Crank shaft HP

Don't confuse *% drag factor* with total *absolute drag factor*. Its all pure guessing game until the drive train absolute drag factor per rpm is measured directly. 50 hp going 100 mph or 150 hp going 100 mph both have identical hp drag to add/subtract, but the 50 hp will have higher percentage of its power drained out to do 100 mph compared to 150 hp. What we will find out if sticking to punching hobot on this is eventually we will come up with a set hp number to add or subtract from rwhp measures. My best guessimate at this point is AMC drive train only sucks up 4-6 hp, up to 100 mph range. So if you see 100 rwhp, implies 106 shaft hp.

Did the Citroen Dueux Cheveau really only have two horsepower (deux cheveau)? They were not muscle cars, but ran along at freeway speed just fine and were not a light car either.
Must have been 2 Shires in there if they were only 2 horsepower.


One other observation relating to hp ratings. I can tell you thst one of my Vincent twins, which is Black Shadow tuned (55 crank hp factory rating)is a more powerful beast than my 850 Commando which is rated at between 58 and 65 crank hp, depending on the source.

Glen

jseng1 said:

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?

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Jim,

I would stick with the 10hp figure assuming peak torque at around 7,000rpm. You are placing a load on the drive train that is basically double the normal or standard load. This is not a dry friction problem so naturally the friction does not double with the load but there is an increase (certainly not a decrease nor does it stay the same).

Jim,

The only way you will get the situation specific number is to measure it, or more like measure the differences between the two.

No inertial dynos but eddy brake (or similar brake) dynos.

Measure HP off the rear wheel for various rpm and then do the same measurement off the crankshaft without a primary chain or belt.

Worntorn... please now take Vincent & Commando to a dyno & run them consecutively, then post graph, for us to view torque/hp/revs comparison, & have another look at the H-D 1000 V twin dyno chart in that `72 Cycle Superbike comparison, similar perhaps to Vincent, torquey feel, pulls well against tall gearing, but dies in the arse when revved out..

I dont care about a line on a piece of paper, I have ridden and toured 30,000 miles with the Vincent mostly two up with a full compliment of gear with many miles logged pulling up long and steep mountain grades to the high passes. I would never expect the Norton to handle this kind of load and keep pace, I know it wont do it!
When it is time to pull out and pass an 18 wheeler doing 55-60, drop the Vincent down a gear and you are doing 90 mph when you pull back in, this is fully laden with two large passengers (im 250pounds with gear on).
The Commando is a great, torquey bike, but it just doesnt pull quite like that, no way.

Glen

"For us"...Worntorn, so we can see what you get to [empirically/viserally] do...the dyno dont lie [ NOT saying you are about this].

Here's a great summary by Dances from the 143 mph 850 post. He agree's with my educated 4-6 hp total drag guesstimates, which is rather strange for a change. Ignore his total drive train percentage though as that has a direct relation to the power level applied, not how much hp it takes to turn a drive train to some rpm. If 5 hp lost in drive train then 50 hp crank losses 10% in path to rear patch while 100 hp would only lose 5%. BTW above don't mean 100 hp gets better gas mileage, even though its got a more efficient drive train loss compared to 50 hp with identical drive path.


The system is comprised of the primary chain, gear box, rear chain and tire.

Chains are listed as anywhere from 93% to 98% efficient so let's have a stab at it:
(for reference, another gentleman provided a similar analysis somewhere on this site)

Primary 93% to 98%
Gear Box 93% to 98% Should be closer to 98%, especially in fourth gear lock up
Rear Chain 93% to 98%
Tire to road 93% to 98% I have no idea what this number actually is
Product 75% to 92% System efficiency
Inferred loss 25% to 8%

So for a wild azz guess the system loss is likely between 25% and 8%.

I have heard a number bantered around over the years and 10 hp sticks; this is with a stock Commando configuration. As a weak arguement we have all heard Norton advertisements of 60hp for the 750cc engines yet rear wheel dyno is more like 45-50hp which supports the 10hp loss estimate if we assume Norton was advertising crankshaft Horse Power. Using the bounding analysis above of 25% and 8% renders 15hp and 4.8hp loss respectively.

Now to the point of whether loss is a constant for a system or varies based on power. Since power is a product of force times distance divided by time; a given rpm with two different power inputs means two different loads (forces). So in a frictionless system you can load it and load it and there will be no change but our poor Commandos are less than perfect so an increase in power (load) will result in an increase in loss, but not by a lot. How much of an increase in loss will there be if you go from 45hp to 80hp; I don't know but I do know that the loss is more sensitive to rpm. Most of the power increases on modified Nortons is around +20% to +30% over stock. If we accept the +20% to +30% as increased force or load and also understand that the friction loss is not linear (only a fraction of the increase in load) then you should see that a small fraction of +30% does not amount to a whole lot.

