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 Lower intalled height to eliminate valve float
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DanM
Sitting Bull

163 Posts

Posted - 18 Jan 2019 :  12:21:06 PM  Show Profile  Reply with Quote
Sometimes it's great to learn engine theory to help set expectations and set requirements for possible use of modern technology upgrades(e.g. advantages and tradeoffs of roller cams, EFI, etc.)

Sometimes its good to hear experience to help select from available standard approaches (e.g. cam duration for max RPM/power at tradeoff of idle quality)

Sometimes it's necessary to eliminate existing problems.

Valve Float at 5300 rpm seems a little low to me but what are your experiences.

Background: 400 ci, 8.9:1, XE lobes 212/224 duration, moderately worked over #96 heads, built by a well known respected builder from Central Virginia. No smoking guns so far.

At the chassis dyno the torque curve is as expected, wide and flat and peaks at around 3500-4000. HP curve rises, then goes almost completely flat from about 4000 to 5000 then steadily drops as expected. The problem is that something strange happens at precisely 5200. It sounds bad. The dyno owner says it sounds like "reversion"? but not sure. The air-fuel ratio guage wacks out. Power drops off a cliff.

On the track I set my 4L60E to shift at 5200 and nothing wrong happens. If I set it to shift at 5300 I get 100 rpm of noisy power. If I set it to shift at 5400 I get 200 rpm of noisy power. The ETs for shifting at 5200 are nearly identical to shifting at 5400 so I choose to shift at 5200 to avoid the noise.

It's not a total destruction noise. It's more like you may hear from mild knocking down at 2500 rpm if that were a problem.

Two years ago I had the Comp Cams 988 springs and saw this problem on the dyno. I upgraded to the 995s and the problem improved but still exists. Therefore I concluded it isn't a spring problem.

However, just now, on another thread I listed the spring pressures. Indeed the 995s are stiffer than the 988s but the installed height is taller (1.7 vs 1.6) and thus the seat pressure for the two springs is the same, about 115 pounds. The nose pressure is very different (316 vs 232.)

Question: Could my problem indeed be valve float? Can I correct the problem by changing retainers to set the installed height of the 995s to 1.65 or 1.60. This will increase the seated valve pressure to 135 or 155 pounds and still leave me able to get 0.502" of exhause valve lift without coil bind?

Again. The problem occurs at a very precise rpm point. It's totally repeatable. If it were some air-fuel-flow reversion thing I might think it would be more variable.

Finally, I was super super careful about setting my adjustable valve "poly locks" to minimize lifter pump up. There's only about 0.020" of "negative lash?" you know what I mean.

Steve C.
Chief PONTIAC

1973 Posts

Posted - 18 Jan 2019 :  2:23:45 PM  Show Profile  Reply with Quote
Have you or your engine builder measured and verified your actual installed height to be 1.700"? Have you or your engine builder tested the springs at the actual verified installed height?

Related. Applies to any valvespring from any company......

From a valve spring catalog.... "Note: spring tensions often vary measurably within the same production runs; therefore it is recommended that EACH SPRING be tested on an accurate spring tester and the springs installed at the recommended SEAT PRESSURE."

"Never trust catalog stated pressures, they can and do vary"

My engine builder checks new valve springs with their retainer attached before he installs them with a Rimac machine. Again, NEVER trust the published figures ! And always be aware springs can lose pressure after run in and over time.


Edited by - Steve C. on 18 Jan 2019 2:49:02 PM
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Steve C.
Chief PONTIAC

1973 Posts

Posted - 18 Jan 2019 :  2:49:16 PM  Show Profile  Reply with Quote
" Keep in mind that most cam manufacturers tend to recommend springs that are on the minimum side of pressure, to too weak. If you add 15-20 lbs for their suggested pressure you'll be pretty close to where you need to be. They tend to base their spring recommendations off of Chevy engines, I think. They don't take into consideration things like valve seat angle, and valve weight, etc."
Paul Carter

A good example in my opinion is the Comp 995 spring often regurgitated by Comp for use in a Pontiac applications at a pressure many would find inadequate. All too often the Comp Tech people, and depending on which work cubicle the call gets routed to, just regurgitate their standard recommendation and it's taken as gospel. I've known of many applications where the 995 spring has lost pressure and the engine combos nose over at rpm.

That said, many use and report no issues with them.

.

Edited by - Steve C. on 18 Jan 2019 2:50:59 PM
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Steve C.
Chief PONTIAC

1973 Posts

Posted - 18 Jan 2019 :  3:19:20 PM  Show Profile  Reply with Quote
Another topic that applies.. your distance from coil bind at max valve lift. If you are using the Comp XE lobe 5441 on the intake with a 1.5 rocker ratio in theory it has 0.447" net lift.
Coil bind on the 995 spring is listed at 1.020"

Do your homework !

