Thread: 3.5 high comp/low comp

The difference is about 6.5cc only, a lot of surface area and a big bubble in the head which sits on an angle.

Actually the measured difference will only come out at about half of that as thats about how much of the head cc is measured. 4cc from 437.5cc or about 1%

Can you decipher much by pressure testing?

There is a good reason to leave the 101 with a low compression.
The 101 is most likely to be driven as a three speed in the real world and needs to lug in gears and under load.
Even though the power of the lower compression engine is less, it will in practice be a softer motor and not has harsh and less likely to ping under load.

Originally Posted by jimbo110

The original compression ratio is stamped on the block, but piston or even gasket changes will change the ratio.

Larger than standard bore size will also increase Compression ratio as well, Regards Frank.

certainly you can get the number from a compression test....

assuming your gauge is accurate go through and do your dry compression test then the wet.

working in PSI your Max compression/14.7 gives you your X:1 figure although you may need to adjust it by a couple of points but it should give you near enough to work out a the 8. side of 8.13:1

So my V8 4.2 had around 220 PSI. per cyl.
Thats High comp?
It ran beautifully on gas.

(It was an import from a Rangie LSE) but reconned here with new pistons.

sorry guys, I forgot some of the math on that...

220:1 comes out at about 10.5:1

The dry compression test is the one that comes out closest and the direct method without all the funky stroke VS bore math works for the series engine......

I'll see if I can unprotect the spreadsheet thats got the math for it at work.