What kind of pipe should i buy for my Polaris XLT indy special. I want something that is a reasonable price but still produces horsepower.

Sleds MUST MUST MUST have back pressure. Buy a pipe and can. Thats the only way to go.



Bauer

If you think about it, your exhaust ports and your intake ports are open at the same time on your cylinder when the cylinder is at bottom dead center. The reason all the fresh fuel does not just go zooming out the exhaust at this moment is because there is a pressure wave created by the velocity of the exhaust hitting the most constricted spot in the pipe and it rebounds back at the EXACT moment the intake fuel is starting to exit the cylinder, which forces MOST of it back into the cylinder to be compressed and burned.

The pipe is VERY important on a two-stroke engine, the shape of the chamber, the distance to the restricted spot, the heat of the pipe (air travels faster when it's hot) all are critical elements in pipe design. That is why straight pipes don't work on a two-stroke.

Like Bauer said, you HAVE to have the backpressure to make the power.

I thought that it was negative pressure that a 2-stroke needed. Doesn't the fat portion of your pipe cause the gas to rapidly expand and crate a vacuum that sucks out the cylinder volume?

Ah, found the info again on howstuffworks.com:
(http://www.howstuffworks.com/question636.htm)


Why is there a bulge in the exhaust pipe of my dirt bike?

That bulge is called an expansion chamber, and it is used to increase the horsepower of the engine (see this page for a photo). This technique only works on two-stroke engines, which is why you see it on a lot of dirt bikes but not on street bikes. Most street bikes use four-stroke engines.

The basic idea behind an expansion chamber is to use the momentum and pressure of the exhaust gases to create a pump that squeezes more air and fuel into the cylinder during the intake stroke. It does the same sort of thing that a turbocharger does, but it does it without moving parts.

If you have read How Two-stroke Engines Work, then you know that the exhaust and intake parts of the cycle overlap. As the piston moves down, it uncovers the exhaust port first to let most of the exhaust out. Then it opens the intake port to let fuel/oil/air in. With a correctly-tuned expansion chamber in place, two things happen to help the intake process:

* As the exhaust gases expand into the expansion chamber, they create a vacuum at the exhaust port. This vacuum pulls fuel/oil/air into the cylinder.
* As the shock wave of the exhaust pulse hits the end of the expansion chamber, it echoes back, pushing any fuel/oil/air that got pulled through the exhaust port back into the cylinder. This page has a nice graphic that describes the process.

By pulling extra fuel/oil/air through the cylinder and then pushing it back in, the expansion port has the effect of stuffing more fuel/oil/air into the cylinder on each stroke. This gives the engine extra power in the same way that a turbocharger does.

Excelent discription.



Ah, found the info again on howstuffworks.com:
(http://www.howstuffworks.com/question636.htm)
Why is there a bulge in the exhaust pipe of my dirt bike?

That bulge is called an expansion chamber, and it is used to increase the horsepower of the engine (see this page for a photo). This technique only works on two-stroke engines, which is why you see it on a lot of dirt bikes but not on street bikes. Most street bikes use four-stroke engines.

The basic idea behind an expansion chamber is to use the momentum and pressure of the exhaust gases to create a pump that squeezes more air and fuel into the cylinder during the intake stroke. It does the same sort of thing that a turbocharger does, but it does it without moving parts.

If you have read How Two-stroke Engines Work, then you know that the exhaust and intake parts of the cycle overlap. As the piston moves down, it uncovers the exhaust port first to let most of the exhaust out. Then it opens the intake port to let fuel/oil/air in. With a correctly-tuned expansion chamber in place, two things happen to help the intake process:

* As the exhaust gases expand into the expansion chamber, they create a vacuum at the exhaust port. This vacuum pulls fuel/oil/air into the cylinder.
* As the shock wave of the exhaust pulse hits the end of the expansion chamber, it echoes back, pushing any fuel/oil/air that got pulled through the exhaust port back into the cylinder. This page has a nice graphic that describes the process.

By pulling extra fuel/oil/air through the cylinder and then pushing it back in, the expansion port has the effect of stuffing more fuel/oil/air into the cylinder on each stroke. This gives the engine extra power in the same way that a turbocharger does.[/b]