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Buell Forum » Knowledge Vault (tech, parts, apparel, & accessories topics) » Dyno Charts/Testing (Show us the POWER!) » Dyno Test Results - Anti-reversion cones

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You've seen these things hanging on the pegboard at your local Harley shop, a strange cone shaped device that slips into your header at the exhaust port and promises to improve torque. The same basic thing is sold under a variety of brand names and generally runs anywhere from about $30 to $80 a pair. But do they really work?

Why Would They?

I mean hey, the cone is making the pipe smaller for a short distance. Smaller means more restriction, which means more pumping losses, which means less power potential, right?

Well, yes, but (there's always a but) don't forget the effect of wave travel in an exhaust system. Pressure waves, both positive and negative, are traveling up and down the pipe, and depending on the type of wave and when it hits the engine, it can help you or hurt you. A negative wave hitting the chamber during overlap is a good thing, it helps the next intake charge and results in more cylinder fill. A positive wave does the opposite and can cause poor fill, excessive heat, and even detonation. The idea of the anti-reversion cone is to let the negative waves pull exhaust out of the engine more easily than the positive waves push exhaust back into the engine. So maybe there's something to this?

The test mule chosen was a '99 M2, equipped with it's factory original header and muffler. A Mikuni carb and Force air filter are the only power-enhancing mods on this bike (well, that and lots of hours tuning). We know that an aftermarket muffler gives a nice mid-range torque bump and we were hoping for a similar effect from the cones.



After several hours of testing, including multiple jet changes just in case optimal jetting was affected by the cones (it wasn't), we came up empty. Bottom line, the cones had little effect until about 4500 rpm, at which point the extra restriction started making itself known. The evidence would suggest that the cones are just ineffective at slowing down the wave. Bottom line, while I can't rule out that there may be some exhaust systems that benefit from this type of device, this stock '99 M2 system isn't one of them.

Aaron Wilson
NRHS

Author Message   Blake Posted on Wednesday, October 23, 2002 - 04:15 pm:        Would they be more likely to help the cruiser guys with straight pipes?   Sarodude Posted on Wednesday, October 23, 2002 - 04:37 pm:        Hey, was this article destined for Battle2win? Anyway, the question I have is this: How does the cone differentiate between a positive wave and a negative wave? It would seem that among the various things these cones might cause is a loss of desirable negative waves at the right time. I think Blake is onto something with regard to application. I THINK that what the cone does is actually split up part of the wave energy, causing reflections and making some percent of this wave take a longer / shorter 'path' to a valve open event, effectively broadening the powerband. ANTI-reversion? It seems, based on my silly guess, that it just SPREADS OUT the reversion - and the good stuff too. -Saro PS - I take NO RESPONSIBILITY for the incredible likelyhood of my above statements yielding vast quantities of cow dung.   Aaron Posted on Wednesday, October 23, 2002 - 06:42 pm:        " Hey, was this article destined for Battle2win?" Yes. "How does the cone differentiate between a positive wave and a negative wave?" Apparently it doesn't. I could see how the shape could create more resistance to flow in one direction than the other, but not a pressure wave. Yes, I could see how it could have the same effect as a baffle, i.e. diffuse the wave. But it doesn't even seem to do that. All it did was cost a little top end power. It would be interesting to test it in a drag pipe setup, but I haven't done that.   S320002 Posted on Wednesday, October 23, 2002 - 07:28 pm:        Aaron, In my experience AR cones are used on drag pipes and do provide some benefits. It would be interesting to see how they work on the Buell headers sans muffler. Greg   S320002 Posted on Wednesday, October 23, 2002 - 07:35 pm:        I just noticed that the cone you uses has a "bell" on both ends. Most do not. The purpose of an AR cone is to prevent "back wash" into the combustion chamber. The bell on the down stream end of the AR con tends to defeat its purpose. Greg   Dynarider Posted on Wednesday, October 23, 2002 - 08:06 pm:        I tried some of these in my old Khrome werks drag pipes on my 96 Dyna. I didnt dyno test before & after, but with the cones the bike definately had better pickup on the top end. I would say for the drag pipe crowd they are a small but still noticeable improvement in power.   Bandidobuell Posted on Friday, February 06, 2004 - 01:06 pm:        I read an article in THE HORSE backstreet choppers, about the cones.The test mule was a 103 inch S&S motor with open drags.They lost hp across the entire powerband,minus 7 at 5500 rpm.   Tramp Posted on Tuesday, June 14, 2005 - 08:59 pm:        The Horse is a swell source for moto-fiction. college art students in mufti as bad roger corman flick extras. popular rag with the red and gold, though   Buelldyno_guy Posted on Monday, September 05, 2005 - 12:36 pm:        We use them on all free flowing exhaust that have a reversion issue on the dyno. Our experience is not that they change the numbers too much on way or the other, but they slow down and help with the reversion I see in my A/F during the run, I can tune better when they have been installed. (Note) mufflers with any normal amount of back pressure do the same thing. They are part of the kit we sell when we sell and install Rienharts, or Thunder Headers and a Dyno. ... Hope this helps. ... Terry   Buelltroll Posted on Monday, September 05, 2005 - 03:29 pm:        How come you never replied to my email Terry?

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