/Take-Surge.html


Edited by - Steve C. on 26 Feb 2015 09:28:26 AM
Go to Top of Page

Steve C.
Crazy Horse

1672 Posts

Posted - 26 Feb 2015 :  10:11:58 AM  Show Profile  Reply with Quote
Pushrod stiffness
For many years, engine designers were, in large proportion, blissfully ignorant of the behaviour of the valvetrain, partly because there was no method by which dynamic valve displacement could be measured, and no easy way to calculate the behaviour of the system. With the advent of both specialised software and test machinery, however, the very thin and flexible pushrods of years past have been supplanted largely by much more substantial items with greater stiffness. In terms of being in proper control of valve motion, these are undoubtedly the correct way to go, but moving in this direction can appear to lose performance initially.
https://www.highpowermedia.com/blog/3184/pushrod-stiffness
Info from Manton:
http://mantonpushrods.com/tech-info/facts/
Go to Top of Page

cortcomp
Coyote

USA
5335 Posts

Posted - 26 Feb 2015 :  12:14:07 PM  Show Profile  Visit cortcomp's Homepage  Reply with Quote
"Used were Comp Pro Magnum roller rocker arms, valvesprings with 153 lb seat pressure "

I had the issue cliff eludes to (cutting out at 5200 rpms) but found i had the wrong springs, and i didn't check them prior to install. They ended up being 95 lbs closed. I replaced with crane (i think) springs that ended up being around 125 open and that motor had no problems reving to 6k, quickly in second. It loved it. however, never made it back to the dyno to see if that and higher ratio rocker arms moved the power any, mode more, etc. I thought being 125 was kind of a bit much, but almost 155 lbs? I wonder if that would make the clacking noise more distinct in that cam.

I know the cams aren't exactly the same engine family to engine family, but is anyone running anywhere near that? That seems like a lot compared to even comps recommendations (of course we know what that's worth.)

Edited by - cortcomp on 26 Feb 2015 2:14:55 PM
Go to Top of Page

Phil
The Great White Buffalo

USA
7214 Posts

Posted - 26 Feb 2015 :  2:04:00 PM  Show Profile  Reply with Quote
I always thought the standard Comp 995 spring recommendation was suspect as well. Yes, it was THAT obvious.

Bowties are for Pee-wee Herman. "Chevy": even the name sounds cheap, but not as cheap as your Pontiac will be with an LS transplant.
Go to Top of Page

Steve C.
Crazy Horse

1672 Posts

Posted - 26 Feb 2015 :  5:08:24 PM  Show Profile  Reply with Quote
A friend had 995 springs at a normal installed height, after use they dropped to a similar 95 lbs seat pressure. Pontaic 445 based combo was nosing over at about 4800 rpm, with the XE hyd flat tappet lobe in use it should of normally peaked well above 5500+ rpm with adequate spring pressure.

A fwiw, a race type short travel hyd lifter would be a better choice for higher rpm applications assuming a little more valve train noise is not a problem. They can be noisy.

Edited by - Steve C. on 26 Feb 2015 5:46:14 PM
Go to Top of Page

Steve C.
Crazy Horse

1672 Posts

Posted - 26 Feb 2015 :  5:21:43 PM  Show Profile  Reply with Quote
Just keep in mind that 153 lbs seat pressure was a specific small block chevy application at 6200 rpm. And again note comments about valve train mass (weight). I'm speaking of the valve side of the rocker arm.
And not a recommendation.

Ken Keefer (Pontiac Dude on PY) had no issues with the 995 spring at about 125 lbs (to 130 ) on most hyd flat tappet cams. And the comments made were not always involving higher RPMs. And the discussion was often including XE lobes.

One important thing to note, as with almost all valve springs they will lose pressure after run in. Could be 10 pounds seat pressure!

And always measure new springs at the intended installed height before installation. Don't assume that "115 lbs".

And keep in mind the discussion can often turn to a higher rpm limited street application with that 125+ lbs seat pressure. Not a '041' type cam and lower rpm with a 100,000 mile expected street engine :)

Edited by - Steve C. on 26 Feb 2015 5:47:43 PM
Go to Top of Page

Steve C.
Crazy Horse

1672 Posts

Posted - 26 Feb 2015 :  6:09:43 PM  Show Profile  Reply with Quote
I don't vote for a Comp 995 spring on Lunati 'Voodoo' lobe profile at 115 lbs :)
Go to Top of Page

Cliff R
Cochise

USA
535 Posts

Posted - 26 Feb 2015 :  6:22:15 PM  Show Profile  Visit Cliff R's Homepage  Reply with Quote
A lot of good info above, and I'll add this. WAY back when the XE cams first cam out, Jim Weise, owner of the Buick board and engine builder tried them, to see if there was anything to the "new" technology over the "old" lazy T/A cams he'd been using.

They XE cams experienced what he described as "lifter crash", power ending ABRUPTLY just past 5000rpm's, and the valve train instability was so severe it actually broke some rocker arms! We swapped out the XE cam for a T/A grind, same engine, no other changes, and it pulled right up to 5800rpm's and made great power.

Here's my take on the deal. Why piss around with cams than use such high opening/closing velocities that they require special attention, spring pressure, lighter parts, or are just prone to issues in the first place?

You are NOT going to make more power than a similar cam that doesn't have any issues at all with "normal" spring rates, been there and done that. So bottom line here, we avoid those parts, and stick to longer duration cams with gentle ramps, even with our custom ground roller cams. There is no want, or need for super quick lobe profiles with these engines, as we can use much slower stuff, and make plenty of power, and long term durability with ZERO issues anyplace when it comes to any of the parts involved, etc.

I would also add that we can NOT compare a Pontiac build to an SBC in this area, as EVERYTHING involved with the SBC is shorter, and significantly lighter, BEFORE we source out even lighter parts for them.

We have also switched to .118-.120" wall custom made pushrods here for ALL of our engines (made that move back in 2006), after noticing "witness" marks on pushrods in several of our engines. The .080" wall pushrods are moving around a LOT in these engines, especially when we increase spring pressure and move peak power up in the RPM range. It's also extremely rare to be able to use a stock length pushrod anyhow, as NOTHING for a Pontiac these days comes out right for valve train geometry when you mock one up. Even different brands of rocker arms on the same build with no other changes anyplace will require different length pushrods for perfect geometry.....FWIW.....Cliff

If you can read this, thank a teacher. If you can read this in English, thank a Veteran.

