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911st 911st is offline
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Join Date: Jan 2004
Location: Sacramento
Posts: 7,269
I love equal length and twin turbo set ups. They are sexy as hell but do have a cost in several ways ( money, complexity, weight).

Just an opinion as understanding of exhaust theory seems to keep evolving.

A well designed single turbo can match a twin turbo system in response untill one gets to mega Hp levels.

Part of a good single turbo design is keeping the two sides of an even fire 6 exhaust mostly divorced from each other preferabley with a split turbine turbo on the single turbo system.

This mostly stops the reversion that is paticular to a common exhaust header that ties all 6 cylinders togeather in which two exhaust valves are then open at the same time which effects each other and premots exhaust reversion. This is the most significant advantage that remains a benifit of a twin turbo system. Keeping there from being overlaping exhaust events on the same manifold.

Yes, turbo headers are different than NA headers. However basic principles do seem to cross over.

Exhaust leaves the cylinder at about 70psi on all motors. On a turbo system the ressident pressure in the header at full boost might be about 10-15psi v a couple of pounds on a NA motor. This seems to slow down the speed of the exhaust but dose not keep good design principles from working to reduce reversion, back pressure, and gain some scavaging at some points of operation.

Thus I suspect equal length tubes on a turbo can probably be shorter than the 32-38" NA ideal and still offer more than just orderly exit of the exhaust events.

Collector design can be just about as important on a turbo. A good collector will aid orderly exhaust and reduce reversion.

No one seems to talk about the secondary tube's importance to a header system. It seems the secondary tube sizing may be as impotartant on a NA header than the primary tube dimension. I suspect a little length to a secondary tube on a turbo system will help to reduce reversion and help scavaging at some points. On a NA motor ideal secondary length seems to run in the 12-24" range and has a significant impact on the TQ band.

Brians twin set up here and his single both probably have better secondary tube demensions that most Porsche turbo 6 designs.

Is it perfict? I do not know. It sure looks like most good design prininciples have been included and no major mistakes seem to stand out.

I would like to see getting the wastgages out of the turbos if possable for increased effecency at the turbine exit, higher differental pressures at the turbine, and possably better response. Still it is a very nice system and should rock with the best of them.

Not an expert.

Last edited by 911st; 07-08-2010 at 07:28 AM..
Old 07-08-2010, 06:10 AM
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