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911st 911st is offline
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Join Date: Jan 2004
Location: Sacramento
Posts: 7,269
I general nothing is is going to beat a well designed equal length header system for getting the exhaust out in the most efficient way.

A well designed exhaust of any type should bump peak TQ and lessen the fall off after peak TQ.

Thus, creating potential for to increase the average HP potential "under the curve".

Header volume seems to be to trade off with all Turbo set ups as to boost onset response no mater if equal length or not. Same thing is true on the intake side. A larger intercooler has to be pressurized before the motor is going to see full boost.

I suspect the WG volume is part of that volume. Most get excited with the short pipes to the turbo but do not think about the WG circuit volume. I would love to see someone fill up a stock system with water and a sortie system and measure the difference. It might not be as much as we would like to think.

As to normaly asperated differences pre-boost, even at idle there is back pressure in the headers as the turbo is creating boost. I think my resident boost at idle was about .2 bar if measured at the intercooler. Thus, we are probably not going to see any scavenging effect nor reduction in back pressure unless we make improvements in back pressure at the turbo (Zork).

There, may be some magic in if the exhaust hits the turbine wheel with consent pressure or in waves. I have not clue about this.

It is pretty well accepted that on a 4 cylinder motor that using a split turbine improves response but that with the more cylinders this advantage seems to fall off to the point there is not any gain with a V8.

What interests me is using equal length and a less restrictive turbine and balancing that the best AFR and ignition set up. But I am more interested in DE's.

If I was commuting I would want higher compression, a small turbine, lowest restriction muffler that I could live with, and smallest volume headers possible (including WG), and good heat. Probably a 993HE based set up.

I suspect there is nothing really wrong with the stock 930 set up as seemingly proven by the Monster CIS build where he gets well over 600hp with them.

Still, as well noted above, this is all application specific.

In some cases making an improvement to an exhaust system that should make a significant improvement is limited or reduced because of restrictions somewhere else.

Just my two cents and not worth a penny more.
Old 01-09-2010, 08:58 AM
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