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You don't say?
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I have to say this idea looked so good that I had to try it. I rode the Low Rider for the first time today since doing the mod. It has a deeper exhaust note and SEEMS to have better throttle response. Nothing earth shattering, though. We'll know for sure if I'm smoking crack when it gets dynoed.
 

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Discussion Starter #22 (Edited)
ToddM said:
Steve, if you look again at that post with the diagram, you will see that it was not posted by me. It was from chas2379. I prefer to drill around the outside the the baffle which makes it easier to fine-tune with the hose clamp. Straight-through airflow isn't desired in this type of system, or V&H would have put their holes in the end of the baffle rather than around it's circumference. Chas2379 partially compensates for his holes in the end by using the washer to inturrupt the airflow slightly.
The modified baffle really changes alot more than just flow and back pressure. It has to do with reversion waves.

Inertial scavenging and wave scavenging are different phenomena but both impact exhaust system efficiency and affect one another. Scavenging is simply gas extraction. These two scavenging effects are directly influenced by pipe diameter, length, shape and the thermal properties of the pipe material (stainless, mild steel, thermal coatings, etc.). When the exhaust valve opens, two things immediately happen. An energy wave, or pulse, is created from the rapidly expanding combustion gases. The wave enters the exhaust pipe traveling outward at a nominal speed of 1,300 - 1,700 feet per second (this speed varies depending on engine design, modifications, etc., and is therefore stated as a "nominal" velocity). This wave is pure energy, similar to a shock wave from an explosion. Simultaneous with the energy wave, the spent combustion gases also enter the exhaust pipe and travel outward more slowly at 150 - 300 feet per second nominal (maximum power is usually made with gas velocities between 240 and 300 feet per second). Since the energy wave is moving about 5 times faster than the exhaust gases, it will get where it is going faster than the gases. When the outbound energy wave encounters a lower pressure area such as a second or larger diameter section of pipe, the muffler or the ambient atmosphere, a reversion wave (a reversed or mirrored wave) is reflected back toward the exhaust valve without significant loss of velocity.

The reversion wave moves back toward the exhaust valve on a collision course with the exiting gases whereupon they pass through one another, with some energy loss and turbulence, and continue in their respective directions. What happens when that reversion wave arrives at the exhaust valve depends on whether the valve is still open or closed. This is a critical moment in the exhaust cycle because the reversion wave can be beneficial or detrimental to exhaust flow, depending upon its arrival time at the exhaust valve. If the exhaust valve is closed when the reversion wave arrives, the wave is again reflected toward the exhaust outlet and eventually dissipates its energy in this back and forth motion. If the exhaust valve is open when the wave arrives, its effect upon exhaust gas flow depends on which part of the wave is hitting the open exhaust valve. A wave is comprised of two alternating and opposing pressures. In one part of the wave cycle, the gas molecules are compressed. In the other part of the wave, the gas molecules are rarefied. Therefore, each wave contains a compression area (node) of higher pressure and a rarefaction area (anti-node) of lower pressure. An exhaust pipe of the proper length (for a specific RPM range) will place the wave’s anti-node at the exhaust valve at the proper time for it’s lower pressure to help fill the combustion chamber with fresh incoming charge and to extract spent gases from the chamber. This is wave scavenging or "wave tuning". This is done with a tunable baffle such as the modified Pro Pipe baffle with the bolt and washer which can be turned in or out while on the dyno without removing the baffle.

From these cyclical engine events, one can deduce that the beneficial part of a rapidly traveling reversion wave can only be present at an exhaust port during portions of the powerband since it's relative arrival time changes with RPM. This makes it difficult to tune an exhaust system to take advantage of reversion waves which is why there are various anti-reversion devices designed to improve performance. These anti-reversion devices are designed to weaken and disrupt the detrimental reversion waves (when the wave's higher-pressure node impedes scavenging and intake draw-through).

