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Motorboatin' SOB, Headlight Cleaning Guru
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Discussion Starter #1
curiousity has got a hold of me. i understand that too big a pipe size will cause a loss in torque. but what about keeping the correct pipe size, and then having the pipe expanded to be welded to a muffler that has a larger diameter inlet and outlet (example: single 2.5" pipe expanded right before a 3" in/out muffler, then right after the muffler, reduce the pipe size back to 2.5"). would this have the same effect as opposed to running all 3" piping?
 

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shouldn't have any problems, when i cut my cats out my 92 lx i removed the resonator too and welded in a solid 2.5 pipe, from there it went back to the stock 2.25 pipe to the rear mufflers.. didn't notice any difference in torque just a slight difference in volume

i highly doubt it'll have the same effect, if you think about it, just because a 3" pipe is placed later down doesn't mean you'll be flowing a full 3", think of nascar with there restrictor plates, your only being allowed to breathe 2.5" -theoretically anyway

btw mike, i love your avatar
 

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Motorboatin' SOB, Headlight Cleaning Guru
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Discussion Starter #3
well, i know there wouldnt be any issues, but im asking if the loss in torque would be noticeable or not. my aforementioned setup would have the pipe size be increased to be mated to a midmounted muffler (not pipe) and decreased back to the same size after the outlet. the pipe size would only change at the muffler.
 

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As long as you have a bottle neck of 2.5" it will be the same as if you had pipes all the way at 2.5". Just expect a change in sound.
 

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As long as you have a bottle neck of 2.5" it will be the same as if you had pipes all the way at 2.5". Just expect a change in sound.
Common misconception that just isn't true. The longer the run of pipe, the more restriction there is. This means that the full length of a pipe acts to restrict flow, not just the smallest point. If you've got 20 feet of 3" pipe with a 2.5" inlet, it will flow more than a 20 foot run of 2.5" pipe.

Mike
 

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Motorboatin' SOB, Headlight Cleaning Guru
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Discussion Starter #6
If you've got 20 feet of 3" pipe with a 2.5" inlet, it will flow more than a 20 foot run of 2.5" pipe.
understood, but my situation is the opposite. there is no pinch point throughout the entire exhaust system. i would have an inlet and outlet that is bigger than the pipe diameter, so would the flow suffer due to the increase?
 

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I wouldn't worry about it. The muffler itself is a restriction that will more than offset the difference in pipe size. I think you're making more of this than you should.

Mike
 

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Motorboatin' SOB, Headlight Cleaning Guru
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Discussion Starter #8
nah, im just inquiring about the flipside of the issue.
 

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There's a really good column in the most recent issue of Popular Hot Rodding about exhaust theory that might help you find the theoretical answer.

The real answer here is that the loss would be as a percentage of the current power. With your 3.8, a small percentage of next to nothing means you'll never notice a difference. :)
 

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There's a really good column in the most recent issue of Popular Hot Rodding about exhaust theory that might help you find the theoretical answer.

The real answer here is that the loss would be as a percentage of the current power. With your 3.8, a small percentage of next to nothing means you'll never notice a difference. :)
And so the magazine myths continue on as internet facts. Amazing. The dumbing down of the internet users continues. Hey, of course, "peak" dyno horsepower is what counts too. Gotta keep the magazine crap going.

Brad
 

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What about those nasty bends after the stock manifold in the stock exhausts are those restrictive? I was thinking about have new pipes put on removing 2 cats and running new pipe from the manifold to the single 3rd cat before the resonator. Is that worth it? I dont plan on doing a full new exhaust til I have a good reason to do it but just that part, combined with the violin case seems like its really not letting the engine breathe.
 

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What about those nasty bends after the stock manifold in the stock exhausts are those restrictive? I was thinking about have new pipes put on removing 2 cats and running new pipe from the manifold to the single 3rd cat before the resonator. Is that worth it? I dont plan on doing a full new exhaust til I have a good reason to do it but just that part, combined with the violin case seems like its really not letting the engine breathe.
What is the point if you don't take out your major restriction? That single pipe going back is really small. I will tell you though that any inlet improvements you make will be choked by the exhaust. Few minor differences between your 4.6 exhaust and my 5.0. The true duals made a huge difference on mine. Applified by the gears I'm sure but just shows what the motor wants.

Brad
 

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And so the magazine myths continue on as internet facts. Amazing. The dumbing down of the internet users continues. Hey, of course, "peak" dyno horsepower is what counts too. Gotta keep the magazine crap going.

Brad
So you saw the article? I'd be really interested in your analysis of it, and where they went wrong. Or are you talking about this whole thread in general? Enlighten us.
 

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So you saw the article? I'd be really interested in your analysis of it, and where they went wrong. Or are you talking about this whole thread in general? Enlighten us.
Popular Hot Rodding has had a couple of very good ones from true pro's. The problem is they end up contradicting these same pro's with general comments in their everyday articles. If we are just talking exhaust, not headers, on a stock engine you can't go to big. On a modified engine, if you lose torque due to exhaust, the cam timing events are wrong. Too many times, especially on mods such as cams, to our MN12's that is exactly what goes wrong. There are no off the shelf setups for our size of car so anyone installing these packages is already involved in compromise. The loss of bottom end torque (really not torque but horsepower) is caused by moving the power curve to higher rpms while trying to move a heavy a s s car withit. What seems to offset that is smaller pipes but that is simply restriciting the overall curve to gain through a narrow low rpm band while killing the the whole rest of the powerband. Seat of the pants improvement low, yes, actual no.