Edited by - Cliff R on 26 Feb 2015 6:23:02 PM
Go to Top of Page

Bob Kaplan
Cochise

USA
417 Posts

Posted - 26 Feb 2015 :  6:49:37 PM  Show Profile  Reply with Quote
What valve springs do you like for a street engine?

The surgeon general said nothing about smokin a chevy...
Go to Top of Page

Steve C.
Crazy Horse

1672 Posts

Posted - 26 Feb 2015 :  8:00:33 PM  Show Profile  Reply with Quote
Much would intend on the actual spring installed height. And if a 'Voodoo' lobe :)

Crower 68405 at 1.650" with 120 seat pressure after run in would make a nice starting point, again depending on the cam lobe in use.

( opinion )

Edited by - Steve C. on 26 Feb 2015 8:02:24 PM
Go to Top of Page

Bob Kaplan
Cochise

USA
417 Posts

Posted - 26 Feb 2015 :  8:11:36 PM  Show Profile  Reply with Quote
Do you like the Crower springs over Comps 995.

The surgeon general said nothing about smokin a chevy...
Go to Top of Page

Phil
The Great White Buffalo

USA
7214 Posts

Posted - 26 Feb 2015 :  9:38:34 PM  Show Profile  Reply with Quote
Great thread guys!

Bowties are for Pee-wee Herman. "Chevy": even the name sounds cheap, but not as cheap as your Pontiac will be with an LS transplant.
Go to Top of Page

Blued and Painted
Chief PONTIAC

USA
3404 Posts

Posted - 27 Feb 2015 :  12:40:32 AM  Show Profile  Reply with Quote
With aluminum heads @ 9.3 I would go conservative.
A crower solid. 60310 + 1.65's and a tight 10 inch converter might be an option.
Back off the exhaust valve adjustment and tighten down the intake.
Alowes for the use of lifters with the oil hole on the face
http://www.cnc-motorsports.com/crower-60310-solid-flat-tappet-camshaft.html


Bull Nose Formula/ 461/ Q-Jet/
TH400/ 3.08 8.5 / R44TS.

Edited by - Blued and Painted on 27 Feb 2015 12:58:08 AM
Go to Top of Page

Cliff R
Cochise

USA
535 Posts

Posted - 27 Feb 2015 :  06:20:38 AM  Show Profile  Visit Cliff R's Homepage  Reply with Quote
I absolutely HATE Comps 995 springs and refuse to use them. Right to start with the dampner needs to be ground flat and smoothed or it will EAT the shims or into the head under it, and can/will put a LOT of metal into your assembly.

The pressure on them is ALL OVER THE MAP. I've tested several sets, and found them to be a LOT higher than the specs Comp posts for them, even using the retainers they supplied with them.

Of course I'm going back at least 10 years, but tossed the last set aside that was sent here with some heads to build, after finding the seat pressure over 160lbs at the correct installed height. I called Comp about it, and the "tech" simply said that they will "soften" up about 20 lbs on the seat after "run-in". OK, so they loose pressure, is that before or after they wipe the cam out?

For most Pontiac builds we use the Crower 68404 springs for 1.6", and 68405 springs for 1.7" installed height. They are direct replacement springs and have proven to be excellent parts for these engines.

I even ran a set of 68405's on my last set of KRE heads for many years, and bought a replacement set when the engine was torn down for "freshening" up. It had at least 1000 runs on it, and many thousands of street miles at that time. I checked the entire set, and they were right on the money for seat and open pressure, so I put them back in service.

For bigger lobe profiles requiring springs with more pressure and room for high lift we get the springs from Dave at SD Performance. He has found springs that work well with roller cams using .380" and .400" lobes, and supplies them to us along with custom length .120" wall pushrods per application. ZERO issues with any of his stuff in any application at any power level......Cliff

If you can read this, thank a teacher. If you can read this in English, thank a Veteran.

Edited by - Cliff R on 27 Feb 2015 06:22:03 AM
Go to Top of Page

Steve C.
Crazy Horse

1672 Posts

Posted - 27 Feb 2015 :  08:54:52 AM  Show Profile  Reply with Quote
Keep in mind the origonal subject here was involving a hydraulic flat tappet cam.

More often than not Dave at SD Performance used the Crane 99893 valve spring, but as Cliff eluded to that was typically for hyd roller profiles like the the 'Old Faithful' cam. I presume he still does today. And this was typically with the alum d-port heads. And again the actual installed height of the valves with their retainers installed must be measured and varified, and hopefully with spring cups or spring locators installed to protect the alum material. These valve springs also typically loose a bit of spring pressure after run. I know of one set that after run in ended up at about 145 lb seat pressure at about 1.785" installed height, here a set was removed and checked after the engine dyno session. Another set after 7 passes on the drag strip were down to 130 lbs at about 1.800" IH.

My old Crane catalog on hand for this 99893 spring suggests 149 lbs at 1.800" IH.

( not a recommendation, again just conversation )

Edited by - Steve C. on 27 Feb 2015 09:21:40 AM
Go to Top of Page

Steve C.
Crazy Horse

1672 Posts

Posted - 27 Feb 2015 :  10:39:22 AM  Show Profile  Reply with Quote
Never assume the specifications stated on the spec sheet for a specific valve spring to always be correct. Test them before installation as they often will vary slightly. Many shops use is a Rimac machine to measure valve spring pressure. Make sure the machinist measures and verifies the actual installed height on the cylinder heads, don't guess or assume, and have on hand the actual retainers you will be using. The spring with it's retainer installed is compressed to the exact installed height and the resultant seat pressure is indicated.

And don't trust out of the box aftermarket cylinder heads are always correct with their stated published installed height. They can vary slightly. (as do the published combustion chamber volume, but that's another subject )

And at times as Cliff mentioned they could be from a bad batch and be way off as when he found a set of 995 springs at 160 lbs seat pressure! I had a similar experience years ago on a solid roller set up using a set of Lunati valve springs. At the time the published spec sheet indicated they were rated at 200 lbs seat pressure at 1.850" installed height. When a few springs were tested the actual pressure was closer to 219-220 lbs at a much higher 1.917"-1.920" installed height. If installed at the rated 1.800" IH the pressure would have been crazy high. And later with a phone call to a Lunati spring engineer he stated despite my published spec material on hand they should of checked closer to 200 lb at 1.815" installed height! Numbers stated and tested were all over the map.