How Much Valvespring Coil-Bind Clearance Is Safe?

https://www.hotrod.com/articles/how-much-valvespring-coil-bind-clearance-is-safe/

Edited by - Steve C. on 18 Jan 2019 3:21:45 PM
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DanM
Sitting Bull

163 Posts

Posted - 18 Jan 2019 :  4:47:29 PM  Show Profile  Reply with Quote
Thanks Steve.

I'm using 1.65 rockers. With that lobe I'm getting 0.492/0.501 max lift on the intake/exhaust.

If I change my installed height to 1.6 that means the spring gets down to 1.108/1.100 intake/exhaust compared to the 1.020 coil bind height. That leaves 0.088/0.080 to spare which will account for 0.020" of lifter lash and 0.060 of margin.

Score!

Also I like the rule of thumb numbers of needing 20 more pounds to accommodate reality. I would add 20 or 40 pounds depending on which installed height I choose.

So that answers all the technical questions, or at least addresses them.

The BIG QUESTION is do we think the power problem I described is classic valve float due to light pressure by the spring when seated? Or could it be lifter pump up? (note: my oil pump is not super high pressure. It cruises around 40 psi and idles around 10. I think it maxes at 50 psi warm.)
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Corncob2061
Cochise

USA
388 Posts

Posted - 18 Jan 2019 :  4:59:29 PM  Show Profile  Reply with Quote
Sounds like valve float. Adding enough seat pressure would give you more rpms. I would want to check pressure before making a decision to do that.

I do not use or recommend XE cams on 30 degree intake valve engines that have the capability of making power past 5000 rpm. EVEN IF there is no audible valve float, they consistently fall short on hp. Big ratio rocker arms add to the problem. A wide well broken in seat contact area adds to the problem as well. The XE profile shuts the intake valve fast enough to make the valve bounce off a 30 degree seat. On a little cam like this you should be able to increase the seat pressure and get some more rpms out of it. If someone is absolutely desiring to run a XE cam and make power past 5k, I will suggest converting to a 45 degree valve. Or at least having comp nitride the cam to help it handle the extra seat pressure.

If you want to run more rpms with a XE, in addition to adding spring pressure, going back to a 1.5 rocker should help too.
Jay

Edited by - Corncob2061 on 18 Jan 2019 5:06:47 PM
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Lee
Sitting Bull

182 Posts

Posted - 18 Jan 2019 :  5:23:47 PM  Show Profile  Visit Lee's Homepage  Reply with Quote
"HP curve rises, then goes almost completely flat from about 4000 to 5000 then steadily drops as expected." That sounds peculiar to me. I've seen Pontiacs plateau for a few hundred rpm, but not for a 1000rpm range. Sounds like SOMETHING is limiting the power at that level - maybe fuel flow, maybe an exhaust restriction... something is bottlenecking at that point.

Have you tried shifting earlier? Couple of points here:
1. Are you sure your tachometer is accurate? My factory tach reads about 500rpm higher than actual.
2. Is the tranny STARTING to shift at 5200, or finishing? I've seen trannys that need to be told to shift 200 to 500rpm early, so that the engine rpm does not go higher than I want.
3. 5200, IMHO and experiences, is rather high for a 400 with just 212 intake duration.
4. I had a 455/6X combo in the early 90's, a bit more cam than you. It ran 13.8's shifting at 5000. Dropped the shift to 4600 and ran 13.2's


CURRENT: '73 T/A clone, starting to get less boring!...
67 Firebird (sold) 11.27 @ 119.6 Feb. '05 issue HPP
69 Falcon wagon, 10.51 @ 130mph Feb. '10 issue PHR (sold)
72 Cutlass Convertible, first car, owned since '82, now with a 6.0 LS, mild, putting just under 400 hp/tq to the wheels.
www.LNLPD.com
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Corncob2061
Cochise

USA
388 Posts

Posted - 18 Jan 2019 :  5:52:23 PM  Show Profile  Reply with Quote
One thing that might help detrermine if the problem is valve float or something else. If I recall correctly, you had your car on a wheel dyno with 1.5 rockers and then with 1.65. The different ratio rocker arms should have made some difference in were the valve float occured. Maybe Lee has seen that. I have seen it on some bigger cams, nothing this small though. Jay
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Steve C.
Chief PONTIAC

1973 Posts

Posted - 18 Jan 2019 :  7:24:54 PM  Show Profile  Reply with Quote
"...account for 0.020" of lifter lash"

Explain. I don't understand the term as you use it relating to your hydraulic flat tappet cam.
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Lee
Sitting Bull

182 Posts

Posted - 18 Jan 2019 :  7:39:38 PM  Show Profile  Visit Lee's Homepage  Reply with Quote
quote:
Originally posted by Steve C.