So what does this have to do with anything. Consider the chain drives and the vast variety of conditions the rear chain may be in; from rusted to slithery oily greasy. Sprocket conditions and dirt and chain stretch and chain tension all come into play. It is a real crap shoot as to exactly what your losses are at any given bike condition.

Bottom line is if you want to know, go with the rear wheel dyno and then compare it to a crankshaft dyno. By subtraction you will see the system loss for that motor and drive train. Do it again with a significantly more powerfull motor and I would expect you to see a greater net loss; probably not a lot more but noticeably more. In the mean time, 10hp loss at peak rpm is as good an
Dances with Shrapnel

Mutter Fume ;

750 : 56 Hp , Combat maybe 60 Hp , 850 : 58 Hp . would have to be about right , with a fewe more with a good fit & polishing of the internals .

Consider the early P/R. ran Combat ( SS ) Cam , 30 mm carbs , and they said ran 130 , no troble . Combat Spec. Exceeds Early P.R. , pretty near .

SO , where does this put a 72 750 P.R. with the 32 carbs & Norvil / Dunstal hemi head horsepower wise & speed on optimum ( highest ) gearing .

Not according to the dyno, Matt. Hi-po 850, maybe..

Crankshaft . NORTON had Crank Dyno , so all their figures are From Crank .
Differant knid of crank with these Kawaskis though .

Here is something else to ponder- hp at 5000 rpm for 750 Commando, 750 Combat Commando and 850 Commando,based on Jerry's Norton Technical info torque figures and also torque figure from the big White Norton Shop manual(agrees with Jerry's number)

From the torque figures of 48, 49, and 56 foot pounds at 5000 rpm for the respective Models, the corresponding crank hp figures are 45.7(750), 46.6(750 combat) and 53.4 for the 850.

Glen

Can I bring your attention to the following from;

http://www.factorypro.com/dyno/true1.html

Note the percentage loss from the various sum of parts; tyre loss, valve train loss e.t.c.


Aprilia, RSV4
999.6cc, 2010
Tested by Micah Shoemaker's AF1
2009 #1 USA Aprilia dealer

140.2 True HP


note: claimed crank HP = 180
Take crank hp, subtract 15% from reported reading, take that and subtract 10% for tire losses and 3% to 5% for drive train losses and add 4-5 for the slipon and you come up with about 140 True. Perfect

With all the dynos giving different reading from different parts of the globe, it’s no wonder that it becomes very confusing to an onlooker :!:

http://www.factorypro.com/dyno/true1.html

This is the Calif. shop I spoke with yesterday that Dances chided me on. Tire type, condition and inflation my vary on Cdo's on a roller but the drive train loss is a pretty constant factor across Cdo's, and dyno bragging is all about top end hi rpm power so me and Dances say add 5 hp to rwhp for realistic estimate of shaft hp.
Kind of mixed feeling with this conclusion, one AMC drive train is pretty efficient and two the engines aren't as powerful as our or Norton's wishful thinking.

One can also calibrate one's opinion of a particular dyno report applying the equation, HP = Torque x RPM ÷ 5252, by checking that hp and torque are about equal at 5252 rpm.
http://forums.anandtech.com/showthread.php?t=1925495

DynoDave's past 49 hp dyno win implies 54 crank hp and Jim's 100 rwhp example > 105 @ crank.

hobot said:

Here's a great summary by Dances from the 143 mph 850 post. He agree's with my educated 4-6 hp total drag guesstimates, which is rather strange for a change. Ignore his total drive train percentage though as that has a direct relation to the power level applied, not how much hp it takes to turn a drive train to some rpm. If 5 hp lost in drive train then 50 hp crank losses 10% in path to rear patch while 100 hp would only lose 5%. BTW above don't mean 100 hp gets better gas mileage, even though its got a more efficient drive train loss compared to 50 hp with identical drive path.

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This makes me laugh; consistent in missing the mark.

Your loss estimate started at 10% then 8hp and now 4-6hp....WTF; I would not know what to agree with. :lol: I attempted to illustrate something by bounding it by the universe and you cherry pick the lowest value, the best case scenario. You grab whatever you read and run/broadcast it as your "educated...guestimate". :lol: So ok, your new guestimate is within an order of magnitude. Reminds me of the story about the chemist, engneer and statistician in a duck blind when two of them jump up and fire away at a isolated duck flying by. The chemist was 1 meter low and the engineer was 1 meter high and the statistician shouted out "you got it!"

