Fastest 50cc moped

Douglas Binder /

A few years ago I was driving past the Bonneville Salt Flats and that reminded me that back in the '70s I had wanted to see how fast I could make a moped go. I spent the next year modifying a Puch Maxi to take to Bonneville. As it worked out, Bonneville didn't happen that year due to flooding so I went to the Ohio Mile instead. I clocked a speed of 61.299pmh at the end of a mile. I wanted more so I spent more time and money to go faster. Earlier this year I returned to the Ohio Mile and was rewarded with a speed of 59. Decided that this would be a good time to quit and stop spending money. Anyway, I've been trying to find out what others might have done with a 50cc single speed bike. I've done a google search and didn't find much.

BTW, in the 70s, my goal was to hit 60 so I guess I can cross this off my bucket list.

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Re: Fastest 50cc moped

Do tell more of the story ?

What kit ? Pipe? Carb? Ignition and timing.

With a 50cc Athena Reed kit, big pipe, big carb and Hpi ignition you should get way over 61 mph with a streamline body,

I got 55 mph out of that kit with small/mild pipe and stock points ignition and no streamlining

Re: Fastest 50cc moped

Douglas Binder /

Athena small reed, 21mm Delorto, HPI, custom pipe for the 61mph run. Really, the only things that were stock were the crankcase halves, the secondary shaft, the frame, and the rear wheel.

The second attempt was with an Athena large reed. I made a dyno to tune a variable length pipe and should have worked with the gearing more but decided that ~60 was the limit of the bike. For the engineers among us, the power required to go a given speed is a cube of the speed. This means that to go 70, I would have to produce 50% more power than what I made to do 61. The results of the dyno indicated that this wasn't going to happen. The other direction is to get more streamlined. I did a bunch of fluid dynamics calculations an pushed as hard as I could with the fairing, given my size and a stock frame - the requirements for the MPS class I am in. (Modified Partial Streamlined).

Re: Fastest 50cc moped

Ya your missing something.

Mlm Cali pipe, 6 p pipe or Simo pipe all would seem like they would work better and a 24mm TM flat slide would give a boost over the 21mm phbg.

I get low 60s mph out of a 64cc polini Reed kit 15mm Bing and Cali pipe.

You should port the Athena kit similar to the polini Reed kit, run a 24mm TM and a Cali pipe, that should get you to 65mph easy

Re: Fastest 50cc moped

Douglas Binder /

Perhaps. The 64cc is a 28% increase over 50cc and 65mph requires a 21% increase in power from the 61mph that I hit. A 64cc kit would put me in the 100cc class. Another variable that is really annoying when I went there is the wind. I had some pretty high side winds which affect drag. Also pretty intimidating when you are on a 120 pound bike with a big side area due to the fairing! I was getting blown around pretty badly.

I'm sure I can eek a bit more speed out of the bike but because I am in a motorcycle class (there are no moped classes) all you need to do is show up with an Aprilia RS50 with some mods and you take the record from me. I would like to pursue this more but each event is ~$700 and I need to get my daughter through college.

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Re: Fastest 50cc moped

Yeah it's really impossible to compete with an rs50 or really any variant of it, like this. http://www.motorcycle-usa.com/2008/05/article/salt-addiction-buddfab-streamliner/

I know it's a full streamliner but they still managed ludicrous things.

Re: Fastest 50cc moped

yeah wow thats bad-ass, gotta be the fastest single speed 50cc in america, maybe the world. Some guys took a motobecane to bonneville a few years ago and still only managed 60ish i think, but then again that IS bonneville which will kill you.

we'd love to see more pics of your build if you are so inclined. what gearing, what was your tuned rpm, how did it handle getting up to speed. what clutch setup.

most of us that have spent a lot of time tuning E50's realize pretty quickly that you get to a point where your porting and powerband won't pull low enough to either get you through the clutch and accelerate you, or your clutch will slip too much and effectively rob all your power to pull the tall gears. any thoughts on getting around that, we're all ears...

variable pipe you say? do tell..

Re: Fastest 50cc moped

Douglas Binder /

The variable length pipe has three parts: the header, the mid section that slides forward onto the header, and the rear section that slides forward onto the mid section.