And again as mentioned valve springs often loose pressure after run in. Sometimes a little and sometimes a lot. Example on another solid roller set up I had a set of ISKY valve springs that were rated at 220 at 1.900" on the spec sheet. They were put in at a higher installed height and verified at about 215 lbs seat pressure. After the dyno session we pulled one set of springs from the heads and they tested at 197.5 and 201 lbs seat pressure.

Edited by - Steve C. on 27 Feb 2015 10:43:19 AM
Go to Top of Page

Cliff R
Cochise

USA
535 Posts

Posted - 27 Feb 2015 :  6:13:34 PM  Show Profile  Visit Cliff R's Homepage  Reply with Quote
More good advice, NEVER take anything for granted or at face value with this hobby, and especially with this topic.

Had a set of Iron Eagle SBC heads sent here once to install on a 355 SBC we were building. I took a couple springs off to check them, and they were WAY off for spring pressure, and installed height. They were not only too long and coil binding, being installed at such a low installed height had the pressures off the scale on the seat. There were to date the strongest set of single SBC springs w/dampner I've ever seen. Must have been some sort of "cheater" circle track spring for stock retainers, or something of that nature.

Over the years I've rejected a good many springs from other vendors, so Comp Cams certainly aren't the only ones that don't get this deal right from time to time....FWIW.....Cliff

If you can read this, thank a teacher. If you can read this in English, thank a Veteran.
Go to Top of Page

Bob Kaplan
Cochise

USA
417 Posts

Posted - 27 Feb 2015 :  6:28:50 PM  Show Profile  Reply with Quote
Cliff you got me nerves. I have a XE274 with 995 springs at 1.700 115 lb's on the seat in a 400. The car has been started and the cam broken in.
So far the valve train is very quiet with no ticking. I was going to go with the 60916 Crower but got talked out of it because it was "old school".

On the up side the Quadrajet I built with your book,parts and advice rocks.

The surgeon general said nothing about smokin a chevy...
Go to Top of Page

Steve C.
Crazy Horse

1672 Posts

Posted - 27 Feb 2015 :  7:02:20 PM  Show Profile  Reply with Quote
"Having built quite a few track championship hyd cammed roundy round engines, Ya here about float. Not the lifter 99% of the time, it's not the right spring package."

comp cams 995 springs topic....

http://forums.maxperformanceinc.com/forums/showthread.php?t=620353&highlight=995

Also previously in this thread I stated this...

"Ken Keefer (Pontiac Dude on PY) had no issues with the 995 spring at about 125 lbs (to 130 ) on most hyd flat tappet cams. And the comments made were not always involving higher RPMs. And the discussion was often including XE lobes."

I stated this from memory. I did a search looking for his exact statement regarding the 995 spring in relation to this. Found none.... so please take my statement with a grain of salt. My numbers might be a tad bit off from Ken.

Edited by - Steve C. on 27 Feb 2015 7:08:38 PM
Go to Top of Page

Cliff R
Cochise

USA
535 Posts

Posted - 28 Feb 2015 :  07:29:40 AM  Show Profile  Visit Cliff R's Homepage  Reply with Quote
"I was going to go with the 60916 Crower but got talked out of it because it was "old school"."

The 60916 cam is actually a bigger am than the XE274 if you look at the seat to seat timing.

On the dyno that cam made 419hp/453tq in a 400 build with unported #16 heads and 10 to 1 compression, so hardly "old school" when it comes to the results for the end user.

Installing the larger 60243 cam made 424hp/465tq.

The Crower cams work well because they have MORE seat timing, and wider LSA, and closer to stock opening and closing rates. Keep in mind that with factory heads, which have flat chamber floors and 30 degree seats, they are also going to have excellent low lift numbers. This is one of the reasons an "old school" cam works so well in a Pontiac engine build, as they take full advantage of low lift flow, instead of shoving the valves quickly up off the seats and trying to improve air movement thru the ports with greater .050" and .200" numbers.

Why "beat" up the valve train with "modern" profile cams and rely on stronger springs to keep things in check? There is NO power lurking there for you with one of these engine builds, at least no more than if you went with a slow ramp cam and took full advantage of the flow potential in the heads with lower lift rates.

Jim Hand proved that to use decades ago, swapping out quite a few cams in his 455 and documenting the results. He found that when the smoke cleared and dust settled, that the "old school" Wolverine 5059 cam would get the job done in his 455 build, making more total power than cams with "modern" lobe profiles, even those with more .050" seat timing.

I pay close attention to these things, and have done my own cam testing, and found pretty much the same thing. I did go on to test quite a few roller cams, and have found that with a roller cam, we can effectively use the "modern" technology and find some additional power over a "modern" flat cam. This happens because we take the lifter diameter and maximum tolerable lift rate out of the equation. With stock diameter lifters, the technology is pretty much all played out.

With that said, we did find that by using a "long" duration flat cam, adding Rhoads lifters and high ratio rocker arms to it, that we could make the same approximate power as a very well chosen roller cam at much less cost. The roller cam is still just a tad faster at the track, even when we didn't see the additional power on the dyno pulls, as they allow the engine to rev faster, so the car accelerates quicker.

With my car, changing from the Crower 60919 cam/Rhoads lifters/high ratio rockers to a very well chosen HR cam with the almost identical .050" specs was only worth 3hp/4ft lbs torque on the dyno.

At the track the car picked up from 11.64 @ 116mph to 11.52 @ 118mph, with no other changes. These two runs were the best ever runs with each cam and all other parts exactly the same.

I also averaged all the runs and found about .15 seconds improvement and just under 2mph between the two cams. Hardly worth spending almost another $1000 one a roller cam set-up vs a flat tappet, at least for most folks. I made the switch and haven't went back to flat cams, simply because it takes "scrubbing" a lobe out of the equation, not because I can make a lot more power with the roller set-up....FWIW.......Cliff

If you can read this, thank a teacher. If you can read this in English, thank a Veteran.

