Shortening Propipe?
Tourer
Joined: Oct 2006
Posts: 312
Likes: 0
From: NC
You obviously selected the Pro Pipe for its performance characteristics.
If you do cut the pipe shorter, you will adversely affect the performance characteristics of the pipe as it relates to your engine's valves. The pipe is cut and assembled to specifics lengths based on your engine. Obviously, if your engine is mod'd from the specs used by V&H, your performance curve is also affected.
Better stated....
"When we got it right we would have an exhaust pipe that would carry a positive pressure wave of exhaust pulse down the pipe to the open end. There it would collapse and create a negative pressure wave that would return back up the pipe. If the negative wave arrives back at the exhaust valve just before it closes, it will suck more of the exhaust gases out of the cylinder. This lowers the pressure inside the cylinder and makes the next intake stroke more efficient.
On a 4-stroke, the intake valve begins to open while the exhaust valve is still off it's seat. This is valve overlap. This allows the negative exhaust pulse (the reflection of the positive pulse) to actually pull more fresh mixture past the intake valve and into the cylinder. Here's how it works, and it has nothing to do with exhaust tuning as such.
When the combustion cycle begins, the piston is forced downward; this is the power stroke. Near the bottom of the power stroke the energy is mostly spent and the exhaust valve starts to open. It will actually start to open slightly before bottom dead center. The exhaust charge then begins to rush out the exhaust pipe.
The exhaust gases rushing out are further assisted by the piston pushing up on the exhaust stroke. This forms a stream of hot gas in very rapid motion away from the cylinder. This stream of hot gas has inertia and it will tend to continue moving in the same direction out the exhaust pipe even after the piston stops pushing it. This creates a region of reduced pressure in the vicinity of the exhaust valve.
By opening the intake valve just prior to top dead center, while the exhaust valve is still open (overlap), the gases going out the exhaust pipe will begin pulling the new intake mixture in behind them. Or, the intake stream will try to flow into the region of reduced pressure behind the exhaust stream, if you want to look at it that way. So overlap merely takes advantage of the inertia of the exhaust gases and the low-pressure region that it produces near the exhaust valve at the end of the exhaust stroke.
That part of the overlap design is common to all 4-stroke engines in order to gain additional charging of the cylinder with fuel mix at high RPM. The higher the RPM we design for, the greater the intake and exhaust overlap we build into the cam lobes. Most engines are fitted with exhaust manifolds that collect all the gases from a bank of cylinders. They also usually have a long pipe and muffler. So, while the physics of gases in motion will apply there, tuning for the exhaust pulse will not."
If it is all about looks.....cut the pipe.
If you do cut the pipe shorter, you will adversely affect the performance characteristics of the pipe as it relates to your engine's valves. The pipe is cut and assembled to specifics lengths based on your engine. Obviously, if your engine is mod'd from the specs used by V&H, your performance curve is also affected.
Better stated....
"When we got it right we would have an exhaust pipe that would carry a positive pressure wave of exhaust pulse down the pipe to the open end. There it would collapse and create a negative pressure wave that would return back up the pipe. If the negative wave arrives back at the exhaust valve just before it closes, it will suck more of the exhaust gases out of the cylinder. This lowers the pressure inside the cylinder and makes the next intake stroke more efficient.
On a 4-stroke, the intake valve begins to open while the exhaust valve is still off it's seat. This is valve overlap. This allows the negative exhaust pulse (the reflection of the positive pulse) to actually pull more fresh mixture past the intake valve and into the cylinder. Here's how it works, and it has nothing to do with exhaust tuning as such.
When the combustion cycle begins, the piston is forced downward; this is the power stroke. Near the bottom of the power stroke the energy is mostly spent and the exhaust valve starts to open. It will actually start to open slightly before bottom dead center. The exhaust charge then begins to rush out the exhaust pipe.
The exhaust gases rushing out are further assisted by the piston pushing up on the exhaust stroke. This forms a stream of hot gas in very rapid motion away from the cylinder. This stream of hot gas has inertia and it will tend to continue moving in the same direction out the exhaust pipe even after the piston stops pushing it. This creates a region of reduced pressure in the vicinity of the exhaust valve.
By opening the intake valve just prior to top dead center, while the exhaust valve is still open (overlap), the gases going out the exhaust pipe will begin pulling the new intake mixture in behind them. Or, the intake stream will try to flow into the region of reduced pressure behind the exhaust stream, if you want to look at it that way. So overlap merely takes advantage of the inertia of the exhaust gases and the low-pressure region that it produces near the exhaust valve at the end of the exhaust stroke.
