Commando HP and Torque

Most motorcycle horsepower figures are probably bullshit. If a dyno is calibrated by putting a Yamaha Vmax on it and adjusting it to read 150 BHP, the calibration a graph is probably a straight line between zero and 150 BHP. In effect, the actual horsepower figure does not really matter because when you use a dyno, you are usually only looking for an improvement. If you watch the second part of the following video, you will see what Bob McIntyre used to do to tune his motor. His test brake might have had a lever arm which was calibrated with a dead-weight tester - but I doubt it.
 
The best type of racing for testing power is quarter mile racing. The Commando made good grades there. It certainly outperformed bikes such as the lighter Triumph Bonneville (46 bhp?) BSA Super Rocket ( also rated at 46bhp) or even the Norton 650SS, rated at 49 bhp.

By that measure the rated crankshaft HP of the Commando seems about right
On the other hand maybe they were all over rated.
The dyno numbers all depend on the dyno used and the correction factor of choice.
The quarter mile times are down to bhp, as long as the rider has the basic skills.


Glen
 
acotrel said:
In Australia, all calibrations are supposed to be traceable to the standards in the National Measurement Laboratories. The 50 BHP of the Manx was probably measured on a Heenan and Froudr test brake and is probably pretty genuine. In the early 1960s, I watched Jack Forrest trounce all the Manx Nortons in a race, with a 650ss, so a 650ss probably delivers much the same as a Manx. I think any Commando would be a bit slower. Theit bigger capacity would not mean much.
The dynos which are currently used measure torque and the calibration of some is adjusted so they read a certain value for a Yamaha Vmax. The calibration is not usually based upon the normal measurement standards.
If you ride a genuine petrol fuelled Manx, you can get a basis for comparison when you ride other bikes down straight roads. My mate's 650cc Triton delivers much more power than a Manx. It is faster in a straight line. But not around corners. My Seeley 850 might be slightly faster in a straight line, but only because it is faster as it enters the straights. I accelerate hard from much further back in corners.
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Yes, many dyno figures seem rather ‘rubbery’.
Many years ago I had my mildly improved MGB on the dyno and the operator pronounced it was developing around 75hp (if I remember correctly). I think the original brochure had it at well over 100. I was initially disappointed until he pointed out that he Considered that an excellent figure in comparison to other MGs he tuned and pointed to several much larger engined cars in the workshop that didn’t develop much more power.
Then, tongue in cheek, he asked me how much power I would like it to develop as he could adjust the dyno to indicate any power I liked, something he said the ‘hot rodders’ insisted on
Alan
 
I might still have the Sportbike magazine from a few years back that offered dyno numbers from multiple S Cal dyno shops. They took the same litre Sportbike to 7 or 8 shops, all in one day.
The output numbers ranged from 111 to 163.
" We"ll get you to those dynos that are putting out the really big numbers everyone wants!" was the opening line.
S'truth I suppose.

Glen
 
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acotrel said:
Most motorcycle horsepower figures are probably bullshit. If a dyno is calibrated by putting a Yamaha Vmax on it and adjusting it to read 150 BHP, the calibration a graph is probably a straight line between zero and 150 BHP. In effect, the actual horsepower figure does not really matter because when you use a dyno, you are usually only looking for an improvement. If you watch the second part of the following video, you will see what Bob McIntyre used to do to tune his motor. His test brake might have had a lever arm which was calibrated with a dead-weight tester - but I doubt it.
Click to expand...

Thanks, Al. I enjoyed those videos.
Jaydee
 
jsnorton said:
I can not seem to find the factory stated Horse power and Torque for a 1973 Commando 850 roadster Mk1. Does anyone know offhand ?
Thank You
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The (excellent) French manual from 'Revue Moto Technique' :

Commando HP and Torque

Measured at the gearbox.
 
In documentation I have from the 50s produced by GM for fleet truck buyers, there are pages for each engine showing curves for net and gross hp and torque. These are listed as "certified" and signed off by an engineer. Is one to believe the engineers had put their credibility on the line by signing off on these charts? Would fleet buyers call them on it if performance did not prove out. I don't know but a later set of dyno runs by McGurk written up in a 1955 Hot Rod Magazine article showed much lower figures than the certified GM pages.

A 261 C.I. inline six rated at 145 only produced 114 crankshaft Hp on McGurk's engine dyno. What the real world figures were is a bit of a mystery as they were looking for improvement with various modifications and were able to considerably beat the factory figures with a still streetable engine, 165 vs 145. Given the tractor-like basic design and limited head potential that'a about all one could expect.
 
