going to purchase afr 190 aluminum heads for my bird.it has a stock lower end and a modified intake with all the bolt on's-asm runners edelbrock base,ported plenum--running slp 1-3/4 headers also 6 PSI boost-i'm thinking that with the aluminum i can increase compression. so the afr's come at 68 cc,the stock iron heads are 64cc(so i would loose compression) and vettes aluminum heads are 58cc .so should i have them milled to 58 as i know many people are running 6 psi on vetts with no problem.i've also read that vette's hawe the same compression as the iron head l98's even with the smaller cc heads because of a thicker head gasket but don't know if this is bull or not
thanks


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350 tpi,paxton sc,slp exaust@headers

 

on blown applications the exhaust port seems
to be the measurable restriction. if you are
planning on high rpms 220cc w/80cc exhaust.
just some observations ive made on some of
my experiences.
airdeano

 

I'd recommend finding some 64cc heads. With stock cast heads or even aftermarket cast heads you're restricted by a few tenths of a point in compression because of hot spots in the cast material. Aluminum heads you can go a little higher, i.e. 10:1 is fairly safe if you run 92 octane. 58cc heads would be great but when going blown I know that I would want to stay on the safer side of the mix, and if you go with a thicker head gasket and more compression your chances of blowing that gasket increase. Also adjusting your compression via head gasket thickness is VERY unwise, becaues once you raise that head gasket you raise your "squish/quench" area and become even MORE prone to pinging. Keep your squish around .035, and your compression ratio on aluminum heads around 10:1, unless blown then you may want to step it down. If you go to cast heads go .5 points lower on compression than you would aluminum, Good luck!

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[This message has been edited by tpi_roc (edited November 19, 2001).]