I have 58cc AFR 190 heads. I've heard 11:1 CR is pushing it w/ alum heads and high octane pump gas and 10:1 CR is pushing it w/ iron, is this true? What CR should I aim for w/ the alum AFR's for a street car? 10.1:1 too much?

 

Compression isn't only dependent on head material or octane, alot has to do with the cam. For example 11:1 with aluminum heads and a very mild cam can cause detonation, but with a more radical cam would be ok.

If you're not running a very lumpy cam somewhere in the mid 10's with aluminum would probably be ideal with a mild cam, but to take advantage of the heads great flow.. I'm assuming you are doing a 350, duration @.050" should be around 225. If you are running a good exhaust (headers, no cat, free flow muffler) i would say you would be better off with a single pattern cam, otherwise (emmisions chocking converter) go with the dual.

I've seen cast iron headded 350's with just shy of 11:1 with cams running in the 230+ duration range on high octane without problems, I've also seen 9:1 iron with mild cams that ping like crazy.

Free compression could be had by zero decking. This gain won't require any change in octane and give more hp. The motor I'm building now has the pistons sticking out of the block by .003" which will net me .035" of piston to head clearance. Don't go below .025".

 

well how am i doing then?

compcams .550/.575 244 / 255 @.050
brodix aluminum heads with 11.2:1 comp
plan on running pump gas 92-94 octane.

it better be fine or im gonna shoot the engine builder

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87 z28 bowtie aluminum 420small block dry sump crower lt. wt. knife edged crank oliver lt wt rods brodix track 1's super ram intake slp 1 3/4 headers accel dfi art carr 700 r4 3.42 gears ssm sub frame/ladder bars.....other parts on the way ,soon to be finished!! couple more weeks!!!

http://people.ne.mediaone.net/gdm

 

It is a 350, .030 over bores. I'm using the 58cc AFR heads like I said earlier, but the cam is a LPE 219/219 @ .050", .560"/.560" lift w/ 1.6 roller rockers, C/L 112 used w/ a superram. The car will always have 92 octane and will be driven 95% on the street. I want a decent CR, but w/ a little safety factor built in.


[This message has been edited by BuckeyeROC (edited August 22, 2001).]