i am going to look at a kdx 220 that supposedly has a dent in the expansion chamber of the fmf torque pipe. the owner says that the local shop told him that the dent wasn't big enough to affect performance. i was just wondering if you guys have any experience with this and how bad of a hit can you take without affecting overall performance?
dented expansion chamber.
- Thread starter bluespark
- Start date
domino dave
Member
- Sep 24, 2003
- 136
- 0
OK you guys .... I really wish I could find this article. I do however remember it very well.Especially since it went against everything I would have believed to be true. It was in a dirt bike magazine a couple years ago,and somebody posted it right here on this site.Anyway they took a 125cc with an aftermarket chamber and put it on a dyno.Then they started laying into the pipe with a ballpeen hammer.Each time they would dyno again.The dings(some were big),resulted in horsepower gain! .... Except when the dings were in the first 4 inches of the pipe,which then resulted in power loss. ... Dave .... I'm not joking!
domino dave
Member
- Sep 24, 2003
- 136
- 0
The article was in Motocross Action magazine. I have the link but it is no longer any good ... Not saying I agree ... I've heard from others here that this place does good work http://www.piperepair.com/ Dave
domino dave
Member
- Sep 24, 2003
- 136
- 0
OK Bluespark ... Here's what I was looking for ... Interesting read . quote:GreenPeace
Registered
Join Date: Dec 2002
Posts: 105
Sorry, school was never my favourite subject....
Anyway, i found the article. Here goes:
Friday September 30, 2005
The Big Dent
Posted by: at 8:21 AM CST
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
Registered
Join Date: Dec 2002
Posts: 105
Sorry, school was never my favourite subject....
Anyway, i found the article. Here goes:
Friday September 30, 2005
The Big Dent
Posted by: at 8:21 AM CST
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
ws6transam
Member
- Nov 17, 2005
- 309
- 0
...Except center cone dents are so buglin' ugly to look at.
They make you look slower, too. I got one in my procircuit pipe, and it was the result of a layover in the woods. I didn't even stall the motor, just fanned the clutch, stood it up and rode off.
They make you look slower, too. I got one in my procircuit pipe, and it was the result of a layover in the woods. I didn't even stall the motor, just fanned the clutch, stood it up and rode off.
domino dave
Member
- Sep 24, 2003
- 136
- 0
