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911st 911st is offline
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Join Date: Jan 2004
Location: Sacramento
Posts: 7,269
This graph is just a tool to help us understand how far out there we might be with most combinations of boost and CR. I suspect few have though of the concept of Effective Compression Ratio. Vender's are offering 8/1 CR pistons sets that help our pre boost torque. That is great but if the buyer is running 1 bar boost, they might not otherwise know how close or if they are going over the edge or that they need to work on making sure there timing, IC, AFRs, and turbo efficiency is such to allow doing so.

It is a good point about differences in motor designs and differences and motor efficiency's (VE). We may want to be cautious in comparing ourselves to boost levels being run with more efficient motor designs. Is this why we can not run 22 lbs of boost?

Most of our air cooled turbos are running basically pretty similar non overlap cams and are of similar architecture which should make them reasonable comparable among themselves. The graph is helpful to better understand what the upper limits might be for different motor combinations we might consider.

Yes, differences between our motors should be considered when targeting a given ECR. A 3.2 turbo conversion motor w no intercooler and mild cams might want to run a lower ECR than a motor with aggressive cams, a very efficient intercooler, big effecent turbo where everthing is dialed in to work.

I suspect the normal aspirated 993 might give us a hint as to where our upper limit as to ECR might be on pump gas if we get everything right. Even then, we need to make sure we get our timing and fueling right. Piloting one's self against the curve can help one to understand how close to the limit one might be.
Old 04-08-2009, 08:17 AM
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