94gtcobra

What exactly does compression ratio's mean.

WhiteWindsor

The higher the compression the more power on a n/a engine. Two most deciding indicator's are the pistons and head cc's. Here is a definition.

http://en.wikipedia.org/wiki/Compression_ratio

r.barn

There is also static compression ratio and dynamic compression ratio

Static is what everyone thinks of.
Dynamic take into account things like stroke length and valve timing.

67mustang302

Yeah, dynamic compression is what really matters since it takes into account what's actually happening when the engine is running.

OnyxCobra

It's the ratio of the amount of space in the cylinder from whent he piston is all the way down to when it's all the way up. ie 10:1 means it takes 10 of whatever unit you're using and compresses it into 1 of the same unit, so like 10 cubic inches into 1 cubic inch. I realize thats a mess of a sentence lol.

94gtcobra

So what would be my compression ration in my car? I have Edelbrock Performer 5.0, GT-40P's ported .30 over, Crane 1.6 rr, E-303 cam with stock shortblock.

67mustang302

It's not a stock shortblock if it's .030" over. What pistons are in it? You need to know the piston type and size of any pop-up or valve relief/dish to get an accurate calculation of CR.

94gtcobra

No, only the heads are porterd, the pistons and block are stock.

w8less

they cant be stock if the block is .030 over. Most pistons anymore will bump the compression some. Also if they cleaned up the heads any i am sure they milleed it even slightly so that will also change the compression some. A lot of things are needed to be anywhere near close

94gtcobra

The block is all stock, only the heads are ported.