That part of the overlap design is common to all 4-stroke engines in order to gain additional charging of the cylinder with fuel mix at high RPM. The higher the RPM we design for, the greater the intake and exhaust overlap we build into the cam lobes. Most engines are fitted with exhaust manifolds that collect all the gases from a bank of cylinders. They also usually have a long pipe and muffler. So, while the physics of gases in motion will apply there, tuning for the exhaust pulse will not."
If it is all about looks.....cut the pipe.
Last edited by Roadrider18; Jan 17, 2012 at 08:08 AM.
Ultimate HDF Member
Joined: May 2008
Posts: 6,642
Likes: 48
From: Ogden, UT
You obviously selected the Pro Pipe for its performance characteristics.
If you do cut the pipe shorter, you will adversely affect the performance characteristics of the pipe as it relates to your engine's valves. The pipe is cut and assembled to specifics lengths based on your engine. Obviously, if your engine is mod'd from the specs used by V&H, your performance curve is also affected.
Better stated....
"When we got it right we would have an exhaust pipe that would carry a positive pressure wave of exhaust pulse down the pipe to the open end. There it would collapse and create a negative pressure wave that would return back up the pipe. If the negative wave arrives back at the exhaust valve just before it closes, it will suck more of the exhaust gases out of the cylinder. This lowers the pressure inside the cylinder and makes the next intake stroke more efficient.
On a 4-stroke, the intake valve begins to open while the exhaust valve is still off it's seat. This is valve overlap. This allows the negative exhaust pulse (the reflection of the positive pulse) to actually pull more fresh mixture past the intake valve and into the cylinder. Here's how it works, and it has nothing to do with exhaust tuning as such.
When the combustion cycle begins, the piston is forced downward; this is the power stroke. Near the bottom of the power stroke the energy is mostly spent and the exhaust valve starts to open. It will actually start to open slightly before bottom dead center. The exhaust charge then begins to rush out the exhaust pipe.
The exhaust gases rushing out are further assisted by the piston pushing up on the exhaust stroke. This forms a stream of hot gas in very rapid motion away from the cylinder. This stream of hot gas has inertia and it will tend to continue moving in the same direction out the exhaust pipe even after the piston stops pushing it. This creates a region of reduced pressure in the vicinity of the exhaust valve.
By opening the intake valve just prior to top dead center, while the exhaust valve is still open (overlap), the gases going out the exhaust pipe will begin pulling the new intake mixture in behind them. Or, the intake stream will try to flow into the region of reduced pressure behind the exhaust stream, if you want to look at it that way. So overlap merely takes advantage of the inertia of the exhaust gases and the low-pressure region that it produces near the exhaust valve at the end of the exhaust stroke.
That part of the overlap design is common to all 4-stroke engines in order to gain additional charging of the cylinder with fuel mix at high RPM. The higher the RPM we design for, the greater the intake and exhaust overlap we build into the cam lobes. Most engines are fitted with exhaust manifolds that collect all the gases from a bank of cylinders. They also usually have a long pipe and muffler. So, while the physics of gases in motion will apply there, tuning for the exhaust pulse will not."
If it is all about looks.....cut the pipe.
If you do cut the pipe shorter, you will adversely affect the performance characteristics of the pipe as it relates to your engine's valves. The pipe is cut and assembled to specifics lengths based on your engine. Obviously, if your engine is mod'd from the specs used by V&H, your performance curve is also affected.
Better stated....
"When we got it right we would have an exhaust pipe that would carry a positive pressure wave of exhaust pulse down the pipe to the open end. There it would collapse and create a negative pressure wave that would return back up the pipe. If the negative wave arrives back at the exhaust valve just before it closes, it will suck more of the exhaust gases out of the cylinder. This lowers the pressure inside the cylinder and makes the next intake stroke more efficient.
On a 4-stroke, the intake valve begins to open while the exhaust valve is still off it's seat. This is valve overlap. This allows the negative exhaust pulse (the reflection of the positive pulse) to actually pull more fresh mixture past the intake valve and into the cylinder. Here's how it works, and it has nothing to do with exhaust tuning as such.
When the combustion cycle begins, the piston is forced downward; this is the power stroke. Near the bottom of the power stroke the energy is mostly spent and the exhaust valve starts to open. It will actually start to open slightly before bottom dead center. The exhaust charge then begins to rush out the exhaust pipe.
