How much is my comp ratio going to change going from a 84cc head to a 78cc head thanks in advance

Go to the Wallace calculator site and plug in your info

I looked but didn't see it I'll have to look again thank you

wallaceracing.com/cr_test2.php

well less than a full point.

Found it thank you

6 cc on an 8 to 1 engine is a small change. 8.0 to 1 would be 8.4 to 1.

6cc on a 12.0 to 1 engine is a lot more. 12.0 would be 12.9 to 1---well over double what 6cc does to an 8 to 1 engine.

Above example was for a 418 c.i. engine. A 340c.i. engine will net more increase and a 500 c.i. engine will net less.

It's goes from 10.75 to 11.8

Can't see it being more than a point on a 10 something compression engine with only a 6cc difference. More like probably a little more than 1/2 a point. It isn't a big difference

On a stock stroke 440, +.030, where the starting cr is 10.75......... Lowering the volume at tdc by 6cc's(chamber volume goes from 84 to 78), changes the cr .66........ So, 10.75 would end up at 11.41.

It just happens to work out that on stock stroke 10:1 440, 1cc is worth about a tenth of a point of compression.

Are you really at 10.75 comp now with a 84cc chamber? You must have domes then.

A 6cc smaller chamber on a 440 from a 10.75 comp will be 11.43


A flat top 0 deck, 4.32 bore 440 will be 10.158 comp with 5cc valve reliefs and a .038 gasket, {With a 84cc Chamber.}

I bought some RPMs84cc they was 82cc(on the box)I had them milled .040 got 75cc and I wish I wouldn't have. Now mite have to mill again one day. time dose it. I don't think that's the best place to look for horsepower.