highest horsepower potential 125cc motor?

[reckon]

some of you guys are so good at motorcycle trivia, I thought maybe I could ask for some help:

what is the highest horsepower potential 125cc motor in your opinion?

I am building a 125cc speed record bike, and had planned on using a nitrous injected RD125LC yamaha twin two stroke motor, but a motor guru I know said I could get more rpms, and horsepower out of a supercharged 4 stroke 125CC twin.

anyone care to chime in a brand, or motor manufacturer?

torque really doesn't matter, and as far as durability goes it only needs to survive a 2 mile full power run, three times to make it.
power adders are allowed, as is nitrous oxide and turbochargers too,......

so if you are building a fantasy 125cc motor, how would you go at it?


thanks in advance for any information


:teeth

 

[squid vicious]

No info for you, unfortunately, but do keep us posted on your progress!

How fast are you aiming for?

 

[reckon]

posted by squid vicious
No info for you, unfortunately, but do keep us posted on your progress!

How fast are you aiming for?

to break H.P. Mullers 50 year old record of 150.00mph (obviously I need to go faster than that)


gives me something to do when it rains :teeth

 

[uhmeebuh]

gives me something to do when it rains :teeth

It's supposed to rain tomorrow - you wanna do a valve adjustment on my bike? :teeth

Seriously - 150mph?!? Any idea what kind of set up Mr Muller used 50 (!!!) years ago? It takes a serious amount of power to push through that much wind. I'm guessing a 2 stroke with nitrous and a turbo/supercharger. I think you would want to make it light but not so much that it would get blown around... What kind of faring?

 

[allergic2death]

my buddy had a 2004 kx 125 two stroke that was way faster than i thought a 125 could go! cool project sounds do able with all the different metal hardening processes they have now

 

[billswim]

I would think you'd be better off starting with something a litle more modern like a 125 2 stroke single from a newer dirt bike or a GP bike but the dirt bike parts would be much more available and cheaper. I'm not very knowlegable about 2-strokes and nitrous but I do think you can turbo charge 'em fairly easily.

I've been involved in a couple of car speed record attempts and let me tell you something...aerodynamics are the key! We were pushing 200 mph witha 2.0 litre car and after our first effort we did some calculations and we needed 18 more hp per MPH after about 180mph OR we needed to get the drag down. We chopped the car, shaved everything that stuck out and taped up all the gaps, making the car as smooth as possible and with the same motor went 15 mph faster! Next time we had a more powerful motor and a slipperier car and went over the 200 MPH mark.

 

[oliver]

I would think you'd be better off starting with something a litle more modern like a 125 2 stroke single from a newer dirt bike or a GP bike but the dirt bike parts would be much more available and cheaper.

I used to race 125cc karts a few years ago, and the last race I ever did was at Fontana. Normally, we'd run on 3/4 mile-ish "sprint" road courses, which allowed speeds of only 95mph at the most. But at Fontana the kart could actually reach its top natural speed of (in my case) just under 120mph. These were still (unfaired) sprint karts and thus had roughly the aerodynamics of a sail. Better bodywork would yield approx 125mph.

We were putting out about 44HP from a naturally aspirated Honda CR125 two-stroke dirt bike motor. Rules allowed a programable ignition, but there were many rules governing just about everything else, including the (still large) bored-out 38mm carburetor. I would think that another N/A 5HP would have been possible if the rules were thrown away.

I would also think that a motorcycle has better aero than a kart, and would be good for what...maybe 125-130 MPH with the same power? That's not that far off, and I have a buddy who has pretty extensive experience with two-stroke nitrous applications...:shhh

 

[Joebar4000]

Honda made some 6 cylinder screamers back before the rules changed.

Swissauto made a 250cc inline 4 with an enormous turbo that pushed out 250+hp at something silly like 26,000 rpm, but it only had a 1" stroke.

Your best bet might be to start looking for Japanese market 125 4 stroke and put a big turbo on it. I don't think you'll get much more than 50hp out of a 125cc 2 stroke - that's about what the factory teams were getting per cylinder from the 2-stroke MotoGP bikes.

Frankly, it'd probably be easier to build your own using a 250cc inline 4 either sleeved down, or with a reduced stroke. Lotsa work either way. Most off the shelf 125 multis couldn't pull the skin off a rice pudding...

 

[stangmx13]

isnt it not at all possible to supercharge/turbo a 2 stroke motor... at the moment i cant think of any possible way reed valves would work w/ that external pressure.

general rule of thumb ive heard from a couple engine builders.. of engines w/ the same cc's, the one w/ larger bore, shorter stroke will make more HP. Joebar's idea to reduce the stroke on a 250cc seems like a good idea if u have the $$ for the crank work n custom rods

i also highly doubt a bike is more aero than a kart. the low to the ground kart wont have nearly as much pressure drag as a motorcycle. im guessing aerofoils arent allowed in the class ure lookin into??

