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Cone engineering 12” reverse cone

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Cone engineering 12” reverse cone

PostAuthor: mr vroom » Fri Jul 20, 2018 5:08 pm

Just mounted this on my 81 XV750. Like the sound but definitely has more backfiring than my last muffler. Nothing I can’t live with but wondering if I need to adjust my jet or Something and which way or perhaps it has an air leak that I need to test for. Any thoughts? Thanks
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Re: Cone engineering 12” reverse cone

PostAuthor: Hellgate » Fri Jul 20, 2018 7:14 pm

I've got a 20" on my bike for the past 4 years with a baffle, with an probe hole drilled in the center. Doesn't backfire, pops a bit on runover, but no bangs.

My guess, vacuum leak, or way too rich.

Keep in mind a 12" muffler is lawn mower sized so between pulses air will suck back into the muffler and light off unburned gasses. Big V twins like big mufflers, ideally a 2:1:2 configuration.
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Re: Cone engineering 12” reverse cone

PostAuthor: nanno » Sat Jul 21, 2018 4:16 am

What Hellgate said and to be fair and if I didn't care about looks I'd go for an even larger cone than "just" a 20". A mate I've built an exhaust for is running some almost 30" Twin-Contis and not only do they sound the absolute dogs, but he makes heaps of power - even with a slightly older exhaust design...
http://viragotechforum.com/viewtopic.php?f=12&t=43227 - Nanno's accumulated findings (and blatant show-off) - infos on my TR1's, my performance and reliability mods and a bit of show-casing of the stainless steel exhausts I build

http://greasygreg.blogspot.co.at (My blog - Greasygreg.blogspot.co.at)
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Re: Cone engineering 12” reverse cone

PostAuthor: bstig60 » Sat Jul 21, 2018 6:39 am

I'm no expert with exhaust systems, but the less back pressure in the exhaust system you have the more low end torque you are going to lose... If you aren't running a baffle, it gets worse...
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Re: Cone engineering 12” reverse cone

PostAuthor: nanno » Sat Jul 21, 2018 9:52 am

Unless you build the header pipes around this problem by making sure you increase scavenging via y- or x-pipes...
http://viragotechforum.com/viewtopic.php?f=12&t=43227 - Nanno's accumulated findings (and blatant show-off) - infos on my TR1's, my performance and reliability mods and a bit of show-casing of the stainless steel exhausts I build

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Re: Cone engineering 12” reverse cone

PostAuthor: mr vroom » Sat Jul 21, 2018 11:15 am

“Unless you build the header pipes around this problem by making sure you increase scavenging via y- or x-pipes..”

Sorry, but could you explain this? Not sure what you mean. Pretend you’re talking to a 6 year old...LOL
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Re: Cone engineering 12” reverse cone

PostAuthor: Flyingdog » Sat Jul 21, 2018 1:26 pm

bstig60 wrote:less back pressure in the exhaust system you have the more low end torque you are going to lose... If you aren't running a baffle, it gets worse...

That' true and false. And..not true that running straights is bad for an engine. This is when the output of and engine (pulses) come into play. That, coupled with size of pipe (diameter & length), exhaust velocity, scavenging all have to be taken into count. That's why you don't see mufflers/baffles on Top Fuel or Funny cars. :bg:
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Re: Cone engineering 12” reverse cone

PostAuthor: nanno » Sat Jul 21, 2018 1:27 pm

You know what Richard Feynman once said? If you can't explain a problem in a really simple manner, you haven't fully understood neither problem or solution.

Ok, this is going to be a bit lengthy and some of the aspects are somewhat oversimplified. (I studied physics at college and spent multiple terms working out gas dynamics and it is... mind boggling like you wouldn't believe.)

First of all let's start with a few false assumptions:
1) Backpressure creates torque.
No it doesn't. Primarily backpressure prevents gasses from leaving the combustion chamber.

2) Free flowing exhausts / straight pipes with no backpressure at all will create top end power.
Again, no they don't. In some instances they can, but generally a straight pipe will create a pulse at a very narrow RPM range and cause massive tuning issues at all other ranges.

3) So was it all a scam? Nope, you just have to view it from a broader perspective.

Firstly imagine we're pumping water/jelly through the exhaust and not gasses. In some areas that's highly inaccurate (especially when the influence of exhaust gas temperature is concerned), but it's a good approximation else where.

Now if you pump water through the cylinder the inertia of the flowing water will always pull the water that runs behind it with it (creating a more or less pronounced vacuum). With that being said, when you merge two streams of water somewhere, this will also affect the water coming from the other pipe. Which is why those Y-pipes help with scavenging the cylinders making the powerband dramatically wider and increasing low-end torque as you're basically doubling the amount of water going through the pipes and pulling the water out of the cylinder which is currently not firing. This also affects the fill grade of the cylinder as there's more water being sucked in. This is extremely noticable at lower RPM.

So much for scavenging. Theoretically you could also do this with backpressure that has to be overcome, it's basically viewing the same problem from the other side. With a controlled amount of backpressure, you can ensure that there's always enough (spent) gasses in the exhaust to actually create the suction effect decribed in the previous paragraph. (As you noticed, we've moved away from water, because now we're getting to the limits of our model...)