Pipe.jpg

Because I am only going faster in land speed racing, I don't need to lengthen the pipe, only shorten it as I accelerate. I used the clutch lever as a ratchet to shorten the pipe a little each time I pull the lever. The ratchet device is crude but it works. I 3d printed it.

ratchet.jpg

I needed to understand how the different lengths affected the torque at different speeds so I made a crude brake dyno from a motorcycle front brake. It measures torque and rpm, giving me horsepower.

Dyno.jpg

Re: Fastest 50cc moped

wow... that is pretty funny though...

Re: Fastest 50cc moped

Douglas Binder /

Getting going is a huge problem. The clutch is slipping till I'm doing almost 40. I used both the Treatland Jammer and the 1977 Superclutch. Both are great but I needed such a high engagement point that I ended up with the Jammer because I could use stiffer springs. The setup is useless on the street, but I don't ride it on the street.

I believe that I was geared too tall. I can go back and study my torque curves and see if I can optimize better. I need to check but I was hoping to break into the 70s so I was running something like 19x36. At these LSR events, you spend a huge amount of time in line. There are maybe 150 vehicles running one at a time and you keep creeping forward in line. I felt that I could regear and try again but my gut feeling (something us engineers shouldn't listen to) was that I was reaching my aerodynamic limit and I wouldn't gain much speed. I think 70 is unobtainable with my current setup so I packed it in. As it stands now, the bike holds the fastest speed of any 50cc motocycle at the Ohio Mile. I feel pretty good about that, especially that it is a single speed.

I'd like to go back and push the record higher but I have no place to test and it is way too expensive for me to do the testing in Ohio.

Re: Fastest 50cc moped

there's definitely more in that top end. What are your port timing numbers? where's your squish? what's your compression?

The variable pipe is cool but I have to wonder if it's hurting peak power. 70 might not be doable but I bet you can squeeze another few mph with careful tuning.

Re: Fastest 50cc moped

Douglas Binder /

Other details. The front end is from a Honda XR80. Bolted right up. Swingarm is custom. To start the engine I modified a pit bike pull starter to engage the allen head bolts holding the flywheel on. The fairing was designed in Autodesk Inventor and analysed using Autodesk CFD. A friend CNC routed the plug and I pulled the fairing straight from the plug. Normally you pull a negative mold so that you can duplicate the fairing but this is a one off and it was quicker this way.

Re: Fastest 50cc moped

Adam Klags MPG /

didnt tomahawk build salt lake racer, and the problem was the torque lost trougn tires and salt. I believe for 50's different material wheels would be needed

Re: Fastest 50cc moped

Douglas Binder /

No question that there is more to be had. I could see shooting for 65 and I would if I could test locally and swing the cost to get there. If I was smart I would sell the bike so that I can't get tempted. As it is, I am an engineer and I keep asking "what if...".

Oh yeah, it is a stock Athena Large Reed cylinder. It pulls over 12K rpm.

Re: Fastest 50cc moped

Douglas Binder /

Traction is a huge problem at Bonneville but I don't know how bad it would be at this power level. If I were rich, I'd be glad to find out for you!

Re: Fastest 50cc moped

i've seen some 50cc french bikes well into the mid 60s

Re: Fastest 50cc moped

I think Doug is dedicated to single speed

Re: Fastest 50cc moped

Douglas Binder /

I am. It's because I'm not that smart.

Actually, it is because I wanted to see how much I could so with very little. It would be fun to push an RS50 to the limits of the MPS class but I think my wife prefers that the bike can't go much past 60!

Re: Fastest 50cc moped

Good job. That's an impressive speed for a 50cc single speed. Even if you can get a bit more rpm out of the motor, your powerband becomes even more narrow and with a single speed you dont have the advantage of several gears to help keep you in that powerband. An easy way to get a little bit more speed would be go wrangle up a 5ft 100lb jockey to pilot it.

Re: Fastest 50cc moped

19x36 is crazy. I had a bike with 18x36 and it would top out at the same speed as when I geared it 16x36 but rev higher and get there faster. I realized I was bogging the engine down because of the gearing.

