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911nut 911nut is offline
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Join Date: May 2001
Location: Michigan
Posts: 2,511
Originally Posted by 911st View Post
On the C2T the cat/muffler is the dog. The muffler in the pasanger rear fender is not restrictive and you can pass a tennis ball through it.
Apparently you haven't driven a Turbo with a high flow muffler or you wouldn't say that. The stock muffler turns the exhaust thru 180 degrees, which makes it more restrictive than a RarlyL8 muffler.
Originally Posted by 911st View Post
My belive is the C2 and most the turbos do not need headers. The magic is eliminating as much back pressure as possable after the turbine wheel.
Those who have headers report boost onset occurring at a lower rpm, making the Turbo perform closer to a normally aspirated car, which some people prefer.
Originally Posted by 911st View Post
It is my belife that the B&B has a poor wastgate design that tricks the wastgate into providing higher boost than intended. When I had my C2T several of us that ran Tial WG's that had to use lower boost springs to get the boost we wanted.
I use a .7 bar spring to obtain .9 bar on my car and I have stock exhaust up to the turbo. This seems to be more of a tuning issue. The springs could be labeled "sexy", "more sexy" and "very sexy" for all the difference it makes. In the end a boost gage is desirable when using an aftermarket W/G for proper tuning.
Originally Posted by 911st View Post
I still think the magic on a C2T is a vac sensing WIR, cat bypass, and gears from a C2/4 3.6. The stock first is tall and expensive to change our but putting 2-5 in it makes for a closer range gear box that keeps you in boost and the power band between shifts.
The 930/965 engine uses a boost sensing WUR so I don't understand how a vacuum sensing WUR would work on a turbo car. Can you elaborate?
Originally Posted by 911st View Post
I also changed the orintation of my custom compressor bypass valve. It was open all the time and slamed shut only when I lost vacunm with acceleration for instant boost. My boost stayed at over .8bar between shifts with no compressor stall.
The recirculation valve is closed until the engine makes vacuum to open it, reducing the high pressure trapped between the throttle plate and the compressor. This keeps the compressor spinning faster in ambient pressure air.
I had an issue regarding the low rpm drop due to the recirc system dumping the air into the intake. I would have to wait forever for the revs to drop enough to shift without destroying my clutch. The turbo would slow way down. I no longer dump that air into the engine but out to the atmosphere. No waiting to shift means a compressor that's still spinning fast and more instantaneous boost.
Paul B.
'91 964 Turbo
Port matched, SC cams, K27/K29 turbo, Roush Performance custom headers w/Tial MV-S dual wastegates, Rarlyl8 muffler, LWFW, GT2 clutch & PP, BL wur, factory RS shifter, RS mounts, FVD timing mod, Big Reds, - 210 lb
Old 12-03-2008, 01:47 PM
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