Fast Eddie said:
That probably where they got it from…?
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Not likely as it is taken at gearbox and it looks to be about 53+-?
If they were just copying the manufacturers claimed output it would be a higher number and not at gearbox.

Glen
 
Thomasa said:
In documentation I have from the 50s produced by GM for fleet truck buyers, there are pages for each engine showing curves for net and gross hp and torque. These are listed as "certified" and signed off by an engineer. Is one to believe the engineers had put their credibility on the line by signing off on these charts? Would fleet buyers call them on it if performance did not prove out. I don't know but a later set of dyno runs by McGurk written up in a 1955 Hot Rod Magazine article showed much lower figures than the certified GM pages.

A 261 C.I. inline six rated at 145 only produced 114 crankshaft Hp on McGurk's engine dyno. What the real world figures were is a bit of a mystery as they were looking for improvement with various modifications and were able to considerably beat the factory figures with a still streetable engine, 165 vs 145. Given the tractor-like basic design and limited head potential that'a about all one could expect.
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It just depends on the dyno used and the correction factor used. There are many different correction factors.

I was told of two well known racing Nortons. One made a dyno chart showing 80 rwhp.
The other bike made a best run of 62 rwhp on a different dyno.
In a race the 62 HP bike passed the 80 HP bike on a long straight.

So the dyno numbers can really be confusing.

Glen
 
worntorn said:
Not likely as it is taken at gearbox and it looks to be about 53+-?
If they were just copying the manufacturers claimed output it would be a higher number and not at gearbox.

Glen
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If you believe that to be correct, then what’s the explanation for people getting low 40s on the dyno ?
 
Fast Eddie said:
If you believe that to be correct, then what’s the explanation for people getting low 40s on the dyno ?
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Many also get high 40s rwhp.
Then add the desired cf and you are good to go.

When you have two Nortons dyno tested , one at 62 rwhp and the other at 80 rwhp but the 62 rwhp bike clearly has the greatest output, how much stock should one put in any dyno number?

I think dynos are a great tuning tool, same, dyno same bike, but not so great at indicating actual chiselled in stone real world output.



Glen
 
worntorn said:
Many also get high 40s rwhp.
Then add the desired cf and you are good to go.

Glen
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So the factory used a high correction factor ?

Its either that, or they just plain lied (there was a lot of it going on back then).

Dave Nourish (who knew cos he did both, and had nothing to gain by the point) said there was 5 BHP difference between crank and wheel figures.

The most common figure I see for stock (ish) Commandos is low 40s.

So, irrespective of a little debate either way, my main point is still that the factory claim of 60bhp for a stock, none Combat, production line Commando jus’ ain’t true if we’re talking real world output unless the dynos people are using are exaggerating the figure down !?

If the 62bhp bike passes the 80bhp surely we all assume its the 80bhp figure that’s the one in dispute ?

Then so it is when we’re comparing 40 something rwhp dyno findings to the 60bhp factory claim.
 
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I have been reading about correction factors, although I have only scratched the surface.
One of the most common factors used today is SAE J1349. It corrects to a standard for temp, humidity, barometric pressure plus adds 15% for driveline losses.
Another older standard added 18% for friction plus corrected to different weather standards.
The highest cf encountered so far is a DIN cf that gives crank HP figures even higher than any of the SAE measurements.
So yes, it is quite possible that Norton measured at the rear then used a cf.
They also might have just fibbed. As you say, many were doing this.
I'm not sure!
When I get off the 46 claimed HP BSA and onto the 58? claimed bhp Norton, the Norton feels like it has twice the oomph of the old A10.

So all very confusing.
The results of my recent roll on race only added to the confusion. I was almost hoping that the hopped up 750 would rocket away like a 60rwhp bike vs a 40 rwhp stocker, but that didn't happen.
Surely that is a better test of relative power than any dyno?

Glen
 
worntorn said:
The results of my recent roll on race only added to the confusion. I was almost hoping that the hopped up 750 would rocket away like a 60rwhp bike vs a 40 rwhp stocker, but that didn't happen.
Surely that is a better test of relative power than any dyno?

Glen
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Yes it is, it proves they were basically the same (although, as I said before, your gear-change technique was excellent, was your buddies as good?).

So, we know the 750 and 850 are very close indeed, which given the almost identical internals, does add up.
 
