Andy , will you encourage the owners of the seized 300's to post up . Collectivly we must be able to work through it and find out why it is happening . Or else we suffer ridicule and be labbled bush mechanics !
My bike has run as expected and never seized for no reason .when it did - it was a hole in barrel powervalve shaft that caused it (2nd hand ) .
I would never go back to a 250 as I could never get the same performance out of one .
They're fair points Andy and I respect that and each to their own. IMHO, I've not ridden a 250 since my 300s that have been comparable performance wise. A piped and kitted mid 60s 250 feels pretty weak in comparison. Although my tuned 300 made only 2bhp more than my standard one, it felt pretty nasty in comparison. It revved faster than any 250 I've ridden and I was sold as soon as rode it.
Personally, I think it was good for 75-76 with careful set up, and understanding how to make the PWK39s work with the motor. I also realise that it's most likely the pipes restricting them, and need some specifically designed for the motor to see what difference these would make. The pipes I ran with them were early TYGA, and I know that my HARC Pros give another 2 bhp on my old 250 for comparison. Perhaps they'll do the same. They're also lighter which is a bonus! Ultimately, this'll reduce the EGT and with straighter outlets, could solve much of the unreliabilty issues.
Wanting a 250 is correct, but it was the aspiration to own an NXA, not another MC21/28!
My other long term project is to design a bottom end and to make a V4 1000 using CR250 top ends. Then I won't care about 250s and 300s! It's just taking so long to model the crankcases!
Neal: It's still the same spec as is up on this site. _________________ NSR300R - Why did i ever have a 250...
I expect most people who jump on a 300 will "feel" the same as you, and many will jump on one after either a long period of not riding, or after rebuilding what was previously a tired 250. However, my 250 shows a graph that easily matches your 300 (on the same dyno), but a "good" 250SP is lacking considerably behind them both. That SP on the graph is Nigel Moss's... and it's also done a hell of a lot of track days, and has never gone pop either! (Sorry!)
I'm sure if you came to one of our Donington days we could probably get you a ride on Steve's old F3 in exchange for a session on your 300. It would actually be interesting to hear what Andy makes of your bike, given that he's both a 2-stroke and NSR newbie! He's only done one track day on it so far, so everything is still new for him.
And... you want an NX6, you do! It'll probably be cheaper than designing your own V4 too! _________________ Andy.
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The best NSR250 I've ridden was my MC28 racer. On avgas and with lots of modification, ram air and Harc-Pro pipes (1995), it made 76hp on our dyno. The follwing year we couldn't fun SS spec, and the full HRC SP kitted NSR made 69hp on avgas. Mine, with a bit of cheating on the intake side of the carb and an aluminium ignition rotor made 70hp.
An average derestricted/piped NSR250 MC21 on that same dyno made about 62-63hp.
The 300's have gone through quite a few changes. First the compression was too high and suffered detonation, so cylinder heights were changed. Then exhaust port shapes have been played with. Now I cut the exhaust port, the bottom of the cylinder and the rear boost port on the CNC machine. Then blend by hand. The heads started off as NSR150SP heads, but now after experimenting with different squish ratios, they are totally different. They are pretty much the same compression ratio, but have a lower squish velocity. This helped limit detonation and improved over rev.
The best one I've seen is my mule. It's very different to all other 300 kits in that it runs an adjustable ignition and HRC38 carbs, and also ram air. It started life at 70hp (on the same dyno as above) and through continued development the last time it was on the brake it hit 81hp. This was using different pipes too.
The biggest difference was found with the ignition and RC valve timing. I was getting approx 75-76hp using MC21 PGMIII, PGMII F3 & PGMII NF5. But with the ability to mess with everything electronic (and starting with the F3 ignition curve), I dialed it up to about 77-78hp at peak. Playing withe RC valve timing gave another big dollop of midrange.
Then I fitted different pipes and midrange dropped my 3-4hp but added the same up top about 500rpm up the scale. Thes were basically modified NX5 pipes. I cut the header off too, and remodeled it to be a straight fit against the port.
Then a ring end snagged the cylinder wall and left a gouge, which stopped play.
I know why this happened as I'd bee playing with transfer widths and although I'd compensated for new ring movement, it seems that I hadn't accounted for worn rings! and the ring end started to drop into the auxiliary transfer port. Luckily it did no more than gouge the cylinder a tad. Rendering it unusable but at least it didn't grenade the whole thing.
One issue with the 300 is the different angle of the exhaust compared to the 250. So when the 250 pipes are fitted, there is a mismatch, which we get around by using an angled flange. To be honest, there's an angle that exhaust flow doesn't mind, but beyond that it is affected. If and when we look at this flange, unfortunately it is outside that parameter. Not a huge thing but it does affect it. If/when we finally catch up with our two stroke pipes backorder we will make specific 300 pipes.
Pistons have always been a subject of discussion. I have had a cast piston crack on my bike after about one year of abuse. I have never had any trouble with the wiseco.
