6400 rpm in top

Measuring the torque at the rear wheel won't move the max torque from 5000 rpm back to 3000 rpm !!!

No it won't.
I was attempting to make you feel better about your 52 foot pound number, which is also about the max at rear wheel shown on the chart, albeit down low, not at 5000.

Glen

worntorn said:

I was attempting to make you feel better about your 52 foot pound number,

Click to expand...

You mean explain how the factory claimed such big numbers,
when no-ones bike actually produced that..... ?

The shown 850 power curve doesn't reflect that max torque at 5000 rpm,
so it can't be drawn correctly either.. Dang, not worth back-calcing the numbers.

OK, it was a failed Dale Carnegie 101 experiment, won't happen again. :?

The factory torque rating for the MK3 850 of 56 ft. Lbs (at crank)at 5000 rpm correlates to a horsepower output (at crank) of a shade over 53 bhp at that rpm. That seems in line given how variable dyno numbers are.

Glen

A Combat must down shift below the normal 850 to stand a chance up to almost the ton and required two down shifts on my SV to keep up with a seasoned rider exiting tights on vaction in the twisties on soft air tire and significant cargo looking just as easy as a guy in a deck chair. Only thing I noticed on the few 850s I've 'wrung' out is the pull just runs out too soon.

You are talking about two different things when you are talking about top speed and the time over a 1/4 mile

Click to expand...

Nope sir in thrilling real life with more that one in a rush theres often ticking away passing opportunity to get done, often as last one to pass out of a hot shot squad to shoot through the fast disappearing passing space they left and then keep the rush going loner/strong than them to ctach back up with the cluster for fun. I like watching the cool cycles and decent pilots taking turns, mostly the same way though. This is not racing as the elites can smoke even race Commandos so more like fighter formation joy rides that takes at least 13-ish sec 1/4 m accelerations to a dozen+ mph above the ton on every stretch ya ain't preping for real turns. I can not keep up with these squads on my SV if theres any straights over 1/2 mile or so d/t its lack of acceleration over 90 yet developes 42- lb ft 69 hp 360 lb cycle famous for V twin corning torque but also as girls bike for this reason. Ya can't hot rod them much over 80 hp or crank lets goes. The all out short life race engines can get 120ish hp for a race or so. I'll hold my factory Combat mid 6000's for miles at a time with increasing pull on tap but decidet no more Trixie straining into red zone so if left behind oh well was fun while it lasted.

No cycling for me indeterminate time so thinking to get a GPS/Accelerometer to pass around and collect tales.

Due to the calculations involved, my understanding was that power and torque readings from ay given run will alway cross (be equal) at 4,500 (or there abouts).

Of so, these graphs have fundematal flaws in them, and would appear to be not very useful.

The torque and hp curves will cross at 5252 rpm - and be numerically equal - IF and only IF the torque and hp curves are drawn to the same scale.

Note that these graphs have different scales (each side) for hp and for torque.
So cannot cross in these circumstances.
It is merely convenient, for interpretation, to have the scales drawn the same, not a necessity....
Cheers.

Rohan said:

The torque and hp curves will cross at 5252 rpm - and be numerically equal - IF and only IF the torque and hp curves are drawn to the same scale.

Note that these graphs have different scales (each side) for hp and for torque.
So cannot cross in these circumstances.
It is merely convenient, for interpretation, to have the scales drawn the same, not a necessity....
Cheers.

Click to expand...

Indeed, two separate scales, should have realised that!

After looking at some other dyno charts for 850s,I think the Duckworth chart is fine.
Whitworth Ranch provided a dyno chart for his 850 and these comments:

"Horsepower was 46.59 at just under 6000 rpm with a nice curve. For torque, it's easy to see why these engines feel so good on the road. It's making near-peak torque well under 3000 rpm and doesn't dip much before the "second' peak of 44.34 at 4600 revs. "

The scale of the Duckworth chart may be deceptive for the torque line. As near as I can tell, it shows a peak of about 52 foot pounds at about 3200 revs but still has about 48 foot pounds at 5000 revs. Slightly higher number than Whitworth Ranch had, different dyno and different bike, but essentially the same near flat torque line from 3000 rpm to 5000 rpm.

Glen

Cycle's graph of the JPN which was basically to Mk2A spec.
This shows maximum torque at 5,000 RPM.



http://www.classicbike.biz/Norton/Mags/ ... on-Cyc.pdf

There seems to be a dirth of dyno information posted on Commandos. I did find this chart online taken from an old access Norton thread on Jim Comstock's dyno day. Too bad it is so blurry. The shape of the torque curve is near identical to the Duckworth curve, the big ball down low then near flat most of the way thru the range. I believe this is from a fairly standard 850 that Jim tested, one that dyno'd well.



