Fuel Flow Rate for a Commando 850

norbsa48503 said:

Well it was a few years ago But here's the sheet from that day. Only as good as the dyno but it was rear wheel.

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It doesn't chart RPM?

Dynojets - at least the models used at typical shows and meets and a lot of small shops don't. They can't load an engine, they just measure how quickly the rear wheel spins up a flywheel and calculates HP based on how fast it spun up. They don't have way to measure engine RPM and there is no way to "hold" the engine at any RPM and measure HP at that point. It's not like a Mustang or other water brake or eddy current dyno that would be used by a major engine builder or car/motorcycle company. But they're a fraction of the cost and useful for "casual" work.

MexicoMike said:

Dynojets - at least the models used at typical shows and meets and a lot of small shops don't. They can't load an engine, they just measure how quickly the rear wheel spins up a flywheel and calculates HP based on how fast it spun up. They don't have way to measure engine RPM and there is no way to "hold" the engine at any RPM and measure HP at that point. It's not like a Mustang or other water brake or eddy current dyno that would be used by a major engine builder or car/motorcycle company.

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So estimated max HP and that's it. Mostly for bragging rights with your idiot friends?

Well, they are used by some performance shops but...well, yes, pretty much what you said!

comnoz said:

And here is the best from Fuelie on a pretty conservative Superflow eddy currant dyno. Jim

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Is that corrected for altitude :?: At any rate, pretty good for a "street" Norton

Jean

Jean, It is corrected for altitude using the SAE formula. There are several different formulas around for correction. One of the reasons for different figures from different dynoes. Jim

Does that mean the power shown is what it "would be" at sea level or is it what you have on tap at a mile high :?: In the real world, at your altitude, what do you have for power :?: I was told at Bonneville, the power was much reduced, someting like 25-33%, is that accruate :?:

Jean

That means that the power on the slip is what the bike should make at sea level. I am at 5000 feet here so I don't see that power until I go down the hill. Then if I removed about 100 lbs of excess weight [me and the bike] it would be pretty quick. It will still run a decent top speed though.
Salt Lake kills a bike because of the altitude plus the drag of the salt on the tires. How many times have you heard "that isn't so fast, my bike will do that" - well, not at the salt flats it won't. I have never run one there but that is something I hope to do yet. Jim

"So estimated max HP and that's it. Mostly for bragging rights with your idiot friends?"
Well Dave, Sorry you have such a low opinion of me.
The dyno I used was the only one around here. At least I did the test, spent the time and 45.00. I did the test after noticing that my 750 would out run the local 850's around and to work on the carb jetting. RPM'S are shown on different pages of that report torque on another and so on. The dyno was in a Big Dog dealer and was used to re-jet after doing exhaust system changes. Mr. West who did the test has seen a ton of HD's and S&S on his machine said that he was impressed, for a 750 it made good power. Good enough for me to think it not too far off. Yes after you have spent money and time on your machine and it seems to do well on its own and with other like machines you might be less likely to question the absolute accuracy of the dyno against other dyno’s. I did richen the lower end and lean the top end after this run and it helped me get the bike running better so it worked for me.
The point of posting it for the purpose of this conversation was about fuel flow at max output of the engine and trying to get that part of the problem dealt with. Not to brag about the power but to tell what I found out about the restrictions I found in the fuel system that held it back. The max flow is only needed in a narrow band of RPM’s 5000-7000. If you’re going to do this out on the street regularly you have to know some things about how it’s working in that range and the dyno lets you see things that you can’t see while driving at that speed. So you and others can adjust the figures to what ever you think they are in your world or on your dyno. I met Kenny C. at the old Grattan track by the fence we talked about front end kits a couple of years ago so when he implied that I was high on the HP claim I posted the sheet. I now regret being baited but as I said it seems to work for me in my world.
Jim’s results are amazing he is making the 50 HP at 5400 RPM if I read it right. Way beyond what carbs could ever do on a bike. The best part is finding that power down in that range were it is so useful on the street. I should have taken him up on his offer to ride that bike at the Michigan rally.

