I'm sure there is a fairly simple solution to this but it has been annoying me all weekend, can't seem to get my head around the maths....

If a standard 2.0l pinto has a cr of 9.2/1

skimming 1.5mm off the head gives 10.2/1

so given that, how mouch do i need to remove from my head to give about 10.5/1 with a 2.1l block ?

Help!

[Edited on 4/3/07 by DaveFJ]

is the standard comp ratio of 9.1:1 is right then the combustion chamber is 55cc, so if you bore out to 2.1 you have a bore of 93.2mm so to acchive a comp ratio of 10.5:1 you need a combustion chamber vol of 50 cc exactly so i recon that if you have a 2.1L engine you need to skim 0.77 mm of the head. but that is assuming that the part of the chamber you are skimming is perfectly cylindrical, please dont hold me to this but i recon that with the above assumptions 0.77mm should be about right

hope that helps

Matt

hold on a miniute that doesnt sound quite right....give me a moment

removing 1.5mm off the head of the 2.1 will give a compression ratio of 10.75

is that close enough for you?

cheers

Matt

It's basically impossible to calculate this accurately, because the area of the combustion chamber reduces as you machine the head down, e.g. the first 1mm skim will reduce the volume of the chamber more than the next.

To work this out accurately you need to measure the combustion chamber height required by filling the chamber with the desired volume using e.g. paraffin to reduce meniscus, and then measuring from top of liquid to the gasket face.

think I'll just say sod it and go for 1mm off.....