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Brian R
Crazy Horse

USA
1672 Posts

Posted - 22 Aug 2017 :  2:19:21 PM  Show Profile  Reply with Quote
For years I have asked advice on Cams for my particular engine. Many have been helpful but it always seems that my engine is stuck somewhere between wimp a$$ low compression and high compression. Recommendations fly for both ends of the spectrum but I can never get a cam recommendation for my in-between motor.

I thought I would put out a possible custom cam for your opinions please.

Engine/Car:

461, 9.2:1 compression,
Edelbrock heads ported to flow around 310 on intake. 2.11/1.77 valves
Oversized RARE exhaust mainfolds into a 2 1/2 inch dual exhaust with x-pipe and free flowing mufflers.
Intake (not now as I plan to replace rhe Performer) Performer RPM going on.
Quadrjet by Cliff
Cool setup except I dished the pistons too much and killed the compression.
71 Lemans convertable - heavy, on scale shows apx 4100 lbs
Turbo 400 tranny
3:55 rear

Proposed cam with explanations which I hope you guys will comment on:

Going hydraulic flat for various reasons so I am limiting to that for this discussion

LSA: 108 - I always get recomendations for wide LSA but doesn't that bleed off compression? I am already low

Duration at .050: (int/exh) 225/230 - Reading says that longer duration also bleeds compression

Lift: Went big hear to allow more in/out and to make up for the smaller duration: 495/510

What do you think? Basically trying to find a middle ground to replace the damned noisy Comp XE in there now. From what I understand, the reason they can be loud is the steep ramps they use. Looking forward to your thoughts.

Lobe Dur .050 Dur.050 Lift Lift
Sep Int Exh Int Exh
108 225 230 495 510

loosetappet
Sitting Bull

113 Posts

Posted - 22 Aug 2017 :  10:32:52 PM  Show Profile  Reply with Quote
Very close to a Crower 60210.
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Steve C.
Crazy Horse

1675 Posts

Posted - 23 Aug 2017 :  05:39:49 AM  Show Profile  Reply with Quote
Since crower cams are being mentioned here in conjunction with a 108 lobe separation.

Not necessarily a recommendation, but if it helps for a general comparison my engine builder used a Crower 60211 hyd flat tappet (236/242) cam w/1.6 rockers in 4.250 stroke combo using 87cc Edelbrock heads, cleaned up only no port work to speak of, 10.3 compression. It used a Performer RPM intake, Holley vacuum secondary 750 carb and 1-7/8 headers. On the engine dyno it made 513-518 hp at 5200/5300 rpm.


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Steve C.
Crazy Horse

1675 Posts

Posted - 23 Aug 2017 :  05:50:29 AM  Show Profile  Reply with Quote
I've mentioned before I used a 108 lobe separation on the combo linked here to help with my low compression ratio on Edelbrock heads. That and in past builds over the years the 108 provided great results. Also in conjunction with the lower compression the XE cam here has shorter seat timing (advertised duration) than the typical Crower cams, that is positive in my opinion. Just be aware of the obvious in that the narrow lobe separation will reduce idle quality slightly.

http://www.pontiacstreetperformance.com/psp/rebuild455sc2003.html
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Phil
The Great White Buffalo

USA
7219 Posts

Posted - 23 Aug 2017 :  08:24:15 AM  Show Profile  Reply with Quote
Expect a tighter power band too, and on the lower end.

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.
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Steve C.
Crazy Horse

1675 Posts

Posted - 23 Aug 2017 :  08:36:13 AM  Show Profile  Reply with Quote
Your comment... "Duration at .050: (int/exh) 225/230 - Reading says that longer duration also bleeds compression"

As I eluded to above you should be looking at the seat duration not the .050" duration. Just keep in mind not all companies use the same values to measure the advertised duration of their cams. Comp rates there hyd cams at .006" tappet lift while others may use another number such as .004".

Also to take advantage of the fact that Edelbrock heads flow well at higher valve lift look for a lobe to maximize lift while only adding a minimal amount of duration.


Edited by - Steve C. on 23 Aug 2017 08:42:56 AM
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Steve C.
Crazy Horse

1675 Posts

Posted - 23 Aug 2017 :  12:47:16 PM  Show Profile  Reply with Quote
For conversation as a example. What lobe would be desirable with low compression and provide additional valve lift....