"...account for 0.020" of lifter lash"

Explain. I don't understand the term as you use it relating to your hydraulic flat tappet cam.



I believe he is talking about preload. Probably a bit under 1/2-turn preload. If the lifter pumps up, he'll loose ~0.020" of "margin" for coil bind.

CURRENT: '73 T/A clone, starting to get less boring!...
67 Firebird (sold) 11.27 @ 119.6 Feb. '05 issue HPP
69 Falcon wagon, 10.51 @ 130mph Feb. '10 issue PHR (sold)
72 Cutlass Convertible, first car, owned since '82, now with a 6.0 LS, mild, putting just under 400 hp/tq to the wheels.
www.LNLPD.com
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Steve C.
Chief PONTIAC

1973 Posts

Posted - 18 Jan 2019 :  7:42:55 PM  Show Profile  Reply with Quote
Ummm, new to me but I'm used to lash relating to a solid cam. Thanks.

Tested on a Spintron machine Comp engineers find a hydraulic lifter "gives" just a little as you load it under running conditions. They use .006-inch numbers to represent a "real world" dimension for a running engine with hyd lifter tappets. It reduces net duration at the valve under running conditions.

Edited by - Steve C. on 18 Jan 2019 7:48:04 PM
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DanM
Sitting Bull

163 Posts

Posted - 23 Jan 2019 :  11:34:19 AM  Show Profile  Reply with Quote
Lee, I think the bottleneck is the cam duration (but that's the big question.) Carb is a well tuned Qjet. that should be fine. Pontiac stock dual plane intake runners are matched to head ports. Heads are moderately ported #96s. Headers are 1 3/4. Mufflers are the giant ones that Jim Hand uses. Ignition is Summit HEI, nothing special. The torque curve is smooth and peaks where expected 3500 - 4000 at 310 ft-lb. It gradually falls off as expected. I wish the HP curve kept rising. I'll take photos of a few of the relevant dyno runs and try to figure out how to post pictures. Let's table the dyno speculation until I can get those photos posted.

My transmission is a custom built 4L60E. It shifts faster than you can think. SNAP. done. It will break the tires loose in the 1 to 2 shift. Kind of stiffer than I would like but it's what I have. I selected that shift point based on the dyno curve. Because of the short 1st and 2nd gears (3.06, 1.62) I need to run high in the rpms so that after shifting it ends up at 2750 and 3210 from 1 to 2 and then from 2 to 3 respectively. If I shift earlier I will drop down so low that I lose all my power. So even though the power curve is dropping off quickly, getting up to 5500 will benefit me after the shift by dropping down to only 2910 and 3400. If I shift at 4500 I would drop into 2nd gear at 2380. Yuck. I will happily go to the track in the spring and do a comparison of shift points from 4000 to 5500.
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DanM
Sitting Bull

163 Posts

Posted - 23 Jan 2019 :  11:46:18 AM  Show Profile  Reply with Quote
Jay, yes you remember well. I'll find the dyno curves and post them to show the details of 1.5 rockers vs 1.65.

I would hypothesize that the valve float would be less for 1.65 rockers since the force of the spring gets a better lever - 1.65 - onto the cam. At 1.5 the force of the spring only gets 1.5 onto the cam. On the other hand, at 1.65 the lifter and pushrod and valve have to move further and therefore slam down faster. So, it could end up being a wash. Do we know for sure? I am not doubting your experience Jay. Changing rockers would be a fairly easy thing to do.

Steve, Jim Lehart's shop in Virginia built the heads. I trust he did a quality job. I will call them to ask about measurements if they exist. The problem is Jim is retired out west now.
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Steve C.
Chief PONTIAC

1973 Posts

Posted - 23 Jan 2019 :  12:18:33 PM  Show Profile  Reply with Quote
If records do not exist on the cylinder heads in my opinion, and if they were mine, I'd have them checked independently elsewhere. Also if they were mine I'd also pull a few valve springs off the heads and have them tested at the actual installed height once that is known. Most machine shops use a Rimac machine to do this. The spring is compressed to the installed height and the resultant seat pressure (closed) is indicated. Have them checked with the retainer that is in use.

There are on-head checking devices to check the pressure with the springs installed on the cylinder head. With them it means you only need to remove the valve covers to perform your check. However I will caution you that when they are used they often will not indicate the same results as a Rimac machine. Example on my current cylinder heads they test much lower. Personally we only use this type of checker for tracking how the springs are holding up with use. We check them once a year at the same time we check the valve lash.


Valve Spring Installed Height: Why It's Important and How to Measure It....

https://www.onallcylinders.com/2013/08/23/valve-spring-installed-height-what-it-is-and-how-to-measure-it/

Edited by - Steve C. on 23 Jan 2019 12:24:13 PM
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Corncob2061
Cochise

USA
388 Posts

Posted - 23 Jan 2019 :  9:37:51 PM  Show Profile  Reply with Quote
It would probably only take one weak valve spring to make the engine react like it did.