Re: Fastest 50cc moped

It didn't have pedals but in the mid 60's Kreidler set land speed record at bonneville flats of just over 200kph. It was 50cc but a far cry from a moped.

Re: Fastest 50cc moped

♥Maize♥ BLK Wrote:

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> 19x36 is crazy. I had a bike with 18x36 and it

> would top out at the same speed as when I geared

> it 16x36 but rev higher and get there faster. I

> realized I was bogging the engine down because of

> the gearing.

Yes that may be his problem 19x36 way is too much gear !

16x35, maybe 17x36 gear with a mlm Cali pipe should do like 66-67 mph

Re: Fastest 50cc moped

Matt Mahloch -- MBM Customs /

Where's the video?

Did you try less gear? That's a insane gear ratio for a 50cc only expecting to go 60. You would need something like 16x42 or 17x42 and let that thing wind out to 14,000 rpms and be in the upper 60's. I'm sure you'd need to change your porting from where you're at now based on the speed you hit with your current gearing but letting that thing wind will help out. Think horsepower not torque.

That $700 exterence fee is insane, just to test it on the street, keep after it. I bet somewhere in the mid 70's is the limit for a 50cc single speed.

Things like wheel bearings, crank seals, brake drag, drive chain, tires, etc all are huge.

Re: Fastest 50cc moped

Yea you would want to start with a 14,000 rpm plus figure and build the rest of the bike around that. Degrease wheel bearings and just shoot some light oil in before the run. Tires at insane pressures. Super light gear box oil. Aero helmet

Re: Fastest 50cc moped

Douglas Binder /

I'd love to learn more about that. The only record I could find was in '81 with a speed of 75.697mph. 200kph would be over 124mph. Someone hit 121mph in 1956 with an NSU but that was configured as a streamliner.

Re: Fastest 50cc moped

Douglas Binder /

The video is really boring. Little bike on a big runway.

I geared the bike based on the dyno pulls, the desired speed of 71mph, and the aero drag as calculated using computational fluid dynamics. If I go back, I won't be so greedy and shoot for mid to high 60s. I'll also try to clean up the breathing at 10-12K. Got to be careful when modifying the porting. Go too far and you are buying a very expensive cylinder. The other thing is that issue of getting the engine up to 12K with a single speed. I've spent a lot of time fiddling with the clutch to get it to engage at 7K and do so smoothly and consistently. Needless to say, it gets quite hot. I toyed with the idea of a torque converter but that goes against my intent to do this as a single speed. After a point you should just get a motorcycle with a transmission.

The $700 includes the $300 fee to the event, the hotel, food, and gas. If I go back, I will give serious consideration to sleeping in my truck!

Re: Fastest 50cc moped

Nice bike! I really like your sliding pipe ratchet system, but I think your pipe design is killing power.

Ideas:

- Decent high peak hp pipe with an atac valve(check out jbot's boner! lol) to regain some umph down low, maybe used together with a sliding header for more overrev.

- Mount a powerjet, make it switchable so you can turn it off past peak power; this will counteract the carbs tendency to go rich up there and gain you some rpm.

- Get engmod2t, you wont regret it!

Here's what drives me:

Screenshot_20160826-222302.png

Over 40 years ago a 50cc bike built for handling and acceleration, not just outright speed, exceeded 200kmh(124mph) during a race.

What happened? Why isn't this common stuff nowadays?

Re: Fastest 50cc moped

NEMA Victor (3 Knees Down) /

Alex Degnes Wrote:

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> Over 40 years ago a 50cc bike built for handling

> and acceleration, not just outright speed,

> exceeded 200kmh(124mph) during a race.

> What happened? Why isn't this common stuff

> nowadays?

I think the issue is that they had 12 speed gearboxes and the tracks were mostly straight. You are correct in insinuating that we all lost the dark art of tuning very fast 50cc 2T though. I can't account for how long their engines would last though...

Re: Fastest 50cc moped

Omfg... Ratcheting clutch lever adjusting pipe. Mind blown

Re: Fastest 50cc moped

You could use a ratcheting bicycle shifter to control a pipe, or even preload on a variator contra spring.

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