Commando HP and Torque

I have recent dyno figures for standard 750 and that indicates 48 at the rear wheel, a standard 850 will be low 40's. There are also dyno traces from the 70s in existence, I've seen them but not sure where the files are now.
Not sure how much testing Norton did, but I do know they had an engine dyno at Thruxton race shop, I was stood in the room they operated it in only 3 weeks ago.
One thing that also seems to be overlooked is spring rate and cam lift as this can also sap power. Its an area where trade off can be made, approaching max lift with high spring rates could work against what is trying to be achieved.
One successful race team from the early '70s used skimmed heads, HC pistons and most surprising a standard cam.
 
Madnorton said:
I have recent dyno figures for standard 750 and that indicates 48 at the rear wheel, a standard 850 will be low 40's. There are also dyno traces from the 70s in existence, I've seen them but not sure where the files are now.
Not sure how much testing Norton did, but I do know they had an engine dyno at Thruxton race shop, I was stood in the room they operated it in only 3 weeks ago.
One thing that also seems to be overlooked is spring rate and cam lift as this can also sap power. Its an area where trade off can be made, approaching max lift with high spring rates could work against what is trying to be achieved.
One successful race team from the early '70s used skimmed heads, HC pistons and most surprising a standard cam.
Click to expand...
You can't compare if different dynos, operators, different day even.
 
The crossover point torque and HP is due to the equation 'One horsepower is equal to 33,000 foot-pounds of work per minute' which gives 5252rpm as the crossover.

But Luwig's graph is HP vs m/Kg. so the crossover point is different, you will have to do the calc based on the new ratio to confirm the new crossover point.
 
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Among all these things there can be subtle, un-noticed things. I'm working on a Combat right now and noticed that the intake manifolds that came with the bike were made offset. The bore of the manifold matches the bore of the carbs but did not line up when connected - about 1/16" offset. I have two other original sets that matched the carb bores and line up almost perfectly. Not sure how much effect that would have but I would imagine some.
 
worntorn said:
"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
Click to expand...
I think the only way to square this one away is to put a stock MK3 against a stock 750
There's no point otherwise
 
High performance mirrors. Instead of objects being closer than they appear, they are further back than they actually are with high performance mirrors during testing. Kidding

Since this thread is barely on topic anymore... Does anyone have a Norton 750 with a TGA/Molnar light weight crank in it that could share their before and after HP feel experience? I think a Maney crank is about the same thing. However, Maney cranks are out of production.
 
Fast Eddie said:
To what do you attribute the increased power that your bike seems to have then Glen ?
Click to expand...
There's nothing special about it, still all original internals, so it's probably very similar in power to other 850s.
I suspect that if I encounter a good stock 750 and it is run hard, it will be a close race.

I do think the 850 has a slight advantage due to cubes.
The valve size problem isn't much of a problem if revs are kept to 6 k max. The stock cam works also best below 6 k. Maybe that is why the designers left the valves at 1.5" for the 850. It's in keeping with the bulletproofing of the engine that occurred after the higher revving Combat disaster.
If a big cam is used then the useful rpm range moves up and the 850 valves are just too small over 6k rpm.

Glen
 
Schwany said:
High performance mirrors. Instead of objects being closer than they appear, they are further back than they actually are with high performance mirrors during testing. Kidding

Since this thread is barely on topic anymore... Does anyone have a Norton 750 with a TGA/Molnar light weight crank in it that could share their before and after HP feel experience? I think a Maney crank is about the same thing. However, Maney cranks are out of production.
Click to expand...
Lightweight cranks are more divisive than oil shut off valves… or even M3 Commandos !!

Many will say that the reduced torque is a bad thing. A heavy crank stores energy which provided motion between power pulses. So a light crank does not have the bottom end torque feel of a heavy crank.

But, a light crank definitely spins up faster, it provides a far more lively feel.

As to whether or not one is actually better than the other is difficult to say and is the subject of heated debate! Steve Maney had one of the most successful classic racing Commandos out there, and he made his cranks light. He could have made them any weight he wanted to, so clearly he believed light to be better.

