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Post by KSR Moto on Mar 19, 2018 8:14:00 GMT -5
I was wondering what is the fastest top speed that you guys achieved on a modified gy6 engine and what is the best mod for the buck, I want to hear some opinions😉
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Post by 90GTVert on Mar 19, 2018 8:48:43 GMT -5
139QMB (GY6 50) or the 150s?
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Post by KSR Moto on Mar 19, 2018 9:06:12 GMT -5
I mean for this engine 139QMB (GY6 50) I forgot to mention which😬
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Post by dexameth on Mar 19, 2018 9:53:32 GMT -5
Back in my prime, my qmb139 build was hitting 60mph. Check the Speed List on here...
Best bolt on stuff in my opinion:
Naraku 52.4mm kit
Performance Cam
24mm carb and intake (stock gy6)
Koso variator with Dr. Pulley sliders
Also, I've swapped from a short case to the long case, with a super tall tire and I did the 49/17 gears. I weigh 165 pounds I was full tuck to achieve these speeds. Still, #50notuck...
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Post by KSR Moto on Mar 19, 2018 10:56:18 GMT -5
Woow nice, that is very powerfull setup,but I have stock engine with performance exhaust and pod filter running on a 88 main jet(I used 80 but realized it was running too lean), it has a short case with 10" rims, and although it takes a long time it can reach 80kmh or 49-50 mph it can do it,my expectations were that 52mm bore is capable over 70mph. Or was I expecting too much from that small engine?
What do you think about performance transmissiom gear set from scrappydogscooters?
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Post by fugaziiv on Mar 19, 2018 11:13:00 GMT -5
Woow nice, that is very powerfull setup,but I have stock engine with performance exhaust and pod filter running on a 88 main jet(I used 80 but realized it was running too lean), it has a short case with 10" rims, and although it takes a long time it can reach 80kmh or 49-50 mph it can do it,my expectations were that 52mm bore is capable over 70mph. Or was I expecting too much from that small engine? What do you think about performance transmissiom gear set from scrappydogscooters? A 52mm kit is not going to hit 70mph without a whole lot of additional work and custom work like porting... and a stroker and gears, and nitrous... and a 100lb rider... and a downhill stretch. 60mph is probably the absolute top that is feasible out of a QMB engine right now with really good bolt on parts, and to hit that speed, I think you gotta max out at about a 165lb rider. Gear sets are great on BBK engines, but on a stock engine often times can't take advantage of the taller gearing due to lack of power. You might even lose speed. On a stock engine, you've got way more potential locked into the variator. Matt |
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Post by 90GTVert on Mar 19, 2018 11:25:27 GMT -5
Go look at the speed list and see how many setups have made it to 70MPH. Then note how many are 49cc based four-strokes.
For some perspective; I've had one small scooter that went 70MPH. It was a 103cc big bore, stroker, 2T. The old 50mm bored, cammed, ported BVH, CVT worked, etc... 139QMB that I had wasn't even near the same league as it. A few cc from a 52mm bore would still not have made it anywhere close. I'm not saying a 139QMB can't go that fast, but it won't be a regular speed on any sort of usable/reliable street build.
Don't believe the YouTube comments and people on other forums that claim 70MPH with bolt-ons out of these engines. GY6 150s with small amounts of work don't go an honest 70MPH. I think a lot of people either exaggerate/lie or have speedometers that are calibrated wrong or reading in KPH instead of MPH. This is why I wanted to do The Scoot Speed List. Numbers look a lot different once you start demanding proof.
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Post by KSR Moto on Mar 19, 2018 11:26:08 GMT -5
Interesting... I still think that it could be done, not with just bolt on parts and not without some serious work but I think it could be done
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Post by KSR Moto on Mar 19, 2018 11:30:26 GMT -5
I'm not saying a 139QMB can't go that fast, but it won't be a regular speed on any sort of usable/reliable street build.[/quote]
I agree it would be crazy unreliable
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Post by 90GTVert on Mar 19, 2018 11:30:28 GMT -5
You will need to be a serious enthusiast with some cash to spare. Parts are going to get destroyed shooting for 70MPH under 100cc on a 4T. I'm all for watching someone do it, but most will move on to swapping in a 150 or buying a bigger scoot or maybe a two-stroke build. Remember that horsepower demands increase exponentially as speed increases. The power it takes to hit 70MPH is considerably different than what's required to hit 50 or 60MPH.
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Post by KSR Moto on Mar 19, 2018 11:43:38 GMT -5
You will need to be a serious enthusiast with some cash to spare. Parts are going to get destroyed shooting for 70MPH under 100cc on a 4T. I'm all for watching someone do it, but most will move on to swapping in a 150 or buying a bigger scoot or maybe a two-stroke build. Remember that horsepower demands increase exponentially as speed increases. The power it takes to hit 70MPH is considerably different than what's required to hit 50 or 60MPH. I get your point and I think that you're right, I am asking this because I only have one scooter but 3 engines,one is stock 50cc with performance exhaust and pod filter, the second one has 47mm kit,and the third one is for parts I am very satisfied with both fist and second engine and I swap them around but I use fist one as my daily driver I wanted to do something crazy with my third engine which is currently for parts I was hoping for 70mph, but obiously that isnt going to happen☹ |
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Post by GrumpyUnk on Mar 19, 2018 15:35:51 GMT -5
Back when dirt was new, I rode a Honda CB350. I don't know if it would do an honest 70mph. It might, but not comfortably. Close, but no guarantee.
If you think a machine with a 10" wheel, with a REAL short wheelbase, is easy to ride at that speed, you have more guts or less smarts than me. Your pick. I've seen BIG bikes get squirrely at speed and it will scare the beans out of you. The airflow around my helmet(curved plastic face shield) pulled on the chinstrap enough that is was uncomfortable. I guess I was young and invincible back then.
A more reasonable and attainable target without breaking a lot of parts in reaching the goal, would be 50-60mph. A longer wheelbase and larger tires would make that close to usable in daily driving.
I have noted that the bakelite(?) spacer between the intake port in the cylinder head and the outlet of the curved intake tube can stand to be 'tuned' a bit on some to align the edges of the holes. Just relieving the bolt/stud holes a bit to allow some movement can improve flow at zero cost. I have one that seemed to be installed 'backwards', but there is no 'backwards', it just did not align very well. I'm not so sure getting 19-20mm carbs makes much difference if you have to flow through mis-aligned spacers.
I'll say it. Trying for 70mph on a 50cc would be an achievement, but comes very close to being on the edge of a crazy goal. But, if it blows your dress up, go for it.
tom
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Post by pinkscoot on Mar 19, 2018 15:44:37 GMT -5
I agree with Tom about the tires and wheelbase. I have a Chinarelli Vino clone that I have up to a true 45mph and it was scary. It might have made it to 50 but I wasn't interested in finding out.
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Post by KSR Moto on Mar 19, 2018 15:47:19 GMT -5
I agree that it is very unsafe and dangerous, and definetely not for everyday use
Maybe on a engine with long case and bigger tires it would be safer but not much
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Post by fugaziiv on Mar 19, 2018 15:56:41 GMT -5
I have an old Vespa PX (modified) that is an honest 68-70mph bike. 10 in wheels, drum brakes front and rear, and the engine hangs off the side like an anchor. It is, uhh... exciting at WOT speed. Extremely so.
Matt
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