Crank shaft HP

Fellow Gearheads

If a Nort is putting out 70 HP at the rear wheel. Whats it putting out at the crankshaft?

Jim

90?

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I'd guess at 8 or 10% loss through the transmission.

No real clue, but the 8-10% loss (90% efficient) through the transmision sounds reasonable, generic numbers on chains are in the 95-98% range.
A fully engaged clutch should be near nothing.

I'd guess 70 / (0.9 x 0.95) or about 82 HP.

jrh

Would I be right in thinking that a Commando gearbox will absorb less power in top gear than in say third? In top the gear is simply locked on the shaft so no losses through the layshaft?

just frictional loss of the bearings and the gears turning in the transmission oil.

pommie john said:

Would I be right in thinking that a Commando gearbox will absorb less power in top gear than in say third? In top the gear is simply locked on the shaft so no losses through the layshaft?

Click to expand...

bill said:

just frictional loss of the bearings and the gears turning in the transmission oil.

pommie john said:

Would I be right in thinking that a Commando gearbox will absorb less power in top gear than in say third? In top the gear is simply locked on the shaft so no losses through the layshaft?

Click to expand...

Click to expand...

What I'm asking is : Would you get a measurable difference if you did a dyno run in third gear, then in 4th ( top ) gear?

" If a Nort is putting out 70 HP at the rear wheel. Whats it putting out at the crankshaft? "

MORE . :wink: :mrgreen:

" Would you get a measurable difference if you did a dyno run in third gear, then in 4th ( top ) gear? "

Accoring to logic , these nasty japanese all inirect boxes , you got the increased mechanical loses of the INDIRECTS in ALL gears . Horrible Things .

Were as our SUPERIOR British Machineary , Ran Direct Drive ( Power through Mainshaft only ) in top; therefore lower mecanical losses . However .
You never can tell .
If its giveing more in THIRD ,
Try SECOND .
And STAND WELL CLEAR . :| :mrgreen:

pommie john said:

bill said:

just frictional loss of the bearings and the gears turning in the transmission oil.

pommie john said:

Would I be right in thinking that a Commando gearbox will absorb less power in top gear than in say third? In top the gear is simply locked on the shaft so no losses through the layshaft?

Click to expand...

Click to expand...

What I'm asking is : Would you get a measurable difference if you did a dyno run in third gear, then in 4th ( top ) gear?

Click to expand...

Drum horsepower- yes .... SAE horsepower- no

Drum hp? Havent heard of that unit.
What about pto horsepower, there's a good one to figure out!
While we're at it, I wonder what the drawbar horsepower is of a 70 horsepower Norton?

Glen

worntorn said:

Drum hp? Havent heard of that unit.
What about pto horsepower, there's a good one to figure out!
While we're at it, I wonder what the drawbar horsepower is of a 70 horsepower Norton?

Glen

Click to expand...

Drum horsepower [some dynos refer to it as wheel power] on a chassis dyno is the horsepower measured directly at the drum that the tire is setting on. No corrections. The loses include drive train and tire to drum friction and air conditions. Jim

Norton quotes 60 hp for the stock 850 motor, presumably at the crank

And we know that Jim here has stated his dyno was showing some 45 hp at the rear wheel stock motor

So, high school equivalence math time: 45 is to 60 as 70 is to X

so, 60 x 70 equals 4200 divided by 45 equalls 93.3 horseepower

so my first guess of 90 is now proven mathematically to be pretty close to the 93hp, assuming Norton was correct in their quoting 60hp and all other things being equal, etc etc

and of course things are never equal but that's the best figure I can come up with

waiting for someone to show me why my math is wrong now.........

jseng1 said:

Fellow Gearheads

If a Nort is putting out 70 HP at the rear wheel. Whats it putting out at the crankshaft?

Jim

Click to expand...

Jim,

A rough rule for a Commando is 10hp loss at full tilt so in your instance 70rwhp is 80hp at the crankshaft. This accounts for two chain drives, sloshing around and other friction losses in the gear box and rear tire to roadway loss. This also assumes full tilt high rpm of the engine and drive train components.

I would expect an ever so slight relative reduction in loss with fourth gear but keep in mind there's still all the other stuff sloshing along inside the gearbox as parasitic drag.

