Dyno power!

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stv1jzgte

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Feb 11, 2009
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I've had my new 48cc slant head engine for a month or so, after my old one spun a lil end bearing.
So we thought it would be funny to dyno the bike at work! howd it do? 1.6kw!!! or for you yanks 2.2hp @ the wheel. With 12 foot/pound of torque.
top road speed was 52kmh 44tooth sprocket.
Although i dont have a tacho rpm could not be logged, peak power was at 38kmh.
When i get some batteries for my camera i will post the Graph.
 

Bikeguy Joe

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Jan 8, 2008
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With the reduction, the rear wheel would show more torque....but I was refering to crankshaft torque when I made my statement. There is no way a 2 hp engine could make 12 ft. lbs. of torque at the crank unless it was a slow turning diesel, or very under square 4 stroke.
 
Sep 20, 2008
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Yes thats 100% correct torque at the engine is 1.77ft/lbs @ 4500rpm
Motor Formulas

T = (5252 X HP) / RPM

T = (5252 X 2.2) / 6500

T @ the crankshaft = 1.77 ft/lbs @ 6,500rpm

Multiplied through the internal gear ratio of 4.1:1 we get 7.288 ft/lbs at the engine sprocket. This of course does not take into account any frictional losses within the assembly.

Multiplied again through a final drive ratio of 4.4:1 we get 32 ft/lbs @ the rear wheel. Again: this does not account for losses.

Taking into account:

1) A poor fitting primary gearset. (Typical kit)
2) A clutch that may be slipping a bit.
3) A lousy sprocket to chain fit, and the inherent normal losses from roller chain. (typical kit)

It makes sense that the rear wheel torque is less than half of what would be calculated.

Jim
 

stv1jzgte

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1) A poor fitting primary gearset. (Typical kit) 2) A clutch that may be slipping a bit. 3) A lousy sprocket to chain fit said:
Is there any way of fixing the primary gearset so it spins freely, better bearings perhaps? i cannot physically turn the drive sprocket by hand.
 

stv1jzgte

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so that's for the 48cc... how about the 68cc??? how much torque does it has???
i have had a ride of a mates 66 or 68cc and it does have alot more torque than mine ie throttle persentage.
i would think the hp would be about 3-4 but the torque curve would really climb, As Creative Enginering said poor gear sets and sprocket chain fit could also have a big effect on the end result.

this is what im using.
Dyno Dynamics - Products
 

stv1jzgte

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48cc max 1.2kw(1.61hp)/6800rpms
max speed 40kph(24.8mph)(this is just a estimate the engine kit site gives)
max torque 2.4nm/4500rpms(1.77lbs/ft)
max no-load speed 8500rpms

66cc max 2.0kw(2.68hp)/5500rpms
max speed 40kph(24.8mph)(this is just a estimate the engine kit site gives)
max torque 6.2nm/5500rpms(4.57lbs/ft)
max no-load speed ????rpms

so that's for the 48cc... how about the 68cc??? how much torque does it has??? 4.57lbs/ft
So again Everything above is AT THE CRANK!!!!! Not the wheel
 

Cabinfever1977

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Mar 23, 2009
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48cc max 1.2kw(1.61hp)/6800rpms
max speed 35mph
max engine torque 2.4nm/4500rpms(1.77lbs/ft)
max no-load speed 8500rpms
torque at rear wheel:
50t 8.9lbs/ft
44t 7.8lbs/ft
36t 6.4lbs/ft
34t 6.0lbs/ft
32t 5.7lbs/ft

66cc max 2.0kw(2.68hp)/5500rpms
max speed 35mph
max engine torque 6.2nm/5500rpms(4.57lbs/ft)
max no-load speed ????rpms
torque at rear wheel:
50t 22.9lbs/ft
44t 20.1lbs/ft
36t 16.5lbs/ft
34t 15.5lbs/ft
32t 14.6lbs/ft
 
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stv1jzgte

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Feb 11, 2009
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48cc max 1.2kw(1.61hp)/6800rpms
max speed 40kph(24.8mph)(this is just a estimate the engine kit site gives)
max engine torque 2.4nm/4500rpms(1.77lbs/ft)
max no-load speed 8500rpms
torque at rear wheel:
50t 8.9lbs/ft
44t 7.8lbs/ft
36t 6.4lbs/ft
34t 6.0lbs/ft
32t 5.7lbs/ft

