BHP vs BS ...

At this years Mallory bike festival I had, unbeknown to me at the time, cocked things up with the ignition timing on my Commando.

Now let me be clear, I am no Hailwood, Williams, Rossi, etc. but I have raced a bit and at least know my way around Mallory Park.

There were some tasty bikes out in the sessions with me. A Guzzi Le Man passed me and I couldn't keep with her (yes, female rider). But she was the only rider to pass me and I rejoiced in the ultimate power that my highly tuned Commando must have been putting out, as it was clearly very fast compared to most others out there...

So I was rather surprised when I later learnt that due to the ign timing being out, the Commando was more than 10bhp down on power, putting out 45 point something versus its earlier 56.

So, despite all the bar room boasting that goes on in this game (we all do a bit I guess) a 45bhp Commando still stood out. It makes me wonder what the real RWHP of most classic bikes are, a lot less than their owners realise I guess!

I remember Martin Pink at a Beezumph years ago getting his Rob North 1000 on the dyno, it showed 75 bhp, and was way in front of the other triples whos owners had the bottle to get them tested (A guy on a new ZX7 had just blown his motor on the dyno).
sam

Apparently most of the inertia dynos use a fiddle-factor which makes all of their BHP readings relative to the claimed output of the Yamaha Vmax. Normally it does not matter what the 'true' BHP figure is because the whole thing is comparative between bikes and most guys are only looking for an improvement. My 850 feels as though it turns out 80 BHP, I think it would realistically be below 60 BHP. I think that the only genuine horsepower figure I have ever heard was 50 BHP for the best ever 500cc manx. The best 750cc Triumph twin struggles to get near them. In some Australian historic races guys on Molnar manxes have been up with overbored CB750 Hondas. They don't usually run in the same races, and there are major differences in the handling.

Fast Eddie said:

So, despite all the bar room boasting that goes on in this game (we all do a bit I guess) a 45bhp Commando still stood out. It makes me wonder what the real RWHP of most classic bikes are, a lot less than their owners realise I guess!

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An excellent rider on a 40HP machine can beat a good rider on a 60HP machine (unless you are talking about an oval or straight line)

So, your results can more likely be credited to your riding, rather than HP on the bike. Now, to be sure, the bike's handling and brakes can even contribute more than the engine's sheer HP.

grandpaul said:

Fast Eddie said:

So, despite all the bar room boasting that goes on in this game (we all do a bit I guess) a 45bhp Commando still stood out. It makes me wonder what the real RWHP of most classic bikes are, a lot less than their owners realise I guess!

Click to expand...

An excellent rider on a 40HP machine can beat a good rider on a 60HP machine (unless you are talking about an oval or straight line)

So, your results can more likely be credited to your riding, rather than HP on the bike. Now, to be sure, the bike's handling and brakes can even contribute more than the engine's sheer HP.

Click to expand...

No GP, to be clear, I'm not a slow rider, but I'm no star either. As much as I'd like to take all the credit, I can't!

Fast Eddie said:

grandpaul said:

Fast Eddie said:

So, despite all the bar room boasting that goes on in this game (we all do a bit I guess) a 45bhp Commando still stood out. It makes me wonder what the real RWHP of most classic bikes are, a lot less than their owners realise I guess!

Click to expand...

An excellent rider on a 40HP machine can beat a good rider on a 60HP machine (unless you are talking about an oval or straight line)

So, your results can more likely be credited to your riding, rather than HP on the bike. Now, to be sure, the bike's handling and brakes can even contribute more than the engine's sheer HP.

Click to expand...

No GP, to be clear, I'm not a slow rider, but I'm no star either. As much as I'd like to take all the credit, I can't!

Click to expand...

Two things Nigel, one, OK maybe you aren't a national champ, its good to be honest about our abilities, but I expect you qualify as a good rider with solid track experience, who rides at a respectable pace.

Others may have restrained themselves due to a lack of ability, a lack of track experience, or they were just riding as fast as they enjoyed on the day. Its not racing, why push?, I, like many others, happen to be typically a 'Sunday Man', I usually find a lot of extra pace on race day.

