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Christ · 10-22-2009, 11:45 PM

theycallmebryan - I'm sure that 1" would be better for me, but I simply can't put 1" primaries on it. It's not going to help at all, because I'll end up with reversion. The diameter of the pipe that's already on it, and the hole in the head, is already 1.5". If I were looking to re-map the exhaust port in the head, that would probably be an option, but it's really not right now, and most likely never will be.

beatr911 -

Thanks for the calculator, though I actually have the harmonics formulae written down somewhere. I do alot of exhaust work on cars, but obviously, there is much more room on a car to get desired effects than on a bike.

What I'm looking for is to extend the torque at the 3000 RPM range, because later, I want to gear down so I'm not running so high in the RPM range at 55-60MPH. (I have no idea what it actually runs right now, but it's audibly "up there").

The problem I find with alot of flow calculations is that they do not take into account the bends of the exhaust. While 1" pipe might be optimal for 15HP per cylinder, it's not optimal when the exhaust gasses aren't flowing in a straight or mostly straight line, because the dynamic flow effect of the gasses in the pipe basically makes the cross section of flow smaller than the pipe's diameter. This is the reason that lots of exhaust systems which require bends (like on smaller bikes and such) use aftermarket "whale penis" exhaust pipes, which have a huge blown out section in them. It prevents flow restriction in the bend, although sacrificing velocity a bit to do it. (Some of them also use that space as an expansion chamber, to quiet down the exhaust note.)

For all those reasons, and the fact that I'm not really going to spend weeks fabricating my exhaust for this, I think I'm going to stick with the idea up there ^^^, using the OEM primaries with a collector. Collector size will depend on what size PVC I have available, though.

Later on, I'll probably switch the intake around as well, to run two smaller carbs instead of one carb w/ the 180* manifold. Then I can add in a runner for each carb to help atomize the fuel more, and also to increase harmonic intake resonance at the low band.

10-22-2009, 11:45 PM	#15 (permalink)
Christ Moderate your Moderation. Join Date: Nov 2008 Location: Troy, Pa. Posts: 8,919 Pasta - '96 Volkswagen Passat TDi 90 day: 45.22 mpg (US) Thanks: 1,369 Thanked 430 Times in 353 Posts	theycallmebryan - I'm sure that 1" would be better for me, but I simply can't put 1" primaries on it. It's not going to help at all, because I'll end up with reversion. The diameter of the pipe that's already on it, and the hole in the head, is already 1.5". If I were looking to re-map the exhaust port in the head, that would probably be an option, but it's really not right now, and most likely never will be. beatr911 - Thanks for the calculator, though I actually have the harmonics formulae written down somewhere. I do alot of exhaust work on cars, but obviously, there is much more room on a car to get desired effects than on a bike. What I'm looking for is to extend the torque at the 3000 RPM range, because later, I want to gear down so I'm not running so high in the RPM range at 55-60MPH. (I have no idea what it actually runs right now, but it's audibly "up there"). The problem I find with alot of flow calculations is that they do not take into account the bends of the exhaust. While 1" pipe might be optimal for 15HP per cylinder, it's not optimal when the exhaust gasses aren't flowing in a straight or mostly straight line, because the dynamic flow effect of the gasses in the pipe basically makes the cross section of flow smaller than the pipe's diameter. This is the reason that lots of exhaust systems which require bends (like on smaller bikes and such) use aftermarket "whale penis" exhaust pipes, which have a huge blown out section in them. It prevents flow restriction in the bend, although sacrificing velocity a bit to do it. (Some of them also use that space as an expansion chamber, to quiet down the exhaust note.) For all those reasons, and the fact that I'm not really going to spend weeks fabricating my exhaust for this, I think I'm going to stick with the idea up there ^^^, using the OEM primaries with a collector. Collector size will depend on what size PVC I have available, though. Later on, I'll probably switch the intake around as well, to run two smaller carbs instead of one carb w/ the 180* manifold. Then I can add in a runner for each carb to help atomize the fuel more, and also to increase harmonic intake resonance at the low band. __________________ "¿ʞɐǝɹɟ ɐ ǝɹ,noʎ uǝɥʍ 'ʇı ʇ,usı 'ʎlǝuol s,ʇı"