Two hydraulic flat tappet lobes at Bullet Racing Cam for a intake lobe:

H280/300B
Adv 280
225 at .050
.3000" lobe lift

OR

H276/322
Adv 276
225 at .050
.3220" lobe lift

Match the intake lobe to a exhaust lobe with the desired amount of extra exhaust duration to compliment the cylinder head exhaust-to-intake flow ratio. Then with the desired lobe separation, be it 108, 110, 112, etc.


Edited by - Steve C. on 23 Aug 2017 12:49:25 PM
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Brian R
Crazy Horse

USA
1672 Posts

Posted - 24 Aug 2017 :  10:07:24 PM  Show Profile  Reply with Quote
All good stuff - thank you.

Question, on the LSA, is 108 overkill and what bad effects might there be over a 110?

Does the 108 make any real difference by allowing less compression to bleed off?

Will my idle have more or less lope than a 110?

Will vacuum be more or less than with the 110 ?
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Bill Boyle
Horse Feathers (Charter Member)

USA
4794 Posts

Posted - 25 Aug 2017 :  06:19:16 AM  Show Profile  Visit Bill Boyle's Homepage  Reply with Quote
The lower the LSA the more radical the cam is at idle and that equates to more lope. Vacuum is also lower and may not be enough to run power brakes without a vac pump. LSA effects pressure and opening and closing events have a lot to do with the amount of cylinder pressure any cam builds...this has to be looked at very carefully.

"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.
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Steve C.
Crazy Horse

1675 Posts

Posted - 25 Aug 2017 :  09:42:04 AM  Show Profile  Reply with Quote
For interest you can 'play around' with calculators, example here:

http://www.wallaceracing.com/overlap-calc.php

Go to Bullet Racing Cams where I found the lobes mentioned here for the intake and find one for a exhaust lobe. Input the two with a lobe separation and note what it does to the overlap. There are other calculators of interest on that site. But there not going to provide any definitive answers, just a guide to a trend in the changes.

Your question, "Will my idle have more or less lope than a 110?"
Bill has answered it, in that a narrow lobe separation reduces idle quality. More of the effects with changes here:

http://www.compcams.com/Pages/413/cam-timing-lobe-separation-angle.aspx

It is also subjective. One person's idea of a 'radical' idle will be different from another, example I personally like a lot of lope and do not mind a rougher idle. Related, on purpose I keep my idle rpm in gear at around 1000 rpm even when it might be capable of being set lower ('Splash Lube' in conjunction with a solid roller as one example why). Also the size of the engine has it's effects, example on my current 505 cid engine I recently changed from a 110 lobe separation to a 112. Reason I had to replace my cam because of scuffing caused by a roller lifter but I knew that I was also going to convert to port fuel injection and the wider lobe separation could be beneficial. That said, with the change I noticed very little impact with the idle quality. But making a similar change to a 400 cid engine could be much different.

http://www.bulletcams.com/


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Edited by - Steve C. on 25 Aug 2017 09:43:54 AM
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Steve C.
Crazy Horse

1675 Posts

Posted - 25 Aug 2017 :  10:04:55 AM  Show Profile  Reply with Quote
Side note. Within the calculator link I furnished as noted be sure you use the seat duration (advertised duration) for input, not the duration at .050" tappet lift.

Also, I'd be very curious why you are considering such a 'tiny' cam with 225 degrees of intake duration with your amount of cubic inches. Building a truck motor


Also of interest, a Lunati Voodoo lobe is much quieter than a similar Comp XE lobe. VERY much touted as so. This has to do with the closing profile on the lobe and its effects of the valve as it returns to the seat. The reason for the 'sewing machine' sound with a XE hydraulic flat tappet lobe. UltraDyne lobes are also quieter, they were designed by Harold Brookshire at UltraDyne. Harold later designed the Voodoo lobes while at Lunati before he passed away. Today bullet racing Cams addition to their own lobe designs they have the masters for and sell UltraDyne lobes (listed within their site).

http://www.lunatipower.com/ProductGroup.aspx?id=287&cid=48

Edited by - Steve C. on 25 Aug 2017 10:20:45 AM
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