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The closer they are to the exhaust port the more they negatively affect power.

^^ Indeed. I found the article:

THE QUESTION OF THE AGES
Has that dent ruined the performance of your brand new pipe? If so, by how much?
We strapped a brand new KTM 125 to a dyno and tried to discover what effect dents have on exhaust pipes. Here is the deal.

THE SMALL DENT
After making a few baseline runs on our KTM 125, we mounted a brand new Pro Circuit exhaust pipe. Voila! It gained 1 1/2 horsepower at peak (11,200 rpm). Then, we dented it (exactly 10 inches from the exhaust manifold). To make the dent, we hit the first cone with a ball peen hammer. We hit it hard, producing a two-inch wide by 1/2-inch deep depression.
Small dent results: Surprise! We gained an average of 1/10th of a horsepower from the bottom-end up to 12,000 rpm. Believe it or not, the small dent produced more power through the range and made 1/5th of a horsepower more at peak. After peak horsepower, however, there was a loss of power compared to the undented run.

THE LARGE DENT
Shocked by the results of our first test, we applied more force (via the implementation of a much larger hammer). Our small dent was now a large dent. The new dent was 3 inches in diameter and 3/4 of an inch deep.
Large dent results: Holy smokes! With the large dent the peak power was again 1/5th of a horsepower more, but more shocking was that the powerband was broader at max. On the downside, over-rev dropped off just like with the small dent.

HEAD PIPE DENT
In the first two tests we had simulated typical rock dents caused by roost. In test three we were looking for a head pipe ding (approximately six-inches away from the exhaust flange instead of ten-inches). Our dent was a small, one-inch diameter dent with a 1/2-inch depth. This kind of dent comes from rocks thrown up by your own front wheel, ramming downed bikes or casing jumps.
Head pipe dent results: Disaster! At 6000 rpm we were down half a horse, at 8000 rpm the two pipes were equal, at 11,000 rpm the dented head pipe was down a half horse again, and at peak power it was down a full horsepower. Obviously a dent in the head pipe is serious.

CENTER CONE DENT
Just for kicks, we slammed the side of the pipe (at its largest diameter) with a sledge hammer. This kind of dent is very rare, but can be the result of a fall-over or run-over style accident. To make it more interesting, we left the head pipe dent and first cone dents in the pipe to see if the center cone dent could add to the misery.
Center cone dent results: There was no difference in horsepower output with a center cone dent.

WHAT DOES IT ALL MEAN?
There are three conclusions to be drawn from On The Pipe Racing's speed dent test:
(1) The worst dent is one located in the first six inches of the exhaust pipe. A dent in the head pipe will hurt both the bottom and the top (and the fall-off before peak will be significant). If your exhaust pipe gets a dent in the head pipe (or even worse, is squashed flat) it needs to be replaced.
(2) The typical rock dent in the pipe's first cone (approximately ten-inches away from the exhaust flange) is nothing to worry about. Although it can cost some over-rev on top, it does not hurt horsepower at or below peak (quite the contrary).
(3) Center cone dents are not a big deal.
(4) Check out the GARAGE SALE for newly dented pipes

fuzzy wrote:^^ Indeed. I found the article:

THE QUESTION OF THE AGES
Has that dent ruined the performance of your brand new pipe? If so, by how much?
We strapped a brand new KTM 125 to a dyno and tried to discover what effect dents have on exhaust pipes. Here is the deal.

THE SMALL DENT
After making a few baseline runs on our KTM 125, we mounted a brand new Pro Circuit exhaust pipe. Voila! It gained 1 1/2 horsepower at peak (11,200 rpm). Then, we dented it (exactly 10 inches from the exhaust manifold). To make the dent, we hit the first cone with a ball peen hammer. We hit it hard, producing a two-inch wide by 1/2-inch deep depression.
Small dent results: Surprise! We gained an average of 1/10th of a horsepower from the bottom-end up to 12,000 rpm. Believe it or not, the small dent produced more power through the range and made 1/5th of a horsepower more at peak. After peak horsepower, however, there was a loss of power compared to the undented run.

THE LARGE DENT
Shocked by the results of our first test, we applied more force (via the implementation of a much larger hammer). Our small dent was now a large dent. The new dent was 3 inches in diameter and 3/4 of an inch deep.
Large dent results: Holy smokes! With the large dent the peak power was again 1/5th of a horsepower more, but more shocking was that the powerband was broader at max. On the downside, over-rev dropped off just like with the small dent.

HEAD PIPE DENT
In the first two tests we had simulated typical rock dents caused by roost. In test three we were looking for a head pipe ding (approximately six-inches away from the exhaust flange instead of ten-inches). Our dent was a small, one-inch diameter dent with a 1/2-inch depth. This kind of dent comes from rocks thrown up by your own front wheel, ramming downed bikes or casing jumps.
Head pipe dent results: Disaster! At 6000 rpm we were down half a horse, at 8000 rpm the two pipes were equal, at 11,000 rpm the dented head pipe was down a half horse again, and at peak power it was down a full horsepower. Obviously a dent in the head pipe is serious.

