pontiac 400 6x-4 heads - Performance Modifications - Firebird Nation

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pontiac 400 6x-4 heads


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9 replies to this topic

#1 Mclo

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Posted 4 weeks ago

Hi guys been awhile. so im at still at work on my build. i am building a 461cid slowly. my question is are these cast iron head still good if i would machine them down to 87cc? or should i buy some 87cc from edelbrock? i am a machinist by trade and dont mind doing my own machining but dont want to waste my time machining them if there not worth it

#2 ponyakr

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Posted 4 weeks ago

If you use flat top pistons, you don't need to cut 'em down to 87cc. That would make too much compression for pump gas, if using iron heads, IMO.  


Edited by ponyakr, 4 weeks ago.


#3 b_hill_86

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Posted 4 weeks ago

Im not an engine builder by any means but I am running these heads with a smaller chamber. Are the Edelbrock heads aluminum or iron? The biggest differences I could see would be flow and valve size assuming the edelbrocks are different. Is that what youre asking?

#4 JoePeek

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Posted 3 weeks ago

I have 87cc heads on my 455 (462) and they run great on 93. They are Edelbrock 87 cc (round port to match my exhaust), so they are aluminum. Being that they are aluminum that helps me get away with a bit more compression than an iron head. I've spent a lot of time dialing in my timing and fuel in to this particular car weight/gear combination, so that helps too. Stock 1970 455's for the big cars and GTO had 87cc iron heads from the factory, but that was back when Sunoco 260 was still around, so that put's the 87cc on a 455 thing into perspective. I tried a set of 670 heads (72 cc) on a 455 I had in a D-port car one time years ago and I hated it. If I mixed 93 and Turbo Blue it was happy, but it was a bitch to crank when it was hot (like a lot of Pontiac's with headers). It was my daily driver so I had to make it run on 93. By the time I had taken enough timing out of it for it to survive on 93, it was back to where it was with the stock 8.4 to 1 compression heads that were on it before. I think my case of 87cc aluminum heads, in a 3100 lb. car, 4 speed, 3.42 gear car with timing and fuel to match may be about the edge of what you can get by with. In a heavier car, with a highway gear, and whatever timing is in the distributor you happen to have would be an issue with iron 87cc, or even 94cc heads. To even have a shot at it, aluminum heads will help about 1 compression point, and then some tuning with the timing. There is something to be said about how good you are at messing with timing curves, that may help you get away with a borderline case, but keep in mind that if you may just end up back to where you would have been if you would have used some bigger cc heads in the first place.


Edited by JoePeek, 3 weeks ago.


#5 tjs

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Posted 3 weeks ago

If you dont want to replace the exhaust I would consider either KRE or Edelbrock D port alu heads.Tom



#6 Mclo

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Posted A week ago

tjs do you mean replacing my exhaust valve? my heads already have the 1.660 so i would have to make them to 1.770? doing that i imagibe we need to replace the valve seats?

And thanks JoePeek awsome response i will keep all that in mind and probably just leave my heads alone then and later down the road probably upgrade to KAR or Edelbrock heads

#7 tjs

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Posted 6 days ago

No,buy a set of alu D port heads from either KRE or Edelebrock.Tom



#8 GTOLou

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Posted 5 days ago

The speedmaster heads have had decent reviews so far and are cheap compared to edelbrock or kre's. - they are round port, so you'd have to upgrade your exhaust to round port headers, etc. 



#9 tjs

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Posted 3 days ago

There was a direct compare on PY with a set of Eheads and the SM heads,find it a read it.Get what you pay for.Tom



#10 Mclo

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Posted A day ago

Thanks for all the replies guys. greatly appreciated!!




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