how many rpm is too fast

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blckwlfny1

New Member
Jul 14, 2010
128
1
0
new york
ive read back and forth on the posts and i wanted to know what rpm is too much for the motor to handle. i have a
"80cc" grubee skyhawk
piratecycles h/c head
and a cns carb.
extended exhaust pipe "poo-poo pipe"(...say THAT with a straight face! LOL)

its attached to a sbp shift kit and a 8-speed hub (calculations say max speed is around 35mph @6500 rpm)
...i have it geared pretty low because i deal with a lot of hills and really wanted a no-push start)
On the flat areas I can still max out the throttle and i wanted to make sure i wasnt pushing it too hard. at WOT, it seems to be pretty smooth
How much is too much and how can i tell?

thanks
.bld.
 
Skarrd

Skarrd

Member
Oct 13, 2010
501
2
18
34
Chandler, AZ
curious about this as well.

mine tops out at 30mph with just the 44 tooth gear (i know i'm over revving it at this point)

cruises nice at 25-ish.


but i'm also thinking of getting the SBP shift kit and would be nice to know what these engines can handle as far as a red line

mine's the 2010 GT-5 66cc (80cc) engine.
 
biknut

biknut

Well-Known Member
Sep 28, 2010
6,631
409
83
Dallas
This is my speed to rpm on my single speed China Girl. My bike feels great up to 30 mph with little vibration. Between 30 and 33 vibration goes up noticeably, but it's not to bad for short bursts. I've been up to 35 a couple of times and didn't like the way it felt.

Based on this I'm guessing rpm above 7000 probably isn't good for sustained periods, but 6500 is probably safe.


RPM
1000 4.7
1200 5.7
1400 6.6
1600 7.6
1800 8.5
2000 9.4
2200 10.4
2400 11.3
2600 12.3
2800 13.2
3000 14.2
3200 15.1
3400 16.1
3600 17.0
3800 17.9
4000 18.9
4200 19.8
4400 20.8
4600 21.7
4800 22.7
5000 23.6
5200 24.6
5400 25.5
5600 26.5
5800 27.4
6000 28.3
6200 29.3
6400 30.2
6600 31.2
6800 32.1
7000 33.1
 
C

culvercityclassic

Well-Known Member
Sep 27, 2009
3,115
177
63
Culver City, Ca
Hey Bairdco, i am willing to come get you and bring you to our next ride just to see that bike of yours. We want to have you and enjoy your company. But what I really want is to see how fast that bike of yours is.

I think if I put my kid on aldyno he with spank your ass in a drag race.

It's all in fun but I have offered... Hope you consider

ccc
 
GearNut

GearNut

Active Member
Aug 19, 2009
5,104
11
38
San Diego, Kaliforgnia
Fitting in with what bairdco said, when the flywheels pass you down the road, you have revved the engine too fast.

The ignition is fixed on these engines and that acts like a rev limiter for them.
You would have to be hauling some serious speed down a looong steep hill to over rev them.
 
DanielMaia

DanielMaia

New Member
Jun 24, 2009
309
0
0
Portugal
With my tachometer, it reads 6000RPM at 40km/h, 7500RPM at 50km/h

My top speed was 54km/h, with my 66cc engine, it has 2600km...with a good soul :)
 
earl.k

earl.k

New Member
Jan 19, 2011
242
2
0
34
PA! USA
blckwlfny1 said:
ive read back and forth on the posts and i wanted to know what rpm is too much for the motor to handle. i have a
"80cc" grubee skyhawk
piratecycles h/c head
and a cns carb.
extended exhaust pipe "poo-poo pipe"(...say THAT with a straight face! LOL)

its attached to a sbp shift kit and a 8-speed hub (calculations say max speed is around 35mph @6500 rpm)
...i have it geared pretty low because i deal with a lot of hills and really wanted a no-push start)
On the flat areas I can still max out the throttle and i wanted to make sure i wasnt pushing it too hard. at WOT, it seems to be pretty smooth
How much is too much and how can i tell?

thanks
.bld.
Click to expand...
hello, if you dont mind me asking.. what kind of 8 speed hub do you run? and how is it holding up? iv been looking into a few and cant get much input on anything MB related.:( anything you can tell me would help. thanx
 