I rode at Lydden this year and found myself in close proximity with the CRMC Chairman on both of my bikes, I passed him on one, not the other, he was also riding two different bikes.

We spoke in the evening, he said he had noticed a flash of yellow as I rode outside of him at the Devils Elbow, him on his 500 Ducati Pantah, noting how I powered away up the hill on my clearly faster bike, saying that as his Duke was only making 50 bhp he had no answer...he didn't smile much when I commented that the Yamaha 500 single only made 43 (and I fear I may be exagerating!, and I am sure I am carrying more 'ballast' than he does, though of course the little single may offset that).

Remember, this is a bike with a Rob North designed BSA Fury/Triumph Bandit frame that handles very very sweetly, at least the equal of the Duke! (note, going outside at the Devils Elbow was a successful manouvre for me all weekend, because you can get up to a higher speed and brake harder than those who choose a more conventional line, get on the power quite early and then run on to the tarmac of the rallycross link on the exit to get a faster exit than people expect, hence the extra speed up the hill, because they are not expecting you to be there you can also mess with their corner exit a bit on a bike that turns quick...the Fury does, the Rickman doesn't!)

With my Norton with say 60 rwhp I also tried to ride round him at the Devils Elbow, and inside him at a couple of others, but with him on his 1260 F1 Harris Kawasaki there was no way I could actually make it stick.....

All of this to say.....there are so many variables you can never be sure who or what is really faster, and HP counts for less than you think on short tracks....

My fastest lap of the weekend was a 50.1, on the 500, at 50.3 I was 2 tenths slower on the 750!

I am a big fan of torque - sheer grunt is often overlooked in favor of the big BHP number at the top of the graph.

I think that is where our bikes do well versus some of the revier, more highly strung exotica!

...but a good rider always helps - don't underestimate that - particularly if it's a track you know well, and love!

What would a good torque value for a Commando be and at what RPM range would you expect the maximum torque to be ?

Brooking 850 said:

What would a good torque value for a Commando be and at what RPM range would you expect the maximum torque to be ?

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I'm away from home at present Mike, so no accesss to my dyno notes. But what I can remember is that surprisingly small changes in settings, which had very small effect on peak power had a big effect on moving peak torque around the rev range.
Have you also found similar?
And when are you going to post your exhaust thread?!?

In the meantime here is a chart to ponder. This from Mick Duckworth's book.

You can see that the 850 makes a lot more power than the standard 750 or Combat in the normal rpm range one sees on the road. The Combat makes less power than the standard 750 for much of the range, then comes on strong only at top RPM. With this low power then high power output it must feel like the hit of a peaky two stroke and no doubt it is fun. But so is big torque propelling you forward with ease and no screaming rod bending RPM.

worntorn said:

In the meantime here is a chart to ponder. This from Mick Duckworth's book.

You can see that the 850 makes a lot more power than the standard 750 or Combat in the normal rpm range one sees on the road. The Combat makes less power than the standard 750 for much of the range, then comes on strong only at top RPM. With this low power then high power output it must feel like the hit of a peaky two stroke and no doubt it is fun. But so is big torque propelling you forward with ease and no screaming rod bending RPM.

Click to expand...

Peak torque at 3k and peak power at just over 6k = huge power band. Easy to see why the 850s have a torque monster reputation for sure.

In my miss spent youth I bought a tuned RD250. It had a narrow power band which came in like an electric switch, on/off !
It also drank fuel at a ridiculous rate, but didn't care cos it was a mean, bad, macine...
Well, I thought it was until I was blown into the weeds by a box stock version!
In reality it was rubbish, but the instant power hit made it feel awsome.
Not sayin' nothin' against Combats, jus' sayin' !

I remember being told by a Norton development engineer that on the dyno in Thruxton a 750 or 850 in the same tune could develop the same peak power, but the 850 would make 20bhp more at 4000!

I had one of the first batch of 5 RD250s in the UK, from Mike Wheeler motorcycles in Witney.....it was 'standard' except after servicing/road testing it they (Rod Scivyer) told me it was quicker than their production racer!, we always assumed it had been intended for the gentlemen of the press!

