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beepbeep beepbeep is offline
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Join Date: Jun 2001
Location: Sweden
Posts: 5,564
As spuggy said, big port diameter was chosen on race engines as peak power was important and off-boost driveability wasn't. 3.0L had somewhat choked heads but when diplacement/compression was bumped to 3.3L/7.5:1 Porsche decided to choke ports even further in order to boost gas velocity at lower revs and thus improve VE/torque.

Turbo heads are indeed made of another alloy which is slightly better at withstanding high temperatures (I don't quite remember bu I believe difference was 25 deg. C or so). I believe they quit with this on later 993 heads shich were all made from "hi-temp" alloy.

There are two ways to go. You either use 3.2/3.0 heads and make sure they stay below the limit or use 3.3 heads ported to desired diameter. You never said which kind of engine you are planning to turbocharge as there are additional problems with mating 3.3 heads to Carrera intakes as injector notch doesn't line up.

Personally, I would use Carrera head and Carrera intake and mount slighly smaller pulley for 10% more fan speed. Also, I would move generator out of the fan (and drive it with separate belt) as it loads the belt inertially.
Thank you for your time,
Old 12-25-2007, 09:53 AM
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