what i don't understand, is how something like a westcoast 650 pipe on a 701 wouldn't work out pretty well.
I recently asked this on PWCtoday and pretty much got a "not worth it" and i know this isn't about exactly that but....when you see 701's in stock super jets with stock exhaust....i cant see how that would be better then a 650 west coast pipe...and im referring to this 701 pipe
It has to do with the properties of combustion. I'm not well enough versed to go into specific details but I can give you some info you can use to look up on google if you like. The reasons have to do with a many number of factors such as port timing, exhuast temp, acoustics, air velosity, back pressure.
Trying to keep this simple...
2-strokes don't work like 4 strokes. There are no valves to keep the air and fuel in the ocmbustion chamber. Crank case pressure pulls fuel in and pushes out spent fuel. The fuel would flow right out with the exhaust gases, but the back pressure from the exhuast system keeps this from happening. More important than air pressure is the sound wave of the explosion. The sound travels down the pipe, gets to the end and is reflected back to the cylinder. The air gets back at just the right time to allow all of the spent gas to escape but keep the good gas/air in the cylinder. Too much speed and the gases get stuck inside, causing a build up of heat, more fuel is added through the carb, fuel is waster and performance decreases (believe it or not, the less fuel you use, the more power you get, a lot of fuel is wasted in cooling the cylinders, lean is faster but too hot). Too little sound speed and the clean fuel escapes, leading to a waste of fuel and a loss of power.
This is why the B-pipe is so popular. By allowing adjustment of the water injection, the heat in the pipe can be changed. Sound is faster hotter and slower colder. Adding or removing water changes heat, which changes speed, which changes pressure, which changers power. This also explains why other pipes perform better at different RPM. They have the right design for a specific RPM, but the B-pipe can be adjuested for different sound velocity and thus different pressure and porformance at different RPM. This is also the explination for Electronic Water injection on the B-pipe, it allows a broader range of performance from the pipe by varying the speeds of the air as RPM changes.
Yes, you can put a used kawi 650 westcoast pipe on a yamaha 701 motor. Yes, it will probably work better than stock. however, the pipe specs do not match the port timing and various other factors of the engine performace. You will have a $200 pipe on a motor that performs like it has a $200 pipe on it. And, you will have a lot of hassles making it fit. But for $600-800 you can have a motor that performs to it's potential.
All of these same factors apply to the discussion about the kawi 750 with a kawi 650 pipe. Yes it fits. Yes you can do it. Yes it's easier. Yes most people do it. Yes it will out perform a stock pipe. But no, it will not ever reach it's true potential. Think of it like this. You can replace the stock Kawi 38mm keihen carb with a 44mm mikuni carb, but if you don't take the time to properly tune your new carb, you will only get mildly better performace at the cost of the carb and the wasting of a lot of fuel. However, if you spent the extra money on a jet kit and tuned your motor, you get more power and waste less fuel, giving you a much higher yield for not much more investment.
So back to the original discussion, if the goal is to be cheap and slap in a 750 motor with a cheap pipe and leave your e-box sitting where ever it fits, then you're just as well spending less money on a 650 or the same money doing a good job on a 650. But, the best thing to do is drop in a 750, and instead of spending $200-300 on the wrong pipe, wait and spend $300-600 on the right pipe. It's worth waiting and saving the extra money.
If the OP needs to run the stock 650 pipe for a bit to save for the right pipe, well, that makes ok sense. But to remove a stock superjet pipe to put a $250 Kawi pipe, so it works a little better, well, that doesn't make sense, because you just wasted half of the total cost of buying the right thing on the wrong thing. And then you always get to try to explain to people with funny looks and better performing skis about how you over came the challenge of rigging together a poorly tuned ski. I know showing off my X2 always gave my a warm fuzzy feeling of failure.