I fitted a lightweight Maney crank in my JS long rod equipped 920 and I love it’s revvy nature. But then again I like my 68 T120 and it’s lightweight crank, even though many do not.

So I’d say it all depends on personal taste. If you want a torquey cruiser, I think a heavy crank is best, if (as I suspect you are) you’re trying to further leverage the ‘hot rod’ aspect of your hot rod P11, I think you’d enjoy the lightweight crank.

Of course, be it Molnar or Maney, you’ve also got the added advantage of it being bomb proof.
 
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worntorn said:
There's nothing special about it, still all original internals, so it's probably very similar in power to other 850s.
I suspect that if I encounter a good stock 750 and it is run hard, it will be a close race.

I do think the 850 has a slight advantage due to cubes.
The valve size problem isn't much of a problem if revs are kept to 6 k max. The stock cam works also best below 6 k. Maybe that is why the designers left the valves at 1.5" for the 850. It's in keeping with the bulletproofing of the engine that occurred after the higher revving Combat disaster.
If a big cam is used then the useful rpm range moves up and the 850 valves are just too small over 6k rpm.

Glen
Click to expand...
I know there’s nothing ‘special’ as you’ve told us it’s stock. I’m just threading your posts together in my head Glen, similar weight, fair test, good riders with good technique, yet they disappear in your mirrors. With everything else being equal, the only thing left is power.
 
The hotrodded 750 eventually left me behind, but not by much. A rematch will be interesting.
The other 750 wasn't ridden to it's full potential.
More experimentation is needed.

Glen
 
Fast Eddie said:
Lightweight cranks are more divisive than oil shut off valves… or even M3 Commandos !!

Many will say that the reduced torque is a bad thing. A heavy crank stores energy which provided motion between power pulses. So a light crank does not have the bottom end torque feel of a heavy crank.

But, a light crank definitely spins up faster, it provides a far more lively feel.

As to whether or not one is actually better than the other is difficult to say and is the subject of heated debate! Steve Maney had one of the most successful classic racing Commandos out there, and he made his cranks light. He could have made them any weight he wanted to, so clearly he believed light to be better.

I fitted a lightweight Maney crank in my JS long rod equipped 920 and I love it’s revvy nature. But then again I like my 68 T120 and it’s lightweight crank, even though many do not.

So I’d say it all depends on personal taste. If you want a torquey cruiser, I think a heavy crank is best, if (as I suspect you are) you’re trying to further leverage the ‘hot rod’ aspect of your hot rod P11, I think you’d enjoy the lightweight crank.

Of course, be it Molnar or Maney, you’ve also got the added advantage of it being bomb proof.
Click to expand...
Thanks for the response, Nigel

Yes, it would be for the goofy P11. Hoped you would speak up. I knew you probably had a Maney crank in that 920.

Bomb proof is what I wanted to hear. I figure a lighter crank would allow the motor to last longer the way I like to hold gears. I might have hurt my big end rod bearings already riding the old iron like it was manufactured yesterday. Still investigating where the new noise is coming from pre tear down.

Anywho, less rotating mass suits my riding style better than a heavy crank does. I won't miss the torque. I've lightened up rotating mass with other marques and still enjoyed the ride on the street. Of course, the gearbox probably won't be stock much longer either. Gotta find some use for that RMD money next year. lol

Sorry about the diversion to all the serious types. I know you do not appreciate it. (Insert crying emoji here)
 
Of course there is a point. The bikes are what they are. We aren't going to alter them because someone says "this MUST be this"
Its all just for fun.
Take from it what you may.

Glen
 
worntorn said:
Of course there is a point. The bikes are what they are. We aren't going to alter them because someone says "this MUST be this"
Its all just for fun.
Take from it what you may.

Glen
Click to expand...
The point I am making is these myths and rumours come from back in the day when the bikes were brand new and standard
I suspect a stock (black cap equipped) MK3 commando would be slower and heavier than a stock combat 750
But with a set of pea shooters I think it'd be a different story
It is all a bit of fun
 

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