Edited by - Cliff R on 28 Feb 2015 07:30:45 AM
Go to Top of Page

Rick Denny
Sitting Bull

United Kingdom
200 Posts

Posted - 28 Feb 2015 :  10:50:39 AM  Show Profile  Reply with Quote
quote:


With my car, changing from the Crower 60919 cam/Rhoads lifters/high ratio rockers to a very well chosen HR cam with the almost identical .050" specs was only worth 3hp/4ft lbs torque on the dyno.

At the track the car picked up from 11.64 @ 116mph to 11.52 @ 118mph, with no other changes.



How does 3hp equate to just over a tenth et? does that mean the dyno isn`t worthwhile, or did that cam change suit the whole combination better?

trying to understand because I can`t see the value of dyno time based on this performance.
Go to Top of Page

cortcomp
Coyote

USA
5335 Posts

Posted - 28 Feb 2015 :  11:05:19 AM  Show Profile  Visit cortcomp's Homepage  Reply with Quote
I'm assuming more average HP over the run. To oversimplify, maybe one cam made a broader power curve, while the other one peaked near it but had less power available over the rpm range?

Also cliff dynoes just to know, if you didn't dyno, you wouldn't know if it was worth the time or not.
Go to Top of Page

Steve C.
Crazy Horse

1672 Posts

Posted - 28 Feb 2015 :  11:24:53 AM  Show Profile  Reply with Quote
My inquiry to Paul...

How much valve spring pressure would you recommend with this Voodoo hyd flat tappet cam ?

https://www.lunatipower.com/Product.aspx?id=2356&gid=287

Application :
Pontiac 461, Edelbrock Heads - flow at 310 and I'll presume set up at about a 1.800" installed height. And not larger heaver valves installed. My guess, peak power rpm at about 5300 or so with a dual-plane intake. Street combo, maybe a rare drag strip session.

ANSWER: I set that cam up with 130 on the seat, and 330 open.



Edited by - Steve C. on 28 Feb 2015 11:25:13 AM
Go to Top of Page

Rick Denny
Sitting Bull

United Kingdom
200 Posts

Posted - 28 Feb 2015 :  1:16:39 PM  Show Profile  Reply with Quote
quote:
Originally posted by cortcomp

I'm assuming more average HP over the run. To oversimplify, maybe one cam made a broader power curve, while the other one peaked near it but had less power available over the rpm range?

Also cliff dynoes just to know, if you didn't dyno, you wouldn't know if it was worth the time or not.



ok, makes sense.

to me though, if you went by the dyno figures and highlighting them, it would suggest that either it was a waste of money changing the cam or the wrong one was chosen. if you went straight to the track after the swap, you would have a different opinion as the dyno only showed a 3hp increase whereas the time slip would have shown a much higher gain.


69 Firebird,461,Comp 290b,KRE 85cc, Torker 2,AED850dp,th400,Continental 10" 3200,3.90 10 bolt,KYB gas rear,QA1 single adjustable front,3558lbs. 10.96 @ 123.
Go to Top of Page

Cliff R
Cochise

USA
535 Posts

Posted - 28 Feb 2015 :  1:59:10 PM  Show Profile  Visit Cliff R's Homepage  Reply with Quote
"How does 3hp equate to just over a tenth et?"

From the post above: "The roller cam is still just a tad faster at the track, even when we didn't see the additional power on the dyno pulls, as they allow the engine to rev faster, so the car accelerates quicker."

Keep in mind that on the dyno the engine is heavily loaded, and in the vehicle it can rev much quicker, so the roller cam showed us a bit more at the track than was reflected by the dyno runs.

I would also add that on the dyno the flat cam actually made peak power at 5600rpms' and the hydraulic roller cam at 5400rpm's.

For the number crunchers, the seat timing for the flat cam was 304/314 degrees at .006" tappet lift, and 231/240 @ .050" with .313" lobes. The roller cam had 282/294 and 230/242 @ .050" specs with .361" lobes.

It's also interesting to note that Jeff Kauffman, who ran the dyno, also predicted what the car would run within a couple hundreths of a second just using the vehicle weight and information from the dyno pulls. So he knows full well how his dyno results translate into real power at the track when the car is set up well to use the power, and obviously they are not "inflated" in any way, as it's common to see in this industry....FWIW.....Cliff

If you can read this, thank a teacher. If you can read this in English, thank a Veteran.

Edited by - Cliff R on 28 Feb 2015 2:00:24 PM
Go to Top of Page

Steve C.
Crazy Horse

1672 Posts

Posted - 28 Feb 2015 :  3:07:58 PM  Show Profile  Reply with Quote
"The term "dyne tested" is used a lot these days, and most people tend to accept dyno results as absolute truth. Unfortunately, dyno results are no better than the testing method used to get the results. In other words, unscrupulous operators can make the results come out to be almost anything they want. It all comes down to the testing method and the ethics of those doing the testing."

Years ago I had a specific 4.125" stroke / 450cid combo thought out and built with the specific goal to make 700 hp at or under 7000 rpm. We took it to a well known dyno shop in Houston Texas for testing. After break in and final tuning the best dyno 'pull' was exactly 699.9 hp at 6900 rpm. Honest no lie, it was that close !
I was in the dyno cell watching with my engine builder at the time and after the results were printed out I stated 'damn' with a hint of disappointment out loud and with a slight frown on my face. The dyno operator took note and queried me as to why, he seemed impressed. I then mentioned my goal of 700 hp. He said wait a minute, and made adjustment on the dyno. We did one more pull that resulted in 702 hp. I smiled ! How much he could have manulipated the dyno I have no clue. That said, word on the street suggested it was a respected dyno shop.

Years later with another combo we built it was dyno tested at another shop, it was also known on the street to be conservative if anything. The shop and operator was well respected. The best pull on his dyno indicated 580.2 hp with my combo. Using a well known calculator at my race weight and at that horsepower it suggested the car should have run 124.56 mph. We took my car to the track and it ran a best of 124.28 mph that day. The engine made peak power on the dyno at 5800 rpm and we had a 6000 rpm shift chip installed. Never did experiment with different shift points other than at 6000 rpm. It was a street car and I only wanted to confirm a 10-second time slip. Seldom raced it at that time.

