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Tribal Scout

4 Posts

Posted - 25 Feb 2018 :  12:38:11 PM  Show Profile  Reply with Quote
Looking for Advice: I have a 1967 Pontiac GTO 400/4-speed that was completely rebuilt at a compression ratio of 8.5:1 to run lower octane gas (I generally run mid-range octane) over 10 years and 2000 miles ago. My builder selected a Ram Air Cam to achieve this and get me to his calculation of 409HP at 439Lbs of torque. My engine guy was experienced building drag strip motors so I trusted his selection based on my request for a strong HP motor for street driving that didn?t break the bank. I am running headers with flowmaster exhaust along with a SMI Stage II Rochester Carb w/El choke setup as well as a Pertonix Flamethower HEI.
To be honest, I have not been driving the car much over the years due to numerous reasons, but I have been working on the car and recently updated the suspension for better drivability. I have read and tried numerous options to tune I have read about but still cannot get to optimum tune and idle. I am hoping to gain some knowledge from this forum.
I am running lighter springs in the distributor (which years ago my builder swapped out when he made an attempt at tuning years ago, the plugs are gapped for HEI, I am running manifold vacuum as well. The timing is more advanced then I prefer and I cannot get the motor to idle less than 1000 and return to idle. Engine vacuum is in the 18-20 range.
1. The engine is initially hard to start and I believe the choke is set correctly, I need to feed the engine fuel to start, I sometimes have slight run on after shut down. Once warm the engine seems to run fine with decent throttle response. Am I missing a choke/carb adjustment?
2. During driving or rev-ing the engine the idle does not always drop back to setting, sometimes it stops high or low of my expected idle setting. Would changing the springs make any difference here?
3. Based on my info, Does anyone see why I cannot get my engine to have a nice 800-900 rumbling idle?
Any additional thought's and comments are welcomed!


5391 Posts

Posted - 25 Feb 2018 :  6:57:03 PM  Show Profile  Visit cortcomp's Homepage  Reply with Quote
I'm no engine expert, but based on what i've read here, i don't think the RA cam and 8.5 would go together at all? I'd think it'd be sluggish amongst other issues. Also, at 8.5 you could run just miserable gas. I get by on 87 in my 9.5ish 455 with a mild cam, but i usually run 89 to avoid run on: the combination of lower octane and having the idle bumped up to compensate for A/C and a little idle stumble causes it. If i adjust idle down OR switch to 89 it goes away. Small tuning issue.

Anyways, I'd bet a dollar others are going to step in and say that cam just can't tune/work with that low compression.
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Sitting Bull

153 Posts

Posted - 25 Feb 2018 :  7:31:31 PM  Show Profile  Visit Lee's Homepage  Reply with Quote
The term "Ram Air Cam" can actually mean all sorts of things. If it is a true factory copy, then is it an original Ram Air, or a Ram Air IV, or one of the Ram Air III versions? Or maybe it is an aftermarket design loosely based on one of those R/A designs (of which there are several).

An 041 "Ram Air IV" cam would for sure be too much for what you have. Without knowing what you have, there is no way to guess.

1. Let your motor warm up, and remove the air filter. Look at the choke butterfly - is it totally open (vertical)? It should be.

2. Put in some stiffer springs and see if that helps the problem. Free and easy thing to do.

3. It should idle below 900. I suspect your carb and distributor BOTH need some tuning. Where do you live? Maybe somebody local to you can point you to somebody that can help you.

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.
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Blued and Painted

3458 Posts

Posted - 26 Feb 2018 :  3:04:34 PM  Show Profile  Reply with Quote
All RA 4 versions are a mismatch with your combo.
It was offered by GM with 10.5 to 1 compression and 3.73 or larger rear gear.

For an off the shelf cam, I would not go larger than the crower 60918 or 220 intake duration at that compression level for better drivability.
For more lift, clearance pushrods holes and add 1.65 rockers.

For 450+ hp, you will need some higher flow alunimum heads, roller cam, and upgrade pistons and rods.

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

4 Posts

Posted - 08 Mar 2018 :  10:57:47 AM  Show Profile  Reply with Quote
Thanks, I may have the actual compression ratio wrong, I'll need to dig up the info on the cam. He mentioned that it was a custom grind and that the compression ratio would be lower so that I could get away from running octane boost or premium gas. Had I understood more I would have just left the compression alone and boosted my gas. Anyway, I'm south of Chicago and would like to find a shop that would be help me get the engine dialed in.
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Sitting Duck

1522 Posts

Posted - 09 Mar 2018 :  02:19:19 AM  Show Profile  Reply with Quote

Calvin Hill has a great reputation with Pontiacs in Il/Wi. Give him a call. If he can?t do it I know that he would know who can. I?m not familiar with the shop in Addison. Wayne up here in Wi is who I had build my engine, but not someone who tunes existing builds.

71' GTO Original 400 M20 3.23 posi
13.95@102.1 MPH on street tires

Edited by - 67drake on 09 Mar 2018 03:34:35 AM
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