X or not in SC

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Jun 27, 2006 | 04:05 PM

Vilhuer

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From: Helsinki, Finland

X or not in SC

Will X-Over help in SC car similarly as it does in NA? If it does, what design is best? S4 in question will have 928 Intl 3" headers installed soon and custom exhaust build all the way back. Where would be best spot for X, headers-X-cats, headers-cats-X or some other combination? What shape X? There are probably many different opinions.

Jun 27, 2006 | 04:25 PM

Supercharged
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From: Back in Michigan - Full time!

If you're going to use the headers, you will need to fab your own x-pipe. The headers do not have the same flange locations. Look up Dr. Gas. I believe they sell just the "X" portion which might prove useful.

Jun 27, 2006 | 04:29 PM

Vilhuer

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Whole exhaust including X will be custom made locally from stainless tubes. Just looking for best possible combination what to do.

Jun 27, 2006 | 04:44 PM

bd0nalds0n

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Tony got a lot of torque gains by uncorking his exhaust with a crossover. I think the huffed cars benefit greatly from scavenging.

Jun 27, 2006 | 04:46 PM

Louie928

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Quote:

Originally Posted by Vilhuer

Sure an X crossover will help on a SC car just as on a NA car. You will probably see less boost as you open up the exhaust, but remember that boost is only a measure of the restriction that the blower is working into and not a measure of mixture in the combustion chamber. With a restriced exhaust, you could have significant percentage of exhaust left in the combustion chamber when the exhaust valve closes. At lower RPMs and high boost (possible with a twin screw/Eaton) you might blow out some mixture during the valve overlap period. The GTS has weird exhaust valve timing so I don't know what effect that may have. Opening up the exhaust would definetly would help at the upper end where the GTS needs it.

As for what shape the X should be you can check my web site for some info. www.performance928.com. That's only my opinion though. Also check out Sterling Gee's web site and pictures of his newly fabricated 3" exhaust. http://www.928sg.com/exhaust.htm I think his is about perfect. The placement of the X has some effect, but I wouldn't have a clue to suggest where yours would be. I know in making my own 3" system, there isn't enough room to have the X near the front and have space in the rear part of the heat shield for anything but really short cats or mufflers. Sometimes space considerations preclude having the optimum design. I'll have 12" long mufflers first, then the X. Regarding cats, Dave Lomas at Motorsports in Salt Lake City, UT makes some with long tapered inlets and outlets. Those will be best. The short inlet/outlet on standard cats hurt flow.

Jun 27, 2006 | 05:17 PM

Vilhuer

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Thanks. Headers and pipes are going into S4 which has Murf SC. Engine is othervise stock. So X it is then. Space is problem obviously but we figure something out. Sterling's site is one very good model to emulate. Just looking for other options.

It would be virtually impossible to install SC on GTS in here legally. I'll have to settle for mods which are not visible on outside, other than 3" exhaust that is but it'll have to wait it's turn for six months at least.