Good morning all,

A bit of a post here...
As someone who has raced RGV's and Honda RS250's, I am currently toying with the idea of racing an NSR. I am looking at either an MC18 or MC21 and preferably an F3.
I know that back in the day at Derby Phoenix in the F400 (F250) there were a few NSR's raced, but by that time I had moved to GP bikes, so I never really got a good look at one (either in the paddock or on track). I am after knowing what sort of power can be got out of these bikes, with tuning and possible earlier Honda RS25O parts, cylinders, carbs etc. Also I wonder if anyone has a dyno print out that they would be willing to share?
Also what sort of weight these bikes can be reduced to, would also be helpful.
Any other advice or tips would be great!

Many thanks,

Mike
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Runner up Derby Phoenix open 250 2006

The best MC21 F3 I've seen made 74rwhp on pump U/L.



It apparently broke the 75rwhp towards the end of last year, but I didn't witness the run in person, however I don't have any reason not to believe it happened. I think that run was with new heads and on AVGAS. The bike was built and maintained by StephenRC45, who works at GT Performance Engineering in Plymouth, but I understand it has now been sold.

Unquestionably, the MC21 is the best NSR250R chassis. The MC18 is twitchy, but still good, but the MC21 is definitely superior.

Without going into all the intricacies, [very] basically, the later the year, the better the package. However, whilst the most powerful, the MC21 is also the heaviest. Not to say the earlier bikes are bad in any way; the 1987 MC16 F3 is rated at 65ps out of the box on 28mm carbs and analogue electronics, but if you can get a 90/91, that's the one to go for.

HRC TT-F3 quoted figures:

1987 MC16 65ps
1988 MC18 68ps
1989 MC18 70ps
1990 MC21 72ps

Lightest I've seen an MC21 is 112kg, if memory serves me correct. Matt@TYGA says he got his down to 110kg back in the day. Generally, I think slimming one down to 114-115kg is doing pretty well.

Getting down to the nitty gritty... in my personal opinion, and real-world experience, you're wasting your time with RS250R parts. The NSR250R is very similar to the NF5, especially in TT-F3 form, but it's far from simple to use RS parts. You're far better off using the correct HRC parts, or modified NSR parts. Not saying you can't get RS parts to work, but you're going to really need to know what you're doing, and be prepared to spend a lot of time and money on setup. Many RS parts are, without doubt, better than their NSR equivalent [machined RC Valves, for example], but getting all the NSR & RS parts to work in harmony is an absolute minefield, and the end result is not worthy of the effort.

You can use the 38mm RS250R carbs, but you will sacrifice all the bottom-end and mid-range that the NSR is renowned for, for maybe 500-1000rpm over-rev. StephenRC45's 74rwhp MC21 ran the 32mm HRC carbs, would pull full-throttle from below 4000rpm, and out-grunt an early NX5 out of the corners at Donington. (Obviously the NX5 was noticeably faster.)

https://www.facebook.com/502467319852378/videos/132733854804906

I believe Dan Williams still has his TT-F3 spec MC21 for sale that he won F250 on a few years back.
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Andy.
NSR-WORLD.COM

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Hi Andy,

Thank you for the reply. A lot of good information there. Thank you for posting the dyno print also. That has certainly given me some food for thought. I wonder how the NSR MC21F3 Chassis compares to other 250 production race bikes, TZR 3XV, RGV VJ22 & VJ23, Aprilia?
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Runner up Derby Phoenix open 250 2006

I think you would be surprised how well an MC21 will perform with just a sprinkling of HRC bits, ie, jet kit, loom, stuffers, pod filters, ( ram air ), or open carbs, and a decent set of pipes, I had this set up on my 21 with good results, I also think if you go chucking NF5 stuff at it, as Andy said it starts getting complicated to set up, and with the big HP comes the too frequent rebuilds, and you are then getting into RS250 territory, but you probably know all this, good luck whichever way you go.
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Proud Father of , 05 ktm 400exc supermoto 2018 honda crf rx supermoto

rgv mike wrote:Hi Andy,

Thank you for the reply. A lot of good information there. Thank you for posting the dyno print also. That has certainly given me some food for thought. I wonder how the NSR MC21F3 Chassis compares to other 250 production race bikes, TZR 3XV, RGV VJ22 & VJ23, Aprilia?

I spoke to Matt@TYGA earlier, as the weights were niggling me. I was trying to remember something from about 15 years ago... and now it's niggling him too! 🤣🤣🤣

He says when racing, his MC21 was bang on the 116kg limit (Asia Roadrace). His street bike was 115kg, and says 110kg definitely sounds familiar, but can't remember for sure either. We think with a bike full of Ti fasteners/fittings/expansion chambers, alloy screen brace/subframe/instrument mount etc., and carbon bodywork/tank, you could get down to about 105kg these days.... but it would be cheaper to buy an NF5!

Matt has always said his 3XV was a better chassis than his MC21, although [if rules allow] that can be fixed with HRC USD forks. He also said out-of-the-box, the Sugo kitted 3XV was consistently more powerful, but with fine tuning the MC21 was equally as good, if not better. Overall though, he'd always prefer both the Honda's characteristics, and ease of use/maintenance, but it's a very close call. The NSR is exceptionally simple to work on in race trim, compared to the TZR and RGV/RS. (F3 spec is essentially the same as an RS250R NF5)

As Les says, a well worked MC21 with a few choice parts is a cracking bike. Mine makes 66.5rwhp, and still runs OEM twin ring pistons and standard PGM-III ignition. It also runs period Ethos pipes from the early 90s, and I am sure would be be better with new TYGAs. (I just love my Ethos pipes though, and have never seen another set!)



