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      04-30-2009, 04:07 PM   #49

Drives: 991 GT3/997TT
Join Date: May 2007
Location: Birmingham Al

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Originally Posted by smdandb2 View Post
Here is the map cleaned up a bit. I was able to interpolate the data to get the efficiency islands made with a good amount of certaintly.

I know you need to know the VE of the N54 amongst other things to get really correct calculations, but if you just work on a VE of 90% you can see some of the PRs obtained with the tunes that the turbo is going WAY outside the map. Shaft speeds must go thru the roof when trying to hit higher boost levels in the upper RPMs. No wonder power tapers of so much on the dynos you see.
Actual VE would be interesting, but as I stated earlier, that's taken into account when looking at the PR. As I also stated earlier, its fairly obvious that on the right octane, the turbos are very capable of ~42lb/min as the fact that the cars tend to make right at 420 whp before craziness is required. That amount of flow requires around 2.3 PR absolute, which falls precisely into the range of the flow map that extends out that far.

As far as turbo rpm going "through the roof" at higher boost levels, small turbos run much more rpm than larger framed ones. Yes, at 17-18 psi, the compressors are sitting at around 190-200k at max power, which is actually mapped on the flow chart. High rpm? Yes. But within the feasibility of system to actually have it mapped and before the (theoretical) choke line of the map. Many times turbos are pushed well beyond charted flow and RPM. Mitsu turbos in the 4G63 world have been doing this for decades.

Finally, looking at the map you put together, it's also fairly obvious why 15 psi on pump fuel is the magic number for that octane. Efficiency stays relatively high at a PR of 2, with peak flow at around ~38 lb-40/min, it stays within the 65% range. Compressor RPM also stays relatively in check as well.
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Last edited by A418t81; 04-30-2009 at 10:05 PM.