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-   -   Compression Ratio Choice (http://986forum.com/forums/performance-technical-chat/54522-compression-ratio-choice.html)

3RotorRx7 10-21-2014 09:18 AM

Compression Ratio Choice
 
Trying to decide on a compression ratio for a build on 2003 2.7 Boxster motor. I already have the top end ported by Hoffman Automotive Machine, and cams. Will be doing upgraded connecting rods, ARP bolts, and coated bearings. I see that the RSR motors are running 14.9:1. I will be running 109 unleaded race fuel. I will primarily be running it in FP autocross type events, and some track day sessions. Any advise would be appreciated.

Thanks,
Erik

BYprodriver 10-22-2014 09:19 AM

Quote:

Originally Posted by 3RotorRx7 (Post 422435)
Trying to decide on a compression ratio for a build on 2003 2.7 Boxster motor. I already have the top end ported by Hoffman Automotive Machine, and cams. Will be doing upgraded connecting rods, ARP bolts, and coated bearings. I see that the RSR motors are running 14.9:1. I will be running 109 unleaded race fuel. I will primarily be running it in FP autocross type events, and some track day sessions. Any advise would be appreciated.

Thanks,
Erik

I assume your new cams have increased duration & lift so you have already lost some cylinder pressure from the stock 11 to 1. lnengineering.com makes pistons for this so I would get all your spec's together & call LN to see what they recommend.

Jake Raby 10-22-2014 04:37 PM

The law of diminishing returns will impact the engine past 12.75:1 static with the stock DME. I see very limited gains with high CR and the M96 engine, but all that CR is fairly effective at snapping a crankshaft. The last 14:1 engine I built snapped the crank in 3 places.


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