I'm considering getting an NSR250 (probably an MC21, as they're fairly common here in Australia). I was wondering, how much power is possible from the engine, and how hard is it to get?

I don't mind the idea of the 300 kit from Tyga, as a more mid-range oriented power curve might make getting used to a stroker easier. With the 300 kit, what other modifications (apart from exhaust and removing restrictor and such) would I need to get 80HP? Has anyone here got one with that much power? What are some realistic figures from just the 300 kit and other small mods?

The other thing is - what transmission mods would be needed if it did make 80HP? Can the stock MC21 handle that much power?

http://nsr250.net/forums/viewtopic.php?t=3827
_________________
MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball

Thanks David, hadn't seen that thread yet - although fonty stresses a million times in there that it's for 250cc bikes only, and those legal for 250 proddie racing. There's power to be had from a 300 kit, and so I'm more interested in such bikes.

Sure, just thought I'd give you an idea of what's available from the 250. To be honest - and having not ridden a 300 - the two stroke engine isn't meant to be about big numbers as much as the way it delivers those numbers.

The feedback from the 300 kit seems to be that they're fast but not as fun to ride, as there's no discernable step in power which pings you forward at 7000rpm. And that's the most fun part about two strokes. an old RD350 or TZR 250 are really top fun even though they make a lot less than 80hp.

It's all in the delivery darling!
_________________
MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball

If you can get 80 bhp out a 300 then all power to you, maybe 70 or so with a really good midrange is all anyone seems to get, considerably faster than a "normal" 250 but there's similar (if not more) power in the 250 if you look hard enough.

I believe Matt's had a lot more out of the 300 but with some hefty mods.
_________________
Please do not PM me technical questions, if you can't find it on the Forum start a thread

Thanks fonty, much appreciated.

We did an MC28/300 (MC21 flywheel) on the dyno this weekend... 55hp.

I know the motor is good, as I supplied a brand new crank for it, and everything was carefully measured before assembly.

The power delivery one the road makes it very useable though, with loads of power from very low down.

There's 80hp inside a 300 kit somewhere, but as Fontyyy says, getting it out is no mean feat! You fit a 300 if you want all brand new parts instead of repairing and replating 250 parts.

You'll see 60hp out of an MC21 for pennies, low to mid 60's depending on the condition and setup of the motor. Mid to upper 60's once you get insided the motor a bit, and nearer 70hp with some extensive modifications.

Over 70hp is possible, as can be seen by the MC21F3 graph in Dave's link, but you are talking a lot of work and a lot of money. Also, that 250 makes even more torque than a 70hp 300!
_________________
Andy.
NSR-WORLD.COM

Please keep all responses to Forum posts on the Forum so that others may benefit.

Please DO NOT PM me for technical advice. My time is precious, and you will probably receive a faster response on the Forum anyway.

Check us out on Facebook! Please "like" our page!

Andy wrote:
You'll see 60hp out of an MC21 for pennies

cost me no more than a bit a time on the dyno to get 60.5 from my stock mc21 with no more than a moded air box, Swarbrick cans and wire/gps splice.

I think that if you could get a set of pipes that are designed for the 300 kit, it would perform better than the 250 pipes and perhaps be good for a few more hp.

Joel

Your right they would but Andy and Stephen have looked in to this and the chamber on the NSR 150 is alot bigger than the 250 so if you made 2 up then they would be too big to fit inside the fairing's and you would have very little ground clearance when you try to lean the bike over and not much clearance from the ground to the underside of the chamber's.
_________________
Harley Davidson is the worlds most efficient way to turn petrol into noise without the harmful side effect of horsepower.

For sure there is a possibility of 300 specific pipes making a difference somewhere, but it's not the be-all and end-all of the problem.

StephenRC45's MC21/300 made 70hp, but it was by no way a standard 300 kit by the time it was making half decent power, and my '21SE would still reel it in if he so much as even slightly over-revved it, due to power not so much tailing off, but more like hitting a brick wall! There was no doubt it was a quick bike, but it was no hot 250!!

Like I say, if you want all new bits, then buy a 300, but if you want a proper motor, build a 250!!
_________________
Andy.
NSR-WORLD.COM

Please keep all responses to Forum posts on the Forum so that others may benefit.

Please DO NOT PM me for technical advice. My time is precious, and you will probably receive a faster response on the Forum anyway.

Check us out on Facebook! Please "like" our page!

The 300 is a very good road bike, but like Andy says its not much faster if at all than a good 250. They make great midrange and low speed riding is much improved over a 250. However once you get motoring the 250 wins out. After quite abit of work I managed (with the help of Matt) to get my 300 to make just over 70bhp. This was a around 7bhp better than my road going 250 and like I said as a road bike it was great.

I then turned back to 250's and put the 300 away. That was close to a year ago, since then I've manged to get my 250 to produce more peak power and more peak torque than the 300. The 300 does still make more torque and power in the midrange but not by a huge amount any more. Where the 250 really scores is in over-rev. The 250 just keeps on going. The 300 makes 70bhp for around 150rpm compaired to the 250's 600rpm. The 250 also drops off alot less letting you really rev the 250 where the 300 just can't do this.

There will be more gains to be had from the 300 but you are always drawn back by the design of the cylinder, at the end of the day that cylinder was designed to make around 28bhp so to get 70bhp out of a pair of them is already doing rather well.

NSR300 vs NSR250F3


_________________
If I have to take the carbs off once more...