If you agree that you are all over the road with this then yes, we do agree.

As cited in my summary elsewhere: best case of 4.8hp loss and worse case scenario is around 15hp but 10hp loss at max torque or max rpm is a reasonably good estimate between bounding conditions and is what I have presented. You cannot discount the drive train and tire loss as we are talking about RWHP (rolling road type dynos).

As an example to illustrate this point in finer detail, and if anyone is interested, there's a simple illustraton (formulas) for rolling resistance and rolling resistance HP from a tire. This is presented in the following text by John Bradley titled: "The Racing Motorcycle - A technical guide for construction"

Using the typical laden weight of a Commando with a 200 lb rider, recommended 26 psig rear tire inflation and the factory indicated weight bias of 45.5% front and 54.5% rear (which is afwul by the way) you have the following power losses:

50 MPH 0.6HP
80 MPH 1.4HP
100 MPH 2.2HP
115 MPH 2.9HP
120 MPH 3.2HP
143 MPH 4.9HP

This is the tire rolling resistance power only and illustrates that you really need to understand numbers being reported. I wonder now if some dyno's factor this in when reporting torque, speed and power. Maybe some knowledgeable bloke who runs dynos can chime in here.

So as an example, using a primary chain efficiency of 97% and a gear box efficiency of 98% and a rear chain efficiency of 93% and a rolling road dyno pull to 115 MPH which is a reasonable speed for a well sorted stock Commando and 60 Crank shaft HP we have a mechanical loss of 7HP and from the table above a rear wheel loss of 2.9HP for a total of 9.9HP loss. Round to 10 HP since I don't know what I am doing and subtract from crankshaft horse power and I get 50 RWHP which is what I have seen on the dynos. The primary chain and gear box should be in the best of shape in terms of lubrication but the rear chain is a real crap shoot given the variety of conditions it can be in when a dyno pull is conducted.

So if you do the dyno pull in third gear you should have less tire loss (lower speed tire) but more gear box loss. What is the specific relative value of this trade off I do not know.

Bernhard said:

With all the dynos giving different reading from different parts of the globe, it’s no wonder that it becomes very confusing to an onlooker :!:

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+1

What they are good for is tuning and relative performance improvements on the same bike; regardless of the exact indicated torque and rpm.

J.A.W. said:

What purpose does it serve to concern youself with 'crank' hp - if you are going to use the bike as intended, anyhow?

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So I can relate to the manufactures of JS rods & lightweight pistons and determine if further lightening of reciprocating weight is possible and at what saftey margin. They go by crank HP. So far they've been subjected to 150 crank HP on Nitrous oxide. Thats a bit extreme.

hehe I thought you'd recoil and skip over my earlier questions on tire drag, but will take your slaps for the juicy tire drag details. I reflexly stated 10% cost d/t communes with Steve Maney on his 100.4 hp 920, which if drive train costs ~5 hp and tyre ~5 hp, then what does that imply on his shaft power? I accept your ballpark 10 hp total drag on this over mine if that matters anyone but me. Basic moral I take away, our drive train ain't costing no 20 or even 15% in the big hot rods.

The most realistic way to measure everything, power to rubber, is distance / time of some mass. Seems most pleasing characteristic of Norton twins are their ability to run up to maximum a bit sooner than others of similar power. I'm taking some risks with Peel to get more of it too.

Classic Racer Sept/Oct `07 J.P.N. feature P.33;
States that the 4th place P.Read `72 Daytona Commando used a...
" 69 bhp production racer" mill, the lower tune & Read's mechanical sympathy being the reason for the good finish, as it was slower by ~40 mph than the 2 stroke 750 triples that chewed up their tyres, & still not as fast [top speed-wise] as the winning factory Yam 350s.

J.A.W. said:

Classic Racer Sept/Oct `07 J.P.N. feature P.33;
States that the 4th place P.Read `72 Daytona Commando used a...
" 69 bhp production racer" mill, the lower tune & Read's mechanical sympathy being the reason for the good finish, as it was slower by ~40 mph than the 2 stroke 750 triples that chewed up their tyres, & still not as fast [top speed-wise] as the winning factory Yam 350s.

Click to expand...

You need to remember that these articles are written by journalists who take information from people who may or may not have the correct information in the first place and may actually be expressing an opinion rather than facts.