BMW1100LT Turbo Required Compression Ratio
Turbo Mini Forums

Hi All,

A mate has worked out some comp ratios for me:

18cc omegas with valve cutouts for bmw head.
18cc piston, maybe 19 with cutouts, 18 in head, approx 4 in head gasket.
In a 1380 that would give a compression ratio of 9.6:1, in a 1330 it would be 9.3:1, a 1293 would be 9.1:1, thats to high for turbo.

Whos currently running this set up, what comp ratio are you running and how did you acheive it?

Thanks in Advance

Wayne

Does that include ring land and area above piston at TDC?

9.1-9.6 iron block / ally head sounds perfect to me

Yes i moved to the darkside

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As Brett has said above, you can get away with higher compression due to the ally head.

I will be aiming to run 9.1:1, although my original target was 8.75 but this is infeasible without running the pistons down the bore, or doing ridiculously large dishes in the pistons.

Judging by what others are managing (30psi on 9.1:1) I'd say run with that.

In the 13's at last!.. Just

yep 9:1 and 30psi is fine. my head gasket has started showing signs of making an imprint into the cylinder head though. lol

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1/4mile in 13.2sec @ 111 terminal on 15psi

CR is often set to far on the safe side imo there is good free power to be made up until det..

Great News, thanks all. As the block is standard bore it looks asthough I only need go +20 to 1293cc with the 18cc pistons and 1mm gasket :) Happy bunny. I just need to get my hand in my pocket now :(

As stated you should be fine.

A good example although a vastly different engine is the Honda s2000.

On a standard engine many setups have proven to be reliable with an excess of 300bhp/L. All on 11:1