BHP vs BS ...

Status
Not open for further replies.
???
Not sure that I have even heard of a dyno that could draw.
And power curves have to be calculated and drawn to suit...

Whatever, the 850 torque and power curves don't even match.
(Apart from that torque curve is just ridiculous.)
Note that the 850 torque curve is lower at some points than one of the 750 curves, but the calculated power curve is above it !!!
That is some serious flawed work...

Think about it.
The 850 is shown as getting 50% more torque at low rpms than the 750's.
From the same cam, head, carbs and just 10% more capacity.
Somefinks seriously wrong here.
And it doesn't match the stated torque max quoted for the 850 @ rpms.

As discussed earlier, it seems that the torque curve has been drawn flipped over/mirror imaged.
i.e. not terribly useful at all.

So this graph falls more towards the BS side of things, as far as the 850 is concerned anyway.
 
It's perfectly possible to have a torque curve like the 850 one in that graph. It's remarkably similar to my BMW, However, rohan's right in that the graph doesn't match reality... the 850 shows more power than the 750 at 6500 but less torque. That simply can't be true.
 
pommie john said:
It's perfectly possible to have a torque curve like the 850 one in that graph.
Click to expand...

Old JAP sidevalves come to mind.

Actually, a lot of bikes in the 1920s were like that.
All done by 3000 rpm, so you rode the bike in the lower rpms and forget about revving it.

BUT, Nortons claimed the 850 had a max torque of 56 ftlbs @ 5000 rpms,
and that graph SURE DOESN'T SHOW THAT.

If the torque curve was flipped over, it may do though.
Perhaps the colour transparencies got mixed up in the publishing stage ?
A slightly higher version of the green curve (10% higher) would fit that 850 description perfectly....
 
Rohan said:
pommie john said:
It's perfectly possible to have a torque curve like the 850 one in that graph.
Click to expand...

......
If the torque curve was flipped over, it may do though.
....
Click to expand...


The more I look at it, the more I think this option is right. If I had more time, I might plot a curve for the reversed torque curve and see how it matched.
 
Here is a graph from a 1974 850 road test. The torque curve clearly doesn't match the one on Duckworth graph.
BHP vs BS ...


Another 850 test from '73 states: "Claimed torque @ rpm lb.-ft. ........ 49 @ 5000".
 
MichaelB said:
Being how horsepower and torque cross at 5252 rpm in the real world, that chart is faulty.
Click to expand...


I think they do cross at 5252 on the chart. Possibly the problem is optical illusion with two scales which are greatly different, the torque scale being quite fine and the hp being coarse plus at different levels on the page.
Drawing a vertical line thru the 850 curves at 5252 or thereabouts, I see 45 hp and 45 ft. Lbs.
Looking at the chart at the 3,000 rpm level and drawing a vertical line, the hp shown is about 20 for the Combat, 22 for the standard 750 and 30 for the 850. This corresponds with the torque values shown at 3000. 30 hp for the 850 means 50% more torque than the Combat at 20 hp.

Glen
 
worntorn said:
I think they do cross at 5252 on the chart. Possibly the problem is optical illusion with two scales which are greatly different, the torque scale being quite fine and the hp being coarse plus at different levels on the page.
Drawing a vertical line thru the 850 curves at 5252 or thereabouts, I see 45 hp and 45 ft. Lbs.
Looking at the chart at the 3,000 rpm level and drawing a vertical line, the hp shown is about 20 for the Combat, 22 for the standard 750 and 30 for the 850. This corresponds with the torque values shown at 3000. 30 hp for the 850 means 50% more torque than the Combat at 20 hp.

Glen
Click to expand...

YAHTZEE!
 
You mean more like this?
The dyno operator ran it to the rev limiter each pull as it was still making power

BHP vs BS ...
 
When I first started racing, I had a very difficult bike. One of the very old riders said to me 'it is all about getting racing miles under your belt and the bike has to do something for you'. With a commando, you have a choice - you can make it all top end power or you can increase the midrange torque. If you raise the overall gearing and the bike accelerates faster - what have you done ? One of the main things is that the handling must suit the power characteristics. It is possible to build a manx Norton which will jump all over you and grab you by the throat.
I can see value in correlating dyno numbers with on-track performance. However the comparisons are subject to calibration and measurement errors.
 
worntorn said:
Looking at the chart at the 3,000 rpm level and drawing a vertical line, the hp shown is about 20 for the Combat, 22 for the standard 750 and 30 for the 850. This corresponds with the torque values shown at 3000. 30 hp for the 850 means 50% more torque than the Combat at 20 hp.
Glen
Click to expand...

Your still not on the same page as everyone else on this Glen.
take a look at the other 850 dyno charts here.

Duckworths 850 torque line is seriously flawed,
max torque should accur about 5000 rpms, not 3000.
As already mentioned, it looks like the line has been flipped/mirror imaged.
Adding 10% capacity just shouldn't add 50% more torque....
 
Rohan said:
worntorn said:
Looking at the chart at the 3,000 rpm level and drawing a vertical line, the hp shown is about 20 for the Combat, 22 for the standard 750 and 30 for the 850. This corresponds with the torque values shown at 3000. 30 hp for the 850 means 50% more torque than the Combat at 20 hp.
Glen
Click to expand...