I tried not drilling the oil holes on the front of the piston at first build, but scuff marks told me that the lubrication was needed.
Looking at Stephen's NSR500 cylinder, I can see hints of my 300. Looks like we've gone along similar routes such as exhaust width and exhaust bulge width (as a percentage of the bore size). And transfer direction and roof angles are very similar. Mine being a tad flatter on the main transfer. Port width as a percentage of bore is again very close. The exhaust and transfer durations are different, but this is obviously because the NSR500 works about 1000rpm lower down the rev range than my engine. The 500 runs to about 12k, mine to 13k.
The RC valve in the NSR500 is of course delicious, and I wish we could find the time and enthusiasm to make then like that for both the NSR250 and 300. Mine is of course welded and ground to be as flush a fit as possible in the port when fully open.
Some of you may have seen the numbers Stephen has posted in the 500 section about squish area ratio etc. Well, consider that the NSR150SP heads were 55% at first, which was causing the high MSV. Now considerably lower, but the 500 still has a lower squish area ratio, so that's something worth considering.
So what's in the future for the 300? Well, I spend hours looking at the cylinders, and I have many ideas, but time is the biggest factor. As it is I have 6 cylinders on the bench to cut now, but they're all done to the usual latest spec.
To be honest, after so long playing with this kit, I'm thinking of keeping it as is. We've sold close to 100 kits since it's inception and I just don't have the 'play time' available that I used to have for this sort of thing. Shame, but that's life in business I suppose.
As a final note, about tuning secrets and what have you.
Andy's right in that learning about this stuff takes years and usually a lot of time and money is involved. We will all help out where we can, but no one is ever gonna tell you everything. And for sure if any of my customer 250's or 300's were on track alongside mine, mine would always be faster
Hi Matt ,
Can you post a comparison between a customer tune 300 and a 250 ?
I feel that Andy has old info on 300's and bases his comments on these .
100 kits sold ! That's great , hopefully they will chime in .
maxim wrote:
My other long term project is to design a bottom end and to make a V4 1000 using CR250 top ends.
I have had a few dreams/ "thought experiments" about doing something like this. Probably fairly common among 2-stroke nutters.
But what puts me off is trying to fit four 250cc pipes on a bike. They are simply going to be too long.
This pretty much made ME give up on the idea.
Comments? _________________ [color=#808080][size=9]Yes,.. I too know how to waste Time and Money,...
I think you'd have a harder time fitting 2x 250 pots side-by-side on a compact crankcase than fitting pipes to it, because surely if you were going to make a V4, two pipes would exit under the seat?
Better off, in my opinion, to attempt a 500 V-twin. Everything about a 1000cc V4 is impractical. _________________ Andy.
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Yeah, the two rear pipes exiting under the seat would be quite big. Possibly too big? I'm especially thinking too long?
As you say, V4 1000 = pretty impractical.
It would be interesting to know, as you increase the cc of a V4 two stroke (in total design), what becomes the main difficulty in terms of a race track capable motorbike, and what cc is practically achievable. Not exactly a well defined question I know, but you get my drift. _________________ [color=#808080][size=9]Yes,.. I too know how to waste Time and Money,...
If I had the money and the facilities, it would be a 500cc V4. Everything about it is right... from the physical size of the motor, to the power output, which I guess is why it was the premier class for so long.
If you were to build one from scratch using MX barrels as a base, up to 576cc would be available. 160hp would be a realistic goal. Any less would be a waste of effort, much more would become financially unviable. _________________ Andy.
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Please DO NOT PM me for technical advice. My time is precious, and you will probably receive a faster response on the Forum anyway.
I think you'd have a harder time fitting 2x 250 pots side-by-side on a compact crankcase than fitting pipes to it, because surely if you were going to make a V4, two pipes would exit under the seat?
Better off, in my opinion, to attempt a 500 V-twin. Everything about a 1000cc V4 is impractical.
Hi Andy,
Totally agree with you, in my opinion would be better to attempt a 500 V2.
My thought from a long, long time was to replicate the NX6 engine. how much would cost to replicate it?
I mean, sand mould for the crankcases and cylinders would be the most expensive part of the project. I was discussing about this option with some italian people involved in the creation of the RSA's and they are open to do it if there are some people interested as they need to produce a minimum series, otherwise would be absolutely anti economical.
The problem there is that there were less than 40 NX6's ever made, so spares a extremely rare. Steve's problem at the moment is finding a clutch cover for his spare motor, so finding cases and a cover for someone to take casts from is going to be near impossible.
On the other hand though, getting a barrel to duplicate wouldn't be a problem, nor would measuring crankcase volumes and crank dimensions be either. _________________ Andy.
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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.
A friend has offered to cnc new barrels from billet if needed when hrc run out of stock. So far though top end parts are not an issue. I think 300's would go much better with a dedicated set of pipes and crank cases but this defeats the object of the kit. _________________ If I have to take the carbs off once more...
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