Getting the peak horsepower with carbs isn't too much different. Getting the wide spread of power is where fuel injection helps. You can tune the motor closer to the danger points when there is electronic timing and mixture controls to keep you on the safe side. Jim

norbsa48503 said:

I met Kenny C. at the old Grattan track by the fence we talked about front end kits a couple of years ago so when he implied that I was high on the HP claim I posted the sheet. I now regret being baited but as I said it seems to work for me in my world.

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No no, you misunderstood. I wasn't calling YOU out or baiting at all. I was referring to all those folks I've heard over time making pie-in-the-sky hp claims for their bikes (perhaps because some folklore Norton marketing literature told them so). Invariably they are disappointed when they get to the dyno and see the real world numbers. I have a dyno, and I've seen in person the shoulders drop, the scowls, the life creep out of folks when the real world numbers tell it like it is.

I think 49hp at the wheel is not unrealistic with a well tuned stock motor, and you have the sheet to show for it (with the only dispute being the variations from dyno to dyno, which we all agree is a legitmate discussion). If someone makes claims of, say, 65hp (I think somewhere in some literature this was claimed for the Combat motor) I will call them out.

Now, let's talk about front-ends.

-Kenny C.
NYC

I recall (maybe incorrectly?) that the Norton claim was 70HP for the combat motor, at least initially.

norbsa48503 said:

Well Dave, Sorry you have such a low opinion of me.

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Woah, this wasn't directed at you. It was for the squids at the bike shows who throw their bikes up on a dyno just for bragging rights. Has nothing to do with you.

Stock 750 was 60 HP claimed and Combat was 65.

Shows how good my memory was Further to this I just found a copy of the 72 Commando brochure which lists 58 HP at 6500 RPM for the standard compression (8.5:1) engine and 62HP at 6200RPM for the "High compression," (9.5:1) engine which is listed as available in the roadster only. I assume that high compression version was the Combat motor?

My head is spinning trying to keep up with you guys.

Mike, my remembrance is that the 750 Commando (standard) was 9:1, while the 750 Commando Combat was 10:1. The compression was lowered with the intoduction of the 850 to 8.5:1 to keep the engines from exploding. These numbers are identical to those appearing in the "Norton Commando Technical" section of this forum. Wikipedia mumbles something about a 1973 reduction to 9.4:1, but that likely represents a detuning of the 1973 Combat.

Regarding horsepower, I was gratified to read Jim C.'s dyno result on a Mikuni 34-based 850. The 35-38 max HP that he reported is completely consistent with the fuel flow limit imposed by the Mikuni.

Here's a screen shot of the section of the 1972 commando brochure that I was referring to:

I'm so confused. Is there no ground truth?

Sure they just had littler horses than most. Jim

I don't have much faith in the measured HP at the back wheel or crank, what matters I think is the actual pavement performance. Back in '71 I think it was Cycleworld organised a drag strip shoot out with several of the leading contenders. The Combat won over the triple smoker Kawasaki 750 Mach 4! I think it pulled a 12.5 and I think, memory fades - here that Mick Hemmings actually was sent to California to promote the model. In 1973, at Elvington airfield Yorkshire one cold and damp October, the factory put a 850 through a max speed run of 141MPH.

None of this is HP we haven't got. It was careful tuning, everything optimised, selected gearing, jockey riders, road sloping in the right direction, favourable wind and generally power to weight ratio. The Combat dragster had a 19T sprocket and maybe would have lasted till the end of the day and blown up. The 850 was geared with 24T, it had barely enough power to shift into top and need several miles of road to max out. But, they got the official printout and they bragged about it. I run an 850 with a single 34VM Mikuni and not much of an airfilter, 22t box, stock motor with Dunstall pipes. Sounds great, goes great up to 5500RPM and thats 99MPH / 160Kph and I'm breaking the state speed limit, my neck and my arms. There ain't any more power worth wringing out of it after that. So if that's done on 40HP or 60HP, to me it is simply irrelevant.

Mick