View Single Post
911st 911st is offline
Registered User
Join Date: Jan 2004
Location: Sacramento
Posts: 7,269
Originally Posted by rsrfan View Post
Along with the earlier onset of boost, the after market "shorty" headers ala B&B have been documented on the "other" forum to produce an additional 100 lb foot of torque over the factory system on the dyno at 3000 RPM. Regardless of the horsepower gains this IS significant.

I am not disputing that this is the case.

However, how it is done is not due to a superior header design. The added HP I suspect is from the higher boost they trigger due to the poor design of the wast gate circuit. Again, there are reported cases of adding this system and then triggering the over-boost switch with no other changes. This would not happen if the WG circuit worked correctly.

The earlier boost comes from creating a more significant pressure differential on each side of the turbine wheel. This is better achived on the exit side of the turbine with any straight through low restriction muffler. It is not effected that much by the the header portion.

I would prefer SSI, or 993 to B&B. If we buy into the idea that the B&B is a benefit because of there shorty design and small volunm, then the SSI should have to be judged and inferior with it's long primary tube design. However, the SSI and 993 would likely last longer and be subject to less need of a reweld.

Equal length short headers are alwas a good idea. For a race car "short" equal length with good colectors is a more effecent design and worthy of the effort. They offer a more orderly exaust path and thus result in more even tempetures at the exaust valves.

With the newer design turbos that have a much higher ratio of turbin to compressor we are pushing higher back presures in the exaust system than ever before. As such I belive the header design is less important. Because of this we now have more issue with the WG being able to exit the gasses that use to go through the turbine.

I very much like the 993 turbo set up idea and if I needed HE's it would be my pick. However, from an operation point, I do not see much benifit over stock as a header. However, if the WG issues can be improved upon, that could be an added benifit. The other benifit noted is configering it for a ture split scroll turbo system.

I still suspect the headers to be a small part of how we go about improveing boost onset and reducing lag on a CIS motor in the HP ranges we make.

Just food for thought.
Old 01-03-2009, 01:43 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #56 (permalink)