CENTER CONE DENT
Just for kicks, we slammed the side of the pipe (at its largest diameter) with a sledge hammer. This kind of dent is very rare, but can be the result of a fall-over or run-over style accident. To make it more interesting, we left the head pipe dent and first cone dents in the pipe to see if the center cone dent could add to the misery.
Center cone dent results: There was no difference in horsepower output with a center cone dent.

WHAT DOES IT ALL MEAN?
There are three conclusions to be drawn from On The Pipe Racing's speed dent test:
(1) The worst dent is one located in the first six inches of the exhaust pipe. A dent in the head pipe will hurt both the bottom and the top (and the fall-off before peak will be significant). If your exhaust pipe gets a dent in the head pipe (or even worse, is squashed flat) it needs to be replaced.
(2) The typical rock dent in the pipe's first cone (approximately ten-inches away from the exhaust flange) is nothing to worry about. Although it can cost some over-rev on top, it does not hurt horsepower at or below peak (quite the contrary).
(3) Center cone dents are not a big deal.
(4) Check out the GARAGE SALE for newly dented pipes

Hmm, interesting. I have a moderately-sized dent towards the end of the pipe and in the fat part, a few little dents on the bottom, and a small dent about 6 inches from the port. I was going to pop 'em out and then clean it up to look nice, its a little rusty right now

while I've read that I still cant stand the dents,If you want to try a interesting way to get dents out that doesnt involve the possibility of a exploding pipe.

Now this won't work on bad dents or creased dents but I have had luck with it a few times in the past.

Take a hair dryer or preferably a heat gun and heat around the dent to where it gets good and hot.Once that is done immediately take a can of canned air(i used duster brand)turn it upside down and in a circular motion freeze the crap out of the dent.If you get lucky and its done right expect a loud pop and the dent to disappear.

BobbyZ wrote:while I've read that I still cant stand the dents,If you want to try a interesting way to get dents out that doesnt involve the possibility of a exploding pipe.

Now this won't work on bad dents or creased dents but I have had luck with it a few times in the past.

Take a hair dryer or preferably a heat gun and heat around the dent to where it gets good and hot.Once that is done immediately take a can of canned air(i used duster brand)turn it upside down and in a circular motion freeze the crap out of the dent.If you get lucky and its done right expect a loud pop and the dent to disappear.

I've gotta try that on my truck........ that is sweet!

BobbyZ wrote:while I've read that I still cant stand the dents,If you want to try a interesting way to get dents out that doesnt involve the possibility of a exploding pipe.

Now this won't work on bad dents or creased dents but I have had luck with it a few times in the past.

Take a hair dryer or preferably a heat gun and heat around the dent to where it gets good and hot.Once that is done immediately take a can of canned air(i used duster brand)turn it upside down and in a circular motion freeze the crap out of the dent.If you get lucky and its done right expect a loud pop and the dent to disappear.

thats funny, I was actually considering that idea but I never thought it would be strong enough to pop dents out of metal. Ill need to try that tomorrow- I mean later today haha

It wont always work,and it is best for thinner metals,but I got a few dents out of my fmf pipe on my old kx 250 with it.The easiest one was from it falling from it's stand.Now my pro circuit on the kdx was a no go with doing it this way.

My grandfather taught me this years ago with dry ice instead of the canned air,after I plowed my bike into my grandmothers car.

I kinda liked the popcorn idea from youtube. Just fill the pipe and ride, right?

rbates9 wrote:I kinda liked the popcorn idea from youtube. Just fill the pipe and ride, right?

my favorite is the one with the "magnet" from the same guy...so strong it can move the car!

NEW RIDING PRANK!!! Any one that rides with people with out any kind of spark arrester NEEDS to pour some pop corn down the silencer. It should make it to the expansion chamber and roll around in there until it pops.

rbates9 wrote:NEW RIDING PRANK!!! Any one that rides with people with out any kind of spark arrester NEEDS to pour some pop corn down the silencer. It should make it to the expansion chamber and roll around in there until it pops.

scheckaet wrote:freeze method should work..

Can you explain how this method work?

not gonna go into details with that but water expand when it freezes, should pop the weakest part, either the dent or ... the seams if you're not careful...
You can argue all you want with me (cuz i got the feeling you or someone will ) but it's known to work...

scheckaet wrote:not gonna go into details with that but water expand when it freezes, should pop the weakest part, either the dent or ... the seams if you're not careful...
You can argue all you want with me (cuz i got the feeling you or someone will ) but it's known to work...

I can see it working, as you said the dent "should" be the weakest point. But depending on the dent I could see a seam splitting also. I think if I were going to give it a try I would probably put it in in the morning and keep checking it every hour or so. I have a couple of dented pipes in the garage I might just try this on just to see what happens.

I think I will do this with pictures just to put it to rest as long as I can find enough room in the freezer. I'll post something soon.

mmm...i did the freezer dent removal method, filled the chamber with water, drained a little out for space and put in in the freezer overnight,(much to my wifes disgust)....anyway, the 3" dent popped out really well, leaving only a small ding of about 1"!....well, in my infinite wisdome, i thought it best to do the procedure again do get the last of the dent out...

yeah, you guessed it...an 8 inch gash blurted out the side!...it took me ages to reshape and weld it....definitly face slap time...