hi everyone im new here the site and forums look great. like most you here i am a two stroke nut. anyways i was wondering if there are any physical differences between the mc28 and mc21 engines. also i was wondering if anyone has one of these engines for sale as i am looking to buy one to start my supermoto project. anyhow what do you guys think of say an nsr300 supermoto 70bhp and 105kg anyone yum yum.

cheers juan...

There are several differences but none that matter with regards to fitting or crossing over any parts.

The '28 engine is less powerful as it's barrels are ported less for top end power and it's flywheel has less timing advance.
The '28 crank is (apparently) better.
If you've got the whole lot the '28 carbs are more annoying to work on as the needles are near impossible to swap with the carbs in place.
The '28 has the boost bottle on the air box.

But as a whole you can bolt an entire '21 engine into a 28 or vise versa and swap barrels, cranks etc. without concern.

I think a 70bhp 250 sounds nicer
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hi fonty cheers for the info i think i will be going for the 28 simply for the fact that it is the latest engine but if a 21 engine pops up i may use that. i know this sounds a bit strange but the bike i want to build will be a sort of concept along the lines of aprilias sxv supermoto bikes except my bike will probly be some sort of cr/crf frame adapted to take an nsr 250 engine, i was just wondering what you guys thought of my idea of an nsr250/300 supermoto/crosser?

cheers juan...

Hi Juan

In regards to your engine / bike idea i like the idea but the reality may not be a particularly competitve bike......

I have raced Supermoto, Supermotard, 250 Production/F3 (RGV's, NSR's etc) and currently Motocross (CRF450).

The problem (i believe) you will have is a major lack of torque and lacking a broad power curve, which is how those bikes can go so fast with such little outright HP.

A friend and i are also building a crf450 in to an NSR frame (very slowly, and the project may have stalled..!) and the engines actually weigh about the same, so no gain there.

Like i said, it would be a great project bike but if winning races is your goal i suspect you may not be quite on the right track.....

Perhaps the 300cc kit would even things up a bit....?

Good luck.


Mark

hi rgv i understand what you mean bout this bike not being competitive which is why i have thought about this bike as a street project im just thinking that this engine would be great fun just as a street/fun bike and yes with a 300 kit it may well be competitive . also i think the 300 kit would be a good method of counteracting the effect of not having the wind protection of an nsr. i was just wondering surley someone must have tried this before as this really would be my idea of a perfect bike a 250 supermoto vtwin with a crazy two stroke powerband, i reckon if honda made a bike like this it would sell like hot cakes, well to us two stroke nuts at least:_)

NSR250 makes more torque than a CBR400!

If you want grunt out of a 2-stroke, tune the MC21 motor to F3 spec!



There's nothing wrong with that power curve, and that motor has even more grunt now it's been fine tuned!
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I say go for it. I'm all into strange ideas, and why the heck not. Who cares if it's not competitive if you're just going to hoon around the streets on it. One of the best times I had was chasing a YSR80 round the streetsand through the traffic. I was getting left on the straights, but was making up ground in the traffic jams. I was on an NSR50

I've got my old CR500 frame propping up the workshop wall, and I keep threatening to put an NSR250 motor in it just for a laugh. But then again, after looking at those crossers that the US blokes are turning into road racers, and that seems like a project for my CR500 SM to get into.

cheers for the graph andy, matt- i agree strange ideas are the best because although i was thinking of a doing a kx500 ally framed supermoto which we all know would be a hell of a bike its just that i dont think an nsr250 supermoto has been done before it unique and still a hoot to ride, maybe people have never tried this before because it sems too complicated but i think it should be possible and if so im gunna have a go at it.
on another note i have some more elaborate plans which are just pipeline dreams i.e megasquirt fuel injection which has been done on and rz350 and it improved the bottom end and made it very smooth. anyway too many ideas at one time now i just need an engine so if anyone has a nsr250 engine for sale please let me know as i would be interested in buying either a mc21 or an mc28 it doesnt matter if the topend is in a bad way or if it has no top end as i plan on fitting a 300 kit to it.

also i have a question for matt, i was just wondering is the 300cc cylinder and head any taller than the standard setup?

ps i am in south devon uk

cheers for all the help. juan..

anyone heard of tdr250. its the same sort of idea. i ran one for almost a year as everyday transport and it was great fun. although you need grunt on the supermotos you'll be running much lower gearing and that will help keep it in the power all the time.
the tdr was fun but if you can get anywhere near 70 bhp and 105kgs it'll be awesome
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Where in South Devon Juan? I am (usually) in Exmouth. StephenRC45 (who's F3 graph I posted) is in Plymouth - ours are the two Cup Noodle bikes on the homepage.

Maybe we'll need to meet up when I am back in the UK soon. Interested to see how you get on with the idea!
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hi andy i am near newton abbot and go to college there, the nsr project is a bit of dream at the moment as i am just trying to finish my ally framed crm250ar at the moment which didnt go that well and this is why when i do the nsr project it is probably going to involve alot of planning but its going to happen for sure. at the moment i am thinking of what frame would be best for the nsr engine thats why at the moment i am trying to get hold of an engine so i can get an idea of the size and dimensions. it would be nice too meet up and have a look at your bike as i have never actually seen an nsr in the flesh.
anyway enough waffaling for now.

ill let you know when ive finished my crm project (soon hopefully) then maybe we could meet up and have a chat.

thanks for the help juan..

Actually Sandking raises a good point, with the bike geared to max out at say 160-170 km / hour the torque and power may very well be competitve, and a lot of fun.

Even the CRF450 geared for road racing feels like a limp biscuit. They feel very slow but still seem to hustle around bloody quick, actually a bit boring until you get in the groove properly.

Your project geared down for the kart / supermoto tracks may very well have enough grunt to be competitve.

As i mentioned, the engines weigh the same so whilst there is no advantage, there is also no disadvantage!

Good luck.

Mark

hey rgv i think your porbably right about the gearing. As i think with the right gearing and tuned to the limit a 250 v twin would give a crf an ass woopin.i was just wondering are there rules against racing v twins in motorcross or supermoto??

cheers juan...

Hi Juan

I don't believe there are issues within supermoto re v-twins (i.e Aprilia RXV450/550 v-twin) but there is potentially an issue with motocross.

AMA (american) MX regs has previousley had a singles only policy but Aprilia are trying hard to get this changed, a lot of countries follow either the AMA or the FIM rules pretty closely.

Not sure what set of rules various countries follow, however, unless your at national level i can't see it being too much of an issue.....

Mark

hey mark, i think that if aprilia do use there posistion to get the rules changed it may give the two strokes a foot back in the door as i hear that the 125 two strokes are now allowed up to 144cc and ktm have already made a production 144 and its also a possibilty that the 250 two strokes are going to change to 300cc two strokes, if this were the case then surely a geared down and tuned nsr300 engine would give the fourstrokes a little something to worry about .

here in england dep run a 125 two stroke challenge they are also planning or already have started an open class challenge, so in actual fact there is some good news for the two strokes.

juan..