It's a real simple rule, specific to efi, if you have to make inlet or outlet smaller to get your car to perform, the cam is wrong. No ifs. I know I will get arguments with I did this and got this or so and so said, this article said, etc. Just think of it this way, would you rather breath through an open mouth or a straw? Try it. At some point common sense needs to rule.

Brad
 

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Bradone I also chopped off my muffers so the remaining stock portion of my exhaust would be the 3rd cat and the resonator and the Y exiting into down turns. The resonator isn't restrictive enough to remove I dont think. But maybe the Y after could be, I know my engine doesn't make enough power to justify duels in terms of bang for buck. Has anyone thought of a cheap exhaust exiting on the side, not pretty but fully unrestrictive. That would loud lol!!!! nothing but a cat on each pipe hehe angry hornets here I come!!!! maybe :)
 

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Popular Hot Rodding has had a couple of very good ones from true pro's. The problem is they end up contradicting these same pro's with general comments in their everyday articles. If we are just talking exhaust, not headers, on a stock engine you can't go to big.
This is a pretty broad statement. Specific to the MN12? After the cats? Before the cats? How far from the exhaust manifold do I have to be for size to not matter?

On a modified engine, if you lose torque due to exhaust, the cam timing events are wrong. Too many times, especially on mods such as cams, to our MN12's that is exactly what goes wrong.
Explain, please. What difference does it make if I have a stock cam or an aftermarket cam?


There are no off the shelf setups for our size of car so anyone installing these packages is already involved in compromise. The loss of bottom end torque (really not torque but horsepower) is caused by moving the power curve to higher rpms while trying to move a heavy a s s car withit.
Why is the distinction between torque and hp important?

What seems to offset that is smaller pipes but that is simply restriciting the overall curve to gain through a narrow low rpm band while killing the the whole rest of the powerband. Seat of the pants improvement low, yes, actual no.
Above, you said the exhaust is moving the powerband upward in the RPM range. Here, you say it's choking the motor. Can you be more specific about what causes each affect? Bigger pipes, smaller pipes? What's the ideal pipe size for a stock motor?

It's a real simple rule, specific to efi, if you have to make inlet or outlet smaller to get your car to perform, the cam is wrong. No ifs. I know I will get arguments with I did this and got this or so and so said, this article said, etc. Just think of it this way, would you rather breath through an open mouth or a straw? Try it. At some point common sense needs to rule.

Brad
This is the part that interests me most. Why is it specific to an efi engine?

Thanks,
Tobey
 

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This is a pretty broad statement. Specific to the MN12? After the cats? Before the cats? How far from the exhaust manifold do I have to be for size to not matter?


Explain, please. What difference does it make if I have a stock cam or an aftermarket cam?



Why is the distinction between torque and hp important?


Above, you said the exhaust is moving the powerband upward in the RPM range. Here, you say it's choking the motor. Can you be more specific about what causes each affect? Bigger pipes, smaller pipes? What's the ideal pipe size for a stock motor?


This is the part that interests me most. Why is it specific to an efi engine?

Thanks,
Tobey

Tobey,

I have read enough of your posts. I will not come out to play. You can't quote correctly when you have the line two spaces up.

Brad
 

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Motorboatin' SOB, Headlight Cleaning Guru
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Discussion Starter #18
What about those nasty bends after the stock manifold in the stock exhausts are those restrictive? I was thinking about have new pipes put on removing 2 cats and running new pipe from the manifold to the single 3rd cat before the resonator. Is that worth it? I dont plan on doing a full new exhaust til I have a good reason to do it but just that part, combined with the violin case seems like its really not letting the engine breathe.
please dont hijack my thread. i am only asking about pipe size and loss in power here. you can hijack when i see pics of this milf...
 

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Motorboatin' SOB, Headlight Cleaning Guru
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Discussion Starter #19
Explain, please. What difference does it make if I have a stock cam or an aftermarket cam?
the amount of duration? but that has little to do with pipe size. header primary size may play a small factor.

im lost on the cam issue as well. brad, im not too sure if the wrong cam is to blame. yes, having the right cam does make a difference in power levels, but there's more to consider. aside from exhaust, it appears that lost torque is due to folks slapping together an engine with mismatched parts. i notice on here and other boards that people build an engine (i.e., 5.0 parts on a 5.0-based stroker) and they wonder why they arent making the power they expected to make.
 

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Tobey,

I have read enough of your posts. I will not come out to play. You can't quote correctly when you have the line two spaces up.

Brad
I'm not baiting you. I'm not being a jerk. I really don't know much about exhaust theory except for what I read in the magazines. You seem to have experience/knowledge, I want to understand. I'm asking questions because I'm truly interested in what you know and how you learned it.

If you want to limit the scope of your response, what I'm most interested in are the first and last questions. You say the size doesn't matter, I want to know how far from the manifold this rule goes into affect and why. And I'm very curious why you think EFI responds differently than a carburetor application.

Again, I'm not being a jerk. I just want to know the justification for your statements before I take them as fact.
 
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