Edited Date/Time
1/26/2012 9:36pm
Ok, I understand the backpressure/sonic wave idea behind the design of 2T pipes, and why some of them are therefore longer and thinner, some shorter and fatter.
However, after seeing the dramatic difference between the pipes on say, Windham's CRF and Dungey's SX, can someone enlighten me as to why the pipes would be so drastically different? Since the combustion process is primarily controlled by cam/valve timing, what does the pipe length have to do with it?
Thanks in advance.
H
However, after seeing the dramatic difference between the pipes on say, Windham's CRF and Dungey's SX, can someone enlighten me as to why the pipes would be so drastically different? Since the combustion process is primarily controlled by cam/valve timing, what does the pipe length have to do with it?
Thanks in advance.
H
I remember reading an article a long time ago about a test rider who could notice the power difference when the only change was the thickness of the pipe material. Now that's impressive...
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I've done a little digging since I posted and I take it the same principles at work in 2T design are at work in 4T design, just to a lesser degree. They're still playing with the milliseconds of charge flow and micrograms of fuel mixture that can be affected outside the control of the valves. I guess at this level, every teensy bit counts. And exhaust changes are easier to do that cams.
Is that about right?
H
those bulges in the header, if you were wondering, are anti reversion chambers, which have been on race car headers for 30 years. they keep exhaust pulses from interrupting the downstream flow of exhaust gasses. i think fmf calls them "power bombs"?
cam swaps are useless without coinciding tuning. the power gains will be minimal. same with headers. you might feel it on the "butt dyno" but usually "butt dyno" feelings are actually what you call "torque spikes" which are a result of poor tuning. the problem is, you can not tell a moto redneck this, they will ALWAYS argue that it "feels" faster, when in reality, there is just a lean spot in the fuel curve that gives that illusion. smoother is faster, 12:1 AFRs from idle to redline, throw as much timing as it can handle until it detonates, then back it off.
thats where efi comes into play. much easier to tune than carbs because you can just look at a computer monitor, and click a mouse to change your a/f ratio and timing as long as you have enough injector flow in it.
Thanks Chuck, uhhh, Mr. Bronson.
H
I'm jus' knowin'...
silly me.
or.....
you could just get real.
On the other hand, race team headers for someone like PC, R&D is a big part of developing their engine power curve. They are probably running custom headers that aren't available to the public. They usually do alot of testing on the track and dyno to develop a good standard header that will allow cam adjustment. If you read any tech articles by race team motor gurus, different engines are not used for SX and MX like one would think. The team will usually use the same engine, but adjust cam timing and ignition mapping to produce a bottom to mid engine for SX, and then a mid to top end engine for MX. More then likely, they have a header to match each application.
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