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Lukesportsman Lukesportsman is offline
Join Date: Apr 2003
Location: Terre Haute, IN
Posts: 2,940
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What R we doing with exh ports?

After a very lengthy discussion with a local Porsche builder and head porter he has inserted some hesitation of the 3.2 heads. He is nearly insistent on starting with 3.3 heads for torque. He strongly feels that the 41mm intake is way overkill for a turbo and that it only highlights the weakness of the exhaust flow. His thoughts are that it will only let more in with the boost to be bottle necked on exit resulting in hotter heads yet. This in combination with the reduced port velocity increases the need to turn up boost magnifying the above problem to gain back the lost torque.

Question: Real world, how much torque is killed in driving with the 3.2 heads at 7:1 compression? Will 3.2 heads really create a pig off boost? I understand port velocity, but if the 3.2 heads are well received as some of the best, why would it be SO BAD for a 3.3?

How/who can make this up on the exhaust port? I saw his numbers and that some of the stock flow balances were awful down in the lower 60% range. This isn't great NA, but is sad for boost. What solutions are out there? I really don't want to trade down to 3.3 heads.

I'm also looking to go TT with smaller GT's to help bring in some low rpm boost flow. I don't plan to go beyond 1 bar and I'm running 91-2 full finned, Carrera cams, 3.2 intake, 993TT HE's. I'm essentially building a TT 3.2 which has been done before, but this engine builder (who isn't necessarily stuck on the way factory the factory did it) just seemed quite doubtful on the whole 3.2 top end under boost. This will be in a 22-2400 lb chassis...not a #3100 930.
Luke S.
72 RS spirit 2.7mfi, 73 3.2 Hotrod on steelies, 76 993 3.3efi TT, 86 trackrat, 91 C4s widebody,02 OLA winning 6GT2, 07 997TT, 72 914 v8,03 900 rwhp 996TT
Old 03-03-2007, 09:00 AM
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