Compression question
Turbo Mini Forums

Hi all

I know my cylinder head has had additional work carried out on it to reduce compression and so have the pistons. However this work was carried out many years ago and I don't remember how much of the material was removed. Is there a way I can roughly work out the compression ratio if I don't know this information?? Will a compression tester help to give an idea and if so is there a guide to show that eg 10psi = 9.4:1

Hope this makes sense!

Rich

I noticed when I did a compression test on my standard 1275 turbo engine it gave readings around 12 bar

when I recently did a compression test on my new engine with 8.4 cr (28cc with standard +40 pistons), it gave readings of 10 bar per cylinder.

I have changed to an MG Na cam as well though so this may probably effect it to. but I think when my new engine had a standard head on with MG cam it gave readings near 12 bar also.

So I reckon you could say 11 bar may give a cr of 8.9 (8.4+9.4/2) if the cam isn't to wild ?

The only real way to knpw is to burrett the chambers and pistons etc

Hope this helps.

Edited by Brocky on 17th Sep, 2007.

BTW - I took my buddy VTEC Pete out for a spin this weekend, and even though I am running her in, he gave it a name, the "Brocket"...cause I'm a brocket maaannn, nah nah nah nah nah nah nah nah nah nah nah....

Build thread - http://www.turbominis.co.uk/forums/index.php?p=vt&tid=7483

Katy Mini Owners Club Thread - http://www.turbominis.co.uk/forums/index.php?p=vt&tid=505552

Let's make sure you embarrass at least one VTEC MINI today !

https://www.facebook.com/groups/17557298589...096464253807802

burette, cd and oil to measure the size of the chambers in the head, then alex's compression calculator is very useful

http://www.afracing.com/CR.xls

ok thanks for info guys!

Pressure redings do alter with the cam profile, the wilder the cam the lower the pressure. Saying that most turbo builds have a conservative profile cam, so it shouldnt change that much.

As a comparison, my 1400 with a calculated 11.5:1 compression ratio and a kent 274 cam pushes 18 bar on the gauge!! lol it nearly maxes out the gauge

Only real way to determine compression ratio is to physicaly measure everthing, then work out the static and the dynamic compretion ratios.

heed Mini Sprocket advice its spot on !!!