drilled 6 5/16 holes and used a sawsall didn't have a bigger bit but could tell the diffrence in low end had it in low range and the bike almost came over on me and I weigh 380 pounds and the rims and tires must add another 100 lbs. going to rejet and get a filter should have even more

 

Just did mine last night,havent rode it yet.With 6 1/2" holes and removing the spark arrester it is louder than I expected it to be.Probably too loud for hunting,but just fine for screwin' around on the trails or at the river.
Ill go for a ride tonight,then check the plugs and see if I need to rejet.I just used a sawzall to cut on the weld,then made a drill bitt buy weldind a piece of round bar on to a normal bit,and drilled away.Be careful to drill fairley straightt into the muffler so you dont come out the side.I ran into one snag though,When drilling my first hole,the bit didnt want to come out real easy so I put the drill in reverse to help it out,all pretty normal....but the chuk was hitting the inside of the muffler a little and when I reversed it the chuck loosened up and dropped the bit inside[img]i/expressions/face-icon-small-sad.gif[/img].Had to take the muffler off and cut the front of it off to get that blasted bit out!!Belive me I tried everything befor cuttin,but that bit was not comin out.So just aword to the wise dont drop nothin in there(bits,bolts pets,small children)cause its a pain to get it out.

 

I also did the exhaust mod using a 1/2" bit, and it was louder than I expected. If you hollowed out the tip like I did than there is a quick fix to the loud problem. I managed to find a thick washer that just fit in the end of the muffler, and drove it in with a hammer, and didn't even have to weld it in. The smaller the hole, the quiter the machine. It looks nice and still sounds good. The nice thing about not welding it in is that you can change the noise level to go hunting, and switch back to open for screwing around.

 

So all in all everyone is getting noticable power gains with this mod? Interesting...I am contemplating purchasing a full system, but I don't have the money to spend on it, especially if I'm going to purchase the CDI. I'm getting married in August and I would be castrated if she found out what I am doing.

It would be interesting to hear reports on two identical bikes with same mods, one with the exhaust mod and one with an aftermarket exhaust. I'd like to see the exhaust mod results are comparible to an aftermarket system...I know there would be definate weight savings with the aftermarket system.

Does anyone have any hard evidence as to comparitive results between the two?

 

Just thinking...what if you put bigger holes in instead of 1/2" or 7/16" or 5/8"?
What about 3/4"?

 

3/4 might be alittle big you might as well just gut it out. Like I said I drilled 5/8 holes and my neighbors thought it was a very low flying helicopter

 

on my prarie i nocked the center out and then drilled 6 1/2 inch holes its realy loud i can hear it a half mile away. I noticed an increas in mid rang not a big increas just an increase

 

parker,

My friend just did the exhaust mod and replaced his pro circuit T4. We're going for a run on Sunday to compare against my bike with the T4. It's definately quieter than a T4 but I'll give you a more complete comparison next week.

 

did mine eariler today. (7) 7/16 holes with a 12" bit. Never had to remove the muffler off the bike. Took about 1 hr total. Including: cutting, drilling, and welding back.

I rode it about an hour after the mod. The throttle seems snappier, quicker, more responsive, felt like it gained some torque, you could tell it was breathing easier. Slightly louder but not much. My girlfriend thought it sounded the same, she had rode it three times before, and did not notice it being louder at all.

Great mod for the money, (had to buy a $15 drill bit.), and give a buddy some beer for welding it.

Thanks to Nyroc for discovering this, its much better than paying $200 plus for a aftermarket muffler.
Also it looks stock, so you can sneak up on people.

I left my outside tip alone, so it appears totally stock. However, I did cut almost all the inside tip off.

 

I removed the pipe to cut off the end cap
Put the exhaust in a vise,and cut just ahead of the weld,be careful and cut through 1 layer of steel.
Iused a hacksaw,it took about 5 minutes.
After cutting ,just tap the end with a hammer ,it will come out
When drilling the holes stay towards the inner half,so the drill chuck will clear the muffler.

I DRILLED 8 3/8 HOLES

after welding cap back on paint it black while still warm,the paint bakes on

SOUNDS GREAT!!!!!