Why can't reversion be reduced without increase in back pressure (baffling)?

Is this universal physics regardless of reciprocating engine design? Shorter pipes - don't permit exhaust pulse to echo back?

 

There are various ways to reduce reversion that dont introduce back pressure, but the problem is quite complicated, the frequency of the pressure pulses will vary with rpm and all sorts of interference and standing wave patterns will be happening inside the pipes. And most often we dont want to introduce moving parts, so it is in the nature of the beast that improvements in one rpm range will cause more trouble in other rpm ranges.

The classic lollipop is actually a very clever way to reduce reflected waves. The main reflection comes from the end of the pipe, where the pressure wave meets open air, and is reflected back in the pipe. The lollipop is a washer placed close to the end, and this washer will also reflect wave energy. But the clever thing is that a wave reflected against a wall will have 180 degree phase difference to a wave reflected against open air, so in theory the two reflections will cancel each other out. This cancellation in real life will not be perfect, but a lot of the reflected wave energy actually disappears.

 

Operating RPM, pipe length, dimeter, & exhaust velocity affect the reversion process, as does cam timing and overlap. Reducing the overall length of an open pipe changes the RPM at which the reversion wave hits the exhaust valve.

 

I think a lot of this is caused by the common motorcycle pipe sizes being VERY large compared to cars for the displacement and horsepower that they make. Dual 1.75" exhaust on a 100 cubic inch engine is major overkill, destroying velocity and allowing the gasses to cool and slow down rapidly.

 

Yeah, there has to be something radically different, otherwise all car motors would have lollipops, unless it's just that car owners don't know and don't care about maximizing power output, which I suspect is at least part of this.

Harley has only two cylinders, that are odd firing. Means odd timing exhaust pressure pulses out the pipes, unlike engines with more cylinders. But even more cylinders can be exhaust pulse tuned with long tube header pipes designed all equal length with a conical collector union to smooth pulses out into the large end pipe.

Anyway, it is what is, I wonder if lollipops help any Harley exhaust or only certain designs?

 

Cars have room for much longer pipes and much larger mufflers, so there are more options for handling the reverse waves. And these days most performance oriented cars are turbo charged, which means wave reversion is a non issue.

Lollipops are often used in straight, non baffled drag pipes, such pipes are basically perfect wave reversion generators so the lollipops make a big difference.

Pipes with mufflers, crossover chambers and 2-1 pipes are usually designed to reduce reversion by other means but lollipops can still be very helpful sometimes.

 

Thanks for the schooling, I appreciate it.
Yeah, I know about X crossovers and 2--->1, but did not know these pipes were too short generally to get rid of all the exit reversal. So, I appreciate that. My bike has just 1 Y crossover welded in from the factory, but I'm gonna leave it at that for a Heritage, I like the dual swept pipe look. Not enough to keep the whisper quiet factory mufflers, though.. I think the more modern looking S&S Grand Nationals look ok. The whole bike doesn't need to resemble 1960, or whatever.

I'm discussing if I could retrofit DK's lollipops to my Grand Nationals with them.

The only real news in my OP post is Gale Banks is out there preaching DK Customs religion, too. That was a new weekly flyer I get from him.

 

@DK Custom

I ordered your smallest lollipops (#118) to fit my inner baffle tube pipe. 1.490 inch I.D.

I'm still curious of the better architecture is keeping baffles + small lollipop, or remove baffles + big lollipop. The outer pipe shell is a 3 inch dia.

 

You will always get the best power by using no baffles and the patented Thunder Torque Inserts™.How to Reduce Reversion without increasing back pressure

As we’ve seen, baffles reduce reversion, but at the cost of increasing back pressure. There are a variety of other attempts at reducing reversion without increasing back pressure...but we have not seen significant benefits from any of them (torque cones, etc.) other than the decades old lollipop.

CLASSIC LOLLIPOP




Many years ago we spent countless hours working to see if we could Improve the old lollipop (washer on a bolt) design. We made dozens and dozens of prototypes, all in an effort to reduce reversion without increasing back-pressure.

Street Testing and Dyno Testing of hundreds of variations finally evolved to the Thunder Torque Inserts™ seen below. They have a rounded wave shape that makes the exhaust gases flow easily over them on exit, and the cupped shape on the other side catches the reversed pulse wave (reversion), preventing it from traveling back up the exhaust tract. These are Patented due to many unique features.

The bottom line is that they create very little increase in back-pressure, and in fact, speed up exhaust gas velocity because of the unique shape. At the same time they reduce reversion.



Here's a video you may find interesting.

You Tube

 

@DK Custom

Let me be clearer what I'm after: optimized sound and torque levels.

Not too loud, not too quiet, and within that, best performance for torque.

Factory mufflers are way too quiet. I exchanged for S&S Grand National slip on mufflers with "high flow" catalysts. These are somewhat too loud, with a snapping sound note. They came with installed baffles. These new mufflers produce noticeably faster exhaust flow - I can feel the exhaust hitting my legs standing 3 feet away, not so with the stock exhaust. I think the exhaust outlet tubes are the same diameter between factory and S&S (1.5 inch O.D.), which means S&S catalyst is higher flow and / or less restrictive baffle.

So - would removing the baffle + adding the big insert make the exhaust louder than now (baffle without insert)? Yes, no, don't know, please.'

Otherwise I will proceed with leaving baffles in and adding the #118 inserts. No need to sell my on your design, they arrive tomorrow.

Thanks again.