Darwantae951

Hello all!

I'm looking at exhaust systems and I was considering buying the fabspeed 3'' downtube with their 4'' cat back exhaust system. On their website they say that it's for high horsepower cars making over 350 hp...is there a disadvantage to having this exhaust on my car if it's not over 350 currently? Eventually it will be, but will it flow too much? All thats on my car right now are Autothority Stage II chips, SFR stage 1 headers, and soon to be a Tial 38mm waste gate. TIA

-Darwin

SD Porsche Fan

Maximum Boost Designing, Testing, and Installing Turbocharger Systems - Bell, Corky. p 131
"For our purposes, we shall call the exhaust system everything after the turbo. Virtually all turbos require special tail pipes. Stock, non-turbo tail pipes don't cut it. Seldom to aftermarket tail pipes prove satifsfactory either. An exhaust system is an accumulation of optimized, carefully thought out features. The objective that must be met in correlating these design festures is the creation of a clean-running, acceptable noise level, lowest-possible-back-pressure tail pipe.
RULE back pressure in an exhaust system is evil.

If the turbo could step up an dictate terms for design of exhaust systems, it would categorically state: NONE!"

pg 139 "Make sure the exhaust flow area is maintained through the tips."

Porschefile

There is no reason whatsoever to be running such a large exhaust on a 4 cylinder. Lindsey's claims and supposed dyno proof on their website are false. Boost spikes equal instant torque gains like they show with their supposed dyno proof. I still can't believe LR perpetuates this lie. 3" is perfectly sufficient for everyone on the 951 board plain and simple. I challenge anyone to prove me wrong because I have seen plenty of proof otherwise. The only situation I could see warranting such a large exhaust on a 4 cylinder would be a 3.0L+ motor with something larger than a T4 T67 and putting out 700+rwhp. With a large enough turbo you might get enough backpressure to warrant a 4" exhaust, though AFAIK there is no one here at those kind of power levels.

Some proof of what I am talking about: Link Scroll down to Nize's dyno (hope you don't mind Nize). Hmm, 345rwtq out of a stock k26/6. How's that possible? 19psi boost spike, that's how.

Cory9584

wouldent too big of an exhaust cause more turbulance since theres not enough exhaust to even come close to filling it?

Sam Lin

The turbo gains its power from an energy differential across the turbine. That energy is pressure and temperature. The less backpressure in the exhaust, the greater the pressure differential.

There's no reason to not run the biggest exhaust you can on a turbo car.

Sam

RKD in OKC

First off the LR 4 inch exhaust is not really 4 inches. It starts at 3in and increases in increments to 4 inches towards the muffler.

Secondly, flow wise the stock is actually a very good exhaust and nicely sized for all but the most aggressive power makers. Porsche engineers ain't no dummies.

The optimum exhaust for a turbo is a tip mounted to the outlet that fairs out to look like a horn, ie trumpet. This directs the flow and turbulence away from the opening for the least amount of backpressure on the turbo outlet. However this is both very very loud and not practical at all for routing exhaust away from the engine bay.

The next thing to consider is the outlet size of your turbo. Mine is not 3 inches so I don't need a 3 inch downpipe. The stock downpipe is the same size as my turbo outlet.

Based on the horn thing, I like the LR graduated LR exhaust on concept alone. My exhuast including downpipe gradually increases from the turbo outlet od to the muffler and tip. I like that.

And as for the data on the LR site, they are reporting the data they got in testing. I just don't understand how that could be misleading. The thing they were trying to do is reduce the backpressure created between the head and the turbo inlet by making sure there was the least restriction in the exhaust after the turbo as possible. If you push air thru a pipe the resistance against the walls of the pipe creates backpressure. Increasing the size of the pipe over it's length reduces the resistance and resulting backpressure for a pipe of the same length. Hence the LR 4 inch graduated exhaust. And yes, it did reduce the backpressure before the turbo.

Porschefile

The most ideal exhaust is none on a turbo application (well technically a short dump pipe like RKD is describing). While they state that there was very little peak power gain, they go on to state that from the 4" they see 75lbft of torque more at 4k then with the 3" exhaust. Not to mention there were variables of the boost dropping off from 18psi on the first run and a higher 101F temp. I'm sorry but that just doesn't add up. I think it is much more likely that there was inconsistant boost control between runs, causing an early boost spike on the second run. MBC's can have issues like this, especially when temperature changes are involved. I'll say this much, at one point I had a tapered 3" to 3.5" to 4" exhaust like that (built by someone here on the "list, can't remember who though) on my stock 26/6 setup with a maf, vitesse chips and running 1bar. Apples to oranges I know, though the only thing I felt was slightly better top-end pull and a loss of low-end torque.

333pg333

My understanding was that it could help top end power but at the sacrifice of low end torque. Good for the track but not for most street applications.

hally

Disadvantage would be the noise.

billindenver

So there are no Lindsey exhaust equipped people in here to review their system for us? A racing buddy of mine put the 3" on his 951 and said it dramatically reduced his spool up time.

Bill
89 GT-3s

evil 944t

Uhh, "how can that be misleading?" I got some diet pills for you..lol

I would believe it more from a 3rd person party with no conflict of intrest..see my point? They are in the market to sell. I'm not saying they are lying rather don't believe everything you read.

I would rather trust any data from an engineered and tested part(computer model, air flow studies etc..) rather than welding pipes up and throwing it on a dyno.

toddk911

The only thing I can think for their gains is maybe the 3" to 4" gradual increase acts as a venturi effect and actually "sucks" more exhaust increasing the velocity of the flow ore so than a straight sized exhaust.

HIGHBOOST

The optimal exhaust construction would be to have a conical section with 7 to 12 deg. gradual increase in radius right at the exhaust diffuser. If you are considering noise, then usually backpressure and noise are inversly related.

Here is an informative article written by an ENGINEER at Garret.

http://www.tantrumwerks.com/html/Split%20DP%20support%20theory.pdf#search='larger%20turbine%20less%20WG%2 0work%3F'

toddk911

"exhaust diffuser."

Is that a fancy term for muffler????

toddk911

So upgraded/better designed headers make a big difference and keeping stock downpipe and going to bigger 3-4" exhaust will account for the 7-12 degree increase?

Someone above said "Porsche ain't stupid" 100% correct. They have a 2.5" exhaust for a 250ish hp car. So if this came from the factory with 300, 350, 400hp than they might have gone with a bigger exhaust.