Your still not on the same page as everyone else on this Glen.
take a look at the other 850 dyno charts here.

Duckworths 850 torque line is seriously flawed,
max torque should accur about 5000 rpms, not 3000.
As already mentioned, it looks like the line has been flipped/mirror imaged.
Adding 10% capacity just shouldn't add 50% more torque....
Click to expand...

Well I often do end up on a different page than others, so that's routine.

It has been suggested (mainly by you)that Mick Duckworth's torque curve shown for the 850 out of kilter from the horsepower curve for same. Using a straight edge and estimating values as closely as possible with the scales provided, every point I check is fine +- 1 lb or so. The chart he provided was for quick comparison only and obviously not intended for detailed examination or it would be in proper easy to read graph paper form. Just the same, for six points I checked with a ruler, the horsepower value =torque x rpm divided by 5252 each time.
He does seem to have an 850 with a lot of low down grunt, though they are that way.
Perhaps Duckworth tested a very strong 850, or perhaps he used charts from different dynos for the three bikes. I might ask him the question, I see he has a facebook account.

Glen
 
This was extensively discussed before - when when you grabbed that screengrab of the graph. !
You don't recall that we concluded the 850 torque curve was nonsense ?
And it had been flipped/mirror imaged....

Compare the torque curve with the legit 850 one that LAB posted, or the hotrod of brooking850.
There is no comparison with the torque curve shapes.
Duckworths one just doesn't make sense as it is shown there - and the 850 torque and power curves don't even (quite) match each other,
compared to the 750 ones !

There is also tha matter than 10% more capacity CANNOT simply give 50% more torque !
That is one seriously flawed 850 graph.

Be gentle on Mick.
It was probably a mixup in the transparencies at the publishing stage (?).
 
Gentlemen, may I politely suggest that both of you seem to have presented your sides.

Glen, if you can speak with Mick, that would be very interesting. But I don't think I'm only speaking for myself in urging you guys not to spend 10 more pages arguing this one until there is more to discuss.
 
Brooking 850 said:
You mean more like this?
The dyno operator ran it to the rev limiter each pull as it was still making power

BHP vs BS ...
Click to expand...

Mike, that's is one nice looking graph!

Any chance that you could do a back to back of the Maney vs peashooters next time you're on the Dyno?
 
Nigel I have a slightly older graph with the straight pipes and peashooters, although unfortunately from a different dyno.
And you know as well as I do that no matter what the figures show (good or bad), I will get crushed on here for posting different results on different days and different operators!!!
I will none the less.
The new exhaust system has raised the torque figures and I now get full power all the way to the rev limiter.
Comnoz has suggested I could get a few more ponies going leaner, I tend to err on the rich side to give me peace of mind as these things to lean out off the throttle.
I am still only running standard Vvs, standard manifolds and 32 mm Premiers.
Very happy with the new system and I will complete the 2 into 1 thread with pics and the graphs.
Regards Mike
 
Brooking 850 said:
And you know as well as I do that no matter what the figures show (good or bad), I will get crushed on here for posting different results on different days and different operators!!!
I will none the less.
Click to expand...

If you did a valid dyno test, how can anyone dispute that ?
Although it may be interesting to explore how they are different.
 
Fast Eddie said:
Gentlemen, may I politely suggest that both of you seem to have presented your sides.

Glen, if you can speak with Mick, that would be very interesting. But I don't think I'm only speaking for myself in urging you guys not to spend 10 more pages arguing this one until there is more to discuss.
Click to expand...

Some of us were concerned that Glen was blythely sailing along, ignoring all the comments that that 850 torque curve was flawed.

Mick is going to have to explain how that 850's torque curve was TOTALLY transformed from the 750's,
when it should have just been a maybe 10% beefier version of the same thing.
Changing, totally, the torque curve like that is no minor matter
Especially with basically the same cam, heads, carbs, exhaust.

A bike with 50% (!!) more power like that down low (than the 750) would be an absolute rocketship.
 
Hi Rohan, I had some quite bizarre dyno differences on the same day with one system , it turned out a huge storm was on its way and as it got closer to where we were operating the barometer was dropping rapidly so had a huge effect on readings.
Robbed nearly 10% off what I knew I already had !!
Anyway will post what I have found so far as it is only relative to exhaust systems I am testing
Regards Mike
 
Rohan said:
This was extensively discussed before - when when you grabbed that screengrab of the graph. !
You don't recall that we concluded the 850 torque curve was nonsense ?

.
Click to expand...

I do recall that discussion, but the "We concluded" part was down to that Rohan Gang of One.

I'll take Nigel's advice and drop this. As Brooking 850 points out, it is almost guaranteed that any dyno chart will bring out the pitchfork mob. Awhile back, in the Vincent section, I posted a dyno chart from Terry Prince's fuel injected alcohol burning Vincent ( 165 rwhp) and it was immediately suggested that the chart number was surely too high, must be wrong.

So it seems dyno charts, fun though they might be, are up there with religion and politics as subjects best left alone.

Glen
 
I find the discussion of dyno charts interesting. It is a way forward. I had very hard lessons with a bike which was all top end. You only had to blink and it was sideways. I can still feel the pain even after 30 years. Rohan has got a very big armchair.
 
Status
Not open for further replies.
Back
Top