A flat tappet cam lifter and pushrod does have enough mass to make the bigger rocker arm ratio effect where the valves float much. Some of the hyd roller cam lifters are massive enough they seem to like the high ratio rocker arms or at least not mind it. On flat tappet cams it is the inertia of the valve when the valve is closing that causes valve float.

We have one roller cam engine that has a rev kit on it. If your not sure what that is, it has springs that are wedged between the head and the roller lifter, the pushrods go through the center of the springs. In theory, the valve springs do not have to force the lifter down on the cam lobe. The rev kit springs are doing that. You would think that would give it some more rpms, IRC, the rev kit springs run about 120 lbs force on the cam. In reality, the REV kit name is a little decieving, the valves float only slightly higher with the rev kit, and the recommended valve springs pressure is the same with or without them. We run it because it seems to increase the lifter life on street engines.

If you were to go back to 1.5 rockers, I would only switch the intake valves back. Leave the 1.65 rockers on the exh, they should not be causing any problems at all. Comps XE cams run magnum profiles on the exhuast, which less aggressive, and the exhuast valves are 45 degree seats as well. Jay




Edited by - Corncob2061 on 23 Jan 2019 10:08:16 PM
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Steve C.
Chief PONTIAC

1973 Posts

Posted - 24 Jan 2019 :  07:30:09 AM  Show Profile  Reply with Quote
I respectively disagree with a change to a 1.5 rocker arm ratio on the intake without the installed height verified and known. This because of the the topic already presented, his distance from coil bind at max valve lift. This presumbing the Comp XE lobe 5441.

Edited by - Steve C. on 24 Jan 2019 07:30:47 AM
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Corncob2061
Cochise

USA
388 Posts

Posted - 24 Jan 2019 :  09:25:38 AM  Show Profile  Reply with Quote
It was not my intention to suggest switching the rockers before the spring pressure, installed height, and coil bind are known.

Plenty of stock 30degree valve pontiacs with XE cams go to 5500-6000 with 1.5s. This little XE cam shuts the valves just as fast as a big XE cam, and it is going to take more seat pressure than usually running the 1.65s. Jay

Edited by - Corncob2061 on 24 Jan 2019 09:36:11 AM
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Steve C.
Chief PONTIAC

1973 Posts

Posted - 24 Jan 2019 :  09:29:56 AM  Show Profile  Reply with Quote
Thanks Jay, a misunderstanding on my part. I did not pay attention to the wording "IF" you change.

Edited by - Steve C. on 24 Jan 2019 09:31:09 AM
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Corncob2061
Cochise

USA
388 Posts

Posted - 24 Jan 2019 :  09:47:53 AM  Show Profile  Reply with Quote
If the springs check out, but have room for more pressure, I would consider leaving the exhuast alone and increase the seat pressures on the intakes only. Odds are the exh are not the problem. Jay
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Lee
Sitting Bull

182 Posts

Posted - 24 Jan 2019 :  11:14:57 AM  Show Profile  Visit Lee's Homepage  Reply with Quote
For comparison, I'll post a few Pontiac dyno graphs that I have handy.

This is a stock '69 400, with headers. It shows the rwhp as delivered and after tuning:


Here is a different basically stock '69 400 with headers. It had an Edelbrock 1406 that had been "tuned & rebuilt" by some moron (bottom graph) and then I built & installed a Holley (top graph).



The dyno glitched towards the end of this pull, but you can extrapolate the missing data. This is a stock 400 shortblock, 8.3:1, SD Performance 6X heads, Performer, Qjet, RA exhaust manifolds, 224/236 115lsa HR, and manual transmission (hence the ability to start the pull at a low rpm)



Here is a 16 D-port 400, headers, PerfRPM, UD 231/239 either 110 or 112 lsa, over 10.0:1 and run marginal on 93 octane:



Here is a 455, stock (old style) E-heads just over 10.0:1, Dougs headers, factory intake, Q-jet, 228/228 HFT cam, 112lsa/110ICL, 1.65 rockers:



Notice the HP curves. They are different, but none of them flat-line like you mention.

Now look at this one:



Note that this last set of data has a narrowed RPM range being shown, which makes the graphs have a bit less of an obvious "curve."

The bottom two lines were a stock 350, before and after tuning. The middle line is a basically stock 7.8:1 455, 222/242 116lsa low-lift, Performer, Q-jet, going through the same stock exhaust manifolds and 2" head pipes (about 2' of headpipe, feeding into 2.5" pipe) that the 350 used. All three of those graphs have very flat HP graphs.

