Quote:
Originally Posted by VaFish
It's probably not done much because for the cost and work involved the pay off isn't that great.
Besides once you get the engine cranking out tons of horsepower, then you have to upgrade suspension, brakes, frame, ect......
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The problem is that you will not get out tons of horsepower from the Ninja 250.
The distance between the two cylinders is relatively small, so you will not be able to bore it up a lot. I would guess that you can go up to ~280 cc at best.
Lets assume that you`ve bored the engine and had someone manufacture a set of pistons. You will also need new piston rings and new pins, because the pistons are larger.
You would also have to rebuild the engine (new gaskets, bearings, etc..), while it is disassembled, so you can make sure that it will run nice. Considering that you are in the USA - labor and parts for the whole process will cost a few hundred dollars.
Okay, so now you have 30cc more under your seat, but the bike runs worse. Why?
To benefit from the larger displacement, you will have to push more fuel in the cylinder. You will have to tune your carbs properly. Keihin CVs are good (I`ve seen cars running with them), so new needles or a jet kit should do the job.
Pushing more fuel in means that more exhaust gases will come out from the engine. I am not familiar with the Ninja`s exhaust system, but you may need a new one (mufflers and pipes) and/or engine head work.
You fixed your fluids flow, how much power do you get?
Less than 10 hp. Sure, you will get a better power distribution across the RPM range, but is it worth it?
In case you are going to race it in a certain class - go for it, but you will have to do a lot more to be competitive.
In case you are doing it to proof the concept or for fun - go for it, but there are a lot other projects that will yield more results @ the same cost.
If you are thinking that you will make the Ninja faster - yes you will, but the gain will be small, especially considering the expenses. It will be easier to find a larger bike. Even a 300/400 will perform better.
All the best,
zilog