Only thing is that 750 has high lift cam, raised compression and head work done, so maybe not near identical internals. For mods it is closer to your 850 than my 850, which just has the silencers changed. Not really the best comparable for the MK3, but the owner is game. I think he knows how to crank it on too.
Next time he'll get the camera
Fast Eddie said:
Yes it is, it proves they were basically the same (although, as I said before, your gear-change technique was excellent, was your buddies as good?).

So, we know the 750 and 850 are very close indeed, which given the almost identical internals, does add up.
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worntorn said:
Only thing is that 750 has high lift cam, raised compression and head work done, so maybe not near identical internals. For mods it is closer to your 850 than my 850, which just has the silencers changed. Not really the best comparable for the MK3, but the owner is game. I think he knows how to crank it on too.
Next time he'll get the camera
Click to expand...
Ok, but in that case, I don’t quite know what you were trying to prove in that ’test’ ?!

Obviously his bike should produce more power. That is surely indisputable. Basic physics comes into play here. Perhaps it wouldn’t be as good two up, canyon carving fully loaded up long inclines, etc. But outright power? The cam and the CR and the head work (assuming that was done right) MUST achieve that.

I guess what it has shown is either that the guys riding technique wasn’t as good as yours, or his engine building technique was off ?

As far as standard 750 vs 850 goes, here’s my 2 cents:

The engines are virtually identical in terms of cams, carbs, stroke, overall head design, etc, etc. I’m not sure about CR though, my own 850 was under 8:1 as measured.

The 850 has an extra 70cc which should make itself felt in terms of extra grunt. But in terms of extra power, unless the 850 engine has been tuned to maintain (at least) the same MBEP as the 750, then it is unlikely to produce any more actual peak power.

The valves will hold the 850 back, as we know, they’re more or less ‘right sized’ for a stock 750, but slightly under sized for an 850. This will prevent the 850 matching the 750s MBEP.

IF the 750 does have a higher CR, then this would give it a small additional edge in terms of MBEP.

Then it probably comes down to head type, although the same overall design, Norton used various heads giving different port sizes and CR. So in stock form, without any porting work, this could make quite a large impact IMO.

Then there’s the riding style, the 850 will almost certainly accelerate faster by using rpm which accesses the torque, especially in the lower gears. The 750 will accelerate faster if it’s kept in the rpm for max peak power, and it’d need this right from the off. The 750 will never win a roll on in the same gear as the 850.

My understanding was that Norton‘s intent with the 850 was to achieve similar performance as the 750, but at lower stress ie rpm. And I think the above points back that up. Like Japanese bikes of the time however, bikes with a noticeable ‘power band’ do deceive the arse dyno into thinking its going faster. Maybe there’s some of that going on in the general ‘750s after faster’ discussions ?
 
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"Ok, but in that case, I don’t quite know what you were trying to prove in that ’test’ ?!"

That started with two claims being made by a friend who has owned a 71 750 for awhile now and recently added a 74 850 to his herd.
Claim1, which was also made several times in a recent thread here.
-The 850 is much heavier than 750, not only in handling but also in struggling to move it around the shop.

Claim 2. Also made many times on this forum.
The 750 is a faster accelerating bike than the 850. My friend claimed " much faster" Others have just said faster.

Of course I challenged both of these claims. The weight claim was easy to disprove.

We weighed his 750 and his 850 on the same hanging scale (both Interstates with equal fuel)
The 850 was just 5 lbs heavier, inconsequential. Definitely not a noticeable amount.

I then challenged him to a roll on with using my MK3, supposedly the slowest Commando ever produced.
The result wasn't good for the 750 but I suspect he did not make full use of the 750.

Another friend who was following this discussion said he would slaughter the 850 with his 750 , which has a Comstock head , D port exhaust , etc etc. He tells me that iy is a very strong 750 and he has owned a number of Commandos, knows them well.
It also has an Alton starter so weight of the two bikes is very close.

That was the close race.
That 750 did pull away nicely between 80-90 then things stayed even again until we shut off at about 110+-
So Im not sure if we proved much with that one except that the mods help, however the gains are perhaps not as much as folks think? The stock setup seems to give a pretty good run.
And given the mods on that 750, a stock 750 against an 850 is going to get left behind. Even against a lowly MK3.

So claim number 2, stock 750s are a faster accelerating bike than stock 850s, would appear to be wrong as well.
I should add that we are also old guys having some fun with motorcycles. So we will run again , this time giving the jump to the MK3 and see what happens. I think I have a shot.




Glen
 
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