The second to the top replaced the manifolds and 2" head pipes with Tri-Y headers, feeding directly into the existing 2.5" pipe. The top graph was replacing the entire exhaust behind the headers with 3" with Borla ProXS mufflers.

IMHO, the stock manifolds/2" headpipes were a bottleneck, both to the 455 and even the 350. HP reached a certain point and could not exceed it. With that restriction removed, HP increased with RPM as expected.

I have also seen other cases of bad mufflers (typically Flowmaster) causing power to "go flat" or even drop prematurely.


CURRENT: '73 T/A clone, starting to get less boring!...
67 Firebird (sold) 11.27 @ 119.6 Feb. '05 issue HPP
69 Falcon wagon, 10.51 @ 130mph Feb. '10 issue PHR (sold)
72 Cutlass Convertible, first car, owned since '82, now with a 6.0 LS, mild, putting just under 400 hp/tq to the wheels.
www.LNLPD.com

Edited by - Lee on 24 Jan 2019 11:59:54 AM
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DanM
Sitting Bull

163 Posts

Posted - 24 Jan 2019 :  5:30:58 PM  Show Profile  Reply with Quote
Lee, Awesome plots. I'm a data junkie. really great. You just made my day. Now I really have to return the favor.

My dyno plots look almost exactly like the third from the top (the black and white Winpep, stock 400, missing data, with the RPM on the horizontal axis.) That HP curve is essentially flat from 4200 to 5200. Then at 5400 the curve falls off a cliff. Peak torque is just below 4000 and steadily drops after that.

Almost identical like you snuck into my office and took a picture of my files.

After seeing all these I feel a lot better about my car.

Jay, I was thinking the same thing. Cut my workload in half by doing just intakes. I just now spoke to my mechanic and he's going to look up a past job he did for me to estimate cost. Couple years ago he swapped my springs on a previous set of heads still installed on engine. I can count on cutting that cost in half if I follow your advice.

Even if I don't gain much power (none at all really) or time on the track I need to solve the valve float issue so that the next time I rebuild this engine (to a 461) it can be done more accurately. I honestly think it is not asking too much to be able to rev past 5500 without weird stuff happening.
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Corncob2061
Cochise

USA
388 Posts

Posted - 24 Jan 2019 :  7:39:52 PM  Show Profile  Reply with Quote
The 400 with the 6x heads and the hyd roller cam was impressive for a 8.3 compression engine with manifolds.

The 400 that had the rebuilt Edy carb looked like he was lucky to make it in to the shop. Before and after was night and day.

COOL Lee!

Jay
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Lee
Sitting Bull

182 Posts

Posted - 24 Jan 2019 :  9:01:46 PM  Show Profile  Visit Lee's Homepage  Reply with Quote
Dan & Jay, glad you guys appreciate the data! I wish I could post more, but lost a hard drive that had a LOT of interesting data - these are mainly runs I happened to keep a printout. This is also the first time I noticed how closely the two 69's performed!

The 400/6X was originally supposed to be 9.0-9.2 CR, and that is what the cam was designed to use. I let the owner handle a lot of the ordering to keep the budget down, and we ended up with parts that gave us 8.3 instead. At that point we decided to roll with it, see what happens, and build a different short block if it underperformed. That was several years ago, and the owner just contacted me a few weeks ago - he had just outran a buddy who has a 455 in his Trans Am!

One thing to note about the 400/6X - the TQ curve vs the HP curve. I'v preached for years for people to NOT get hung up on "HP" on these motors, almost all pump gas Pontiacs are going to make more TQ than HP. I've seen too many people hunting for HP that throw away a LOT of TQ for a little bit of HP. Then they get beat by other Pontiacs with less HP :-)

CURRENT: '73 T/A clone, starting to get less boring!...
67 Firebird (sold) 11.27 @ 119.6 Feb. '05 issue HPP
69 Falcon wagon, 10.51 @ 130mph Feb. '10 issue PHR (sold)
72 Cutlass Convertible, first car, owned since '82, now with a 6.0 LS, mild, putting just under 400 hp/tq to the wheels.
www.LNLPD.com
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Corncob2061
Cochise

USA
388 Posts

Posted - 25 Jan 2019 :  2:41:20 PM  Show Profile  Reply with Quote
Of the two 69s that came close in power , one looked like the power came in a lot sooner. Is that a gearing difference or something else?

I am putting the original log manifiolds back on my 77 4 speed T/A with the bigger head pipes when I go back together. New territory for me, always ran headers in the past. Looking at the dyno testing from the last pic, the engine HP has pretty brisk head wind coming compared to what I am use too. Tri Y headers really had big gains.
Yikes!

