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Pontiac Forum: Help with engine upgrades on my 70 gto
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  #1  
Old November 15th, 2018, 12:34 PM
dwd70gto dwd70gto is offline
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Help with engine upgrades on my 70 gto

I currently have a 1969 400 350 hp engine with 6x-8 heads, I know that this has lower the compression down to about 7.5. The engine has the std cam and standard flat top pistons, a performer intake and a 750 q-jet carb. I have a HEI distributor and std exhaust manifolds . The car is a turbo 400 with the 355 posi
rear end. I was thinking about changing the cam and the heads and adding ram air manifolds (because I like them over headers). I was going to go with a Ram air 4 spec cam and some 80 to 85 cc heads. I want to run pump gas and I drive the car on the street all spring, summer and fall. Thanks in advance for your advice.
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Old November 15th, 2018, 06:24 PM
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melsg5 melsg5 is offline
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going for something like the Edelbrock aluminum heads with the round exhaust ports and 87CC chambers should be perfect. I would think real carefully about the RA IV cam with an automatic and stock converter. You may need to run Rhoads lifters to get it to idle properly. Reconsider perhaps going with the HO style 068 cam instead.
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Old November 16th, 2018, 09:10 AM
dwd70gto dwd70gto is offline
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With the 068 cam, will i be able to use std rockers and lifters and get good vacuum for the power brakes.. I was thinking about the 041 cam with 1.65 rockers and the Rhoads lifters.
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Old November 16th, 2018, 09:38 AM
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cammerjeff cammerjeff is offline
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I agree with melsg5 about the cam choice, the RA 4 cam's do not seem to like a auto trans with a low stall speed converter. I like your other choices, but if you do decide to go with 1.65 rocker arms you have to be very carful to check each valve spring for coil bind ( I have seen only 1 or 2 of the 16 have an issue with it) and also pushrod clearance on the head casting holes.
Going with aftermarket heads the pushrod clearance may not be an issue. Anouther set of heads to consider is Kauffman Racing's D port heads. They flow as well as the Edelbrock round ports and can save you $$$ by not having to buy the round port Ram Air manifolds. Just something to consider.

http://www.krepower.com/pontiac%20al...er%20heads.htm
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1978 Sunbird Safari Buick 3.8 2004R
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1973 Lemans Safari 400 4-speed (factory)
1971 Catalina Freeway Enforcer 455 TH400
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Old November 16th, 2018, 11:29 AM
dwd70gto dwd70gto is offline
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I like the idea of the Kauffman heads (85cc) with the d-ports.

Last edited by dwd70gto; November 16th, 2018 at 11:31 AM. Reason: fix spelling and cc size
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Old November 16th, 2018, 01:37 PM
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which ever head you decide on the manufacturer should be able to tell you the maximum lift that the springs can handle so you decide on which cam to go with. The Rhoads lifters can be noisy at idle.
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Old November 16th, 2018, 02:14 PM
dwd70gto dwd70gto is offline
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With the 6x heads and stock cam the car is very slow to respond. If i put the 85 cc heads will that solve the response time. The 85cc heads should get me to 8.75 compression from the 7.5 I'm at now. The engine runs great just not the beast it should be.
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Old November 16th, 2018, 02:17 PM
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Actually with aluminum heads you should be able to go to 10.0 CR without an issue, with cast iron heads I would not push the CR beyond 9.0 on a street car to avoid having to run race gas.
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1978 Catalina Safari Buick 350 TH350 soon to have a Pontiac 400 4bbl installed!
1978 Sunbird Safari Buick 3.8 2004R
1977 Astre Formula 215 Buick V8 T-5
1973 Lemans Safari 400 4-speed (factory)
1971 Catalina Freeway Enforcer 455 TH400
1969 Firebird Sprint 301 OHC-6 T-5
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Old November 16th, 2018, 03:47 PM
dwd70gto dwd70gto is offline
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So are you saying I should look at 72cc aluminum heads to get to 10:1 and run 91 to 93 octane pump gas.
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Old November 16th, 2018, 06:42 PM
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if you have access to 93 octane by all means go for the smaller chamber.
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