76mm turbo - Ford Mustang Forums : Corral.net Mustang Forum
 
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post #1 of 9 Old 07-22-2007, 11:59 AM Thread Starter
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Talking 76mm turbo

What size exhuast does a percision 76mm turbo need? Currently have 3inch
thanks in advance

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post #2 of 9 Old 07-23-2007, 04:01 PM
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thats plenty


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post #3 of 9 Old 07-23-2007, 04:53 PM Thread Starter
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thanks
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post #4 of 9 Old 07-24-2007, 12:34 AM
 
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Proper exhaust size depends on what you're doing. If you're only running pump fuel with the turbo, 3" will be fine but turbo cars will almost always want a larger exhaust. If this is a PT76 GT-S which it more than likely is, I'd generally recommend a 4" system if you're going to be leaning on it at all.

The .96 A/R also would be superior than the .81. Backpressure is a turbo's enemy.
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post #5 of 9 Old 07-24-2007, 12:57 AM
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Quote:
Originally Posted by Mark Conte View Post
Proper exhaust size depends on what you're doing. If you're only running pump fuel with the turbo, 3" will be fine but turbo cars will almost always want a larger exhaust. If this is a PT76 GT-S which it more than likely is, I'd generally recommend a 4" system if you're going to be leaning on it at all.

The .96 A/R also would be superior than the .81. Backpressure is a turbo's enemy.
Back pressure should be considered but maintaining exhaust gas velocity
with smaller tubing is just as important

again its like you said "depends on hp wanted"

If you you want high top end power a bigger A/R and exhaust would
be better but you will sacrifice low end with more lag
and vice versa for having quick spool but running out of breathing
room at higher boost levels and upper rpms.

According to "Corky Bell" a 3" down-pipe will typically support up
to 700 flywheel hp.

If you really want to know for sure, buy the book "Maximum Boost"
by Corky Bell. He gives all the math formulas to properly calculate
exhaust gas velocities for a given engine and exhaust tube size.

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post #6 of 9 Old 07-24-2007, 01:10 AM
 
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Quote:
Originally Posted by r.barn View Post
Back pressure should be considered but maintaining exhaust gas velocity
with smaller tubing is just as important

again its like you said "depends on hp wanted"

If you you want high top end power a bigger A/R and exhaust would
be better but you will sacrifice low end with more lag
and vice versa for having quick spool but running out of breathing
room at higher boost levels and upper rpms.

According to "Corky Bell" a 3" down-pipe will typically support up
to 700 flywheel hp.

If you really want to know for sure, buy the book "Maximum Boost"
by Corky Bell. He gives all the math formulas to properly calculate
exhaust gas velocities for a given engine and exhaust tube size.
Maximum Boost is a great book, definitely recommended.

As for exhaust gas velocity, you are absolutely correct but in a turbocharged application the only exhaust gas velocity that matters is pre-turbocharger. Post turbocharger the only thing you want to do is clear the air as quickly as possible.

Typically, I prefer the larger A/Rs even on low boost applications since when the turbine is more efficient it can clear the spent exhaust gasses easier and avoids the precipitious volumetric efficiency fall off associated with high exhaust backpressures. But again, as it always comes down to - depends on the application. If the engine breaths well at the horsepower you're trying to run it at with the small housing, no reason to go larger until you turn up the boost.
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post #7 of 9 Old 07-24-2007, 08:45 AM Thread Starter
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thanks guys i will be looking for the book now, still learning a lot,, a lot very good information is always helpful
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post #8 of 9 Old 07-24-2007, 12:42 PM
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thanks guys i will be looking for the book now, still learning a lot,, a lot very good information is always helpful
http://www.amazon.com/Maximum-Boost-...4949846&sr=8-1

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post #9 of 9 Old 07-24-2007, 07:32 PM
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Read it as a guide.. Its a fairly old book now and some things have moved on...Especially in ECU tech...
He contradicts himself at times in the book...
A good book to get started ....

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85 Lb inj Custom cam ,P 2000 Haltech ecu...4x's 2 coil wasted spark ignition.Twin SC 61-2s with Dart block, 330/4340 Crank, Oliver rods,7.9/ comp c C.P pistons.. 482 rwkw/ 646 rwhp..A.P 4 pot brakes...TKO
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