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copbait73 copbait73 is offline
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Join Date: Nov 2003
Location: Chesterfield IN
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Originally Posted by TurboKraft View Post
Correct -- the more stock the engine, the less efficient the engine, so the less it is able to consume the greater airflow at lower rpms and the greater the need for the ported shroud to reduce or eliminate surge.

Ex: we had a 930 come to us for tuning on the dyno, only mods were aftermarket headers, 3" muffler, and a GT35R. Stock intercooler, stock boost, stock cams, stock P&Cs. It had compressor surge. The owner took our advice on getting a ported shroud intake and upgrading the intercooler. He didn't bring the car back, did it elsewhere, but the surge is gone. I wouldn't attribute that to the ebay intercooler he cobbled on.

Another 3.3L with stock heads and P&Cs, SC cams, GHL headers, 3" muffler, Andial intercooler. Compact "E" cover on the GT35R that some people claim causes the surge due to the smaller A/R. No surge on that car, on the dyno or road.

There are many terms being thrown around here. My point is to go back to the first. Surge is surge. Surge can happen under load because the engine can not maintain the flow condition vs pressure generated to stay out of surge or closed throttle can cause the restriction and surge. The compressor doesn't know one from the other but its reaction is the same, in the same location.

Theory and maps are great but only guidance. Look closely and the two maps show the opposite of this discussion. The surge line of the unported compressor is generally lower in the critical area up to 2.0P.R.

I ask your real world experience because as a sage chief turbo engineer is quoted as saying "Surge is where the customer finds it." Thank you for your replies as it sounds like the GT35, ported or not, is a risky compressor selection for a basically stock 3.3L 930, therefore probably unacceptable for a 3.0L.

Regarding ballbearings I consider them acceptable for racing applications where any positive margin may mean the difference of winning or losing but they are not tolerant of the wide range of conditions in everyday usage.

Last edited by copbait73; 06-24-2011 at 05:00 AM..
Old 06-23-2011, 03:48 PM
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