2.5, 2.75, or 3” Exhaust for new 95-97 Wit’s End Turbo? (1 Viewer)

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That looks really good, I didn't think the exhaust could fit inside the frame rail where it drops down off the turbo, but there it is. I'm slowly stocking up on exhaust parts to redo it with 4" at some point, I might have to take a look at following your path, plus the tire almost scrubs with it outside the frame rail how I have it presently.
 

bryson

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Correct me if I'm wrong, maybe my theory isn't correct, but I think denting each individual header makes less difference than disrupting exhaust flow post collector. You'd need dual 4" exhaust to roughly surpass the flow of 8x 1 5/8" header. So would like to see them do a test where they disrupt flow post collector. Post collector should see faster air velocity than in each individual header tube, no?

1 5/8" = 2.76 square inches 2.07 square inches
8x 1 5/8" = 22.08 square inches 16.56 square inches
Single 4.5" = 15.9 square inches
Dual 3.5" = 19.24 square inches
Dual 4" = 25.12 square inches

Some of your math is not jiving here, which changes some of your theory...
 
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Some of your math is not jiving here, which changes some of your theory...

I stand to be corrected. Not sure how that happened but just double checked and you're correct. I'll blame it on it being the last week of work, and being mostly focused on moving from NZ to Canada.

So to add, dual 3" = 14.14 square inches

Not sure what the most common exhaust setup is for these cars, but would still like to see a post collector test. Also I'm sure running headers only and no full exhaust on that test frees up a lot of flow.
 

mudgudgeon

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you guys should have a look at this video. might change your opinion on exhaust flow.

https://dai.ly/x3vupq0

Not wanting to be that guy, but what's the point here? How is that relevant to building a complete exhaust?

A short narrowing of a tube creates a venturi effect. Exhaust gas will speed up as it passes a restriction, then slow down again once past the restriction.

A long length of narrower tube causes more flow restriction due to friction as gasses drag along the walls of a pipe.
 
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Not wanting to be that guy, but what's the point here? How is that relevant to building a complete exhaust?

A short narrowing of a tube creates a venturi effect. Exhaust gas will speed up as it passes a restriction, then slow down again once past the restriction.

A long length of narrower tube causes more flow restriction due to friction as gasses drag along the walls of a pipe.

I dunno, I guess i'd always known that you make as fewer bends as possible and keep it the same diameter and use mandrel bent stuff etc. and then these guys are bashing the crap out of their extractors and it's no detriment to power. surprised me, thought it added to the convo
 

mudgudgeon

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I dunno, I guess i'd always known that you make as fewer bends as possible and keep it the same diameter and use mandrel bent stuff etc. and then these guys are bashing the crap out of their extractors and it's no detriment to power. surprised me, thought it added to the convo

Yeah, fair enough. It's a bit surprising, but makes sense too. Crush 2 feet of pipe that amount, I think the result would be different
 
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If the turbo system is designed for a certain exhaust, you go and change the flow, you can easily overboost and trash your motor. This isvwhat happens all the time with gmc syclones and typhoons. Guys put a 3” exhaust on and end up having to buy or rebuild another motor.
 
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Yep that is what I said earlier. People will have to get a boost and AFR gauge if they go this route with the turbo setup.

If the turbo system is designed for a certain exhaust, you go and change the flow, you can easily overboost and trash your motor. This isvwhat happens all the time with gmc syclones and typhoons. Guys put a 3” exhaust on and end up having to buy or rebuild another motor.
 
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If the turbo system is designed for a certain exhaust, you go and change the flow, you can easily overboost and trash your motor. This isvwhat happens all the time with gmc syclones and typhoons. Guys put a 3” exhaust on and end up having to buy or rebuild another motor.

I never heard of this, but isn't the purpose of a wastegate or BOV to limit boost pressure...

If anything you should be able to achieve boost sooner and increase the lower RPM range on the power curve, if guys are blowing motors because they up size their exhaust, I would think there are a couple other factors also involved, like wiring off the wastegate or disconnecting boost line to it and driving it hard.