Like my car and Cliff has you better have a chassis set up and proper torque converter to apply all this horsepower (torque) to the pavement... and be able to do it consistently from run to run.

Edited by - Steve C. on 28 Feb 2015 3:18:44 PM
Go to Top of Page

Rick Denny
Sitting Bull

United Kingdom
200 Posts

Posted - 28 Feb 2015 :  3:22:49 PM  Show Profile  Reply with Quote
interesting stuff.

what I take from this is, use a dyno to tune an engine, carb, timing etc but don`t use it to determine whether or not you chose the wrong combination of parts based on the figures it gives you.

seems to me then, a chassis dyno is more relevant to real world performance as the complete car is being tested rather than just the engine it`s going into.


69 Firebird,461,Comp 290b,KRE 85cc, Torker 2,AED850dp,th400,Continental 10" 3200,3.90 10 bolt,KYB gas rear,QA1 single adjustable front,3558lbs. 10.96 @ 123.
Go to Top of Page

Steve C.
Crazy Horse

1672 Posts

Posted - 28 Feb 2015 :  3:31:06 PM  Show Profile  Reply with Quote
Similar situation with a chassis dyno, results can be all over the place!

Dynos Don't Lie, But The People Who Run Them Can Cheat. We Expose The Tricks Of The Chassis Dyno Braggart And Sort Fact From Fiction.

http://www.hotrod.com/features/0612phr-dyno-accuracy-testing/

http://www.enginelogics.com/dyno-tested/

Edited by - Steve C. on 28 Feb 2015 3:31:39 PM
Go to Top of Page

Bob Kaplan
Cochise

USA
417 Posts

Posted - 28 Feb 2015 :  4:34:30 PM  Show Profile  Reply with Quote
When I degree the XE274 I could see the very fast opening ramp on the dial indicator. This cam idles like a 068 factory cam.
With 230 degrees @ .050 it should idle like Bill Boyles Trans Am. I have the 60916 and I'm thinking of pulling out the XE stick.

The surgeon general said nothing about smokin a chevy...

Edited by - Bob Kaplan on 28 Feb 2015 5:18:16 PM
Go to Top of Page

Steve C.
Crazy Horse

1672 Posts

Posted - 28 Feb 2015 :  5:48:50 PM  Show Profile  Reply with Quote
"Basically, the idea behind selecting a converter is to coordinate the converter stall speed to the engine torque curve. Unfortunately, optimism can have a detrimental effect upon converter selection, especially when it comes to engine output. Inaccurate engine power and torque estimates provided by the customer can have a serious effect upon the performance of the torque converter."

Associated with this is one of many reasons why the engine dyno can be a productive tool. Years ago I consulted with Marv Ripes at A-1 to help develop custom built torque converters for my specific applications. A busy man, Marv was often hard to get on the phone. Once you had his attention and he knew you were serious and not just wanting to order something generic assigned with a part number out of a catalog he would ask if you had a actual dyno sheet for the engine combination in question. He wanted the torque numbers and the curve. That and he would go over completely your chassis set up and performance goals.

A fwiw tid bit, Marv was very instrumental in working with Kris who now owns Continental Torque Converters. Kris also appreciates info from your dyno sheet for a converter built custom for your specific application :)

http://a-1perf.com/ABUS.html
Go to Top of Page

fbird1969
Sitting Bull

170 Posts

Posted - 28 Feb 2015 :  6:05:54 PM  Show Profile  Reply with Quote
I would agree with Cliff as his reasoning is well-documented and the Pontiac heads are known to move substantial air at low lift. Like he says, you can't just look at the duration at .050", the seat-to-seat timing events are a big player too!

Since most people fail to realize this, they base their cam selection on the duration at .050" like in the past, when they should really be focusing on both, picking a cam that's one size larger to compensate for the lost seat timing. This is why the XE262 is often used as a replacement for the 068; although the duration at .050" is substantially larger, the short seat timing will make he cam act smaller. If you were to only compare .050" numbers, the XE256 would appear to be equal to the 068, but we all know that the XE256 will die out long before the 068 (disregarding the tight LSA).

In a way it's like a balancing act between the durations at each lift interval based on the head flow at those same intervals.
Go to Top of Page

Steve C.
Crazy Horse

1672 Posts

Posted - 28 Feb 2015 :  6:43:04 PM  Show Profile  Reply with Quote
But we might often want to consider the effects of additional seat timing in conjunction with the static compression ratio in play. That and the area under the curve of the lobe itself.

Here is some information published by David Vizard that some might find of interest for conversation here around the coffee table:

VALVE LIFT.
"A 2-valve cylinder head typically continues to flow more air up to lift values equal to as much as 0.35-0.4 times the valve diameter. The reason for this is that there is a flow pattern transition period that takes place at a lift value of about 0.25 of the valve's diameter. When this point is passed, if the port has been modified to support flow in this lift region, the valve efficiency actually starts to increase. This is the reason why a 2-valve engine responds to high lift."

"If you want to build a street motor with the most power without a sacrifice of idle and low speed qualities, then lift is the most important factor to maximize, not duration. The best street cams are those that seek to maximize lift while only adding a minimal amount of duration."

Bottom line, the engine wants all the lift it can and thrives on it so run as much as mechanically achievable or prohibitive because of cost limitations (such as in a solid roller cam). Obviously if it's a street application or race application will have a bearing on the situation, most here would be hesitant to run 0.700 lift on the street !

Summary as presented before:

The most important cam design parameters are the four timing events or equivalently the advance, intake and exhaust duration and lobe separation angle.
Once the four timing parameters are established, the cam should be designed for maximum lift
A quick opening and closing cam will provide better low end performance than one that is slower opening.

Some will not agree with this, but many professionals and tech information presented within the performance industry do.

Edited by - Steve C. on 28 Feb 2015 7:01:48 PM
Go to Top of Page

fbird1969
Sitting Bull

170 Posts

Posted - 28 Feb 2015 :  6:59:59 PM  Show Profile  Reply with Quote
Steve, wouldn't the most optimal engine configuration open the valves instantaneously and close them instantaneously at the optimum opening/closing points? (Assuming that the valve does not "bounce" back on the seat like the XE cams) My thought is that the fast ramp cams get closer to achieving this (just as the really old grinds are way far away from this). The difference is that now, with new advanced lobes, the timing/duration needs to be different to accommodate this.

