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Discussion Starter · #1 ·
I love my Street Bob, but if I could change anything, it would be the pipes. I have a denim black s.b. and would like to have denim black pipes instead of the chrome ones it came with.

I've watched a lot of videos, but I might have missed the answer to what I am asking. Aside from the look and sound, what are the benefits of changing the pipes out? Better performance? The 2nd thing I would change would be the air filter setup. I think I saw somewhere that if I did that, I could possibly gain a performance boost, but would need to get it re-tuned. Would I need to do the same for the pipes?

Comments welcome.
 

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Wayward Son
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Pipes are like a human exhaling. The better you exhale the better you function.
Having said that. They also provide back pressure. Necessary for, among other things, torque.
Yes. Changing pipes, to the right pipes, will improve performance. 2 into 1`s probably being the best.
A free(er) intake will improve performance as well. It inhales more efficiently. The pipes help exhale more efficiently.
The OEM MAP will alter itself somewhat to allow for both changes. But to maximize them a re-map is the way to go.
That allows for the best use of the improved inhaling, as well as exhaling.
Harley engines are really only big air pumps. The more you bring in, the better it is handled inside, the better it exits all go to improving performance.
 

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Discussion Starter · #3 ·
Pipes are like a human exhaling. The better you exhale the better you function.
Having said that. They also provide back pressure. Necessary for, among other things, torque.
Yes. Changing pipes, to the right pipes, will improve performance. 2 into 1`s probably being the best.
A free(er) intake will improve performance as well. It inhales more efficiently. The pipes help exhale more efficiently.
The OEM MAP will alter itself somewhat to allow for both changes. But to maximize them a re-map is the way to go.
That allows for the best use of the improved inhaling, as well as exhaling.
Harley engines are really only big air pumps. The more you bring in, the better it is handled inside, the better it exits all go to improving performance.
Thank you sir. You done learnt me something. I always learn something from you wonderful folks.

:bikerguy:
 

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They also provide back pressure. Necessary for, among other things, torque.
I've always found that to be an odd concept. Why would you want positive pressure in the exhaust system? When both intake and exhaust are open together during overlap, the positive pressure in the exhaust port is going to try to push the intake charge back out of the combustion chamber. This would actually dilute the charge with exhaust gases, lessen combustion pressure and reduce torque. Wouldn't you want negative pressure at the exhaust valve to help pull the intake charge in, thus improving performance? Just a thought.

Bob
 

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I've always found that to be an odd concept. Why would you want positive pressure in the exhaust system? When both intake and exhaust are open together during overlap, the positive pressure in the exhaust port is going to try to push the intake charge back out of the combustion chamber. This would actually dilute the charge with exhaust gases, lessen combustion pressure and reduce torque. Wouldn't you want negative pressure at the exhaust valve to help pull the intake charge in, thus improving performance? Just a thought.

Bob
Proof is in the pudding. I'm not an engineer, but I believe the variance in back pressure has an effect on where in the powerband the performance boost occurs. A totally open exhaust, a la open headers on dragsters, may well produce max power. But it will occur at max rpm, which is typical at the track. Controlling the back pressure is one factor in moving the power and torque lower in the rpm range.

The real gurus will probably be along shortly to blow my opinion up. :D

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Proof is in the pudding. I'm not an engineer, but I believe the variance in back pressure has an effect on where in the powerband the performance boost occurs. A totally open exhaust, a la open headers on dragsters, may well produce max power. But it will occur at max rpm, which is typical at the track. Controlling the back pressure is one factor in moving the power and torque lower in the rpm range.

The real gurus will probably be along shortly to blow my opinion up. :D

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I'm no guru, but there's merit in your ideas. Exhaust flow is a series of positive/negative pressure pulses. Ideally, pipe diameter and length should be such that it creates a negative pressure pulse at the exhaust port, thus providing scavenging of the combustion chamber during overlap. Problem is, any given pipe length and diameter will only provide that benefit within a narrow rpm band. While the pipe may not provide maximum scavenging outside the power band it's designed for, it should at least provide a "neutral" effect with regard to pressure, which is another way to say no back pressure. It's not the back pressure that moves the torque peak down the power band. It''s the use of a pipe that causes the negative pressure wave at the valve to develop lower in the rpm range thus providing maximum cylinder filling through scavenging at the lower rpm. Generally, long head pipes of smaller diameter increase exhaust gas velocity and help develop peak torque at lower rpm, while engines with lots of valve overlap and valve events that are conducive to developing peak torque at higher rpm work better with shorter, fatter pipes.

Bob
 

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Same as with Ford V8's . Too big of an exhaust pipe & tail pipe will kill the torque of a small block . But it will sound great ! My racing days are over so gimma the sound man .
 

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Proof is in the pudding. I'm not an engineer, but I believe the variance in back pressure has an effect on where in the powerband the performance boost occurs. A totally open exhaust, a la open headers on dragsters, may well produce max power. But it will occur at max rpm, which is typical at the track. Controlling the back pressure is one factor in moving the power and torque lower in the rpm range.

The real gurus will probably be along shortly to blow my opinion up. :D

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Well said

Makes your wallet lighter too!
 

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^^^^ Lightens your wallet faster than some women.
 

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Wayward Son
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^^^^ Lightens your wallet faster than some women.
:nod But that is the money I never regretted spending.
But, there have been a few $$$ spent on a few different women. :think

Bike + $$$ = bike still here :D
Women + $$$ = women gone :fitz
 

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:nod But that is the money I never regretted spending.
But, there have been a few $$$ spent on a few different women. :think

Bike + $$$ = bike still here :D
Women + $$$ = women gone :fitz
Maybe you should pay for another hour. :think
 
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