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Default Power cones

Anybody have experience with reversion/torque/power cones for iron head exhausts?
The subject comes up occasionally and I'll be the first to admit I know little about them.
Are they the best thing yet for iron heads, or do they mostly just relieve excess weight in your wallet?
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Have a chat with Kevin @DK Customs ??
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Depending on your goal, choosing the right exhaust systems or setup can be more complicated than most people expect. If you're not chasing HP, what is your criteria for 'good enough'?

I'm not sure any of these threads are related specifically to Ironheads, but they do discuss exhaust systems and mention Torque Cones in the conversation... Have a look at these:

http://xlforum.net/forums/showthread.php?t=51305
See ASWRacing comments at Post# 23, 26, 27

http://xlforum.net/forums/showthread.php?t=22426

http://xlforum.net/forums/showthread.php?t=44182

http://sportsterpedia.com/doku.php/techtalk:ref:carb04



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yep, a lot of discussion on the forum.
but many people call things diff so terminology matters.
if you are talking about the devise that goes into the head end of the pipe, a big waste of money and can actually hurt. when they do work, there is only a sweet spot and it is a very narrow band.
i believe they make a downstream devise called the same thing and it too has +/- and is not a magic bullet.
it would be impossible to have an exh to boost off idle to wot. you must choose via your ride style. ole addage is change one thing, probably will have change another, very true very true.
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Torque cones are like yelling with your hand over your mouth.

From a performance standpoint I would never install them.

Drag pipes suck. There are no band-aids that can be applied that can recover what is lost.
Drag pipes are the problem, the solution is NOT to add more problems to the exhaust.
Sticking things inside a Drag pipe is like trying to fart around a cork.

Guys who insist on using Drag pipes do not care about performance.
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Thanks guys, I knew you'd have the answers. I keep hearing about cones and wanted clarification from people who weren't trying to sell me a set.

Good enough for me is a set of board tracker pipes that are quiet.
I've managed that with 8" universal baffles re-shaped and stuffed up inside.
As short as they are, these pipes are no louder than stock.
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I bought a Jardine + SuperTrapp 2:1 system for my 1200 Evo from Flowmetrics, and Branch told me that an anti-reversion cone will clean up the low speed, but he couldn't sell me one due to patent fights.
He "accidentally" sent me a drawing of a cone, which I fabricated, and yes it cleaned up the idle and low speed response nicely.
What surprised me: this was a 90 hp engine (AP V8 cams, Crane Hi ignition, Branch bathtub heads, Mikuni HS40), and the ID of the narrow end of the cones was only 1-1/8".
No, it didn't hurt the peak power.
No, it's not "backpressure", the cone is a one-way valve preventing exhaust from backing up into the chamber during overlap.
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There are physical mounting differences between an EVO and a IH, there is no way to "secure" a cone to an IH exhaust port.

You could build an Anti-Reversion header pipe but I would not ruin a good pipe to test this theory.

Seems to me it would be better to address the cause of the problem, too much overlap. Rather than apply BandAids to a good exhaust.
I have no problems with my bikes as I do not attempt to run a drag motor on the street.

Some mods are often taken too far, carb size and cam selection run a close second (and third) to crappy exhaust selection.
You have to be realistic when making these choices and take in the how effects of the combination of the entire package will change the outcome.
Looking at the power graph of many of the setups you will find many of them have spikes of "power" in the upper ranges but are completely lacking at lower RPM (which leave them with little if any street-able power).
Choices were made that completely ignore the "area under the curve", usable power beats "dyno power" every time. Usable power rarely needs special tuning considerations simply a good complementary combination of parts.
50hp at 3000rpm beats 20hp at 3000 every time unless most (99%) of your riding is at 6500rpm.

If you have to rev up your motor to take off from a stop, you likely have a bad combination of parts.
This is why strokers are so well liked. Torque is what makes things happen.

Horsepower is a mathematical expression embraced by marketing dweebs to impress farmers....
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I'm definitely no expert on the subject, but I'll chime in with what I've learned from this forum over the years. When talking exhaust, there are two separate but related components you need to consider: the pressure wave and the gas flow. I'll start with the pressure wave since it happens first.

