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911st 911st is offline
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Join Date: Jan 2004
Location: Sacramento
Posts: 7,269
Quote:
Originally Posted by RarlyL8 View Post
... I'm not a fan of the shorty headers for a street car, that is a simple cheap design with no tuning considerations and lousy heat.

Street cars spend very little time on boost so it stands to reason that optimizing off-boost torque should at least be a consideration if not the focus.
Brian, I love your headers and if I was in the market at this time they would probably be my first choice.

However, I would like to balance your comments with a few thoughts.

In principle, shorties are better for a street car, equal length is better for a track car, and stock late 930 HE's are better for heat and lack of maintenance issues.

However, quality design can bring difference in all basic approaches closer to together. Still, if all approaches are optimized, the shorties are going to get us to boost onset sooner and the equal length design in most cases is going to be more effective at getting gross exhaust out of the car for more HP.

As most "non stock" 930 turbo owners are after power, an equal length design will be the most in keeping with this. Add a clear quality advantage and this is a winner without any additional benefits.

As to pre-boost tuning, from my knowledge so far, there is not much tuning that can be done to any part of the exhaust before the turbo that will help in any significant way with efficiency in the area before boost onset unless there is has been gross mistakes made.

With our low overlap cams and the back presser imparted by the turbo, even at idle, there is not any significant opportunity to tune the exhaust to create any meaningful scavenging effect from off idle at say about 1250rpm to boost onset at around 1700-2200 (depending on one's set up).

If we are in need of increasing the power in the pre-boost area we would probably better look for opportunities from things like an increase in displacement, increase in compression, cam design, less back pressure from the turbo and or muffler, and or by optimizing AFR & timing among a few other esoteric things like manipulating CP with acceleration and keeping the BOV open as idle and cruse.

I am not a big fan of shorties as I believe they misrepresent there true benefit which is reducing boost response by maybe a couple of hundred rpms over the late 930 design. Further, I suspect they overstate the increase in HP that comes from improved exhaust design when much of it probably comes from higher boost that seems to be a product of there waste-gate design.

However, they are a great asset to the 930 community as is your new long tube system.

Again, I believe that in principle:

Stock late HE's are a solid system is best for heat, and will require less maintenance than most any aftermarket choices.

Shorties are best for reducing turbo lag with there reduced volume that is more quickly pressurized. And--

True-Equal-Length headers are best for increasing efficiency at exiting exhaust and should best contribute to mid and higher HP levels. I might add some believe they also contribute to more equalized heat at the exhaust valve.

However, in the absence of true arms length testing, we will never truly know.

Last edited by 911st; 10-30-2009 at 02:09 PM..
Old 10-30-2009, 02:06 PM
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