Stuff starts getting tricky, when you realise that gasses are compressible and basically take a moment to create said vacuum as theoretically they stretch like rubber bands until they overcome the inertia of the gas and actually accelerate the gasses in the exhaust. Hotter gasses are thinner, but also contain more caloric energy and thus move faster through the exhaust. Bigger and smaller exhaust tubes can dramatically affect those exhaust temperatures. Which is where modern vehicle manufacturers play around A LOT, also because slower flowing gas will create less noise emission etc.

Additionally the length of the primary headers (up to the first y-connector) affects the overall exhaust temp at merge-point and thus the amount of energy transferable between both streams. The shorter they are the more powerful they are and the more you will notice them at higher RPM, the longer they are the lower the point in the RPM range where they come into effect.

And that's the stuff I play around a lot with my own homegrown exhausts. So far a length of approx. 700mm for the primaries and as much area on the exhausts outlet (currently running 44.5/ 1 3/4") and volume of the muffler itself (I use twin 20" long, round industrial mufflers, very similar to what you can buy as glasspacks in the US) has yielded some nice results. Hence the remark that a 2in1in2 is the best solution. You can achieve the same flow with a 2in1, but you would need a 40" long exhaust with a 3 1/2" outlet.

I actually once ran a MAC with a 40" glasspack and 2 1/4" outlet and that wasn't too bad. But it was a total eyesore.

I hope this somewhat clarifies the matter, unfortunately I had to leave out the aspect that the cylinder bank angle doesn't add up to 180 degrees creating uneven pulses, which means one part of the revolution the exhaust pipe is stuffed full of gasses and then for 290 degrees there's nothing happening and then all of this starts again. Valve sizes, induction tract lengths all of this plays into this equation and can't really be left out, if you're actually calculating the flow-potential of the engine. And once we're down that road we should have a look at valve timing and... :ops:
http://viragotechforum.com/viewtopic.php?f=12&t=43227 - Nanno's accumulated findings (and blatant show-off) - infos on my TR1's, my performance and reliability mods and a bit of show-casing of the stainless steel exhausts I build

http://greasygreg.blogspot.co.at (My blog - Greasygreg.blogspot.co.at)
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Re: Cone engineering 12” reverse cone

PostAuthor: Flyingdog » Sat Jul 21, 2018 1:42 pm

:yup:
nanno wrote:You know what Richard Feynman once said? If you can't explain a problem in a really simple manner, you haven't fully understood neither problem or solution.


Yup.. Here's a simpler version of Nanno said---> https://www.carthrottle.com/post/wg3b6r9/
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Re: Cone engineering 12” reverse cone

PostAuthor: nanno » Sat Jul 21, 2018 2:54 pm

I like their drawings... and the fact that it's even shorter than what I wrote!
http://viragotechforum.com/viewtopic.php?f=12&t=43227 - Nanno's accumulated findings (and blatant show-off) - infos on my TR1's, my performance and reliability mods and a bit of show-casing of the stainless steel exhausts I build

http://greasygreg.blogspot.co.at (My blog - Greasygreg.blogspot.co.at)
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Re: Cone engineering 12” reverse cone

PostAuthor: Flyingdog » Sun Jul 22, 2018 2:58 am

Yea..I got into this exhaust thing back in the late 90s, while helping a buddy on his (track only) YZR. Eyes would start to glaze over after watch him scratch out his figures between intake & exhaust... on paper. LOL :bg: Rode it few times..16k redline always freaked me out. :ops: I mean, I semi knew the importance of a well designed exhaust, but not to this degree. OP..good luck on your endeavor.

http://www.coneeng.com/motorcycle_components.html
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Re: Cone engineering 12” reverse cone

PostAuthor: mr vroom » Sun Jul 22, 2018 5:19 pm

Thanks for the education!

However, I found my problem to be leaks where the front header attaches and where the rear header clamps to the down tube or whatever it’s called. Took it all apart connected things better and tighter and it sounds pretty good now. No popping or backfire. However, I can still feel an air leak in both places so I’ll pick up some high temp RTV and see if that eliminates the leaks. I also ordered some new nuts for the exhaust flange. I fear tightening the existing front ones any more might snap the bolt. Also the bolts ( 2 ended?) seem permanently imbedded in the nuts, so I’m not sure how well that will turn out. I did order some new bolts from parts fish but they don’t look like the ones I need. They seem to have a head on them like normal bolts. Hopefully, they'll just end up as extras.
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Re: Cone engineering 12” reverse cone

PostAuthor: Hellgate » Sun Jul 22, 2018 8:17 pm

Have you slotted the end of the muffler so it clamps well to the collector? If not, do so. As you mentioned, quality clamps are key to a tight seal.
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Re: Cone engineering 12” reverse cone

PostAuthor: mr vroom » Mon Jul 23, 2018 2:37 am

Hellgate wrote:Have you slotted the end of the muffler so it clamps well to the collector? If not, do so. As you mentioned, quality clamps are key to a tight seal.


Thanks. The pipe came slotted and I think the muffler clamp is of descent quality, but now you got me wondering...

Is this the best type? It’s not what I’m presently using.... think I’ll order one from Dime City.
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