bmwpowere36m3 Posted October 30, 2015 Share Posted October 30, 2015 OK, the Arrow headers are welded as so: The pipe diameter from the exhaust port to the first weld flares from 35mm to 37mm and post weld is a constant 37.5mm diameter to the 2:1 link-pipe. Hope that helps gregjet, but from my understanding of fluid dynamics, the increase in diameter would help accelerate the flow. 007 The opposite… increase in diameter reduces speed. Think mass-flow. However "steps" in diameter [in exhaust pipes] can be used to produce reflections. Properly "tuned" those reflections work like a 2-stoke pipe and help scavenge exhaust gases in a 4-stroke at a specific RPM (I believe ideally where the engine produces the most torque). Link to comment Share on other sites More sharing options...
gregjet Posted October 30, 2015 Author Share Posted October 30, 2015 VERY informative. This is exactly what the Formula one and MotoGP bikes seem to be doing. The akro definitely has a constant ID. The divergant in the Arrow will cause a reflected negative pressure wave ( as bmwpowere36m3 says) and may bypass the out of phase problem of the joined pair of pipes. This is dynamics I don't have any extant maths for. May have to go back to first principals to check it out or modify 2 stroke calcs to the longer inter port times and different pressure wave velocity. Lot of work unless I can find it already done somewhere. As I said before , might just go the 2-2 route as the maths is MUCH simpler. BTW it isn't the flow that matters , it is the high pressure transient at the front and rear of the flow and the associated transforms of them. This is where most people misunderstand and where the "back pressure" myth comes from. Any "back pressure" WILL have an effect, but indirectly, by changing the velocity of the sonic transient ( speed of sound) associated with increase in temperature and density of the gas. Same with the idea that loudness is directly associated with power. And that an exhaust must be loud to flow properly. It is perfectly possible to have ultra high flow WITH quietness. The Loudness is caused by the transient ( sound wave front ). Once the transient has done it's work it can be diffused without effecting the optimium tuning. Think about it. Go forth and modify my son...go forth and modify... Link to comment Share on other sites More sharing options...
N/A Posted October 30, 2015 Share Posted October 30, 2015 Cool, thanks for the refresh bmwpowere36m3 - school was a LONG time ago! Look forward to seeing your 2 into 2 gregjet, now I have the Arrow I'll stick with it as it works really well and is not too loud with the baffle in. 007 Link to comment Share on other sites More sharing options...
gregjet Posted October 30, 2015 Author Share Posted October 30, 2015 I won't be building one I don't think. This is just a road bike I am biasing it towards touring. No track or good twisty roads for over a hundred Kms around here. If I was racing it I couldn't make a 2-2 anyway as the only class I could race it in would be F3 and that has a " exhaust must be stock to the last join before the muffler" rule ( or at least did when I was still racing). It is part of the reason that SV650's ruled until Suzuki made the exhaust a 2-1. ER6's don't suffer from the out of phase problem with their inline crank. Go forth and modify my son...go forth and modify... Link to comment Share on other sites More sharing options...
pattonme Posted December 14, 2015 Share Posted December 14, 2015 another one from the Land of the Rising Sun. It's got displacement but unfortunately the merge is before the chamber. I think a bigger pre-chamber and dual inlets was an opportunity missed. http://www.rsgear.co.jp/products/muffler/yamaha_mt07_single/ Link to comment Share on other sites More sharing options...
cotterbo Posted February 9, 2016 Share Posted February 9, 2016 I really love the Two Brothers S1R System. What a great looking exhaust and great sound. Here is the install and sound if you want to check it out. Any idea if the two brothers S1R exhaust requires a fuel management system? I just ordered the S1R black series and it should be arriving today. Cant wait to replace the stock exhaust with this bad boy thanks Link to comment Share on other sites More sharing options...
marthy Posted February 9, 2016 Share Posted February 9, 2016 What about those? They make them in 1 3/8" inlet and you can adjust back psi. Won't win any beauty contest with those but they are cheap enough for testing... http://www.supertrapp.com/product_sections/cat.asp?CatID=35 Link to comment Share on other sites More sharing options...
Guest 2wheeler Posted March 8, 2016 Share Posted March 8, 2016 So I have a buddy who is currently at Bike Week in Daytona. He sent me a pic of Yamha's pro flat track bike with the FZ-07 motor. I took a good look at the bike, and it appears to be a "2 into 1" Graves exhaust. So, my question is for all you "2 into 2" folks out there - if 2" into 2" is the best for power/performance, why isn't Yamaha doing that with their pro bike which is obviously super custom? According to my buddy, there are some of the big wigs from Yamaha there, so he is going to ask them about that "2 into 2" exhaust. I'll let everyone know what they say. Link to comment Share on other sites More sharing options...
danfz07 Posted March 21, 2016 Share Posted March 21, 2016 I really love the Two Brothers S1R System. What a great looking exhaust and great sound. Here is the install and sound if you want to check it out. Any idea if the two brothers S1R exhaust requires a fuel management system? I just ordered the S1R black series and it should be arriving today. Cant wait to replace the stock exhaust with this bad boy thanks Cotterbo Do you have any pics with the black series installed? What are your thoughts on it? Dan Link to comment Share on other sites More sharing options...
topazsparrow Posted March 21, 2016 Share Posted March 21, 2016 So I have a buddy who is currently at Bike Week in Daytona. He sent me a pic of Yamha's pro flat track bike with the FZ-07 motor. I took a good look at the bike, and it appears to be a "2 into 1" Graves exhaust. So, my question is for all you "2 into 2" folks out there - if 2" into 2" is the best for power/performance, why isn't Yamaha doing that with their pro bike which is obviously super custom? According to my buddy, there are some of the big wigs from Yamaha there, so he is going to ask them about that "2 into 2" exhaust. I'll let everyone know what they say. Any update on this? I kind of feel like there's a lot of educated people making exhausts for these bikes, not the least of which is Yamaha's own engineers and while it may be "right" to go with a 2 - 2 system, the difference could be entirely negligible outside of a dyno. Link to comment Share on other sites More sharing options...
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