Specifically designed performance baffles can be extremely effective, as well as heads with D shaped ports. Unlike reversion waves that have no mass, exhaust gases do have mass. Since they are in motion, they also have inertia (or "momentum") as they travel outward at their comparatively slow velocity of 150 - 300 feet per second. When the gases move outward as a gas column through the exhaust pipe, a decreasing pressure area is created in the pipe behind them. It may help to think of this lower pressure area as a partial vacuum and one can visualize the vacuous lower pressure "pulling" residual exhaust gases from the combustion chamber and exhaust port. It can also help pull fresh air/fuel charge into the combustion chamber. This is inertial scavenging and it has a major effect upon engine power at low-to-mid range RPM.

There are other factors that further complicate the behavior of exhaust gases. Wave harmonics, wave amplification and wave cancellation effects also play into the scheme of exhaust events. The interaction of all these variables is so abstractly complex that it is difficult to fully grasp. There does not appear to be any absolute formula that will produce the perfect exhaust design.

And please note that the Pro Pipe performance baffle is straight through without even the plate on the back where I drill my holes.
 

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0043--Licensed to Doof!
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Dang boy, youse musta gone ta skool or sumpin! :blink:
 

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Pphs

Hi Chas,

It sounds like you have a lot of experience w/the PPHS,... not to mention that your posts are interesting... Thanks for sharing your posts w/us.
BTW, do you have any experience w/the PPHS competition baffle? V&H sells the comp. baffle for about $40.00 dollars or so. Their website states that the comp. baffle will increase performance, a little... Have you seen the comp. baffle. I compared the comp. baffle w/the stock baffle, and they are almost identical, except that the comp. baffle has no obstruction, it is just wide open. In your opinion, is the comp. baffle a waste of money? I assume that the design would increase high end performance but your low end torque would suffer, due to the open ended design. Agreed? Your thoughts?

Thanks,

BB
 

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BennieB said:
Hi Chas,

It sounds like you have a lot of experience w/the PPHS,... not to mention that your posts are interesting... Thanks for sharing your posts w/us.
BTW, do you have any experience w/the PPHS competition baffle? V&H sells the comp. baffle for about $40.00 dollars or so. Their website states that the comp. baffle will increase performance, a little... Have you seen the comp. baffle. I compared the comp. baffle w/the stock baffle, and they are almost identical, except that the comp. baffle has no obstruction, it is just wide open. In your opinion, is the comp. baffle a waste of money? I assume that the design would increase high end performance but your low end torque would suffer, due to the open ended design. Agreed? Your thoughts?

Thanks,

BB
Save your money! Never seen a comp baffle in the Propipe that could ever get better all around street numbers than a well tuned standard baffle. Low end power will suffer big time.
 

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I do understand about reversion, Chas. That's another reason I don't run open pipes.... no reversion control. Thanks for the additional info, though. I'm sure the others will find it useful. :)
 

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Discussion Starter #28
GRock said:
Save your money! Never seen a comp baffle in the Propipe that could ever get better all around street numbers than a well tuned standard baffle. Low end power will suffer big time.
I Agree with GRock

The competition baffle is for high compression competition motors not street bikes. HIPPO says the only good Pro Pipe baffle is the standard baffle.
 

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Pro pipe

Roger that... Thanks guys.
Would it be too much to ask for the manufacturers to place such advise on their websites so that the consumer would know what they were purchasing... or what they need for their own application?...
 

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I did the modification to my baffle tonight on my PPHS standard baffle. All I can say is wow!!!! Torque dip is completely gone and sound is much better. The only regret I have about this mod is that I didn't do it sooner. Thanks for posting it!!!!!


Geezer
 

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The attached doc explains the Pro Pipe baffle mod more clearly. The dyno is not mine but a mild build, one with the standard baffle and the modfied baffle with dyno tune on the same day. Notice the big boost in torque on the low end. 95 tq @ 2500 rpm - 100 tq @ 3000 rpm


I know this is an old thread, but I'm very interested in the "attached doc". Is there any way to repost? Im having major reversion issues on my 2000 Wide Glide with PPHS, SE203 cams, & S&S Stealth A/C.
 
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