cobra06

I found this chart that outlines optimal exhaust diameters for turbocharged engines. Good to know if you plan on doing large HP modifications. Helped me with the next generation of exhuasts. I'M going to 90 mm (~3.5 in.).

Exhaust Tubing Size Chart

Horsepower Range.Single Exhaust Diameter Dual
200-300.................3" .............2 1/4"
300-400.................3 1/2" .........2 1/2"
375-450.................4"..............3"
450-550.................4 1/2"..........3 1/2"
550-650.................5"..............3 1/2"
650-800.................-...............4"
800-1000................-...............4 1/2"
1000 +..................-...............5"

Dancing Herve's advice for the day.... <img src="http://boards.rennlist.com/upload/nicnac_dance.gif" alt=" - " />

cobra06

Source: "Scientific Design of Exhaust and Intake systems".
Based on the minimizing backpressure to the outflow of the turbocharger at that HP rating. I also believe the diameter takes into consideration the diameter of exhaust to maintain the necessary velocity of exhaust gas. Charts for N/A systems are somewhat different as expected.

Don't know about the 917, closest I've been to one is #20, that's parked on my bookshelf...

<img src="http://boards.rennlist.com/upload/mona.gif" alt=" - " />

cobra06

CJV
Reading a little further (Pays to just more then look at the pictures). The proportional increase in pipe diameter, increases exhaust cooling. Cooler air is more dense and there is a point where larger diameter exhausts for lower HP engines will decrease flow (pushing a heavier air-mass). The thing is, even w/ lower HP NA engines, 80 mm is recommended for optimal outflow, that utilizes exhaust scavenging and gas density.
BTW the 917K had an exhaust pipe diameter of 114.3 CM, and was of a "very complex design"..thats all I could find on it

<img src="http://boards.rennlist.com/upload/MonaTurbo.jpg" alt=" - " />

johnfm

Cobra

"....917 had exhaust dia of 114.3 CM...."

er, that's 45 inches!!!!!

I think you mean 11.43 cm (4.5 inches)

cobra06

Most correct...never said I was a math major

<img src="http://www.egri.co.uk/smileys/stupid.gif" alt=" - " />

Its about 4.5 inches in diameter

Joe@Fabspeed

That chart doesnt make sense.........the 935s made 800HP and used 2 pipes of 2.5" 63.5mm for exhaust outlets. Dont measure the final exhaust outlet on a megaphone........the rest of the exhaust isnt going to be that big. Dual 3.0" pipes can handle over 1500hp in a turbo easily.

cobra06

This is not a chart for the diameter of the tail pipe, its for the entire system. Its not just one source that points out these recommendations, and I didn't derive them (just do a search on the net, my source is a exhaust design technical text). Many sources say on a turbo no exhaust is the best exhaust (or N/A for that matter as in open headers). What it is really saying is use the largest exhaust possible, one that doesn't allow stagnation and a cool dense mass of air. Provide minimal backpressure, and in a turbo system the only backpressure should come from the turbocharger. Coupled of course with a tuned header. CJV, a stock turbo should be running at least a 70 mm pipe, probably 80 mm. Don't you feel a stock TT would run better and pick up HP with a better flowing exhaust?
But lets face it Porsche had to contend with a diverse crowd of owners, that didn't want too much noise, or the slightest bit resonance, and had to fit it in a cramped space. The only way to put a 4" pipe in the TT is with a straight pipe, it would be tight with a 80 mm tube crossover system.
993RS..I don't get your point about handling 1500 HP, I'M talking about optimizing for that much HP..

BTW the M1 tank has a 1500 HP turbocharged engine, with an exhaust you could craw in.
<img src="http://www.egri.co.uk/smileys/tank.gif" alt=" - " />

HBdirtbag

this chart was made by an exhaust company to go along w/ V8's primarily

cobra06

Um...If you read my source, its a text book and numbers of cylinders has no bearing on it at all. The author, Dr. John C. Morrison is one of the foremost authorities on the analysis of the induction and exhaust processes of high-speed engines.
Like most things in cars variables come into play, seams, bends twists, all change the dynamic of the system. These are starting points or guidelines for high-performance engines.

HBdirtbag

No ****, cause the shop that did my suburbans exhaust work had the chart and they said it wouldn't work w/ my 6 cyl.

retract my last statement then as i've been proven wrong.

Kevin

Cobra;

I did some checking with Borg Warner, the engineering has been done already. The optimal diameter is the outside dimension of the turbine housing. My memory slip at the dimension of the sealing rings? Yes, shorter and larger diameters are optimum but not practical for our cars.

Kevin

cobra06

Kevin, thats got to be about 4", just eye-balling it.
<img src="http://www.egri.co.uk/smileys/jawdrop.gif" alt=" - " />

I Wonder why it isn't the diameter of the turbo exhaust. It must have something to do with volume of gas that can be moved with a particular diameter fan..

Practicality?, when did that ever come into play with these cars...

Thanks, seems like good information