1up3down said:

Norton quotes 60 hp for the stock 850 motor, presumably at the crank

And we know that Jim here has stated his dyno was showing some 45 hp at the rear wheel stock motor

So, high school equivalence math time: 45 is to 60 as 70 is to X

so, 60 x 70 equals 4200 divided by 45 equalls 93.3 horseepower

so my first guess of 90 is now proven mathematically to be pretty close to the 93hp, assuming Norton was correct in their quoting 60hp and all other things being equal, etc etc

and of course things are never equal but that's the best figure I can come up with

waiting for someone to show me why my math is wrong now.........

Click to expand...

45 hp SAE taken at the rear wheel is good for a stock motor. [SAE means it has been corrected to crankshaft power] Drum power only shows 30-something. Jim

Take it down the strip, if you are going significantly faster than 100mph at the lights, then you`ve got a good `un.
What purpose does it serve to concern youself with 'crank' hp - if you are going to use the bike as intended, anyhow?

Crank shaft HP, inserted in text to search up in future on forum search engine.

As the math above reveals, You can not go by percentage of drive train loss unless equal power engines turning it. 15 hp turning drive train will lose a greater % of its shaft power than 150 hp turning the same drive train. The drive train loss is a constant for each type drive train. If it takes say 4 hp to spin drive train to 5000 rpm, then it takes 4 hp from 15 or 150 engine. Issue is no one seems to know what that is in a Norton. As the silly math reveals the Norton drive train is pretty efficient so rwhp is only a bit less than crank hp. Drive train loss with be the same for 15 hp as 150 at the same rpm. If 150 can turn it faster then a bit more heat and friction loss but not very much more to hardly matter, 90 mph compared to 150. Wind resistance is another issue altogether. Norton factory power claims are pure rose compost. Similar to the Triumph 120, 140 etc, implying top speeds of each new model, sure they could, as well as factory Combats can make 65 hp.

Some one needs to put an electric motor in place of crankshaft and measure the watts comsumed at a range of rpm then that graph could be applied directly to rwhp to get crank hp. Regardless only rwhp matters in motorsport world and how vast majority of various craft measured any way. 745 watts = uno hp.

Ok dudes check out this intensely detailed rwhp vs true hp and the long list of tested cycles, with offer to free test a Norton Commando which is missing famous data point.

http://www.factorypro.com/dyno/true1.html
Marc Salvisberg 415 491-5920

Drawbar hp would be hard to do on a motorcycle unless tire replaced by cogged gear interface I'm a bit familiar with draw bar hp form the Tried Iron steam traction engines rallys, These things were hardly ever used to pull stuff but to get the equipment towed to a job site where the main power out put engaged to turn saw mills or pull plows by cable and pulleys set up in fields while engine stayed put. So if a one of these steam beasts had 30 draw bar or road hp their big belt flywheel pulley might be expected to put on 60 hp. There's at least half dozen ways to measure hp, from mule pulling wagons to turbine pushing aircraft.

http://en.wikipedia.org/wiki/Horsepower
Drawbar horsepower (dbhp) is the power a railway locomotive has available to haul a train or an agricultural tractor to pull an implement. This is a measured figure rather than a calculated one. A special railway car called a dynamometer car coupled behind the locomotive keeps a continuous record of the drawbar pull exerted, and the speed. From these, the power generated can be calculated. To determine the maximum power available, a controllable load is required; it is normally a second locomotive with its brakes applied, in addition to a static load.

In real life contests what I found out for me was Torque allowed best acceleration to some speed while hp gave more speed one could continue accelerating too.

Another realistic way to measure hp is time to speed in drag race, provided can hook up the power planting. Taking example of Commando surprising magazine shoot out with 12.24 sec 1/4 ET [assuming ~550 lb pilot/bike] implies 59 rwhp. So if factory was right about 65 crank, this implies drive train loss of only couple of hp as wind resistance would take rather more to over come.

http://robrobinette.com/et.htm
http://www.dragtimes.com/horsepower-et- ... ulator.php
http://www.race-cars.net/calculators/et_calculator.html

I once rode a BSA that had no oil in the tranny. It was very noisy in 3rd and wouldn't rev out. But 4th was OK. In went the oil and all was cured.

As to my HP question. I'm also trying to figure the difference between rear wheel HP & crank HP on 1000cc race motors which approach 100 HP. Would the loss in power be the same ratio (say 10%) or would I just apply a 10 hp loss?