Sounds a bit funny, maybe there is an issue with a weak engine or running to lean/hot with those.
 

mudgudgeon

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I never heard of this, but isn't the purpose of a wastegate or BOV to limit boost pressure...

If anything you should be able to achieve boost sooner and increase the lower RPM range on the power curve, if guys are blowing motors because they up size their exhaust, I would think there are a couple other factors also involved, like wiring off the wastegate or disconnecting boost line to it and driving it hard.

Sounds a bit funny, maybe there is an issue with a weak engine or running to lean/hot with those.

That would be my thoughts too.

An exhaust is just one part of the system. Big changes to any part of a system shouldn't be done without checking on his the system performs as a whole.

Saying an exhaust blows up engines is kind of like saying diff locks break axles
 
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There is no wiring on the wastegate, in traditional spring controlled wastegate systems.




I never heard of this, but isn't the purpose of a wastegate or BOV to limit boost pressure...

If anything you should be able to achieve boost sooner and increase the lower RPM range on the power curve, if guys are blowing motors because they up size their exhaust, I would think there are a couple other factors also involved, like wiring off the wastegate or disconnecting boost line to it and driving it hard.

Sounds a bit funny, maybe there is an issue with a weak engine or running to lean/hot with those.
 
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That would be my thoughts too.

An exhaust is just one part of the system. Big changes to any part of a system shouldn't be done without checking on his the system performs as a whole.

Saying an exhaust blows up engines is kind of like saying diff locks break axles
Someone will correct me if I'm wrong, but I think the boost pressure would be reduced (wastegate never goes off), but the airflow would be increased. Increased airflow = a leaner condition, potentially leading to detonation, and other bad things.
 
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Nope, boost pressure would be increased.

Think about this. The higher the back pressure on the exhaust side of the turbo the less easy the turbine is able to turn. Remember the only thing turning the turbo and providing boost is the exhaust. So if you take a 2.5" exhaust with restrictive bends, 2 catalytic converters, a resonator and a restrictive muffler and replace it with a 3.5" straight through exhaust, you now have very little restriction, the wastegate will not open at the same PSI since the back pressure is what opens the wastegate, if the wastegate isn't opening the turbo is spinning faster, if the turbo is spinning faster it is making more boost. Wastegate tuning by spring pressure is at most a guess. Putting a 5psi spring in a wastegate does not mean you will get 5psi of boost. Hell if the wastegate is not in the correct location you could see 20psi on a 5psi spring. If there is a major change to back pressure you will see more boost.
 
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He's referring to the wastgate as wired shut, or with different springs under the wastegate diaphragm to keep it shut so nothing bypasses the turbine.

Perhaps the GM engines that pop arent able to produce enough fuel to match the air ratios and are running lean/hot. Just a wild guess.

The thing to think about with turbo exhaust turbines, is "pressure differential" it's the difference in pressure from the manifold side in contrast to the exhaust piping side that pulls the turbine along.
 
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Nope, boost pressure would be increased.

Think about this. The higher the back pressure on the exhaust side of the turbo the less easy the turbine is able to turn. Remember the only thing turning the turbo and providing boost is the exhaust. So if you take a 2.5" exhaust with restrictive bends, 2 catalytic converters, a resonator and a restrictive muffler and replace it with a 3.5" straight through exhaust, you now have very little restriction, the wastegate will not open at the same PSI since the back pressure is what opens the wastegate, if the wastegate isn't opening the turbo is spinning faster, if the turbo is spinning faster it is making more boost. Wastegate tuning by spring pressure is at most a guess. Putting a 5psi spring in a wastegate does not mean you will get 5psi of boost. Hell if the wastegate is not in the correct location you could see 20psi on a 5psi spring. If there is a major change to back pressure you will see more boost.


Someone gets it. Thanks for explaining it.
 

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