Compression Ratio Choice

[3RotorRx7]

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]

Originally Posted by 3RotorRx7

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]

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.