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911nut 911nut is offline
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Join Date: May 2001
Location: Michigan
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I, too, have also often thought that having a turbo "plugging" the exhaust path muddied the waters with regard to exhaust scavenging. However, look at pictures of turbocharged race engines (including those produced by the Porsche factory) and you will see every attempt to use equal length headers in these applications. Since race engines get dyno'ed to death, I can only assume that there is benefit it having them. Since these are road racing cars they are required to produce torque at relatively low speeds perhaps this is an effort to enhance off-boost performance too.

There is anecdotal evidence that, for HP/torque gains, B&B is the best and provides a 20hp gain over a stock system and is in fact a better performing system than the GHL system owed to it's better collector design. I say anecdotal because I've never seen any independent dyno results posted (and I have asked people on several occasions to post results so I suspect they might not exist). Also, those who have headers report boost onset and 400-500 rpm lower than what they were seeing with the stock system, as Brian stated. As for boost creep in higher gears, that is the Achilles heel of the aftermarket systems and I assume it's due to packaging constraints. The stock system does well in this regard (the exhaust flow to the w/g isn't being turned 180 degrees as it does in the aftermarket systems). However, I've experienced boost creep in high gears with my stock system. It wasn't severe but was no less annoying.

As for the stock H/E's, lets consider the fact that the exhaust from #4 cylinder is made to travel almost 7 feet ( I measured the path this morning). The path for cylinders 5 and 6 aren't much better (even when looking at the H/E's of the 993 TT, it's apparent that packaging the system was the primary focus of the factory). This represents sizable friction and thermal losses that won't be present in any short-path header system. Why did the factory saddle the Turbo with such an inefficient system? Packaging and cost. There are two things that the factory exhaust system is the champion of: ground clearance and durability. The geometry of the stock system allows it to be tucked under the car to the maximum. The factory's packaging isn't very light, however. The stock system weighs a portly 60 lb. The system is manufactured from ferritic stainless steel, which performs in the "hot end" environment far better than the 304 stainless used widely in the aftermarket. The H/E's manufacturing process obviously shares tooling with the normally aspirated models, yielding a cost savings.

So what we aim the achieve with the 993 H/E based system is a header with factory-like durability, improved performance over the factory system, lighter weight (I estimate a 20 lb savings off the tail of the car and that is a conservative number) and superior cost to aftermarket systems. I feel that we have a really good chance to achieve all these goals.
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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

Last edited by 911nut; 01-03-2009 at 04:58 AM..
Old 01-03-2009, 04:51 AM
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