I have a street legal crf50. As of now it has a piranha 140cc engine, ahp 4 speed transmission, manual clutch, and a 34 tooth rear sprocket and I'm hitting 50mph. I had a goal of hitting 70mph and am falling short, what mods could I do to reach it?
Quest for 70mph
swisscheese32
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I have a street legal crf50. As of now it has a piranha 140cc engine, ahp 4 speed transmission, manual clutch, and a 34 tooth rear sprocket and I'm hitting 50mph. I had a goal of hitting 70mph and am falling short, what mods could I do to reach it?
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70 is very fast for a 50, but is possible, just very unsafe, but i know mine does every bit of 60(daytona 150 in a reeg chassis).
What size front sprocket to you have? if you have stock(14) I would bump it up to at least a 16 (maybe even a 17 or 18)
What size front sprocket to you have? if you have stock(14) I would bump it up to at least a 16 (maybe even a 17 or 18)
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are you limited by gearing or by power??? IE are you bouncing off the rev limiter or is the motor just stuck at an rpm and wont pull any higher?
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Limited by power, when I switch to a big bore exhaust I get an extra 3mph but I HATE how loud it is.
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And it's the stock front sprocket and realistically 60ish would be fine I just want to drive down a 55mph highway and not hold up traffic
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yeah if your limited by power and not gearing time to give that thing some more balls
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yea, if you are limited by power then gearing wont fix it. I just dont see a 140 not being able to get at least 60, my bone stock 50 pulled 32mph(gps). My dr200 has about 12-13hp and it pulled 86 and im guessing that the the 140 has 10-12hp in stock trim, so i see no reason that it couldnt.
also i saw a guy who claimed 70 on a plated crf70 with a piranha 140 and he would cruise at 55
Another issue is size of the rider, im a small guy(5'7 120lb) but if your a normal sized guy that could play into the equation
also i saw a guy who claimed 70 on a plated crf70 with a piranha 140 and he would cruise at 55
Another issue is size of the rider, im a small guy(5'7 120lb) but if your a normal sized guy that could play into the equation
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Wheel size on a 50 vs 70 is going to cause a difference in top speed. Those little 10" wheels have to turn a lot. What size carb are you running & have you tried gearing it down? If you can't rev out in 4th gearing it down a little might help?
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Your gearing is all jacked up for starters. Go to my gear calculator and figure out what your mechanical l top speed is by the gearing in the bike.
You are applying the wrong logic to your speed runs. I can get 55mph out of an 88 and close to 70mph out of a 108 4 speed Honda motor.
Honda50.com Gear Ratio - Speed Calculator
My guess is your are maxing out the RPM's on the motor in top gear. Keep mind the gear ratio calculator doesn't factor in weight, wind resistance, tire resistance, etc. You need to know what RPM's your motor maxes out at to get where you are going and approximately how much horsepower it takes to get to any given speed. THis will give you a start.
You are applying the wrong logic to your speed runs. I can get 55mph out of an 88 and close to 70mph out of a 108 4 speed Honda motor.
Honda50.com Gear Ratio - Speed Calculator
My guess is your are maxing out the RPM's on the motor in top gear. Keep mind the gear ratio calculator doesn't factor in weight, wind resistance, tire resistance, etc. You need to know what RPM's your motor maxes out at to get where you are going and approximately how much horsepower it takes to get to any given speed. THis will give you a start.
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Get a 17T front sprocket on there
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I have the stock carb, will the v2 head bolt on to the piranha? Also what size carb should I look into. I'm not maxing the revs it's for sure a power issue. I'm 5 9 190lbs so that isn't exactly working on my favor haha.
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[h=1].TB Roller Rocker Race Head V2 146cc Big Bore w/VM26 Carb Kit China 124cc & 146cc engines
[TBW9128][/h]
TB Roller Rocker Race Head V2 146cc Big Bore w/VM26 Carb Kit
China 124cc & 146cc engines
Highest Performance Race head on the market with full parts support in stock.
- Roller Rocker Arms exactly like the V2 head for the KLX110
- 28.5mm intake Valve
- 23.5mm Exhaust Valve
- 5mm Valve Stem
- 23mm Exhaust port
- Matching High Compression Piston
- Head kits include all hardware
- 57mm piston with rings, pin, & clips.
- 57mm Aluminum Cylinder
- VM26 Carb Kit
- High performance race camshaft (for the Race Head only)
- Head gasket kit.
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I'm no expert but from what I've gathered the 140 comes set up for more low end power. The v2 would be the ticket but if you don't have that kind of money a bigger carb should really help. A vm26 would be alot cheaper & should really help wake that motor up. I've got a 20mm on my 88 so if you're not a good bit bigger than that, you're not letting that thing breathe.
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Yes a VM26 Kit is a great idea , And a 17T front sprocket ...
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How important is exhaust? Right now I have thestock 50 exhaust on. Does a bigger exhaust make a big difference? If so what brand sells a bigger exhaust that doesn't make my ears bleed?
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Yeah man between the carb & the pipe you're choking that thing. My 88rh on my 3 speed 70 will do 40 with dirt gearing.
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What's a good exhaust to run that is quiet, since im riding it on the street it can't be too loud
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I think no matter what you run, you'll be hard pressed to be louder than a harley. Any pipe that has a quiet core should be decent. Everyone seems to like fmf 4.1 but hear they're loud. Try pulling the baffle out of the stock pipe.
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Harley's don't get harassed by local Leo's but a crf50 driving down a state highway does. Just trying to dot my I's and cross my T's with this build
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