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Discussion Starter #1
I am wanting to run a 4 inch exhaust with a 6 inch stack with my future 4bt is that to big should it be smaller what does bigger exhaust do to performance and EGT's. Thanks in advance for the imput
 

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Besides being a noisey echo chamber, radiating a lot more heat to your engine bay and being a PITA to fit, there are no performance downsides.

But 4 and 6 inch is overkill IMO. Measure the backpressure at the turbo outlet and see what you've got. Unless you get a big pressure buildup, there's no reason to go bigger. Muffler choice will also affect backpressure more than pipe size.
 

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What is a good muffler to run on 3" exhaust?

Daniel
The most free flowing on that your sanity and your local regulations allow.

I prefer to keep mine quiet, my truck has a 2 1/4" exhaust on it. I really should measure the backpressure on it one day.
 

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Exhaust

I am wanting to run a 4 inch exhaust with a 6 inch stack with my future 4bt is that to big should it be smaller what does bigger exhaust do to performance and EGT's. Thanks in advance for the imput
I would start with a 3in downpipe and 3in exhaust any bigger you would loose low end torque there is a yellow bronco with a high performance 4bt in the build up threads take a look, it has a pipe that looks like a 3in
 

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exhaust

Can you explain why a bigger exhaust will lose low end torque?
If you have an exhaust system that is too large for given specs of an engine it would have to rev higher to produce low end torque but would produce higher horsepower. One example when engines started coming out with 4 valves per cylinder the exhausts gasses was flowing out quicker than the 2 valve counterparts but the trade off was low end torque.
 

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I would start with a 3in downpipe and 3in exhaust any bigger you would loose low end torque there is a yellow bronco with a high performance 4bt in the build up threads take a look, it has a pipe that looks like a 3in
I want proof that a smaller exhaust makes more torque on a diesel truck... So big deal that Bronco only has 3", because he probably doesn't need 4" nobody does on the 4bt's, but 4" wouldn't hurt power at all... by 2/3 rule 3" is like 4" on a 6bt and 4" is like 6"... I personally chose 4" because when I had my motor running on a stand with 4" flex pipe to exit the exhaust gases, I had to have that sound(instead of sounding so much like a tractor it's closer to a semi)
 

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If you have an exhaust system that is too large for given specs of an engine it would have to rev higher to produce low end torque but would produce higher horsepower. One example when engines started coming out with 4 valves per cylinder the exhausts gasses was flowing out quicker than the 2 valve counterparts but the trade off was low end torque.
Doesn't work that way and it has nothing to do with four valve vs two valve heads.

The bigger your exhaust, the less backpressure you get. Less backpressure means the turbo spools sooner and you get more low end torque.

Two valve heads used to (like back in the old days) get better low end torque because the extra turbulence caused better air/fuel mixing at lower engine speeds.
But now there's no advantage.
 

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Discussion Starter #11
Doesn't work that way and it has nothing to do with four valve vs two valve heads.

The bigger your exhaust, the less backpressure you get. Less backpressure means the turbo spools sooner and you get more low end torque.

Two valve heads used to (like back in the old days) get better low end torque because the extra turbulence caused better air/fuel mixing at lower engine speeds.
But now there's no advantage.
So big exhaust or not am i going to gain or lose power? how big should my stack be
 
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