Exactly the same setup (no jetting changes), but with a set of peaky pipes made by Martin77, saw it make 67.4hp that day.

If you want a good NSR250R motor, the only place to go in the UK is Performance Engineering. Hand on heart, I can say no one in the UK knows them better than Steve.
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Andy.
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The aspect of being easily able to work on the bike in the paddock is, to me a big aspect. Having raced a NX5, I find production bikes rather annoying in how they are put together and how most jobs are that little bit harder/time consuming compared to a GP bike. I have seen the pictures on GT performance engineering's FB page of the F3-MC21 and it certainly seems so much more like pukka race bike, rather than how a RGV is!
Once again thank you very much for the information
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Runner up Derby Phoenix open 250 2006

The RS250R NF5 crankcases are based on the 1987 NSR250R MC16 (the MC21 cases are purely an evolution of the MC16), and as I say, the F3 is all but RS, but with some mass production based limitations. The biggest inconvenience are the non O-ring heads, which again, rules allowing, can be fixed with VHMs. Also the RC Valve system has 4 cables, 2 direct to each power valve pulley, rather than the more precise dual cable/rose joint setup of the RS, which makes setting and operation a little less accurate.

The carbs are a compound unit, and literally pop off with 2 screws, much to the chagrin of many an RGV and TZR owner, so jetting takes no more than a couple of minutes. Needle changes are by way of quick release retainers, once the two screws on the cover plates are removed, again taking no more that a minute or two to change both. As the carbs are fixed side-by-side with a bracket, it makes one of the air screws a bit of a niggle, but in fairness, these are pretty much "set and forget" really anyway.

The NSR and RS transmissions are virtually identical, and mounted to the same transmission plate, so technically interchangeable, although the NSR clutch and drive are considerably heavier. There are some other minor differences, but irrelevant to this post. The point is that, once again, maintenance is almost GP [RS] like.

Ultimately, and very simplistically, the NX5 is "just" an evolution of the NF5, which was based on the MC16! If anything, the NX5 is slightly more complicated, given that it has a balance shaft!
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Andy.
NSR-WORLD.COM

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Would be great to see an NSR being raced, Dan Williams had a lot of success on his F3 MC21 a few years ago.

If it were me whether you go for F3 or modified production I would go for the MC21 over the MC18 simply because parts availability (new and used) is far greater. Honda still sell new cranks for the 21 (around £700?) the standard pistons which fit all models are still in production.

One of the problems if you went F3 is new piston and crank supplies are long gone (the NF5 and F3 run 14mm little ends as opposed to 15mm standard) I know Dan ran a standard crank and pistons in his F3 (with the double taper NF5 flywheel reground to suit) because of this and his bike still produced very good power I believe.

Tyga have a good range of stuff and are still developing new parts for the MC21, all their exhaust system and rear set parts are sold individually as well so good for crash damage repairs Andy might know if they have any other performance parts in the pipeline?

I have a MC21 track day bike which is currently running a standard dry clutch engine with HRC air tray, pod filters and JHA pipes which makes and makes around 59 bhp on Krazy Katts dyno.

Chassis wise I have an alloy sub frame, fibre glass race bodywork, HRC loom (basically standard loom with the road stuff deleted) NX5 forks and brakes, HRC tacho, Tyga temp gauge, NF5 magtek wheels, NF5/F3 rear brake system, Tyga rear sets, F3 rear shock and probably a few other bits and bobs.

I have yet to weigh it but I have a couple of stock NSR's and a NF5 just pushing it around the workshop the weight difference is really noticeable compared to stock but obviously still feels a little heavier than the NF5.

Hi Paul,

Thanks for the information, especially about the F3 cranks and pistons, something to definitely think about. I have seen that SP125-Racing are selling the 14mm NF5 small end bearings and pistons on Ebay. Are the cranks rebuildable?
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Runner up Derby Phoenix open 250 2006

rgv mike wrote:Hi Paul, Are the cranks rebuildable?

Yes and no! In common with NF5 and NX5 cranks the NSR cranks were designed as a consumable part so Honda never sold rebuild kits but they are rebuildable to a point. The big end pin is integral to the crank web so it is dependent on this being in usable condition and also the con rods being serviceable, the original main bearings are manufactured by Koyo and several people have managed to source these in the past. The centre main bearing has an integral seal on the MC21 and the outer crank seals are standard NSR parts still available from Honda.

have never had an F3 crank in my hand but I believe they are a cross between the NF5 and Roadbike and have the larger "tin" covered flywheels like the NF5, the NF5 con rods and the double taper for the NF5 flywheel. But as I have never seen one in the flesh please don't take this as gospel.

71.13bhp at the rear wheel on AV gas.

Completely stock 1990 NSR 250 RK TT-F3 with a 0.6mm base gasket and less than aggressive jetting and no ignition advance. As Andy said the book quotes 72ps and they make this easily.
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"............should have bought a Honda"