Dirt bike engines in GP bikes?

Anyone have any success/failure using dirt bike engines in GP chassis? The engines seem to be a lot more readily available than honda RS bikes now.

 

Yes, the Moriwaki uses a Honda CRF250x motor. My son's has been very reliable, just check the valves and change the oil every weekend.

 

I'm not sure if your talking 2 stroke of 4 stroke but.... I have a pretty trick project for sale.
Honda Hawk chassis
built KX500 engine
GSXR750 front end
etc etc etc etc etc etc $1500. 79hp and 218lbs

Joe Pommary(spell check) has a built Banshee engine in an Aprillia RS250 chassis.

I got my ass kicked by a Yamaha 450 super single at Nashville... lol

 

It was a Honda, but might not be the best example. It dropped a valve in DSBK. It was super reliable for the first 2.5 years that I had it. It became less reliable the more power I got out of it.

 

O...well...it was a Honda that kicked our asses at Nashville then. lol The guy on the Yamaha Motard was killin it too though.

 

Reliable... and FAST!!

 

I'm currently in a build right now with an RS125 chassis and CRF450X motor. I've seen a couple others that have done the same except using the CRF450R motor. Their biggest complaint was the difficulty in starting after stalling or crashing. I'm hoping the X will alleviate those issues.

The X motor has slightly different cases so it required a bit more hacking of the 125 frame to make it work. Right now everything is bolted in. Just finishing the exhaust and modifying the tank. Then route the electrical system and it should be rolling around Pacific in less than a month.

The R motor definitely has more HP than the X but the X has a wide ratio 5 gear that should help. It also shouldn't be too difficult to boost HP as I develop the thing. Simple stuff like an 07 R head, stainless valves, Ron Hamp cam, etc. The idea is to produce decent power but keep it fairly reliable.

The GP bikes are getting cheaper and cheaper. That's mostly why I went ahead with the butchering of my spare 125. You could grab a 95 RS125 for less than 3K. Then surf craigslist and find a CRF450R (or X) for less than 2.5K. If you can weld and fabricate, then you could have a hell of a bike for 6K or less. The guy who has one here dominates the singles class and is pretty much a cheater bike against the SV's.

50+ hp depending on build...could be much higher if you like to ride that line... With a total weight of around 180 lbs and the handling of a 125. I'm so looking forward to riding mine.

 

Oh, I meant specifically 2-stroke. I'm thinking of building a 125. Wondering if it could be competitive with Honda RS's and Yamaha TZ's? I bought an Aprilia RS a few years back thinking I could run with the Hondas and Yams but found out it's not a "real" GP bike. Brilliant machine but I'd like to compete in maybe USGPRU and I don't want to be 10+hp down on the rest of the grid. How are they on horsepower?

 

I'll qualify this in saying "all dyno's are different"

Draik has a 96 Honda RS125R with two base gaskets on it to "de-tune" it.

39hp...

 

USGPRU a stock RS needs a great rider to compete. Most are 48 to 52 HP. Stock RS on the same dyno would be about 35 HP.

 

I have a CR125 engine in a YSR. *Shrugs*

It's also for sale.

 

So, I'm a bit confused. If you mean how competitive is a dirtbike 2 stroke 125 engine in an RS chassis, I've never seen it done but don't think it would be stellar. The RS's are pretty tuned from the factory and even the previous RS125 89-94 engine doesn't run with the 95 and up RS and TZ's.

A stock Moriwaki with a Honda CRF250x motor makes between 29-35 depending on altitude and the dyno.

Tyler just won a few races the past couple of weekends running a Hotrod Moriwaki against 125's at WERA and USGPRU. If you want to race you would be much more successful putting in a 4 stroke Honda CRF250R or X dirtbike motor than you would putting in a dirtbike 2 stroke 125.

I hope this helps, feel free to ask me questions.

 

Casey Tobolewski was @ NJMP on Saturday haulin' some serious butt on one of these MD250H's

 

:wow:, where did you get those figures??? The 35hp stock is right. The 2009 National champ (for sale btw) put out a whopping 42 HP(corrected)! If you have a 40hp 125, you have a good running motor.

 

^^^^^ That's correct. The most I've heard out of an RS is 45-46 and that was with a true MotoGP HRC Honda RS125 with full HRC kit parts and powervalves. There is a guy that owns a couple of them here in S. Cal and has a dyno. On that same Dyno our Hotrod made 39.9HP.

 

i have built some 500 two stroke roadracers, and it was difficult to make them competitive. i would think a two stroke 125 dirtbike engine would not even be close to competitive to a rs 125 or tz125. first would be the gearing and then the hp would be down. by the time you made it have enough power, you would have spent more money than just buying a real 125 and you would have many one off custom parts on it. fun for a project, but competitive? i dont think so.

 

Decades ago the Kawasaki "Big Horn" was a 350cc single dirt bike engine (F9) in a roadracing frame. But that was because the AMA rules at the time allowed a 350 single to compete in the 250cc class. Even with an extra 100cc, it wasn't really competitive with the fastest TZ250s.

 

I wouldnt think a 125cc smoker would be goof for much on our road race tracks...

 

Wait...let me get this straight. You're looking to put a CR125 (or equivalent) motor into an RS125 chassis?

Seems like a waste of effort to me. Less power, different tranny, need for new front sprocket, etc.

 

not even in your wildest dreams