Well i found a set of AFR heads for sale for a good price....theyre 195's, only thing is they have 60 cc chambers. Will this make too much compression for me to run 93 octane?? Heres my specs

350 bored .040
Speed Pro Flat Top 10.5:1 Pistons (dunno about valve reliefs)
not sure about deck height either but im pretty sure its stock
Will choose head gasket thickness based on suggestions
60 cc chambers obviously

What will my CR be??

 

We need more info on the pistons. What cc chamber are they rated at 10.5 CR?

 

If they are rated 10.5 for 64cc heads, you'll probably be up around 11:1 with 60cc heads.

 

FWIW ~10.5:1 can be done on an iron head SBC with 93 octane, but you will have to take a lot of timing out to avoid knock. I dunno about 11:1...

 

Assuming a stock deck height block and stock compression (pin) height pistons, (piston top is .025" below deck at TDC) 5cc valve reliefs and a .039" head gasket =10.25:1
use a .051" gasket =9.95:1

More deck clerance will lower the cr, less will increase it.

The only way to tell for sure is to assemble the motor and measure it. Every thing else is just a guess.

You can use thick " head saver" head gaskets.
you can open up "deshroud" the combustion chambers on the heads to lower the compression ratio.
there is lots of meat on these heads to do this.

Don't guess, don't assume this or that, don't ask 50 people, don;t worry about it.
Measure it and adjust the cr using one of these methods.
You can calc the cr yourself
here.

typical 350 head gasket bore size is 4.166"
stock deck height is .025" typical valve relief volume on flat tops is 5cc's.

 

His .04 overbore is gonna bring up CR, in case you didn't already take that into account.

 

Ditto the above post. Allen

 

I did.... click on the link , enter the numbers and try it your self.

 

what about on aluminums?? cant they handle a higher CR?

 

????????? Is it farther to New York, or by Bus?

What about aluminum?

Generally an engine with aluminum heads will tolerate about .5 compression ratio more than cast iron, on the same octane fuel.

 

Even at 11:1 you'll be fine with premium pump gas. The aluminum heads disappate heat so quickly it's generally accepted to be like knocking 1 point off your compression. Try replacing iron heads with aluminum heads on a realitively stock low compression motor and you will loss power.

Going to depend on how deep the slugs are in the hole too, if your block is flat decked then all the piston, head gasket, chamber size will come into play, but if your slugs are deep in the hole, you'll lose some compression that way too.

 

thanks for the replys guys....i guess i should just pull a head and do some measurements, but i just wanted to get some general info on what CR COULD be run

 

I'd say keep the AFR's and shoot for a 10:1 CR. If you have to change your pistons then do so.

 

How do i check all the measuremenmts i.e. deck height etc?

 

ttt

 

You can measure the piston deck clearance with the head off the motor.

Bolt a steel straight edge across the deck of 1 cylinder.
Put a feeler guage under the straight edge.
Rotate the crank shaft by hand, bringing the piston to and past TDC. Try different thickness guages till you find the one that just fits.

 

Take the old die grinder to the chambers, and gain a couple of cc's.