Compression for stroker motor.

[2slow4utsi]

I know the higher the compression the more chance of knock but more hp in the low end and faster spool up and the lower compression means less hp but can be regained through more boost but may cause slower spool. What compression should I run on my pistons? I plan on going with Mahle stroker pistons. Let me know guys.

-Danny

 

[JayRolla]

The real question is what fuel will you be using. If you are on pump gas than 8.8:1. If e85 I would run 10.5:1.

 

[2slow4utsi]

Yeah 93 octane. Thanks for the help. Another thing I noticed is there are two different strokes on the Eagle crank 94 and 100mm I believe. Is one more common over the other. I've seen 100mm used a lot more often but why?

 

[delta448]

I would aim for a final CR around 8.5-9.2:1. You have to be willing to run less boost or better fuel the higher you go, but higher CRs are much more efficient at producing power and keeping the engine running cool. Also, as long as you aren't knock limited you can produce more power per psi of boost with a higher CR. Running 20psi on 8.5:1 should net roughly the same power as 15-17psi will on a 9.2:1engine, just with slightly less thermal efficiency. The optimum ignition timing will decrease as CR goes up. This is because of the increased flame speed (and the resulting accelerated rate of rising pressure) that occurs after spark when there is more pre-ignition cylinder pressure. This fights pumping losses, which occur when the piston is pushing towards TDC not only compressing the charge, but working extra to compress a charge that is burning and rapidly increasing cylinder pressure even if there was no compression occuring.

As for the other question, 100mm is the stroke of the stock 2.4L crankshaft. It's often used in a 2L block to create a 2.3L stroker. The 94mm is a bit of an oddball, and not many companies make rods and pistons that work with it, but it is a perfect compromise between displacement and high revving ability when it is used with the taller deck height 2.4L blocks, creating a 2.2-2.3L. This thread may help.

 

[2slow4utsi]

Nice. I just was wondering what compression to run since I'm going with 93 octane. Scratch that. I'm now going to be running E85 .