Provided that the static compression is properly set for the engine/cam combination, I would think that the fast ramp cam would be more predictable as far as dynamic/effective compression and cylinder filling since the closing at .050" and advertised closing of the intake are closer together. This eliminates the variances that can occur at higher rpm when the seat timing becomes less relevant.

I guess in this situation we could assume both cams have the same area under the curve?

EDIT: Steve, I just noticed your edit. I think we are arguing for the same, or at least similar, point!

Edited by - fbird1969 on 28 Feb 2015 8:51:30 PM
Go to Top of Page

Steve C.
Crazy Horse

1672 Posts

Posted - 28 Feb 2015 :  7:07:01 PM  Show Profile  Reply with Quote
Sir, I cannot offer much regarding this other than what I read. I'm not an engine builder and only know enough about cams to get me in trouble :) I have a basic idea but always consult the profesionals within the industry who design the cams. Right now it's at Bullet racing. I currently use a UltraDyne MSP solid roller that made 20 hp more on the dyno than my previous similar Crower cam.
http://www.bulletcams.com/

That said, based on conversation of late on various sites I sure would consider a Voodoo lobe. But again only with proper spring pressure... as I posted here in my previous post with info provided by Paul.

P.S.- And over the years I always use enough valve spring pressure to control the valves. And never skimp on quality with valve springs. If you want to dance you need to pay the piper!

( note I edited my previous post that might be of interest before you asked the question )

Edited by - Steve C. on 28 Feb 2015 7:29:08 PM
Go to Top of Page

tjs44
Cochise

USA
411 Posts

Posted - 28 Feb 2015 :  8:53:44 PM  Show Profile  Reply with Quote
I always try to error on the high side on springs!Been running 200 on the seats with solid rollers on hyd roller cams for maybe 12-13 years now.My last hyd roller lifters on a hyd roller lifter cam had I believe 180 on the seats.Made HP over 6700 as I remember,NO drop off when the pull was ended.Im sure they were good to 7K.Tom
Go to Top of Page

Cliff R
Cochise

USA
535 Posts

Posted - 01 Mar 2015 :  08:45:42 AM  Show Profile  Visit Cliff R's Homepage  Reply with Quote
The problem with looking at camshafts, and different lobe profiles is that folks look at them from a "static" perspective, not dynamic. They fail to realize that the amount of "time" in milliseconds provides opportunities for air movement in and out of the cylinders. Short seat timing events even with greater .050" numbers produce a smaller window of opportunity as the valves are not open as long (time) for each cycle.

They tell us that shoving them open quicker, and higher will overcome the losses in actual time off the seats. This is not actually true, and shorter seat timing also closes the intake valve sooner when the cam is placed at the same centerline as a longer duration (seat timing) cam, so it builds more pressure at low rpm's, and pulls engine power DOWN in the rpm range at the same time.

When we start to look at cams in a dynamic perspective, one can quickly figure out that a bigger cam is a bigger cam, and that lift/rates are severely limited with flat cams by the lifter diameter. Cam manufacturers keep telling us that "more area under the curve" produces more power, and try to sell us on the "modern" lobe profiles as being superior in moving air thru the engine as "old" designs.

From what I've seen there is no "free lunch" here. You can't take a 455 with 230cfm 6X heads on it at 10 to 1 compression using a RAIV size cam, 308/320/231/240, 113 and put in a 274/284, 230/236, 110LSA cam with much quicker lobes and make MORE power. It's going to make quite a bit LESS power.

I actually had the unique opportunity to see this happen when my first 455 was sitting in line at the dyno for the KRE head swap and articles that came from that.

We were sitting at the dyno ready to bolt my engine in place, but had to wait for them to finish dyno testing a 455 with ported 7K3 heads, single plane intake, and 850cfm carb on it. No one knew what cam it used at that time, but it was very "aggressive", really "choppy" idle and sounded like it was really going to do something.

They pulled and pulled on that engine, moving timing and changing fuel curves all over the place, and it's very best effort was 430hp/499tq. Not too bad for a "warmed over" 455, but they though it should have been better. We all made bets on what cam was used in it, and I won the bet guessing the Comp XE284 camshaft.

Anyhow, we bolted down my 455 with 6X-4 heads, Crower RAIV cam/Rhoads/high ratio rockers, stock intake, 1977 Pontiac intake, and stock HEI distributor. Before someone cries "foul" my intake was opened up nicely under the carb in the plenum and my HEI has a positive stop welded in to control the total timing.

Anyhow, very first pull was 455.4hp and over 525ft lbs torque. We moved timing around, and played with fuel curves and managed 540tq on a couple of pulls, but HP hovered around 450 for most pulls.

So we basically back to back tested two 455's with very similar heads. One had a single plane intake and 850 carb, and "modern" profile XE cam with more .050" timing. The other mostly "stock" parts and a modern version of the factory 041 camshaft.

We could cry "foul" here, because we don't know what the deck height was on the first 455, or where the cam was degreed, etc, but the basics of this deal are still in place. My engine outran that one by quite a margin, and used LESS intake, LESS carburetor, LESS camshaft, and about the same compression and head flow.

Anyhow, as much as I love stories to help us learn about these things, you still have to look at camshaft in terms of how much time the valve spend off the seats in comparison to how far they are off the seats. With flat cams were are severely limited with this deal. When you shorten up seat timing, less air moves thru the ports. To trump that problem you've got to get the valves open much more quickly, and hold them open further at every point to gain some ground on having LESS time off the seats. This is why with flat cams we see "old" grinds working so well. It's also why we see roller cams making big power. A roller cam takes the lifter diameter OUT of the equation. We can send the valve up to full lift quickly, hold it open for most of the cycle, then drop it down quickly, without chewing anything up. We also do NOT need super quick actual opening/closing velocity with the roller cam as we can do so much more with the valves at every point during the cycle. So we can get away with less actual seat timing, but still have the a good "window of opportunity" to move air, and make up all of the lost ground from having a smaller cam in the engine.