 

[Accender]

Supermac 125 running on nitro-methane will pull
32 hp @ 22,000 rpm.

Go cart would go 89 mph. (sprint cart)

Thats all I know... but I know it.

A

 

[reckon]

well,..it's NOT impossible,...I mean FIFTY YEARS AGO, a guy did it with a supercharged NSU 125CC OHC single, in a streamliner shell (it looked like a football) he also ran the 250cc, 350cc, 500cc, and 1000cc classes, and set over 16 records that week in 1956.

so whats our excuse fifty years later, with nitrous, and computerized electronic ignition, and vacuum sealed bearings and stuff?

simple

NOBODY HAS TRIED SINCE, on anything but a 125cc gp bike stripped down, and geared up.

I have personally had a bone stock RD125 yamaha, up to over 115mph, with NO FAIRINGS AT ALL, so I know this can be done, albeit pretty sketchy doing that kind of speed on a bike weighing less than 400lbs, including the pilot :thumbup

I have my own fairing design, so we wont go into that here, but yes, aerodynamics is critical to getting THAT kind of speed out of a small bike like that.

I liked the karting idea,...there will be LOTS of parts available, good idea,....the question, WAS,....what motor?

as far as running a 2 stroke with forced incuction, or nitrous, the reed valves still work fine,..you just need a stiffer reed to handle the increased pressure, or you could also choose a rotary valve 2 smoker.

I want a twin, as I think you can get more rpms from a twin, as opposed to a single, and this project is all top end HP, and aerodynamics.

so far so good, anyone else?

 

[oliver]

i also highly doubt a bike is more aero than a kart. the low to the ground kart wont have nearly as much pressure drag as a motorcycle.

Why...'cause there's less air at lower altitudes? :shocked (pretty sure it works the other way around if anything).

Karts are exceptionally wide and have all kinds of protuberences that do battle with the air. There is not a single bit of aero engineering put into them:

As you can see, there is a big radiator sticking up into the air, and the driver's shoulders and head are completely exposed to the atmosphere.

 

[reckon]

ok well,.....

yamaha (actually it's the "dragstar") has a 125cc OHC v-twin, and I found a bike with a good motor,....so

a raked, and extended TZ125 frame, front end, and an extended swingarm, and the supercharged 125cc v-twin, possibly nitrous, and the partial streamliner fairing.

at least on paper, and in theory, I can get the HP and TQ numbers needed to get to 150mph, it'll just be about getting the drag down to where that little "hummingbird" motor will work well enough to sustain those speeds for the half mile needed.

I should run the sticker on the front fairing when I run the bike :laughing

lets see if I can get the thing built, and functional first.

 

[uhmeebuh]

Keep us posted! Sounds like a cool project...

 

[pvd]

i have no idea, but this chart will tell you the top speed given some peak horsepower. assuming same aerodynamic resistance as my model.

 

[reckon]

i have no idea, but this chart will tell you the top speed given some peak horsepower. assuming same aerodynamic resistance as my model.

I had seen that on another thread, and as you can see, I'll need nearly 80HP to go 150.00mph

except for the glaring fact that H. Muller went 150.00mph in 1956, on a supercharged NSU with only 46HP, so I think fairing design, gearing, and where the peak power is in the curve is more important than raw HP all by itself.

because I seriously doubt I can get 80HP from a 125CC motor, and not have it self destruct before the run is over.

we were thinking about 70-73HP is about MAX, and probably more like 55-60HP is what we can expect to get consistantly, or at least consistant enough for 3 or 4 runs.


this shit gives me a stiffy :thumbup

 

[Mickey_D100]

I would LOVE for you to post threads like Moike did with his RGM of your progress. :thumbup

On a unrelated note, I know those shifter carts are fast as hell, but damn, I can't even IMAGINE going 120 in one of these. I've been up to about 50 in one and it scared the piss out of me; they're just so damn twitchy.

 

[pvd]

this may be where the confusion stems.

...on a supercharged NSU with only 46HP...

how was the 46HP measured and was the supercharger at maximum boost at the time? also, my graph reflects a modern road race shape not a land speed record shape.

the math is on my site.

 

[Joebar4000]

For outright top-end, you're prolly better running a turbo - it's 'free' horsepower, whereas running a supercharger is a drag on the motor.

But, finding one that tiny?

You might try picking up this month's Performance Bikes - they're building a bike to try to crack 250mph using a ginormous turbo-ed Hayabusa, and they had to have a custom turbo built. Has quite a few links etc. that you might find useful.

The rest of your work is going to be aerodynamics...I think the CYCLISTS were managing well over 100mph with effectively ~1hp, so you might not need to go overboard on producing power, but rather reducing drag.

 

[eisenfaust]

I think you show there that the trick is to lower the CD to something less than a brick-like .55, PVD.

Looks like 80hp would be needed.

I think it would be easier to get a lower CD than more power.