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Post by andy on Apr 29, 2007 8:20:29 GMT -5
heres one for you technical guys,whilst general opinion suggests straight thro' mufflers give much improvement is it possible this can be over done?i'm running a b.s.a replica muffler which sounds gorgeous,lovely deep sound.my dilemma is this,my bike pulls like a good un midrange but lacks top end.i see a lot of you guys run supertrapps which have obviously got a baffle system.is it possible my muffler is getting rid of the gases at top end to efficiently before they have been burnt?is some back pressure advised?also the bsa muffler is quite a bit longer than most i've seen and has a large diameter tail.thanks.
andy
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Post by flyereddie on May 1, 2007 3:47:41 GMT -5
Hi Andy
The exhaust system can resonate especially if it has no baffles internally, this can cause some strange results. The outgoing exhaust will cause a partial vacuum in the head which helps to draw in a new charge even before the piston starts going down this is fine and will give extra power as the fresh charge replaces any spent gasses, the problem is this effect only occurs at a particular rpm ( depending on the length of the pipe) if you go past this rpm the effect will disappear and in some cases will reverse the and push some gasses back in effectively pushing some exhaust back into the cylinder. This chokes the engine and the power the engine puts out drops, so a shorter header pipe will help the top end but affect the midrange its a bit of a trade off . Baffles in the pipe will not only quieten the pipe but can help dampen the resonant affects so you don't get such a great power gain but also they will work over a greater rpm range. This is not an exact science although if the pipe is straight you can use calculate the length to start with for a particular rpm and play from their .
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Post by andy on May 1, 2007 12:04:25 GMT -5
hi flyereddie,many thanks and interesting theory,i'm really having a close look at the muffler now because all the subtle changes i've tried dont seem to make that much difference.dont get me wrong i'm happy with the bike and as you say there is a trade off somewhere along the rev range so i reckon i'm gonna try this:a cheap shorter muffler that is thro' but smaller exit diameter[got me eye on one off e-bay] and a bigger k&n filter thats got more volume,about the size of a big tin of beans.tho i want to improve top end idont want to lose the midrange which i think is great.plus i dont want to part with silly money for another 10 m.p.h! food for thought.thanks.
andy
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Post by wotavidone on May 1, 2007 23:33:44 GMT -5
I reckon most of us have heard the expression "all noise, no go".
I'd love to lay my hands on a good supertrapp. Its the way you can tune them while they are on the bike that appeals to me.
We've got a bloke here in town who occaissionally has "dyno shootouts". You get to run your bike for $30. I'd run her like she is, then start experimenting with installing and tuning a supertrapp. When I reckoned I had a noticeable improvement - back for another test run.
Still blows me away how much you have to change jetting when you change pipes. In some ways it defies logic.
Mick
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