Jay
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Lee
Sitting Bull

182 Posts

Posted - 25 Jan 2019 :  3:49:03 PM  Show Profile  Visit Lee's Homepage  Reply with Quote
quote:
Originally posted by Corncob2061

Of the two 69s that came close in power , one looked like the power came in a lot sooner. Is that a gearing difference or something else?

I am putting the original log manifiolds back on my 77 4 speed T/A with the bigger head pipes when I go back together. New territory for me, always ran headers in the past. Looking at the dyno testing from the last pic, the engine HP has pretty brisk head wind coming compared to what I am use too. Tri Y headers really had big gains.
Yikes!

Jay




Yes, that was just differences in gearing.


For the headers/logs testing, I'll put the torque graphs down below. Are you SURE you want to put logs on your car????


CURRENT: '73 T/A clone, starting to get less boring!...
67 Firebird (sold) 11.27 @ 119.6 Feb. '05 issue HPP
69 Falcon wagon, 10.51 @ 130mph Feb. '10 issue PHR (sold)
72 Cutlass Convertible, first car, owned since '82, now with a 6.0 LS, mild, putting just under 400 hp/tq to the wheels.
www.LNLPD.com

Edited by - Lee on 25 Jan 2019 3:50:20 PM
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DanM
Sitting Bull

163 Posts

Posted - 26 Jan 2019 :  1:36:45 PM  Show Profile  Reply with Quote
First, im about to lose my temper over my inability to post pictures. I found all my dyno plots and would like to share then. Theres no file upload button on this site.

Advice please?
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DanM
Sitting Bull

163 Posts

Posted - 26 Jan 2019 :  1:40:58 PM  Show Profile  Reply with Quote
Today i did as test. Its 20 degrees and dry. With an engine not fully warmed up, about 150 on temp guage, it ran up to 5500 and was as happy as can be. Minutes later, temp guage at 180, it made the usual angry growl at 5250
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Lee
Sitting Bull

182 Posts

Posted - 26 Jan 2019 :  3:14:31 PM  Show Profile  Visit Lee's Homepage  Reply with Quote
I use imgur.com to host photos. You have start an account, which is free.

Hard to play "find the gremlin" over the internet. It sounds like SOMETHING heat related. Maybe an ignition component is dying, and is aggravated by the heat. I had the pick-up coil go bad in a customer's car years ago - the car would run fine for up to 30 minutes, then start backfiring and acting crazy. After cooling for a bit, it would fire right back up and run great for awhile, then go to crap once it got warmed it again.

Pick-up coil, module, ignition coil, vapor lock, something mechanical that has a clearance too tight.

That said, with your cam and heads, I still see ZERO reason to ever take your motor past 5200.

Oh, what sort of computer is controlling your transmission? You mentioned how hard it shifts. You should be able to tune your line pressure, no need for max pressure at light or part throttle.

CURRENT: '73 T/A clone, starting to get less boring!...
67 Firebird (sold) 11.27 @ 119.6 Feb. '05 issue HPP
69 Falcon wagon, 10.51 @ 130mph Feb. '10 issue PHR (sold)
72 Cutlass Convertible, first car, owned since '82, now with a 6.0 LS, mild, putting just under 400 hp/tq to the wheels.
www.LNLPD.com
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DanM
Sitting Bull

163 Posts

Posted - 26 Jan 2019 :  5:27:50 PM  Show Profile  Reply with Quote
<a href="https://imgur.com/MMwhFdN"><img src="https://i.imgur.com/MMwhFdN.jpg" title="source: imgur.com" /></a>
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DanM
Sitting Bull

163 Posts

Posted - 26 Jan 2019 :  5:29:38 PM  Show Profile  Reply with Quote
https://imgur.com/MMwhFdN

https://i.imgur.com/MMwhFdN.jpg



[url=https://imgur.com/MMwhFdN][/url]
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DanM
Sitting Bull

163 Posts

Posted - 26 Jan 2019 :  5:41:41 PM  Show Profile  Reply with Quote
Sorry about that previous couple posts. Someone feel free to delete them.

Ok, baseline 400ci, 8.9:1, stock exhaust manifolds, true dual 2.5", 1.5:1 rockers, comp cams 988 springs

<a href="https://imgur.com/O8FosdV"><img src="https://i.imgur.com/O8FosdV.jpg" title="source: imgur.com" /></a>
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DanM
Sitting Bull

163 Posts

Posted - 26 Jan 2019 :  5:42:16 PM  Show Profile  Reply with Quote
https://imgur.com/O8FosdV
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DanM
Sitting Bull

163 Posts

Posted - 26 Jan 2019 :  5:42:55 PM  Show Profile  Reply with Quote


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DanM
Sitting Bull

163 Posts

Posted - 26 Jan 2019 :  5:45:47 PM  Show Profile  Reply with Quote
I feel that the sudden drop off was due to bad noise (valve float?) It's also possible that I lifted right then. I think it was valve float because the next dyno plot is a result of upgrading to Comp Cams 955 springs and using the 1.65 rockers. Note that the engine is now able to rev past 5500 but there is no improvement in torque or power across as was hoped because of the 1.65 rockers


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DanM
Sitting Bull

163 Posts

Posted - 26 Jan 2019 :  5:49:50 PM  Show Profile  Reply with Quote
I don't know what was happening in the green curve. I think I lifted.

