Hi Guys, some advise from those who may know. I plan to run my MC18R5 as a period 6, historic race bike, 1983 to 1990. And I'm trying to keep things simple by not running to many systems on the bike that will just complicate things. This is what I have done and plan to do and I'd like anyone who has done so or just has an opinion to comment as to whether it would be beneficial or stuff the whole thing.

blanked off, plugged the powerjets
blanked off the Air solenoid system and done away with the solenoids
turn down the flywheel
removed the RC valve servo and fixed the exhaust valves in the full open position
remove the material in the exhaust ports to match up with the pipes/chambers
cut ports to a 34 degrees blow down
run single ring pistons
cut out the cast in flow deflectors out of the intake tracks
shape up the the cylinder material at the boost ports
get rid of all the unused stuff from the electrical loom, including battery.

Most of it is what you'd call basic tuning, and I am kinda dumbing the engine down, but I think it should work like a normal 2stroke.

That's going to run like crap!
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Vampire?

Most of that list is useless...

Best idea, and about the only one worth doing on it, is to blank the power jets.
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Vampire?

running the powert valves wide open is a pretty poor idea, you'll lose power all the way up to about 10500rpm.

No battery is a terrible idea, the NSRs are mega sensitive to voltage.
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You don't want to be removing the deflectors in the inlet tracks either, you need to be building them up.
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If I have to take the carbs off once more...

You can run single ring pistons, but you need to make sure both the crown height and shape is accounted for. This will entail machining both the barrels and the heads... so again, complicating an otherwise as-good-as perfect motor.
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Andy.
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Thanks , kinda what I expected in some sense, I already have the pistons and done the squish, its good, with a little work to be done on matching up to the transfer at BDC. I get the answer for the deflectors thanks, Ill leave them alone but I can not (RC valves) see how power will be lost ? A bit of tractability maybe but not power when your on it. Once again correct me if I'm wrong but don't the RC vales only operate between 0 and 2500rpms? Any way we will dyno it and find out. ....I do take your point Andy, why fiddle about, and how much will be gained, can't help myself I suppose.

My clubmate did similar mods to an RGV and has it doing nearly 80hp. ... dyno tested, with NSR tyga chambers, bumped compression and some experienced porting, running a capsitor instead of a battery with a KX 125 gen and rotor.on pre mix, no air bleeds no exhaust valves, and it goes like stink, though it did, just nip a rear piston last time out.

I also inetnd to run CR125 Vforce reeds, and if possible CBR600 41mm cartridge forks. And if I still have the cash after getting a crank built, either a ohlins or a zeno in the rear.

Firstly, it's not an RGV, so I shouldn't be comparing what they did and trying the same with your NSR.

Secondly, I'm not usre if you've raced before, but having a bike which makes 80hp at 11,000 rpm and sod all elsewhere will have you spat off, going backwards or siezing at every race - unless you are a Doohan like God.

Keeping the powervalves will not rob you of a single horsepower, but it will give you bag loads of it over a much wider spread of revs, so you can get the gearing alittle bit wrong and still stand a chance.

Unless you're planning on swapping gearox cogs at everymeet so you can be in the powerband at every corner?

You'd be better optimizing the engine as a pretty standard setup, and spending money / time on your suspension and brakes. These will allow you to go faster than another 5hp ever will.
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RC valves are closed until around 8,000 rpm then fully open around 12,000rpm depending on what model PGM/RC valve controller you use.

80hp RGV
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If I have to take the carbs off once more...

An 80hp RGV? Even if that were crank horsepower, and was given a very conservative 12.5% drivetrain loss, 70hp at the wheel would be hugely optimistic for the vast majority of RGV's... speaking from experience!
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hey, hey guys don't go to extremes, Ha, I'll try not to and thanks again for the powervalve figures, that will make me think a bit differently, as it's no trouble to leave them operating. But even with them fixed I don't think the stock port timing is going to be that explosive and I have always gone sideways with porting to increase torque, but hey that's why I put my self up here as a target, to get the facts.'