The exhaust gases rushing out are further assisted by the piston pushing up on the exhaust stroke. This forms a stream of hot gas in very rapid motion away from the cylinder. This stream of hot gas has inertia and it will tend to continue moving in the same direction out the exhaust pipe even after the piston stops pushing it. This creates a region of reduced pressure in the vicinity of the exhaust valve.
By opening the intake valve just prior to top dead center, while the exhaust valve is still open (overlap), the gases going out the exhaust pipe will begin pulling the new intake mixture in behind them. Or, the intake stream will try to flow into the region of reduced pressure behind the exhaust stream, if you want to look at it that way. So overlap merely takes advantage of the inertia of the exhaust gases and the low-pressure region that it produces near the exhaust valve at the end of the exhaust stroke.
That part of the overlap design is common to all 4-stroke engines in order to gain additional charging of the cylinder with fuel mix at high RPM. The higher the RPM we design for, the greater the intake and exhaust overlap we build into the cam lobes. Most engines are fitted with exhaust manifolds that collect all the gases from a bank of cylinders. They also usually have a long pipe and muffler. So, while the physics of gases in motion will apply there, tuning for the exhaust pulse will not."
If it is all about looks.....cut the pipe.
You will not adversely affect the tuning by shortening the very long Pro-Pipe.
Road Master
Joined: Jan 2011
Posts: 893
Likes: 0
From: Knob Noster, MO
To the OP can you post up a dead on side shot of your bike with the pro pipe on? I am thinking about getting this pipe and want to see how long it really is on the bike. I kind of get the picture from your angled shot but want to see a better side shot of it.
Tourer
Joined: Oct 2006
Posts: 312
Likes: 0
From: NC
While this is all good in theory, once you have an exhaust pipe longer than 31", (could be wrong on exact number but believe that is correct) you do not gain anything more with longer pipe. Why do you think all drag cars have pipes of about that length?
You will not adversely affect the tuning by shortening the very long Pro-Pipe.
You will not adversely affect the tuning by shortening the very long Pro-Pipe.
This came from some folks over at Roush Yates Engines in Mooresville.
Doesn't matter if its a V8 or V Twin.
Yet, in all likelihood, one would never see the difference unless at the track and on the clock....or on the dyno.
Last edited by Roadrider18; Jan 17, 2012 at 07:51 PM.
Road Warrior
Joined: May 2009
Posts: 1,760
Likes: 211
From: Manila, Philippines
Bassani Road Rage II have long and short version of the same pipe. If I remember correctly, the difference in hp/tq is minimal if just running a stage 1, but if your doing major engine mods, then the long version gets better results.
I go for cutting em.
I go for cutting em.
Ultimate HDF Member
Joined: May 2008
Posts: 6,642
Likes: 48
From: Ogden, UT
The magic number is slightly less than 31", BUT, that figure is based on the length of the pipe after the union of individual cylinder header pipes.
This came from some folks over at Roush Yates Engines in Mooresville.
Doesn't matter if its a V8 or V Twin.
Yet, in all likelihood, one would never see the difference unless at the track and on the clock....or on the dyno.
This came from some folks over at Roush Yates Engines in Mooresville.
Doesn't matter if its a V8 or V Twin.
Yet, in all likelihood, one would never see the difference unless at the track and on the clock....or on the dyno.
Elite HDF Member
Joined: Aug 2011
Posts: 3,881
Likes: 3
From: Pennslytucky
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Tourer
Joined: Oct 2006
Posts: 312
Likes: 0
From: NC
8541....
You are correct, I meant to say it has nothing to do with the union...
It is the overall length of the pipe...
27" has proven to be too short across the RPM range.
And, 32" is too long across the RPM range.
Optimum length, somewhere in between 27" - 32", will be dictated by engine build and where one desires to operate in the power band curve.
For a stock HD motor, between 30"-31" has proven optimum.
Thanks for catching that typo!
You are correct, I meant to say it has nothing to do with the union...
It is the overall length of the pipe...
27" has proven to be too short across the RPM range.
And, 32" is too long across the RPM range.
Optimum length, somewhere in between 27" - 32", will be dictated by engine build and where one desires to operate in the power band curve.
For a stock HD motor, between 30"-31" has proven optimum.
Thanks for catching that typo!
Last edited by Roadrider18; Jan 18, 2012 at 10:01 AM.
