work out compressoin ratio?

Anonymous · Post by **Anonymous** » Wed Oct 05, 05 6:42 pm

is it possible to worl out the compression ratio of an engine from a compression test?? I know I should have checked this when I had the heads off

I do know the pistons are forged,flat top apart from cut outs for valves,I was thinking of changing the pistons to give about 10:1 or slightly more,but if they are around 9.5:1 ,I don`t think it`s worth the expence etc,any info would be appreciated

Kev · Post by **Kev** » Wed Oct 05, 05 6:55 pm

In a word, no!

Anonymous · Post by **Anonymous** » Wed Oct 05, 05 7:12 pm

thanks kev ,direct & to the point,at least now I know,or don`t which ever way you look at it

Dave-R · Post by **Dave-R** » Wed Oct 05, 05 7:14 pm

The reason Kev said no is because cylinder pressure is more to do with cam/valve timing than anything else.

Anonymous · Post by **Anonymous** » Wed Oct 05, 05 7:16 pm

You mean you had the heads off and didn't do every measurement in the book

oh dear

Dave-R · Post by **Dave-R** » Wed Oct 05, 05 10:05 pm

BUT!

You can tell from the compression pressure if you have enough static compression ratio for your cam.

At the end of the day it is the actual compression pressure that counts.

Anonymous · Post by **Anonymous** » Thu Oct 06, 05 6:09 pm

thanks everyone for your input

the only thing I checked on with the heads off was bore size & condition

no wear in the bores & 30 thou oversize, it has 906 heads,& I remember the pistons were either flush with the top of the block ,or not far off(not a lot of help really

)the only reason I took the heads off was because I broke a stud when I was fitting headers

Dave-R · Post by **Dave-R** » Thu Oct 06, 05 6:30 pm

The 30 thou over will raise compresion and if the piston about flush with the top of the bore it will have a good compression without a doubt.

Don't worry about it. Cylinder pressure has less effect on torque (and HP) than most people realise. Only when every last bit of power is wanted or if you are planning to use a very hot cam should you be concerned about measuring it.

Anonymous · Post by **Anonymous** » Sat Oct 08, 05 3:47 pm

thanks dave

you`ve saved me a few hundred quid that can be used elsewhere!! ,now about that 10" torque converter