Dave, I have raced a few bikes, NX4 RS 125, Moriwaki MD80, VFR400, RGV/yamaha IT490, NSR/yamaha YZ85, to name a few, and currently run a 1981 Kawasaki KZ750 replica P5 superbike and a yamaha 125. I'm not as fast as I used to be but I love it, titanium collar bones and all. I'm no young bloke for sure. And my days of championships are well over, even club ones.

And as for the, RGV it's true, about 78 to be nearer the mark, he also helped me get close to 28 H.P out of a YZ85 road racer, and get almost 30 out of his honda CRF150 that he runs in a NX4 chassis. He also now has 2 NSR MC18's to play with.

This historic racing period 6 250 production bracket, we now have in this country is about to take off like wild fire, and I have already been admonished for running an NSR, considered over here as not as good as the RGV's when they were run at the time, and it was here in that same 250 production class that the Goberts, McCoys, Corsers, Baylises, Malladins, and Cragills came from so there a pretty good history as to what was good at the time, kit bikes excluded. And can I attach a photo file here?

I have been thinking about the ECU's and what Stephen RC45 said about depending on what unit you use, I have 2, both PGM2, but with different manufactures and numbers. Ones an OKI electrical industries model and the others a Shingenden. I assume they are both the same spec, is there a resource here where I can find out this info, as in the parts manuals or workshop manuals with out hassling members for info.

Any standard R5K or R6K PGM-II will be fine, and will happily work for motors reaching well into the high 60's... maybe even more, but I've not actually seen an MC18 make more than that yet. Not saying they can't, just saying I've not personally seen it.

Unlike some other marques, (standard) PGM swapping has no effect on the NSR. Any PGM-II will produce exactly the same results on any MC18 Mk2, just as and PGM-III will work exactly the same on any MC21. No need to look for any "special" code on them, or PGM's from SP models... they're all essentially the same.
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Dave Ett wrote:
Keeping the powervalves will not rob you of a single horsepower, but it will give you bag loads of it over a much wider spread of revs, so you can get the gearing alittle bit wrong and still stand a chance.

Unless you're planning on swapping gearox cogs at every meet so you can be in the powerband at every corner?

And is if to prove the point, Mark Jordan's proddy 250 lap record holding bike;

I've removed the other trace which was a TZ350 as it was there purely to show how well Mark's bike pulls in the mid range. If he can find another 1000 revs the rest of us may as well just go home!

That is how to build a motor that wins races, making an NSR grunt like that is one hell of a task. Steve's F3 was close though James (who owns the Krazy Katt dyno) would argue his dyno read low.
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Strange that you should put up a dyno graph, as I tried to do the same thing with my PGM post, but got a file to big notice, 256Kb or something similar. So what is it, 63hp rw,@ 10.5 and an nice fat and flat torque cure that also peaks very closely, sounds very nice as does a lap record, sweet. If I were to achieve similar figure I'd be more than happy. Thanks Andy for the PGM info, I'll get them both tested, 1 should work I hope.

I have had this conversation with my RGV mate it goes like this, So a sh*t RS 125 will knock out 35 h.p., a reasonably good one about 40plus, a really good one will do 45, then there's the A & B kit bikes and the timebombs. so if you take 1995 NX4 engine and transfer the porting dimensions, head profile, carby and chamber over to an NSR 250 motor, where are you going to end up on the scale of Horsepower as mentioned above. Say the crap one that only does 35, that's 35 x 2 = 70 ... our conversation ends with starry eyes and a certain amount of anticipation.

Now even if that's not rear wheel horsepower for some reason and you loose 13% through transmission loss, @ 9.1 h.p., then your still left with 60.9 h.p and there are not to many RS125's out there that are as rubbish as 30 h.p. .... we are possibly mad, but it's fun