Two Stroke Motocross
Two Stroke Motocross Forum => Technical => Topic started by: JohnN on December 22, 2009, 01:53:14 PM
-
While this is an older article it talks about how the tuning of the pipe started out. A good introduction to understanding the way the expansion chamber on the two stroke works.
How Two-Stroke Expansion Chambers Work, and Why You Should Care.
By Eric Murray , Apr. 23, 1996
http://www.motorcycle.com/how-to/how-twostroke-expansion-chambers-work-and-why-you-should-care-3423.html (http://www.motorcycle.com/how-to/how-twostroke-expansion-chambers-work-and-why-you-should-care-3423.html)
-
You should see the math to build pipes. ??? ??? ??? Really,a lot of math is involved. If some one wants to start out building pipes themselves, buy some books or buy TSR software.
The books I have are:
The High Performance Two Stroke Engine, DR. John Dixon. $59.95
Two Stroke Performance Tuning, A. Graham Bell. $39.95
Two Stroke Tuner's Handbook, Gordon Jennings. Most likely out of print
Design and Simulation of Two Stroke Engines, Gordon Blair. Get through SAE
I have all these books. :) :P :-X
TSR Software, $649.95 for all 19 programs.
I don't have this software although I wish I did. :(
-
I recently heard that alot of how it works is the resonence and vibration, and that when you have a Platnum or Gold pipe it actually hurts the performance.
-
I recently heard that alot of how it works is the resonence and vibration, and that when you have a Platnum or Gold pipe it actually hurts the performance.
Just like any other performasce modification, it's not just bolt on 1 super trick, go fast part and rotate the earth. It requires the "system" to be tuned to the part or parts you have just installed.
Also, the pipe can be tuned to work in vary narrow RPM ranges. So (IMHO) if you by the high RPM pipe, and don't change the squish band in the cylinder head to compensate (plus the regular tune up stuff) you have possibly lost HP. And the p[ipe guy takes the blame for a poorly designed system.
-
Just out of interest - I like my power spread to be like a 'lightswitch' so there is very little bottom end then suddenly you get a death cracker snap and it goes crazy with lots of power in the upper rpms. Does anyone know the best pipe to get for a KX 250 / YZ 250 that would give more that type of performance instead of the more torquey ones for lower RPM power? Thanks
-
Just out of interest - I like my power spread to be like a 'lightswitch' so there is very little bottom end then suddenly you get a death cracker snap and it goes crazy with lots of power in the upper rpms. Does anyone know the best pipe to get for a KX 250 / YZ 250 that would give more that type of performance instead of the more torquey ones for lower RPM power? Thanks
Your best bet is to call FMF and tell them what you want. Again, I think there are some head mods you must do to get full benefit. Just my .02.
-
Some bikes are corked up it's like my car. I take the stock air cleaner assembly off and put a cold air intake on and the car seems to run better. Although there's another problem the exhaust is now restricting the engine to pump efficiently, so what do we do, you guessed it, put some headers and bigger exhaust system on. Now the engine is really pumping air(think of an engine as one big glorified air pump), then there is yet another problem, the damn thing is running lean as hell. Well, you have to jet or tune the engine to run richer.
The two stroke is the same, if anyone remembers the RZ350, they will remember those restricted pipes with the catalytic converter built into them. They sucked up a ton of power, answer to the that, see above statement.J/K People would make there own pipes or get the uncorked Euro pipes.
In the end the engine, no matter what stroke is a air pump, it pumps air like a water pump. There is some math to see how much air your engine pumps in one stroke, but I'm not going there. ;) The experts say a modern 125 two stroke pumps around 173cc of air burned each revolution. A lot of air in a small engine.
-
Here's some stuff that will help you build a great expansion chamber...
(http://www.motocrossactionmag.com/Media/News/GoPipes_0.jpg)
-
(http://www.motocrossactionmag.com/Media/News/GoPipes_0.jpg)
John, where's the link? I'd love to get some of these.
-
The catalytic exhaust on the RZ was a U.S. thing.In Canada,they were a standard exp chamber and silencer.I had 2 of them.Ring a ding ding. 8)
-
The Euro RZ350 pipes work too. I know people used those, they might be the same, not sure. I seen a test in a book between the US and Euro pipes and the Euros killed the US pipe.
-
John, where's the link? I'd love to get some of these.
I just grabbed the photo from the internet... don't know where you could actually buy them. These were probably made by someone like FMF, Bill's or Pro Circuit. It was on the MXA web site.
-
I think a pipe builder has to cut, roll, and weld there own. I can't find much about buying them out right. This makes doing the math by hand easy, that's because I'm not a welder. I do have experience with sheet metal when my Dad raced late models (stock cars). I would help him build radiator ducts, sheet metal interior, and other odds and ends. Oh, the good old times of banging, cutting, and beating my head on a wall. ???
-
You can buy them, your local steel and tube supplier should be able to help you out.