9/9/2018 5:22 PM
Edited Date/Time: 9/9/2018 5:28 PM
KX500 wrote:
"if you want a significant increase in low end power, you need a big bore kit. period"
I figured this was probably the only ...more
KX500 wrote:
"if you want a significant increase in low end power, you need a big bore kit. period"
I figured this was probably the only way to go, until I realized that with this engine, Big bore is 265 cc - a gain of 15cc. Does that even count as Big bore? I mean with an engine like this, how much do you really gain by increasing displacement by 6%? Honest question as I really don't know.
So then I had to wonder if maybe most of the gains were due to the porting that these shops do in addition to increasing cylinder size. I mean if 80% of big bore gain comes from porting and 20% comes from the bigger bore, I'd probably skip the bigger bore - unless of course my cylinder had damage that need bored away.
I wasn't really considering a sleeve or anything else that really bumps up displacement.
ahhh, ok then. they have bigger bore kits for some other 250 bikes, but yeah, if you are only gaining 15 cc's and are just boring your cylinder out to get it you might put it on the bottom of your list. porting for low end power is not going to make a significant change irregardless of what anyone else says. the single biggest gain in low/mid power would be the gnarly pipe. if you don't like how it runs after that, i don't see any point in doing anything else because it seems to me that you are looking for a BIG improvement in low end, plus you stated that you are not a "revver", and this is why i said that you will not get a big change unless you go to a big bore kit.
in general, reducing compression as one person suggested will REDUCE power throughout the entire power band and that defeats your purpose. in your case you want MORE compression to increase overall torque and low end power, however, this is not practical because you can not increase it enough to make a large change, plus if you increase it, you will need to run some type of race gas which isn't practical or cheap.
if you want to soften the power band so it is not so abrupt but don't want to give away much hp doing that, you can try adding a reed cage spacer between the reed and the cylinder but nobody mentioned that yet. some companies sell them for some bikes.
if you want to modify your existing cylinder to get more low end without boring it out to a big bore size, you must mill the base. there is zero other option. as long as the exhaust port remains at the same height it currently is, you can not get much more low end power.
you can mill the base .5 mm then install a head gasket that is .5 mm thicker to compensate for the shifter cylinder and this will help keep your compression close to what it currently is.
as far as changing gearing as one person mentioned, you should certainly try it if you can't get a 300 cc big bore kit and the cheapest and easiest thing to do would be to get a countershaft sprocket that is one tooth smaller. this will make a big change but it will not change the characteristics of the engine other then it will be easier to keep on the pipe and you will have to shift more often., and far more often than you would with a much bigger displacement engine.
another option would be to install a cylinder from an enduro model if it it will fit because the port timing is much milder. this would have a little more bottom end and a little softer power band but it still won't have a ton of low end power like a 500 cc 2 stroke would.
this being said, in the end, there is simply no replacement for displacement.
