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Message started by JohnBoy on 07/05/09 at 19:52:08

Title: Seeking your input!
Post by JohnBoy on 07/05/09 at 19:52:08

Greetings all,
I have replaced the stock muffler with a straight exhaust (the Diamond Jim longshot).
I noticed a few major differences right out of the box. First, it is considerably louder, with a deep raspy gargle on throttling down. Second, it has much better mid range power.
It now pulls pretty good through 80mph and 90 was pretty quick too. Ok, these things I expected to some degree. What I would like your feedback and input on is the lack of vibration that seemed pronounced at 75mph with the original muffler. I made two 12 mile runs up and down the freeway today at 70+ with romps to 90 in between. The engine seemed much smoother?
Is it possible that the engine vibration that we live with is the result of an overly restrictive muffler, and the vibration is caused by pressure waves running back and forth in the header?
Opinions welcome!

Title: Re: Seeking your input!
Post by verslagen1 on 07/06/09 at 11:26:52

It's possible that your engine bolts were loose before.
You had to remove them to pull the exhaust off.
And when you replaced them, they're now torqued to the proper amount.

Title: Re: Seeking your input!
Post by JohnBoy on 07/06/09 at 16:04:45

No, if anything I had torqued the exhaust a bit too tight. I never touched tie motor hanger bolts

Title: Re: Seeking your input!
Post by Hawk on 07/06/09 at 17:37:30

Vibrations on our bike are most prevalent at a "harmonic" frequency (rpm related) of the "system".  In our case, the "system" is the entire engine, mounts, frame, and yes - even the exhaust (since it is bolted directly to the engine).

Perhaps you've hit on an exhaust installation that moved the harmonic frequency to a different range and thereby achieved smoother operation at certain frequencies (rpms.)  Its not for sure this is it - but it might be a factor

I cannot think of anything related to back pressure of the exhaust that would significantly affect vibration.


Title: Re: Seeking your input!
Post by serenity3743 on 07/07/09 at 12:26:54


795C5B5D715C4A330 wrote:
No, if anything I had torqued the exhaust a bit too tight. I never touched tie motor hanger bolts


If you had to remove the right hand exhaust shield/footpeg/rear brake assembly, you did loosen and retighten two long bolts that support the engine at the bottom.  So this might have been a factor.

Speaking of vibration, has anyone ever tried dampening some of the vibration by inserting cushions at the top motor mount, where the bracket bolts to the valve cover and to the frame?  I'm thinking of experimenting with this some.

Title: Re: Seeking your input!
Post by ralfyguy on 07/07/09 at 14:56:43

This might put too much flex on the exhaust assembly and you'd get leaks and/or breaking apart of the whole thing. Also the belt might be runing all over the place when the engine can move to much.
7D6B7C6B60677A773D393A3D0E0 wrote:
[quote author=795C5B5D715C4A330 link=1246848729/0#2 date=1246921485]No, if anything I had torqued the exhaust a bit too tight. I never touched tie motor hanger bolts


If you had to remove the right hand exhaust shield/footpeg/rear brake assembly, you did loosen and retighten two long bolts that support the engine at the bottom.  So this might have been a factor.

Speaking of vibration, has anyone ever tried dampening some of the vibration by inserting cushions at the top motor mount, where the bracket bolts to the valve cover and to the frame?  I'm thinking of experimenting with this some.[/quote]

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