66cc max 2.0kw(2.68hp)/5500rpms
max speed 40kph(24.8mph)(this is just a estimate the engine kit site gives)
max engine torque 6.2nm/5500rpms(4.57lbs/ft)
max no-load speed ????rpms
torque at rear wheel:
50t 22.9lbs/ft
44t 20.1lbs/ft
36t 16.5lbs/ft
34t 15.5lbs/ft
32t 14.6lbs/ft
How have you come up with these figures??
 
Sep 20, 2008
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Clearwater, FL
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if anyone has a engine with diffrent horsepower or rpms and they want the rearwheel torque numbers,let me know and i will list the numbers for it.
Cabin,

The Dyno is reality...anything else is useless...which was my point in citing the numbers game. There are a lot of variables in any drive-train. There are far too many variables to quote accurate rear wheel torque. I'm not bustin' your chops...it's just a matter of fact.

A dyno gives the tuner hard numbers that can be logged. Mods can be made and another dyno test can prove or disprove a performance gain.

Blind numbers are meaningless.

Jim
 

stv1jzgte

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Feb 11, 2009
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Cabin,

The Dyno is reality...anything else is useless...which was my point in citing the numbers game. There are a lot of variables in any drive-train. There are far too many variables to quote accurate rear wheel torque. I'm not bustin' your chops...it's just a matter of fact.

A dyno gives the tuner hard numbers that can be logged. Mods can be made and another dyno test can prove or disprove a performance gain.

Blind numbers are meaningless.

Jim
Spot on Jim, we know there can be differences between different dyno's giving different reading so regardless of fact the numbers are logged.
This weekend i will be testing a new plug, then 32.1 fuel mix. doing all testing on the same dyno with the same ramp rate.

Also as i said earlier im doing this on a car dyno and have to spin both rollers about 3 meters long combined! A bike dyno has a roller about a foot wide and im sure it would turn alot easier giving better results.
 
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xlite

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Jun 18, 2009
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-Actually if you have a good reference engine and a long gradual hill it's easy to get hp and torque for any bike. I took a mid-power setup to my brothers motorcycle shop and got readings for it on his dyno. Then GPS speed on a nearby 2 mile slope. Now I get very accurate power readings for new installs, suspected power loss situations, or checking tune-ups and mods. We doe need no steenkin' dyno anymore. :)

Top speed readings on a flat were not as reliable because things like wind and rear sprocket size interfered. A steep hill is no good either because most engines never get up to the power band.

It's amazing how bad human perception is at judging power. This accounts for many claims of power increase in situations where mods could not have had any real effect and, conversely, feelings of poor performance when actually nothing changed.
 
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Sep 20, 2008
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Clearwater, FL
web.tampabay.rr.com
"It's amazing how bad human perception is at judging power. This accounts for many claims of power increase in situations where mods could not have had any real effect and, conversely, feelings of poor performance when actually nothing changed."

I can't think of a more complete, and true, statement that describes the interaction between man and engine powered vehicles.

You have a slope, and a GPS...It's this data acquisition that gives you a base line. It may not be a Dyno, but in principle it's similar.

Jim
 
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matt167

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May 20, 2009
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1/4 mile streatch of flatland, and a stopwatch and you'v got a dyno... total weight ( rider and bike ) and 1/4 mile time can easilly be calculated into hp
 

stv1jzgte

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Oh for crying out loud dude! All i have done is have access to a rolling road for free and your all ya dont need a dyno all ya need is a road a gps. Go for it!
Wow i thought i lived in the land of tall poppy syndrome!
Cabin really, think for a sec if i used a bike dyno it would obviously turn easier thus giving a better result. Google ramp rates! Knock all you want buddy i know the facts and the results are real if a little low.
Pull 20 bucks out and take your bike to a ROLLING ROAD DYNO not some engine dyno and see for yourself the results im sure you will make more torque than the figures you have posted.

Regards,
steve