Correct compression ratio n/a
Turbo Mini Forums

Hi to all from sunny Greece, I know it's not turbo but I only trust this forum.
Anyway I have a 1293 engine with276 cam, 1.5 rockers, aldon yellow dizzy. I got given a nicely ported head with 35,6 inlets and 31 exhaust. I bureted the head and got
No1 21.6cc
No2 21.1cc
No3 20.8cc
No4 21.4cc
Pistons have 6cc but not sure (been 8 years since i last took the head off) maybe 8cc, deck height 127mm, bk450 head gasket ring land volume 0.9cc
From my calculations I get 10.37:1 with 6cc pistons and 9.82:1 with 8cc pistons.
I am thinking that I need 10.5 to 11.1 to get the best out of the cam I have. The car will run on shell vpower or bp ultimate fuel and I will also install megajolt is this the correct compression for my application?
How tenths should intake of the head to achieve that?
Please reply for both 6cc and 8cc pistons..
Sorry for the long post but I'd rather get this right
Thanks John

in a 1098 id use about 11:1 11.5:1
whats the bore n stroke on 1293cc? also rod length?

Bore is 71.2, stroke 81.28 and rod length is 146.05mm.
Thanks john

10.5-11:1 I wouldn't think that cam would need any higher

Speeding is like masturbating, everyone does it, but not all of us film it and put it on the internet

[quote=fab,8th Oct, 2010]fuck off

10.5:1 would be good for a road going car with a 276 cam

Life is always a matter of opinion and quite frankly, no ones opinion really matters.

Thanks all for the answers, so I ll aim for 10:5 and a bit say 10:8, is it correct to assume that taking a tenth off the head is like taking 0.5 of a cc?
Cheers john

from what ive worked out you should crank about 180 psi on 10.5:1 and 200psi if you use 11.5:1 (actual about 9.7:1 true CR due to cam)
the reson im saying to use a high CR is its more eccicent at getting the most energy from the air/fuel that mannages to find its way into the chamber vizard says to try your dam best to fill that cylender and then since you cant get much in due the the head desin to squese the heck out of it he also says that A seiyes engines like compression and that the amount of waste energy is grately reudced useing a high CR vs a low CR.

in my engine ill be some where in the 11:1 - 11.5:1 and 15 pound boost but im useing a few things to snuff out det! and these number are to be confirmed as i build! IVC can change a bit there for CR..

just my two bob any comment/info is a good imo

I don't have much 'theoretical' knowledge on this subject I have used online calculators to work out dynamic compression and it's interesting basing it on my dyno results, from the engines I build and varying the compression ratios chasing power I have found a bhp limit and when I run more static compression it limits the amount of ignition I can safely run, so what you give with one hand you take with the other so that's why I say set the compression on the safe side of 11:1

Speeding is like masturbating, everyone does it, but not all of us film it and put it on the internet

[quote=fab,8th Oct, 2010]fuck off

Thanks all for the answers, it seems my calculation are a bit off, with my head I get 11:1 with 6cc pistons and 10:4 with 8cc, only way to find out is to take the current head off. I'll aim for 11:1 which I agree should be spot on.

supermotolee, dose this apply for E85 where you can normally stuff a bunch in timing in? also useing a charge cooler and piston cooling jets
not being silly its a good point you give as some engines make more power with really low cr and a crap tone of boost like top fuel cars dont they have like 5-1 or some crap?