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911st 911st is offline
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Join Date: Jan 2004
Location: Sacramento
Posts: 7,269
All good info and opinions.

Some think having un-equal length headers on a turbo helps improve boost onset as it makes for a more significant pulse to get the turbine spinning. That could be an argument for the 993's or stock HE's.

Equal length is always a good idea. However, from the info I have seen on Carrera 3.2's SSI's do not help with our smog cams any in the 1000 to 2500rpm range. There is about a 7HP bump at about 3500 rpm but by that time on a turbo we should be strong into the boost and any efficencies from the equal length may be minimized. Just a guess as I have not seen any good back to back tests.

I am also suspect of the HP gains with the B&B shorties over stock 85+ HE's. The HP increase is most likely because of the poor wast gate design and reduced back pressure in the muffler. There are stories of some triggering the over-boost switch after a switch to B&B's even though the stock WG with the stock .8 bar spring was retained.

Once we stick a turbine on the headers I suspect a lot of the NA attributes change and the full header system acts more like a pressurized vessel with input holes and one output hole in it. I suspect the best thing about equal length headers then becomes equalizing heat at the exhaust valve.

For a not heat headers or for the track I like the following equal length system.

Maybe adapted with separate WG's and a twin scroll for a track car. However, that means getting away from the K27 turbo family and an increase in cost for the two WG's.

What I do not know is if the efforts warrant the benifit.

For a street car with heat, I suspect it is not worth changing out the stock Euro / 1985+ US HE's. There are better places to spend money.



Again, these are just opinions.
Old 01-02-2009, 08:18 PM
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