Like I mentioned in an earlier response, a long duration cam with high ratio rockers and Rhoads lifters makes very close power to a very well chosen roller cam with about the same .050" specs. We also get very similar engine manners, as the Rhoads lifters "tame" the larger at idle speed and low rpm's.......Cliff

If you can read this, thank a teacher. If you can read this in English, thank a Veteran.

Edited by - Cliff R on 01 Mar 2015 08:49:58 AM
Go to Top of Page

JOHN-M
Buffalo

USA
88 Posts

Posted - 01 Mar 2015 :  08:49:19 AM  Show Profile  Reply with Quote
This has been a great thread. I have the same XE274 in a 434 and I can't stand the noise either. I have the big walker hemi turbo mufflers on my car so the exhaust is fairly quiet. All you hear is cam noise. The only reason I haven't taken it out at this point is that I wasn't sure what to replace it with. I at least have a few ideas after reading this.
One issue brought up about the XE cams was valvetrain instability. I think there might be some truth to that. My engine falls flat on its face at 5000rpms. It will turn more but the party is definitely over at 5000rpms. I had the heads off at one point and had some mild porting done thinking they were snuffing things out. No change. I have plenty of fuel, air flow, and exhaust and we are still done at 5000rpm. I know there are a punch of things that can contribute to this but the cam design might be it.

Edited by - JOHN-M on 01 Mar 2015 08:50:25 AM
Go to Top of Page

Steve C.
Crazy Horse

1672 Posts

Posted - 01 Mar 2015 :  09:47:31 AM  Show Profile  Reply with Quote
Repeat Harold Brookshire's comment....

"You do not have to shut the valve faster to keep the charge from getting out. You have to design the cam so the charge, or inertia ram, is still filling the cylinder when you shut the valve."

JOHN-M
You are correct. Valvetrain instability, can be more than the spring package. One of many considerations is what Cliff and I have mentioned here and that is the pushrod wall thickness. Not for 'every' combination, something to consider. And adding a bit of weight to that side of the rocker arm is of little of concern.

Gentlemen, please note I'm not here necessarily as a fan of XE lobes nor here to indorse them. Thousands have used them with great success, and I guess overlooking a little bit of noise which is a personal situation. Like admiring a rowdy idle, many thrive on it and many get their panties in a wad over it. I know that Pontiac Dude for years has built and used many XE lobes with great success, and at much higher RPMs in combos than most street applications considered here. He knows and understands the importance of a correct spring package in conjunction with these cams. As with the information from Paul Carter that he uses 130 lbs seat pressure on Voodoo hyd flat tappet lobes that open fast, and close slow... spring pressure considered no big deal today within the performance community by many, yet some still shiver at that thought and consider it excessive spring pressure.

But also remember that many of these situations are involving hobby cars often with limited actual millage, maybe weekend use only that might be a 150 mile trip. Or some city driving out for donuts and coffee, or a cruise down to the Dairy Queen :) Combos often not expected to go 100,000 miles.

To each his own.

Go to Top of Page

Steve C.
Crazy Horse

1672 Posts

Posted - 01 Mar 2015 :  10:02:23 AM  Show Profile  Reply with Quote
Google up another opinion off the internet, this from years ago.....

I have talked with Harold Brookshire and Tim Goolsby quite extensively about the Comp Cams issue. I have also spoke with Nolan Jamora and Richard Iskenderian at length too. I have also talked with Comp Cam's Scooter Brothers directly about their cams.

Most of you have already figured out that the acceleration rates on the Comp lobes is very high. They also close the valves very quickly, because they are holding them off the seat for a greater number of degrees when compared to other camshafts.

This requires more spring pressure to keep the valvetrain stable.

Scooter Brothers told me, "This is a trade-off for the quicker valve action and most of these cars are not daily driven so the wear shouldn't be a huge factor..."

In fact, in 2008, the Comp #995 spring increased its rate significanty while the part number remained the same. This caused quite a few problems for the Pontiac community.

Harold Brookshire of Ultradyne contributed to the Voodoo profile design, based on a lobe profile he pateneted in the 1960s with Ultradyne. It is a fast opening profile that decelerates near the nose (to control valve bounce) and a gentle closing ramp. This profile, like the Isky 'Polydyne' are very dynamically stable at elevated rpm and require less spring pressures.

We went from a dual spring with the Crane to a BBC single spring with damper (Isky PN 805-DO) and Isky 507-STA retainer in a 429 Ford turing 7500-7800 rpm. We dropped our valve spring open pressures to under 300 lbs with the Isky.

Less heat, less wear, less parasitic drag.

A noisy tappet/lobe interface destroys the oil fim between the two parts and causes accelerated wear. The process can be slow or fast, depending on a number of factors.

I have seen so many Comp Cam failures around here that I started referring to them as 'Comical Cams' amongst my local gearheads, but losing a cam isn't funny. It is very costly.

One very significant factor that was revealed to me recently was Comp is doing a poor job of heat treating. A local felow is an A&P mechanic and he lost a Comp XE-274 in an SBC after a short period. Everything was matched and verified and each and every spring was tested prior to installation.

He sent the cam out for testing and the lobe hardness (on the lobes that were still intact) was very, very low and inconsistent across the camshaft.

In the 1980s we were sponsored by Isky and, at that time, we were racing a 427 and a 428 Ford in SS/G and SS/K classes. When I started, we were running Crane and fairly high valve spring pressures. When I started working with Nolan Jamora, one of the first things he told me was the Isky Polydyne profiles didn't require that much spring pressures becase they were more dynamically stable.

I stuck with Isky all those years, even after we stopped racing. They always made us anything we could dream up quickly and they are in our UPS zone, so cams would arrive here in just a couple of days.

In 2000, I started using Ultradyne and began a professional relationship with Tim Goolsby. I have had similar success in Pontiacs with the UD grinds and have had several UD grinds done for SBC's. I am very pleased with the workmanship and performance.

I have seen too many Comp Cam failures in properly set-up engines to try them. That's just my opinion, but anything I can get from Comp, both Isky and UD will grind for me on much more stable lobe profiles.
Go to Top of Page

fbird1969
Sitting Bull

170 Posts

Posted - 01 Mar 2015 :  11:15:01 AM  Show Profile  Reply with Quote
While I see cliff's point about needing some extra seat timing, I don't agree that it's the "end all" solution to picking a cam.

