Drilled stock exhaust revisit

[birdman]

'99 GS, Stock except 40/125 rejet.  I am at 5500 ft above sea level elevation.

After rejetting the bike I felt it was flat in the midrange.  Having worked a bit on tuning of other vehicles I did the usual. Help it breathe.
Not having access to parts but loving to test things I did my searches on mufflers here and saw a number of drilled out rear baffle plates.  Some were almost completely removed and others had small holes.  I figured its worth a try.

First, I noticed that the stock mufflers on these bikes varies a bit.  The outlet on mine is about 3/4" diameter.  seemingly small.  Others looked bigger, but without scales I could not tell for sure.

I drilled a hole, 1/2" diameter bit and started it up.  Nasty sounds came out, more like an exhaust leak than open exhaust.  So I enlarged the hole in one direction to 1".  So I have an oval shaped hole .5x1.0 inches.  Also with the 1" dimension the sound should be deeper. It was.
The area of this hole is close to the same area as that stock outlet.

This made for a poppy sounding exhaust and I felt I could live with it for now.
I could see one of the internal tubes through the hole and it is really close to the end of the muffler. 

So with the bike warmed up I ran it.  Definitely louder, sounds much like an old BSA or Triumph.

Now after a few rides I can emphatically say two things.
Throttle response is greatly improved.  Throttle lag is non-existent.
Power throughout the range is also improved.  Seat of the pants, which hold on a little tighter now, can tell.

There is no flat spot in the midrange and it pulls much more solidly up to 10k.

Having said this I also know that there  is a limit to how much exhaust flow will help you. Too much flow and not enough backpressure hurt torque.  By starting small I think I found a sweet spot for my bike.  I do not plan to go any larger.

The poppy sounding exhaust almost makes it sound like a cammed drag bike.  But I may opt to install a round resonator tip just to smooth it out soundwise. 

All in all, this small change seems to have made a big difference in performance.

birdman

[ashman]

My old GS came w/ the exhaust drilled out and I was pretty happy with it. There were a few holes drilled w/ 5/16th or 1/2 inch bit. The sounds was kind of poppy when decelerating like you describe. Some members thought it was kind of ghetto but I was happy.



-Ash

[birdman]

So I got rid of the poppy sound from the drilled muffler.


I put a 5 inch length of 1/2" square tube and it totally changed the sound.
Sounds mean and still flows good.  The flash makes it brighter than real life so its not that noticable from the outside.

[The Buddha]

5500 will be a -1 on mains especially. I;d run the 122.5 stock size, maybe even drop the needle back to stock.
Cool.
Buddha.

[starshooter10]

i have 8x 1/2 inch holes in mine....

it's "POPPY" but to me it sounds like a old motorcycle racing game of moto GP or something =-P

i kinda like it... over 4k =-D

[birdman]

I know what you mean about the sound.  It reminds me of some old English bike that way.

Buddha, yes lean at this elevation is good for power.  I am going to take the spacer out of the needle and leave the bigger jets in. 
I also like to run regular gas, so with a little richness I don't have to worry about detonation when its 100 degrees out.
Pistons like that idea too.