horsepower

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vasago

New Member
Aug 19, 2015
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pittsfield mass
maybe someone can give me some info?? my question is how do I know how many hp is my stock china engine pushing?second question,lest say I took a 5 hp engine did nothing but replace my stock china girl would the bike be faster??or would it just have more power? whats the deal can someone give me some info please..
 

Davezilla

New Member
Mar 15, 2014
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San Antonio Texas
There are some GPS apps that can measure your rear wheel hp by comparing the acceleration to the weight of the vehicle, you would need to weigh the bike with whatever else you're carrying and yourself to b et the most accurate reading, the only thing about doing it this way is its still just going to be a rough estimate at best since it's going to be basically the rear wheel horsepower so it can't count for gearing, chains, etc...
There's also the G tec computers but they need a 12 volt source, these also use accelerometers to calculate and they're surprisingly accurate as long as you enter the exact weight of the bike, yourself, and whatever else you're carrying.
 

biknut

Well-Known Member
Sep 28, 2010
6,631
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Dallas
Basically you can calculate your HP by dividing the square of the hair x the heat of the meat after slapping a 5 HP motor in your bicycle frame, and timing how many minutes it takes for your butt to skid across the asphalt after your frame goes times 2.
 

MEASURE TWICE

Well-Known Member
Jul 13, 2010
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Crank length I understand would be for a bike that still retains the pedal and that is attached to the crank arm?

I ridded of the pedals and cranks and now only use foot pegs as a off road light weight motorcycle (3hp Briggs Build of my own).

What or also why is there a listing of spec needed for crank length. Maybe obvious, but not sure.

MT

Figured it out. Only useful for the pedal force in pounds. This is still needed to run the calc, but does not change the HP. Interesting as some info I gave showed a few hundred pounds force to what I would have to use pedal force, were it not that I just deal with my own weight on foot pegs and bumps. It is legal OHV sticked reg for CA, and 3 hp 4 stroke is a bit under-powered considering trails that are too much for it.
 
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racie35

Active Member
Nov 17, 2012
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usa
Horse power is a funny term....I can assure you there's never been a 1 hp engine made that'll do what a horse can do. If you think different,take one and try to move the weight of a horse and jockey around Churchill downs in the next Kentucky derby...at the speed a horse does. Or try plowing a field with 1 hp.
They named the equation wrong.
 

MEASURE TWICE

Well-Known Member
Jul 13, 2010
2,741
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maybe someone can give me some info?? my question is how do I know how many hp is my stock china engine pushing?second question,lest say I took a 5 hp engine did nothing but replace my stock china girl would the bike be faster??or would it just have more power? whats the deal can someone give me some info please..
I think we all may have avoided the question. Oh and sorry to hear from the thread you wrote "just died,PLEASE HELP...??".

http://motorbicycling.com/showthread.php?p=621812#post621812

Also wondering if you fixed it (the top end), as was stated on that thread of what I guess is a two stroke kit. I'm not to knowledgeable of the kits and wonder what China Girl 66/80 really means.... 66cc or 80cc two stroke?
Some sites say: The 49cc two stroke engines supposedly get around 2hp.
Some sites say: The 66/80 cc two stroke supposedly get 5 to 6 hp.

-----------------

Some sites say: The 49 cc four stroke supposedly gets 2.5 hp.

===================

I've dealt with 4 stroke engines and have recently found a web site mentions a rough standard for today is 32cc = 1 hp in a 4 stroke engine. They mention a 123 cc would get around 4 hp. Actually for their calculation 123 / 32cc = 3.8 hp. My older 4 stroke from the 80's era is supposed to only get 3hp and it is 127cc I think. So displacement to hp ratio is getting better. I even hear a motor cycle engine that get 16 hp from only a 125cc so how is that possible. Better design? (I think maybe it has fuel injection which helps & maybe a way to get air in more smoothly porting)

One thing as a rough estimate is two stroke engines I thought usually get twice the hp per cc, than four stroke engines.

All that aside, if you know the horse power and if it is two or four stroke engine, you can know this. Four strokes have better low end speed torque. The two stoke engines need the higher rpm to get more torque. Having twice the horse power on a two stroke engine, but having gears sort of makes up for that I suppose.

Will a bike go faster with a 5 hp 4 stroke engine, compared to what?
If it is a 5 hp two stroke engine compared to a 5 hp four stroke engine, I'd have to guess both the same as long as the two stroke is used with gears.

The choice for gears on a bike using derailleur or the Sturmy Archer 3 or more speeds sound interesting. I've just been OK just doing with 1 speed and turning the twist grip throttle in a more narrow band doing trail riding and don't care to go much more than 15mph.

Have not see any responses back from Vasago, not sure if you got a replacement engine or fixed the one you got?
 
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biknut

Well-Known Member
Sep 28, 2010
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You also have to consider where is the hp being measured from. The crankshaft, output shaft, or rear wheel. That makes a big difference.