I had an XE274 in my 400, 10:1 compression, m20, 3.73 rear. I never dynoed the car, but it sure pulled strong past 5000, and with the 3.73 rear that engine would spin up quick. I changed the rear to a 3.23 and it was a dog (still with 10:1 compression, possibly a tad more). So I installed a summit 2801 cam and the car drove nicely. Certainly not the high revving power surge that the XE274 had at about 3000 rpm, but it drove strong like our stock L34 chevelle that had a similar drivetrain.

This example should tell me that the duration at .050 is more important than the seat timing, because the 2801 has 288 degrees on the seat vs 274 with the XE, but the summit cam acted fairly small compared to the XE.

One can also think of cam choice from this perspective. If you want a small cam for your daily driver/torque monster, you're not going to worry about power over 5000 rpm or thereabout. So squeezing the powerband into a narrower range, i.e. 1000-5000, would make a lot more sense. It might not make the same peak power at ~5600-6000rpm like the 60916 or 60243 would, but would give more power in the "useable range." So in this case, the fast ramp cam on the tight LSA and short seat timing makes more sense.

That quick off-idle surge of power pulling to 5000 rpm will make the car faster in that range compared to the other cams (and most definitely more fun to drive), and the driver would never even know that it fell flat on its face because he had no desire to make power there.

I guess it all comes down to the use of the vehicle.
Go to Top of Page

Chicagogoat
Cochise

USA
823 Posts

Posted - 01 Mar 2015 :  1:58:17 PM  Show Profile  Visit Chicagogoat's Homepage  Reply with Quote
This has been a great thread, I've learned thru my experiences with an XE cam and reading posts here for years that there are better cams out there nowadays for our Pontiacs as well as better potential builds with the aftermarket parts available now versus say 15 years ago. When I had my first 455 built around 02-03 my builder chose the XE284 with the matching comp lifters. I told him I want as much power as possible with 6X's that he milled down for 9.9:1 CR with a hyd flat tap cam. It was a fun motor with a mean noisy idle. I wiped a few lobes 5 years into the new motor, replaced with the same cam then 3 years after that dropped a valve and then I pulled the motor for a rebuild with a new combo in mind. The best runs I ever had at the track was 12.5's. On the street it pulled hard to 5500 rpm before it nosed over. My builder and long time friend knows Pontiacs and has been building Pontiac motors since the 60's. I trust his experience and work, but even he has told me that he's not into the XE cams any more either due to all the points made in this thread about them. He says that good springs, hardware, and pushrods are a must to make these cams perform and more importantly last. He's a big fan of these Voodoo cams and chose it for my KRE D port build he finished for me in 2011 and I installed in the spring of '12. He said that it's a better designed cam and has the performance and extra lift these builds with aluminum heads need to make reasonable power. Ideally a roller cam is better all around and more reliable to boot, but the vast price difference still gives the flat tappet lobes plenty of market share. Some like Ultradyne, Crower, 041 & Summit cams to get the job done and who can disagree with good dyno & track #'s.


Pure Pontiac: learn it, live it, love it!
Go to Top of Page

Rearwheelmaniac
Tribal Scout

USA
7 Posts

Posted - 16 Oct 2017 :  8:02:23 PM  Show Profile  Reply with Quote
Alright pros. I've been trolling this site for a while now time to ask.

With all of the good info, and contradicting stories this is where I am at.

This is my first motor, without my dad being alive to guide me though it.

400 +030.
Zero deck
-10 domes
Have 6x-4@96ccs and 6x-8's at 100ccs.
Lunati voodoo 10510702 - 262/268 @ 112 Lsa
Th350-3:73-2500 stall.
Street. Maybe a trip to the strip or two. Goal is 93 octane or less.
Running a Q-Jet - Cliff you rebuild these to spec?
Have not chose springs yet. Can you recommend a set?
Will be running stock 1.5 rocker arms.


Hit me with it.. am I on the right track?

Which heads? 9.3 something to 1, vs 9.7 something to 1........

New to examining cam specs but this is what I bought.

Do I run with the 6x-8 because of cylinder filling with the voodoo or is this a non issue.

Looking for real advise. No shooting from the hip please.

Thanks in advance fellas.

-Chris

Edited by - Rearwheelmaniac on 20 Oct 2017 11:04:58 PM
Go to Top of Page

Bill Boyle
Horse Feathers (Charter Member)

USA
4793 Posts

Posted - 17 Oct 2017 :  05:49:15 AM  Show Profile  Visit Bill Boyle's Homepage  Reply with Quote
Between 6x heads, go with more static compression--6x-4.

"Dedicated to keeping the classic Pontiac engine alive."

----
400 bored +.030, forged TRW pistons, ported 62 heads, Hedman headers, 2.5 SS dual exhaust X Pypes, Comp 276AH10 cam, Scorpion 1.65 RR, 850 Q-jet, stock intake & tuned HEI; original owner.
Go to Top of Page

Steve C.
Crazy Horse

1672 Posts

Posted - 17 Oct 2017 :  10:00:26 AM  Show Profile  Reply with Quote
Regarding your valve springs...

See my comments on post #33 about distance from coil bind and post #34 here for a suggested seat pressure:

http://forums.maxperformanceinc.com/forums/showthread.php?t=810672&page=2




.

Edited by - Steve C. on 17 Oct 2017 10:03:00 AM
Go to Top of Page

Rearwheelmaniac
Tribal Scout

USA
7 Posts

Posted - 01 Nov 2017 :  10:52:09 PM  Show Profile  Reply with Quote
If I go with the 6-x4's, Will the VD 262 raise the Dynamic Compression too high Due to cylinder filling? I'm now second guessing this cam
Go to Top of Page
Page: of 2 Previous Topic Topic Next Topic  
Previous Page
 New Topic  Reply to Topic
 Printer Friendly
Jump To:
Pontiac Street Performance © 2006-2017 Go To Top Of Page
This page was generated in 0.52 seconds. This Site Sponsored By:
Powered By: Snitz Forums 2000 Version 3.4.05