SuzukiSavage.com - Exhaust design

Fast 650

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Re: Exhaust design
Reply #15 - 02/09/18 at 08:05:42

Dave wrote on 02/08/18 at 10:22:29:

The stock header does work fine....with a muffler on the end.

Open and/or drag pipes are know to create a flat spot or sag at certain rpm's in the mid-range.

And CV carbs exaggerate that effect more than a roundslide carb does in my experience. I am guessing that it messes with the vacuum signal at the carb at certain rpms.

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sandmanred Senior Member Offline SuzukiSavage.com Rocks! Posts: 284	Re: Exhaust design Reply #16 - 02/09/18 at 08:45:35 Was that excel file loaded with the 650 stroke and bore (it came in with 3.7 x 3.7 inches)? Do you have any guidelines for the velocity range to optimize around?
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verslagen1 YaBB Moderator ModSquad Offline Where there's a will, I want to be in it. Posts: 28889 L.A. California Gender:	Re: Exhaust design Reply #17 - 02/09/18 at 09:06:03 longer pipes = deeper tone
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Fast 650

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Re: Exhaust design
Reply #18 - 02/09/18 at 09:41:39

sandmanred wrote on 02/09/18 at 08:45:35:

Was that excel file loaded with the 650 stroke and bore (it came in with 3.7 x 3.7 inches)? Do you have any guidelines for the velocity range to optimize around?

Those numbers were from the last calculations I had done. As far as velocity, the number that I always heard was 280 to 320 fps at peak power rpm is ideal and that is what I am shooting for with my build.

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sandmanred

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Re: Exhaust design
Reply #19 - 02/09/18 at 11:25:23

Thanks for the input so far. It's making me re-think. Now I'm thinking some thing more like the yellow line. It lengthens it out and leaves me plenty of straight to stick a baffle into near the outlet. I still have a lot to go before I get there so I could change my mind again but I wanted to think it through to make sure I have the connection points I need for the potential designs.

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Gary_in_NJ Serious Thumper Offline LS650 Cafe Racer Posts: 2633 Amongst the Twisty Roads	Re: Exhaust design Reply #20 - 02/09/18 at 11:39:45 Where are your foot controls going? I think that location will drive the routing of the exhaust pipe.
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SoC

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Re: Exhaust design
Reply #21 - 02/09/18 at 18:00:51

Since on the subject of exhaust , and this question may seem a little simplistic, but I am working on my exhaust. Is the basic length and where the wave encounters it's first resistance basically what's important in the design assuming you use the stock header. This is not to down play the aspects of wave dynamics, and all that's been touched on, but there is basically free flow through the header (all things equal) and the return wave is influenced by among other things the first resistance it encounters via a baffle or obstruction. I realize there is more complexity to it, but does this seem to be a realistic point to start from.

I just ask as I'm not making any change to the stock header on either of my bikes, I have a Voodoo muffler (and that's a pretty loose interpretation of muffler, if you view the internals of it) to play with on one, and my thoughts are to build a straight pipe approx. the same diameter as the header, with internal insert steel baffles and approx. the same length as the stock muffler with a more down turn out than straight out the rear.

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batman

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Re: Exhaust design
Reply #22 - 02/09/18 at 21:42:03

SoC, The wave isn't influenced by resistance, but by expanding , the velocity drops do to entering a muffler (an enlargement) or atmosphere and is turned into pressure , it then reverses as a negative pressure wave and moves back up the header. the muffler kills noise ,if it has a baffle this will slow the gases and provide some back pressure on the motor ,this helps flatten the torque curve ,making it less peaky. A straight pipe , with or without baffle, will not allow the pressure wave to expand until it reaches the end of the pipe,which makes it bad for wave tuning, and you'll make less Hp .I'm not up on the voodoo muffler but if it's larger than the header pipe I'd go with it or any muffler before a straight pipe.

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SoC

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Re: Exhaust design
Reply #23 - 02/09/18 at 23:23:33

Batman, thanks for the simplified explanation. The Voodoo is a larger diameter. It has an internal pipe and an external, and the baffle is basically 2 opposing cut outs in the internal, bent inward. If you look into it you can see through it to the opposite end with the 2 opposing tabs in the middle sort of blocking the path of flow. I'm sure it will be pretty loud, I am looking into ways to add a baffle insert to it, probably in front end.

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batman Serious Thumper Offline SuzukiSavage.com Rocks! Posts: 3806 osceola new york Gender:	Re: Exhaust design Reply #24 - 02/10/18 at 00:25:57 SoC The ideal place for the baffle is right in the middle, half the openings for the gases to go round the baffle and half to return an exit.
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sandmanred Senior Member Offline SuzukiSavage.com Rocks! Posts: 284	Re: Exhaust design Reply #25 - 02/10/18 at 04:39:18 Gary_in_NJ wrote on 02/09/18 at 11:39:45: Where are your foot controls going? I think that location will drive the routing of the exhaust pipe. Foot controls will be forward anchored to a pair of the bolts through the engine plates.
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IslandRoad Serious Thumper Offline It doesn't vibrate, it purrs! Posts: 1147 The Kiewa Valley, Australia Gender:	Re: Exhaust design Reply #26 - 02/10/18 at 20:46:55 For what it's worth, IMHO, the yellow line looks much better from a purely aesthetic point of view - the curves match the frame nicely! And, from what I understand of the concept of pressure waves, that will give you a more predictable outcome when tuning.
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