On another forum the conversation came up about '98 (or older) RS250 and all the myths about insane horsepower of a 2 stroke. Quick search gave me a spec of 92 max hp on the last RS250 made which was 10 years later, so my guess a '98 RS would be 90hp at the crank at best?

My RG500 is about 100hp at the wheel so I speculated that it will eat any RS in a straight line, even with extra weight that it carries, as they say here in the colonies, "No replacement for displacement"
Someone came back with a 120 hp number for 250GP bikes and I began to wonder what did they run in 250? Always thought they were "production" RS250 with some extra special parts? Please educate me. Thanks

I think they are just "special parts" but there's quite a few of them.



Aoyama's factory 250.



Rich G's NXA

Even from the photo you can see a different frame, swingarm, forks, brakes, engine, wheels, fairing.

Plus they're jetted perfectly for the day and had a top end that morning.

I don't know what sort of power they're making, probably not 120bhp, but you need well over 100bhp to do the 170+mph they did.


This is the only graph I've seen, allegedly a 2005 works Aprilia, over 90bhp for 2500 rpm....
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Engine wise, there is not much similarity between the last full-house GP250 Honda (2009 RSW) and the last production RS, the NXA.
The RSW had different crankcases, cylinders, PV's, pistons, heads, ECU / PGM, carbs, pipes - see pic.

I was told by an informed source that the last factory 250's (Aprillia) were making around 107 BHP rwhp.
Aoyama's 2009 Honda was not far off them on top end.

For the 98 RS, Honda claim 87 PS, or 86 BHP, and this will be at the crank not rear wheel.
I'd expect maximum of mid 70's BHP at the rear wheel (varying on jetting). Obviously the RS can be tuned significantly.

When comparing to your RG500, is your bike tuned? Standard RG's gave around 80 - 85 BHP at the rear wheel.

But anyway, think about power to weight.
Your RG 500 (tuned?), rear wheel power 100 BHP, dry weight around 155 kg, so p/w = 0.645 BHP per kg.
98 RS, dry weight around 102 kg, so p/w = 0.735 BHP per kg.

If your RG is producing 100 BHP at rear wheel, it may well top out at a higher terminal speed than an RS but not by much, but the RS is going to get to it's terminal speed much faster.
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Rich
MC21 Track Bike / RS250 NF5 'Spencer', NX5 'Cadalora' & NXA 'Aoyama' / RS500 / Two Brothers Racing RC30

Thanks for replies!

The conversation was about the seat of the pants feel and "giving up your right arm" for a ride on the RS after someone posted a picture of the older one with ProArm. My reply was that I can loan him a Gamma if he wants cheap thrill and I was quickly shut down with 120 hp claims. Bear in mind that most of us weigh close to what the dry weight of the RS is, that does kill acceleration of a smaller bike. A 100 kilo American on the 100 kilo race bike calculates to 0.346 hp/kg, might not get ahead of the 150 kilo RG with same 100 kilo rider (0.392hp/kg).


I asked the guy who tunes RG's and was told that on a good day my particular bike might read close to 100 on the dyno, it has Crawford pipes and LG filters, not much else, I only had it few years and have not gone nuts with mods yet. I have to admit when it gets on the pipe it feels like 200hp! Had few much faster bikes but none felt as awesome as the Gamma. One problem with is is handling so I got an NSR, RG stays either way.

There is no way anyone is getting 120hp out of a rs250. The guy is delusional if he thinks he is. Mid 90's is pushing it and most likely kitted.

We don't have many 2 strokes, also people here are naive, will believe anything you tell them.

Couple examples: I had a 900SS in mid 90's, before Ducati was popular in US so many people would see Ducati for the first time and come over to look at it and ask questions. Like all European bikes it has "PASS" button that flashes high beam, I was telling everyone that "PASS" activates Nitrous and everyone believed it! No one ever doubted my claims of 200 mph even though top speed was about 135mph. Usually I would tell them the truth after lying through my teeth for couple minutes and watch the relief on their face knowing that their CBR/GSXR/YZF can still stomp my Duc on the straights. (No one here cares about turning, it's all about top speed)

My friend had RZ500, same story, told everyone it was a GP500 machine and had 180 hp, 200 mph...

Best one is when some kids come over to look at the RG and see 260 number on the clocks, they have no idea that it's KPH and everyone here believes that last number on speedometer is actual top speed. More than once I overheard excited teenager telling his buddies "Look! This can go 260!!"

Leighton Walker's NXA after mucho work by Mark Dent;


Mark's dyno is the one used by Bemsee for their cheat catching and restricted power classes, it's generally considered to read about 7% down on the typical Dynojet dyno.
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Impressive power! A look at Leighton's website reveals the following mods, as well as Mark Dent's tune:

Harc-pro kit cylinders
Harc-pro kit heads
Harc-pro kit ECU
Harc-pro kit Gear position sensor
Harc-pro kit exhausts & silencers
Special modded airbox
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Rich
MC21 Track Bike / RS250 NF5 'Spencer', NX5 'Cadalora' & NXA 'Aoyama' / RS500 / Two Brothers Racing RC30

found this

Matt@TYGA wrote:Who knows the real truth about factory horse power? Not I. The A kitted RS250 in '98 (was a '97 NSR250 factory engine) put out 91 horse at the wheel. The factory bikes were about 98~100 back then, with the Aprilia the only one over the magic ton, at about 104.

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As far i know, my friends Aprilia RSW250GP it's about 92hp in her best setup ( 5 times european champion with this bike ), and factory ones were over 100 ( that's in 2005 ), i suppose that the last factory ones were over 105 ( the best ones ). Of course, my friend's bike it's not "standar" spec, but it's far away from the factory ones. He was wilcard at some races and the factory bikes were easy 20 km/h faster, not to mention the tyres ...

Before the Apri, he has a TZ250 ( ex D'Antin team ) before that he had a TSR, and the first 250 he had was a 1998 RS250, if my memory dont fail, TZ was about 85hp ( year 2000 ), and i dont remember anything about the TSR and RS, but i can ask if somebody wants.

120hp in a 250 .... with Turbo ??

fontyyy wrote:Leighton Walker's NXA after mucho work by Mark Dent;


Mark's dyno is the one used by Bemsee for their cheat catching and restricted power classes, it's generally considered to read about 7% down on the typical Dynojet dyno.

Impressive result with harc-pro parts ....

7% down ... uh, 91hp + 7% ... it's near 98hp, i must see that !!!

Some of the factory bikes were definately over 100bhp, as Fontyyy says, the maths are there for anyone to calculate: Q. what bhp does it take to reach 170mph? I was lucky enough to have a full kit JHA (but customer) Honda RS250 NX5, year 2000 and it gave 82bhp - it was fast, but what 100+bhp must be like is something to day dream about.
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I seem to remember reading an Alan Cathcart article in Racer Magazine which stated the KTM250 had 111bhp. Not sure if this was at the crank.

A good friend of mine (Elliot Burgess) use to race an RS250 in the 90's. I asked hime what he got from his bike...

When he got his 250 from Japan it had 68Bhp. The team set it up and got 73/74 ish/Bhp, tuned, it didn't make any more BHP, but gained so much more mid-range! loads of torque! i.e Say 50 bhp at 9000 rpm before, it was nearer 60Bhp after a fettle! All down to crank tune, ignition, airbox, new heads and pipes.

Also to note the bike was only 100KG!!!
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Thompster (aka Simon)

Hey Thompster, i remember Elliot, a good 250 rider, won the ACU 250 championship, when i think it was called the ACU star championship, or something along those lines.
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