When the exhaust valve opens, the high pressure gas inside wants to move quickly toward the low pressure atmosphere at the end of the exhaust pipe. This creates a wave of high pressure that starts moving down the pipe (this is what makes your exhaust note) and it has interesting properties that play a large role in why some exhausts work and others don't. First, the wave is reflected off changes in pipe diameter and the exhaust opening itself - diameter decreases cause a simple reflection (reverses direction), but diameter increases and the pipe opening cause an inverse reflection where the wave reverses both direction and amplitude. The wave traveling back up the exhaust pipe is reversion and can be good or bad - more on that in a bit. Obstructions in the exhaust like mufflers serve to "chop up" this wave, which both lessens the strength of the pressure wave exiting the pipe (less noise) and creates a more chaotic reversion wave (because you can't get rid of it entirely).

The gas flow follows after the high pressure wave. Propelled by the rising piston and the area of low pressure behind the pressure wave, the gas flows out of the cylinder and down the exhaust pipe. As it does, it builds momentum and creates what we call scavenging. The momentum of the exhaust gases means they want to keep flowing, so when the intake valve opens during the overlap period, the flowing exhaust actually helps suck the intake charge into the cylinder and evacuate the remaining exhaust gases.

The interaction between scavenging and reversion is where things get interesting. Remember that the pressure wave gets inverted when it hits the end of the exhaust pipe. When you have two pressure waves occupying the same space, they interfere with each other and the result can either be higher or lower pressure. (Side note, this is how noise cancelling headphones work - by playing the incoming noise half a wave behind, the two waves cancel each other out.) If the reversion wave hits the exhaust port at a trough (low point in the wave), the resulting pressure is lower than it would have been without the wave and your scavenging gets better! But the opposite is also true - if the reversion wave hits at a peak, the pressure is higher than it would have been and it tries to shove the exhaust gases back into the cylinder, messing up your scavenging.

Any tube has a frequency at which it naturally "resonates", which is the frequency at which one whole wave perfectly fits in the length of the tube. This is how wind chimes work and why you can change the note of a glass bottle by filling it. The resonant frequency depends mostly on the length of the tube. In the case of exhausts, being at that resonant frequency is a good thing because the reversion wave will hit the exhaust port at a low point every time. Unfortunately this is only practical if your engine runs at the perfect RPM all the time, since at every other RPM it either won't be helping or will actually hurt. This is why drag pipes suck at midrange but work great at top end - the high RPM is in the resonant frequency of the pipe so you get good reversion and a scavenging boost, but the mid RPM is only half resonant frequency so your reversion wave hits at a peak and screws everything up.

Now, exhaust mods. There have been many users here who have added "lollipops" to their drag pipes and reported performance increases. This is because the extra obstruction at the end of the pipe disrupts the destructive reversion wave inherent in all drag pipes. Some have tried torque cones near the heads without success, likely because this makes the distance from the exhaust port to the first obstruction too short to be useful (short pipes have higher resonant frequencies). Unfortunately there's no exhaust mod that can replace a proper muffler, because the extra baffles chop up that reversion wave better than any home mod ever could. The point is to avoid destructive reversion, and the only ways to do that are to have really long or really short pipes (with resonant frequencies outside the RPM range of the engine) or to chop up the reversion wave into a bunch of mini-waves at different frequencies, which is what mufflers do.

What about backpressure? It's the pressure in your exhaust system in excess of atmospheric pressure, and it's pretty much a bad thing (in our application; cars are another beast entirely). Any pressure in the exhaust system is an obstruction to the exhaust gases getting out of the cylinder. It's created by restrictions in the exhaust, such as bends, diameter decreases, and restrictive mufflers. This is why a free-flowing muffler is your best choice for performance - more flow = less backpressure, good muffler design = less bad reversion. Side note, increasing your exhaust diameter probably won't do much to help performance, because you'd have to have a pretty small pipe to worry about choking the flow more than other restrictions in the system.

Finally, crossover pipes and/or 2-into-1 systems. These offer better performance than single pipes for a simple reason: as fluid flows over a hole, it creates a low pressure zone in the hole. So with a crossover pipe or combined header, the exhaust stroke of cylinder 1 helps improve scavenging on the exhaust stroke of cylinder 2, and vice versa. The extra opening also serves as another place to reflect the pressure wave, further reducing your changes of bad reversion.
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From what I know, the purpose of the cones is to help to cut down on the ill effect of reversion, I made a set from each end of a cheap drag pipe baffle and held into the pipes with three small spot welds (120’ apart). They definitely do seem to have a small but positive effect on any midrange dip. Some people run drags because they like them, some because they don’t know any better and some because they know how to make them work. I run open pipes (XLR style) because I wanted to try to have a machine that mirrors the 1958 XLCH which although was intended as an off roader was by no means a drag bike. The XLRTT also held its own quite well on race tracks with open pipes also offered from the factory.
......Davi.
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