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After looking at the number of exhaust systems offered for the 991 Turbo S I am a bit puzzled as to why only one supplier has done their homework...
"The best exhaust system leaving the turbine seems to be the one which expands rapidly to convert the swirl into turbulent flow." If you take a close look you can see the exit cone in the turbine housing. This continues into the exhaust...
If you want the proper exhaust for a Turbo Porsche the BBI setup is best "in my opinion"...
After looking at the number of exhaust systems offered for the 991 Turbo S I am a bit puzzled as to why only one supplier has done their homework...
"The best exhaust system leaving the turbine seems to be the one which expands rapidly to convert the swirl into turbulent flow." If you take a close look you can see the exit cone in the turbine housing. This continues into the exhaust...
At the risk of sounding like a moron, I'm having a hard time with the concept of "turbulent flow" here.
The shape of the cat bypass pipe shown above is something that we toyed with back in the very early days of the 997.1 and 997.2 Turbo exhaust designs with Tubi. After our testing, we found the equal diameter piping to be much more effective.
At the risk of sounding like a moron, I'm having a hard time with the concept of "turbulent flow" here.
The shape of the cat bypass pipe shown above is something that we toyed with back in the very early days of the 997.1 and 997.2 Turbo exhaust designs with Tubi. After our testing, we found the equal diameter piping to be much more effective.
Have a read here.... http://www.tercelreference.com/terce...st_theory.html
"As for the geometry of the exhaust at the turbine discharge, the most optimal configuration would be a gradual increase in diameter from the turbine's exducer to the desired exhaust diameter-- via a straight conical diffuser of 7-12° included angle (to minimize flow separation and skin friction losses) mounted right at the turbine discharge. Many turbochargers found in diesels have this diffuser section cast right into the turbine housing. A hyperbolic increase in diameter (like a trumpet snorkus) is theoretically ideal."
Have another look at the turbine housing discharge...
In the first 2 editions of Hugh MacInnes "Turbochargers" books (Red covered published in 1971, and Deep Purple 1984) he discusses turbo turbine exit conditions in the "Exhaust" chapters. In both editions The stated goal was to kill the swirling flow.
Have a read here.... http://www.tercelreference.com/terce...st_theory.html
"As for the geometry of the exhaust at the turbine discharge, the most optimal configuration would be a gradual increase in diameter from the turbine's exducer to the desired exhaust diameter-- via a straight conical diffuser of 7-12° included angle (to minimize flow separation and skin friction losses) mounted right at the turbine discharge. Many turbochargers found in diesels have this diffuser section cast right into the turbine housing. A hyperbolic increase in diameter (like a trumpet snorkus) is theoretically ideal."
Have another look at the turbine housing discharge...
In the first 2 editions of Hugh MacInnes "Turbochargers" books (Red covered published in 1971, and Deep Purple 1984) he discusses turbo turbine exit conditions in the "Exhaust" chapters. In both editions The stated goal was to kill the swirling flow.
Turbo vane geometries have changed over the years and now produce less turbulence, that is one of the factors that allow them to spool rapidly at low rpms. VTG is now common in modern turbos and so books that were written concerning performance of Turbos 30 years ago are probably not relevant today. Just a thought............
Take a closer look at the turbine housing again, Porsche seem to be using this old school technology. They are the first turbo housings I've seen with this design...
It is a cone...
My Lotus is using the latest Precision billet ball bearing turbo and it still has a basic straight exhaust exit.... I'm pretty sure Porsche didn't throw out their old text books when designing this setup...
My new billet ball bearing turbo I'm sure would benefit form Porsche's old school tech..
Porsche claims to be using VTG which would mean there are variable stator vanes inside the housing which are not in view. Those are what get adjusted by the ECU in order to minimize turbulence and allow the turbo to spool rapidly even at low RPM.
Porsche claims to be using VTG which would mean there are variable stator vanes inside the housing which are not in view. Those are what get adjusted by the ECU in order to minimize turbulence and allow the turbo to spool rapidly even at low RPM.
The cone shaped exhaust exit is clearly shown in the cut away. It is for reduced back pressure on the turbine wheel...
Remove resistance and you get quicker spool up add to that variable vane tech and you have the best of both worlds for turbo response....
Bring the cone out, move the cat down the line and you have less restriction in the exhaust on the turbo.... That's the whole idea.
Have a read here.... http://www.tercelreference.com/terce...st_theory.html
"As for the geometry of the exhaust at the turbine discharge, the most optimal configuration would be a gradual increase in diameter from the turbine's exducer to the desired exhaust diameter-- via a straight conical diffuser of 7-12° included angle (to minimize flow separation and skin friction losses) mounted right at the turbine discharge. Many turbochargers found in diesels have this diffuser section cast right into the turbine housing. A hyperbolic increase in diameter (like a trumpet snorkus) is theoretically ideal."
OK, so the "theory" they talk about says that the gradual increase in diameter is only to match the exhaust diameter. The theory doesn't say anything about the actual exhaust diameter increasing as well, so I'm still a bit lost.
The goal of any efficient exhaust system is to provide smooth and efficient flow of exhaust gasses, without turbulence. The reason you see that "cone" shape on the exhaust housing is because of the drastic difference in diameter between the turbine wheel and the exhaust piping. In order to reduce exhaust turbulence, that cone shape is used rather then a drastic "step" for this exact reason. Once the diameter of the exhaust piping is met, I don't see why there's any theoretical or practical reason to continue increasing the diameter of the exhaust piping directly after the turbo, especially since it eventually has to be reduced back down, which would cause a restriction and hence, more turbulence.
Necking the exhaust down to a suboptimal diameter is never a good idea, but if it is necessary, doing it further downstream is better than doing it close to the turbine discharge since it will minimize the exhaust's contribution to backpressure. Better yet: don't neck down the exhaust at all.
Hey Tom, I'm just the messenger and a Porsche Turbo guy that want's the best equipment on his car....
After looking at all the exhaust designs out there I decided I wanted one that was designed for performance not sound...
A nice exhaust note is a byproduct of performance... https://www.facebook.com/10000095086...4/?pnref=story
Hmmmm. Let's see. Should I value the opinion of Champion Motorsport with their extensive racing and performance building history, or a self-proclaimed expert who doesn't fully comprehend the principles of physics? Cutting and pasting from a 30 year old tome doesn't validate your (anachronistic) argument. Have you decided to contradict yourself and start modifying your vehicle without fear of "warrantee" issues, as you put it?
Hmmmm. Let's see. Should I value the opinion of Champion Motorsport with their extensive racing and performance building history, or a self-proclaimed expert who doesn't fully comprehend the principles of physics? Cutting and pasting from a 30 year old tome doesn't validate your (anachronistic) argument. Have you decided to contradict yourself and start modifying your vehicle without fear of "warrantee" issues, as you put it?
I'm no expert but I know what will void my warrantee....
Dude do what ever you like, I'm sure your exhaust is loud enough for you...:roll eyes:
The thing about proper engineering is that it is not for noise makers unless that is the goal... Chopping off tappers and **** poor design instead of making smooth radius S bends is the last thing you do to a turbo exhaust...
Any kid with a Civic knows that...
05-07-2015, 10:44 AM
