What would happen if you put a two stroke pipe (fmf fatty for example) on a fourstroke?

Would it even work good, if you got it to fit? Or would you see power losses?

I think it would be kind of like using an FMF MegaBomb headpipe, but then its an even BIGGER expansion chamber.

 

i would guess it would not work out too well. im not an expert, but theres a reason they make pipes for 2 and 4 strokes. i think your "crazy" for thinking that (jk [img]i/expressions/face-icon-small-smile.gif[/img])

 

i want someone to try it though, maybe supersonictoys can, i bet it would sound pretty cool on a bombusa

 

The 2 stroke pipe is it backpressure to create power and suction for the exhaust. Thats what the big bubble is for.

http://img504.imageshack.us/img504/6...strokec6yr.gif

A 4 stroke pipe just needs to get the exhaust out as fast as possible because it has valves to regulate the flow of air/exaust. Hence cam mods....

 

A two stroke exhaust is designed to take advantage of sound wave frequency, or exhauxt pulse frequency actually, but it is easier to picture in your mind by thinking of a sound wave. A two stroke draws air/fuel into the cylinder every stroke, and doesn't have an intake stroke and a power stroke, they are all intake strokes and all power strokes. The two stroke draws the air/fuel into the engine through an intake port, and the exhaust leaves through an exhaust port, and there are no valves. So with each "intake stroke" the air/fuel mixture is drawn into the intake port, on through the cylinder, and part way into the exhaust pipe. Then as the piston goes up it rises above the intake port, and effectively closes the intake port. But since the exhaust port is higher than the intake port it is still effectively "open". The expansion chamber has to be sized and shaped right so that the wave of just drawn in air/fuel hits the end of the expansion chamber, and then bounces back through the engines exhaust port just before the piston rises above the exhaust port and closes it. This rebound like charge of air/fuel actually crams more air/fuel into the combustion chamber just before the combustion stroke, and dramatically increases power. But the frequency of the air/fuel wave has to be right for it to work, and that is why a two stroke comes "on the pipe" once it hits a certain RPM. That is also why changing the length of the head pipe and the diameter and shape of the expansion chamber will change when and how the power is made in a two stroke.

Being as a four stroke engine has an exhaust valve it could not possibly take advantage of the air/fuel rebound pulse from an expansion chamber. So an expansion chamber on a four stroke would do nothing more than slow down the exhaust velocity, and likely decrease power.

 

You can just look at the link ive provided instead of reading all of that. Takes 30 seconds to show what takes 5 minutes to read.

 

Although different than an expantion chamber pipe, a merge collector also works with sound waves. The idea of any good pipe is a good scavenge effect. A two stroke pipe is far too big for a 4 stroke of the same size so you would loose power because of no scavenging effect. The two stroke goes pop every other stroke and the four stroke every fourth stroke.
Merge collectors
Happy reading.

 

Excelent Illistration on the 2 stroke. Do you have one for a tuned exaust for a 4 stroke relative to power curve at low end range and power curve at upper end. Headers can be designed for 4 strokes to peek at short range or hi range.
But using a 2 stroke exaust on a 4 stroke will cause you to make a huge modification on the chamber.

I think on a 4 stroke, it has something to do with the displacment volume of the burned fuel relative to how many rpms you want it to optimize the power curve. Back pressure is used differently in a 4 stroke but it needs to be there.
I needs to breath, otherwise you would suck fresh air back into the combustion chamber making it run Lean and there would be flames blowing out of the pipes when you backoff the throttle if the pipe is to short and does not match the displacment of spent fuel at an optimum RPM.

The idea is the same as tuning a radio antenna to a particular frequency in both cases. Wave length vs frequency

 

How 4 stroke engines work:

http://auto.howstuffworks.com/engine1.htm

How camshafts work:

http://auto.howstuffworks.com/camshaft.htm

 

Yep I saw similar illustrations but nothing in the area of tuned exhaust.

To short or to long headers on a 4 stroke will compromise the performance; otherwise there would be no need for an exhaust pipe...
I just was wondering if there was some info illustrationI could not find on the net that will relate.

What I did find
http://mobile.snap9.com/Article.aspx?ArticleId=118

How It Works
When you look at the four-stroke cycle, you can see that the engine produces all of its power during the power stroke. The gasoline in the cylinder burns and expands during this stroke, generating power. The other three strokes are necessary evils required to make the power stroke possible. If these three strokes consume power, they are a drain on the engine.

During the exhaust stroke, a good way for an engine to lose power is through back pressure. The exhaust valve opens at the beginning of the exhaust stroke, and then the piston pushes the exhaust gases out of the cylinder. If there is any amount of resistance that the piston has to push against to force the exhaust gases out, power is wasted. Using two exhaust valves rather than one improves the flow by making the hole that the exhaust gases travel through larger.

In a normal engine, once the exhaust gases exit the cylinder they end up in the exhaust manifold. In a four-cylinder or eight-cylinder engine, there are four cylinders using the same manifold. From the manifold, the exhaust gases flow into one pipe toward the catalytic converter and the muffler. It turns out that the manifold can be an important source of back pressure because exhaust gases from one cylinder build up pressure in the manifold that affects the next cylinder that uses the manifold.

The idea behind an exhaust header is to eliminate the manifold's back pressure. Instead of a common manifold that all of the cylinders share, each cylinder gets its own exhaust pipe. These pipes come together in a larger pipe called the collector. The individual pipes are cut and bent so that each one is the same length as the others. By making them the same length, it guarantees that each cylinder's exhaust gases arrive in the collector spaced out equally so there