D

dmb

Active Member
Dec 4, 2010
1,354
3
36
lakewood ca
i met baird at the golden west swap last summer, his motorbike locked up, i was checking out the backward barrel and the clamp sprocket on a old bike [40's or 50's] real nice guy, had time for a fat old man! turned me on to pirate [sprocket clamp, i couldn't see using the factory junk] and then when he rode off he was in the wind! cars going 50 mph and he was right with them gone just like that!... very impressive
 
KCvale

KCvale

Well-Known Member
Feb 28, 2010
3,966
57
48
Phoenix,AZ
blckwlfny1 said:
ive read back and forth on the posts and i wanted to know what rpm is too much for the motor to handle. i have a
"80cc" grubee skyhawk
piratecycles h/c head
and a cns carb.
extended exhaust pipe "poo-poo pipe"(...say THAT with a straight face! LOL)

its attached to a sbp shift kit and a 8-speed hub (calculations say max speed is around 35mph @6500 rpm)
Click to expand...
I was just messing with this myself today.
I was going to start a new thread but this will work, pretty similar stats.

I have a 2010 Skyhawk 66cc, CNS carb and jackshaft, but an SBP Expansion Chamber exhaust, Pirate Cycles Intake, NuVinci Dev Kit Hub, but no h/c head.

I figure 6K RPM is playing it safe.
That doesn't mean there isn't more in the motor, it's just a good safe number.

Jackshaft Gearing to my Hub on my bike:
T=Tooth, JS=Jackshaft.

10T motor to 17T JS left gear is a 1.7 reduction
10T JS right gear to the 36 tooth pedal chainring is a 3.66 reduction
30t pedal chainring to 18t Hub is a 1.66 increase

Total Motor to Hub Gear ratio = 3.7:1 reduction.

1 mi=63,360"
63,360" / 81.25" for my wheels radius =778 Wheel Revolutions per Mile.

778 * 3.7 gear reduction= 2878.6 motor rotations per mile at hub.
or at 1:1 hub gear ratio (18 tooth)= 2,878.6 motor rotations to go 1 mile.
6,000 motor RPM / 2878.6 would travel .479 miles per minute, or 28.8 MPH

28.8 MPH * .5 under drive = 14.4 MPH @ 6,000 RPM
28.8 MPH * 1.75 overdrive = 50.4 MPH @ 6,000 RPM

You will have to calculate your derailer gears yourself as my hub only has the 18 tooth drive sprocket, but automatically shifts internally as if the rear hub had a derailer with 950 sprockets between a 9 tooth and a 31.5 tooth bicycle sprocket.

I know, it kind of boggles the mind.
For 950 tooth count changes from 9 to 31.5 bicycle chain size teeth, the sprockets would have to have teeth the size of needles and the chain would have to have links the size of a delicate ladies necklace chain ;-}
 
Last edited:
corgi1

corgi1

New Member
Aug 13, 2009
2,272
3
0
KCMO
When the pieces are comming out faster than you can put them back in,,then that is too high an rpm,lol
 
D

Don P

Member
Sep 1, 2010
234
0
16
indiana
GearNut said:
Fitting in with what bairdco said, when the flywheels pass you down the road, you have revved the engine too fast.

The ignition is fixed on these engines and that acts like a rev limiter for them.
You would have to be hauling some serious speed down a looong steep hill to over rev them.
Click to expand...
so is this why i can't get this thing to go over 25mph no matter what jet i put in it?

it hits 25 mph then kinda shuts down then at 22mph it takes off again. i was thinking fuel?
 
GearNut

GearNut

Active Member
Aug 19, 2009
5,104
11
38
San Diego, Kaliforgnia
If it seems like it is shutting off then going again, no that is not how the engine is supposed to act.
The engine should just rev up to top speed and go no faster, staying at that top speed until you back off of the throttle.
Surging can be caused by a restriction in the flow of fuel from the fuel tank to carburetor or an ignition problem.
Bad fuel valve (stock ones are known to be poorly made), plugged fuel valve screen, clogged fuel filter, poorly vented gas cap, float level set too low in carburetor, bad spark plug, bad spark plug wire or wire connection at either end, loose wire connections between the magneto and CDI would be the list I would go through.
 
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