And here is Whitworth Ranch's 850 . Rpm is cutoff, but first peak in torque is at 2800 rpm. The graph ends at 6000 rpm.



Both of these plus the Duckworth graph show a lot of power down low then a very flat torque line on up, which is the way my 850 works.
The Cycle chart looks totally different again. I have to wonder if the bike tested had a little hotter than stock cam, such as a 2s?

Looking at those torque curves, its difficult to believe some of them are even supposed to be the same engine. !?
If Nortons claimed max torque at 5000 rpm, you'd sort of expect that to bear something close to reality ?

Looking at the 850 curve in Duckworth, the plot of hp isn't entirely related to the torque curve.
Look at that hp curve rising and dipping sharply at ~6000 rpm, and yet the torque curve is BELOW the others,
so how can the hp be higher ??
AND, the 850 torque curve doesn't dip sharply at 6000 either, so why does the hp curve dip sharply ??

This is why we were interested in someone dyno testing a balanced set of pipes,
and then testing the same bike on the same dyno with a set of unbalanced/separate pipes....

Preferably without the plastic airbox version too, which may be a factor in these rather disparate results.
(But with the stock airbox and airfilter setup)

As noted before, that big dip in the torque about 3000 rpm looks terrible, wonder if that is really a feature of a stock bike,
and if it can be tuned out ?
My old 850 felt really strong about 3000 - shame I didn't dyno it ??
Stock ham can aircleaner and air filter setup....

This is that torque curve, reversed.
Pardon the rough look....
You'll have to use your imagination for the rpm scale along the baseline.



More what you would expect, with torque increasing towards the factory claimed max of 5000.
And dipping sharply above 6000 - same as that hp curve.

Here is the graph from the Brian Dolman article in the Feb. 2012 issue of CBG.



None of the test configurations manage to reach the "30 BHP at 3,000 RPM" level on the Duckworth graph, and if the torque figures are calculated from the highest BHP curve of the Dolman graph then max. torque is highest at approximately 5,000 RPM.

L.A.B. said:

and if the torque figures are calculated from the highest BHP curve of the Dolman graph

Click to expand...

Have you, or anyone, actually done this ?

Its worth commenting that hp curves are generally calculated from the torque curves,
and just by looking at hp curves its not at all intuitive where max torque values will be.

Modern dyno's may initially spit out a hp curve, but thats because the confuser has done all the calcs for you.
Engines produce torque, and calculations produce a hp curve.

P.S. That graph is as clear as mud.
Not your fault LAB, before you spit back....

Les,

Interesting information. Can you explain what "venturis on ears" are? I am guessing that it was some sort of modification to the air box "horns'

Thanks,
Pete

And which pipes/test had the 1" mutes ??
They were on the peashooters, not the black cap Mk 1A ?

So the test that gave the highest hp at revs had 1" mutes installed, if I read that correctly.
Does a test there have the mutes removed, and bigger main jets installed, like the manaual says.
Bit loud like that, but a rocketship from what I remember...

Rohan said:

L.A.B. said:

and if the torque figures are calculated from the highest BHP curve of the Dolman graph

Click to expand...

Have you, or anyone, actually done this ?

Click to expand...

Yes (or I wouldn't have said it).

Deets55 said:

Interesting information. Can you explain what "venturis on ears" are? I am guessing that it was some sort of modification to the air box "horns'

Click to expand...

The black airboxes had a rubber venturi (06-4839) on each intake "trumpet" once again intended to reduce intake noise as far as I know, but also tended to reduce performance slightly.

L.A.B. said:

and if the torque figures are calculated from the highest BHP curve of the Dolman graph

Click to expand...

Rohan said:

Have you, or anyone, actually done this ?

Click to expand...

L.A.B. said:

Yes (or I wouldn't have said it).

Click to expand...

And what does the ftlbs @ rpm actually work out to be ?
Save a lot of envelopes..

Rohan said:

And which pipes/test had the 1" mutes ??
They were on the peashooters, not the black cap Mk 1A ?

Click to expand...

What it says is Mk3 pipes, STD silencer, as this graph is dated May 1973 "standard" obviously refers to peashooters, not what eventually became the standard black cap 850 MkIII silencer referred to on the graph as the "Mk1A" silencer.