SteveA said:

I remember being told by a Norton development engineer that on the dyno in Thruxton a 750 or 850 in the same tune could develop the same peak power, but the 850 would make 20bhp more at 4000!

I had one of the first batch of 5 RD250s in the UK, from Mike Wheeler motorcycles in Witney.....it was 'standard' except after servicing/road testing it they (Rod Scivyer) told me it was quicker than their production racer!, we always assumed it had been intended for the gentlemen of the press!

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Mike Wheelers!
The shops still going strong, and I believe Mike is too. Until 2 years ago Wheelers was my local for MOTs, octane booster, etc!

Nigel, I did PM you awhile ago, just finished 2 x weekends with the new exhaust and a dyno run as well after a weekend of racing and after minutes of the last race while the bike was still hot.
Thread to come over the next few days
Regards Mike

It has previously been discussed here that there is something SERIOUSLY WRONG with the way those 850 torque and power curves have been drawn. !!

That torque curve that makes more torque at lower rpm is just screwy.........
It appears to have been printed reversed, and then the power curve calculated from it - sort of.

!!!!!!!!

Someone has grabbed the pic from where it was discussed here too...

Fast Eddie said:

You can see that the 850 makes a lot more power than the standard 750 or Combat in the normal rpm range one sees on the road.

Click to expand...

worntorn said:

In the meantime here is a chart to ponder. This from Mick Duckworth's book.

Click to expand...

Brooking 850 said:

Nigel, I did PM you awhile ago, just finished 2 x weekends with the new exhaust and a dyno run as well after a weekend of racing and after minutes of the last race while the bike was still hot.
Thread to come over the next few days
Regards Mike

Click to expand...

Can't seem to find the PM Mike. Can you resend please?

The best thing I ever did was fit very short offset fork yokes to the Seeley so that it oversteers in corners when cranked over. It means I can use the torque characteristic way back in the corner, well before I can even see into the next straight-away. There is a problem with doing that if you are on the circuit with modern bikes. Most of them have big fat rear tyres and tend to run wide. I often turn under them and if they blast down off the ripple strip there can be a coming together about 100 metres after the corner. If they can get the power down without high-siding, they will beat you to the next corner.
I find the commando quite disconcerting, I always feel I am giving it too much stick while cranked over. The Seeley frame, close box and low weight help a lot. It is a very safe ride.

I raced regularly for about 12 years in the 60s and 70s with bikes that tended to run wide in corners. The main one was a short stroked 650 Triumph in a featherbed frame. I never discovered a way to make the bike tighten it's line in corners and I only found out with the Seeley by accident after I went close to having a big crash.
The Seeley has 27 degree head angle, about 35mm offset on the fork yokes and a wheelbase of 54 inches. If you read Kenny Cummins write-up on his bike, he uses a similar offset on the fork yokes. I suggest it is very important to get it right, especially the settings on the rear shocks. The amount of self-steering you get depends on how much the bike squats. You can tailor it to suit your nerves.

worntorn said:

In the meantime here is a chart to ponder. This from Mick Duckworth's book.

You can see that the 850 makes a lot more power than the standard 750 or Combat in the normal rpm range one sees on the road. The Combat makes less power than the standard 750 for much of the range, then comes on strong only at top RPM. With this low power then high power output it must feel like the hit of a peaky two stroke and no doubt it is fun. But so is big torque propelling you forward with ease and no screaming rod bending RPM.

Click to expand...

Being how horsepower and torque cross at 5252 rpm in the real world, that chart is faulty.

MichaelB said:

Being how horsepower and torque cross at 5252 rpm in the real world, that chart is faulty.

Click to expand...

Not so, actually.
That comment ONLY applies if the torque scale and hp scale are drawn equal on the graph,
Since they are not, the curves COULD still be valid.

BUT, the 850 torque line doesn't match anything in the real world, and is just silly when you contemplate it.
And the power curve drawn from it doesn't even match it.
The torque curve appears to have been (possibly) flipped over... (?).

The 750 curves as drawn appear to be authentic/valid/real.

Are those DRAWN, or were they printed out from actual Dyno results?