I guarantee no stock china girl has 5 hp at the rear wheel.
 

sbest

Member
Nov 3, 2015
343
2
18
Nova Scotia
Poor guy, just gets on here and 6 days later his engine blows up. What are the odds?

Measure Twice, the numbers can be even larger than you think. My 125 KTM here puts out nearly 40hp at the crank as do most 125 motorcross bikes, the 250s put out around 50hp. This little 125 can easily run down the highway at 140kph (87mph).



Traditionally it was figured that 2 strokes could make double the hp of 4 strokes mainly they fired twice as often. This was the basis of 250 4 strokes competing in the 125 motocross class, and 450s in the 250 class. Research and development has pushed the advantage to the heavier more complicated 4 strokes like this Husaberg 450 (my son riding, not this old fat boy).



It all depends on the state of tune. Race engines work at higher pressures and RPM than plebeian work engines so race engines often make 1hp per 3-10cc. Work engines have long life and low stress in mind and may take 40cc to make 1hp. That said, my plebian minivan makes 1hp with every 12cc with no superchargers or other power adder tricks. The times they are a-changin'.

The formula for making horsepower is simple: PLAN = power
Pressure x Length of stroke x Area of piston x Number of power strokes per minute.
From this you must subtract the parasitic losses to get actual output.
(This is in Gordon Jennings "2 Stoke Tuner's Manual" by the way)
So, to increase power you must:
1) increase the cylinder pressure average through the stroke
2) increase the displacement (length x area)
3) increase the firings per minute (RPM or number of cylinders or 2 stroke over 4 stroke)

For us, what does the mean?
1) Add pressure? Compression, air in, tuned exhaust, better burn, spark, port timing
2) Displacement? bored or stroked, it has to be larger, 49cc vs 66cc, 38mm stroke vs 40mm
3) More firings? RPM! Balance the crank, port timing to rev, pipe to make her scream.

And finally parasitic losses? Thinner oils and greases, better alignments, smoother surfaces, more accurate gear and sprocket tooth cuts, lighter rubbing seals or even better just shields, less pumping restrictions and losses, less electrical load.

The PLAN formula gives an idea of what gains for any modification are possible.
5mm stroke? 13% more displacement, 13% power improvement possible
Get the picture?
There is no way a 0.020" (.5mm) over-bore is going to make 20% more power.

So why do these engines only make 1.5 to 3 hp instead of the 12 or so that a 50cc motocross does?
Have a look inside one of those engines. Between the ports is only a narrow 2-3 mm band.
Almost the entire cylinder diameter of this 125 is a window to allow mixture and exhaust to flow.



Plus the intake and exhaust tracts are tuned to pump flow through those ports,
PLUS the whole thing fires at 10,000 - 15,000 rpm or more.
The little China Girl cannot do that.

Steve

 
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MEASURE TWICE

Well-Known Member
Jul 13, 2010
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It was and older Yamaha 125 cc that I rode trails on the 4 stroke.... think it was 16 hp. Old lawn mower Briggs engine on my bike 127 cc is from 70s to 80s era? It is 3hp and now they are about 4 hp for 127 cc lawn mower engine. A lot now say in Torque not hp any more.

I took it to some trails that were intermediate and thought they should have been labeled expert. Just controlling down hill idling the engine or engine brake in lower gears, my wits! Nope did not lay my friends Yamaha bike down or worse, leg underneath etc.

The seat I liked so much better than by motor bike's seat, was of no help on what seemed 30 to 40 degree angle slope. I was on the pegs and low center of gravity crouched down to prevent spilling.

Yes, the breaking of a new kit engine on a bike sucks. Worse for me it would be 7 year in the making, ugly true, but my bike officially is legal for off-road only and state recognizes it. I have a 3.5 hp that could fit in its place when and if my engine on it now goes. I almost seized permanent the engine on 100 degree F heat weather I was riding. Oil thinned and burned faster than I thought. Wish it had a clear view of oil level without opening the oil dip stick plug as some engine do have, as well as low oil shut down.

MT
 
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sbest

Member
Nov 3, 2015
343
2
18
Nova Scotia
A big project I had on the go was 200cc Yamaha Blaster that is 17hp stock. Motor is similar to the Yamaha DT200 that is 32hp stock so was an easy blueprint to get there. Beyond that my son and I were able to squeeze out nearly 40 hp out of an engine that started at 17hp. Here are some picture hinting how:

Epoxy filling intake, stuffing and flowing


Head combustion chamber design, 2 of many tested


Mild porting, but big windows all around, nice burn on that well run chamber


Drilled in the right place made power. This was a well worn pston and cylinder and was a test bed for how much is too much?


The bridge is actually stock width because the piston bridge cannot be narrowed without weakening it, so we went wider at the outside. Note the tight fit of the reed at the sides and no reed stops. A bit of epoxy has flaked off the port of this well worn cylinder.


The Blaster was a great learning tool too, but I have high hopes for making good power with the Happy Time!

Steve