In the red curve I had some carburation issue.

The blue curve is the "typical" result. Smooth, strong, predictable.

Then a year later I returned with headers and a new set of heads with mild porting and the same 955 springs and 1.65 rockers. Notice that the fuel mix was leaner than ideal.



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DanM
Sitting Bull

163 Posts

Posted - 26 Jan 2019 :  5:54:47 PM  Show Profile  Reply with Quote
I figured out how to tune the secondaries on my Qjet and returned 3 months later with my best results to date. The owner was nice enough to pull up my old files and overlay the progression of improvement: 2015 baseline, 2017 lean, 2017 mixed better.

288 HP. The max torque number indicated is suspect. I believe down at 3500 the setup was still getting loaded to full throttle and was rocking. 320 is probably real.



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DanM
Sitting Bull

163 Posts

Posted - 26 Jan 2019 :  6:01:30 PM  Show Profile  Reply with Quote
I came back one more time with a spare set of secondary rods and a timing light. I fiddled around a few times and got no improvements. However, these runs we ran up to 5700 rpm and were trying to investigate the raspy sound which is tbd but possibly valve float.

Again he overlaid the 2015 baseline with two more plots from that day. The fuel mix is perfect. I don't like the HP curve where it breaks over at 5100 and 5200. Some weird stuff at 5500 in the red curve.

Still, overall I'd have to say I'm happy with things.



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DanM
Sitting Bull

163 Posts

Posted - 26 Jan 2019 :  6:12:52 PM  Show Profile  Reply with Quote
I must say, that 5/15/2017 plot is pretty sweet. I'm getting practically peak HP at 5500 rpm. You can see in the AFR curve that it just starts to lean out. The owner wasn't sure if the lean plot is real or a result of misfiring due to something else. Still.

The springs in that May dyno run were only 2 months old. It's hard to say whether they softened up in later months and that's causing my issue. For sure, in the 6/6/2107 dyno plots it was making the noise that is of concern but the power curves still hold fairly steady out to 5600. Who knows that if I kept the fuel rich like 10:1 or 11:1 it might go away.

Maybe I will buy that valve spring pressure gauge and check everything. This might all be in my head. The noise is real though.
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Steve C.
Chief PONTIAC

1973 Posts

Posted - 26 Jan 2019 :  7:00:28 PM  Show Profile  Reply with Quote
Before purchasing test equipment you might consider looking for a machine shop and check their cost.
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Corncob2061
Cochise

USA
388 Posts

Posted - 27 Jan 2019 :  9:37:17 PM  Show Profile  Reply with Quote
quote:
Originally posted by DanM

I don't know what was happening in the green curve. I think I lifted.

In the red curve I had some carburation issue.

The blue curve is the "typical" result. Smooth, strong, predictable.

Then a year later I returned with headers and a new set of heads with mild porting and the same 955 springs and 1.65 rockers. Notice that the fuel mix was leaner than ideal.







The choppier later pulls were probably a difference in tuning, but look more like what valve float would look like. Starts to get choppy then follows with a sharp down trend, versus the blue curve that is smooth.



The graphs were it the power is nosing over at 5200 are fairly smooth? Could be valve float though. I think spring pressure is a good place to start looking.

Jay



Edited by - Corncob2061 on 27 Jan 2019 10:52:18 PM
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DanM
Sitting Bull

163 Posts

Posted - 28 Jan 2019 :  11:20:37 AM  Show Profile  Reply with Quote
<iframe width="100%" height="300" scrolling="no" frameborder="no" allow="autoplay" src="https://w.soundcloud.com/player/?url=https%3A//api.soundcloud.com/users/579514083&color=%23ff5500&auto_play=true&hide_related=false&show_comments=true&show_user=true&show_reposts=false&show_teaser=true&visual=true"></iframe>
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DanM
Sitting Bull

163 Posts

Posted - 28 Jan 2019 :  11:24:09 AM  Show Profile  Reply with Quote
https://soundcloud.com/user-751610625

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DanM
Sitting Bull

163 Posts

Posted - 28 Jan 2019 :  11:34:46 AM  Show Profile  Reply with Quote
I made some recordings in an attempt to let you hear for yourself. It's so subtle in the recordings that I'm not sure you can even hear anything special.

