How fast can your 80cc really go?

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There is absolutely no doubt you can go downhill at 55mph or faster. It should be equally obvious that if the engine is engaged damage will occur.
 
Get a GPS, set it to MPH (not KPH) and believe what it tells you.

Semi-stock 66cc w/a 44t & 26"ers & a 200lb rider on flat, level ground will do a sustained 33mph - period. No amount of "logical reasoning" or "creative math" will change the facts.

When these bikes are modded, both in engine and with sprockets - we're talking a difference of fractions of a mile an hour, maybe one or two if you're lucky. The faster you get it, the less effect even more radical mods have. Welcome to the world of real physics - drag and wind resistance.

It's exponential btw, if you wanna play with some FUN math :p

I would like to ask though, why is everyone so fascinated with the dead-end of "top" speed? Trying to keep my max of 33mph, I've been much more interested with the infinitely more useful (and competitive) acceleration increase - my "0-30" so to speak.

While a higher top speed sounds more impressive whilst yappin with others (partic if you fudge the numbers) often times you've sacrificed your get-up-and-go to achieve your fabled "Mach 1" - odds are, in a real world race a bike with a slower top speed would still dust you hands down, you'd spend all your time just trying to catch up.

It's ALL about application, I actually ride my bike in this world, not some fantasy oval track lol :D
 
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Getting your top speed from going down hill is downright cheating! Where does it end? Can I go down a hill with an 89° grade? I don't even need an engine and I'll probably be doing over 100.
 
Barely's spot on about chasing mph. while i love the low cruising rpm's and higher top speed of the 36 tooth....... i miss my 44 tooth setup's low end and midrange torque.
imagine a 56tooth! you'd dam near pop a wheelie. add an expansion chamber with steep as cones and you would tear up grass! hmmm.......
 
going down hill I'm always afraid of over revving, or not giving it enough gas, overheating it and hurting the bearings.
 
24 inch mountain bike, 80/66 cc engine, built by the number with stock parts out of the box: 24 mph at almost 6,000 rpm and 6,200 feet above sea level on the flats.

26 inch mountain bike, 80/66 cc engine, jackshaft: 33 mph in 5th gear at almost 5000 rpm and 240 lb rider and 6,200 feet above sea level on the flats.
 
distance divided by time = speed. In the late 1800 we invent the automobile in the early 1900 we invent the traffic light. the day after the traffic light went in. We invented drag racing
 
spinning your happy time to 10,000 rpm
43mph 8000rpm
Click to expand...


2mm (1.97) ductile iron rings will not go to 10,000 rpms without a massive case of ring flutter leading to piston smearing -> seizure.


Though I need to know the con rod length to tell you exactly what the limit of the rings is...
 
The secret to hitting higher speeds with a HT engine isn't gonna be through higher RPMs... (these little HT's will never be able to do it.)
It's gonna be through making more engine power & using lower gears!
 
Foximus said:
2mm (1.97) ductile iron rings will not go to 10,000 rpms without a massive case of ring flutter leading to piston smearing -> seizure.


Though I need to know the con rod length to tell you exactly what the limit of the rings is...
Click to expand...






mine is 89mm, the three or four others that i have seen were all 85mm. i've always had the longest rod.
 
i noticed the longer rod when i tried to throw on a new piston and cylinder, wristpin height was 4 mm lower on the new piston. i couldn't find the right piston so i built a cylinder spacer 4mm thick.

0930090946.jpg
 
foureasy said:
i noticed the longer rod when i tried to throw on a new piston and cylinder, wristpin height was 4 mm lower on the new piston. i couldn't find the right piston so i built a cylinder spacer 4mm thick.

0930090946.jpg
Click to expand...


Ok so that wasnt a sexual enuendo joke.... You actually do have a long rod.


4easy, if you want more bottom end power, you should map out your cylinder, see what the absolute lowest you can lower your cylinder while keeping your intake and exhaust ports fully open. Then machine the head the remaining depth needed. the top of your piston will stick through, and as long as your ring does not protrude past the deck you will gain more power.
 
I knew a guy in Job Corps Roswell NM that fell off a 3rd floor ledge in his underware unscathed although quite elebriated hence the nickname "superman" but U take the prize due U is 1 lucky biker!
The trees did ya a favor it was time to change underware anyhow eh?
 
So, I just bought myself a new speedometer, one that's wired, so there's no chance of interference. It's a 20 function from walmart. I am very impressed with it. The initial setup took a few mins, but now that it's all set up, It works flawlessly! I set an odometer timer, every 400km, a service bike symbol will appear! I'm very impressed. So, I ripped down a big hill to see what she can do, my highest speed I reached was 52.4 km/h! That's 32.6 mph. Most of our speed limits here are 50 km/h, so I'm doing pretty good. If you want to get technical, I could've gotten a speeding ticket! Lol. I have only a stock 69.9cc Chris Hill engine. No upgrades. I want an inline fuel filter, aftermarket air filter, and an expansion chamber. Perhaps next summer. :)
 

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