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Old 10-21-2014, 09:18 AM   #1
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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
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Old 10-22-2014, 09:19 AM   #2
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Quote:
Originally Posted by 3RotorRx7 View Post
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.
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Old 10-22-2014, 04:37 PM   #3
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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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