The previous post has a link to 9 files.
MyRecord (2) is the baseline shifting at 5200. The road is damp so at first I have trouble getting traction. Then you hear the rev up to the 1 to 2 shift then the rev up to the 2 to 3 shift. No problems.

MyRecord (5) is also baseline shifting at 5200. Different road. I get into it then lose traction, recover then rev up to 2 to 3 shift. No problems.

MyRecord (6) is the issue, shifting at 5400. Some traction problems at first then rev up to 2 to 3 shift. It's there but hard to hear it.

MyRecord (8) cruising on the highway at about 60 mph, after a few seconds the torque converter locks and the rpms drop by about 200 rpm.

MyRecord (9) cruising in traffic about 50 mph, after a couple seconds the torque converter locks and rpms drop.

MyRecord (10) in traffic cruising at about 70, up hill, more throttle, torque converter unlocks, revs increase

MyRecord (11) "idling" along at 25 mph

MyRecord (12) idling in park. the recording is next to exhaust pipe

MyRecord (14) idling in drive, the recording is next to the exhaust pipe

NOTE: i don't have a crossover on my exhaust. It's true dual so you will hear a distinct thrum on the highway or low frequency beat at idle. To some people (and to me at first) is sounds like a mis-firing cylinder.

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Corncob2061
Cochise

USA
388 Posts

Posted - 28 Jan 2019 :  10:06:48 PM  Show Profile  Reply with Quote
quote:
Originally posted by DanM

https://soundcloud.com/user-751610625





Tried following the link but it said no public sounds? Jay
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DanM
Sitting Bull

163 Posts

Posted - 29 Jan 2019 :  11:49:25 AM  Show Profile  Reply with Quote
sorry about that. I just fixed it. I manually made them all public.

Wear headphones. Your phone or computer speakers won't reproduce the low end in the background which is where all the action is.

track 2 has a sound around 6 seconds that is similar to what we are looking for.

track 6 has the problem. It occurs at about 5.5 seconds. The sound of the problem - as recorded here - is very similar to that of track 2 where the problem doesn't exist.

However, if we assume that there might be valve float prior to 5200 then the sound in track 2 near 6 seconds could be indicative. If you were to be in the car with me it is all more noticeable. I can try to get my hands on a real microphone with a cord. I can place the mic in the engine bay or in the rear quarter panel to get close to the exhaust pipe.

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Corncob2061
Cochise

USA
388 Posts

Posted - 29 Jan 2019 :  11:09:38 PM  Show Profile  Reply with Quote
Car sounds great!

For what it is worth, it sounded like something causing reversion to me, similar to what the dyno operator said. I think they were probably right. My guess, it is starting to float the intake valves. Maybe lost some valve spring pressure, maybe the intake valve seat is geeting a bit wide making it harder to keep seated. Could be some of both. Really sounded good everywhere else though. Jay
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DanM
Sitting Bull

163 Posts

Posted - 10 Feb 2019 :  12:49:52 PM  Show Profile  Reply with Quote
Hey Team,

Yesterday my sonand I used my nifty new Moroso valve pressure guage.



Summary: almost consistently 90 pounds seated
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DanM
Sitting Bull

163 Posts

Posted - 10 Feb 2019 :  12:56:30 PM  Show Profile  Reply with Quote
Using the Moroso 62390 we found good consistency but lousy pressure. A couple springs were at 100 pounds. As well as i could measure the installed heights were correct.

Choices:
Add shims to change installed heights to 1.6 instead of 1.7 to increase seated pressure
Or
Install new springs.

Feel free to advise.
Note: i will pay my mechanic to do the work, heads on engine, drive in and drive home next day.
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Corncob2061
Cochise

USA
388 Posts

Posted - 10 Feb 2019 :  8:22:52 PM  Show Profile  Reply with Quote
Comps 995s are suppose to be about 400 lbs per inch. Shimming .1 should be another 40lbs. 130 sounds better than 90. A .075 should be 120. I think I would shoot for 120. Jay

Edited by - Corncob2061 on 10 Feb 2019 8:42:12 PM
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Steve C.
Chief PONTIAC

1973 Posts

Posted - 11 Feb 2019 :  12:10:21 PM  Show Profile  Reply with Quote
https://www.chevelles.com/forums/13-performance/315159-shimming-valve-springs-how-much-too-much.html
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DanM
Sitting Bull

163 Posts

Posted - 13 Feb 2019 :  7:54:37 PM  Show Profile  Reply with Quote
Two options.

Add 0.075 or 0.100 of shims to current springs. The advantage is Iknow what the real state of affairs is so ishould be able to get it right in one try. Disadvantage is the sprins my be aging. Can one event of"overheating" to 250 degrees ontemp guage kill my springs?

Option2 is to use new springs. Advantage is they are new. Disadvantage is it might take two tries to get it right.

Comments?
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