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BHP measuring


Howard

Well Known and Active Website User
VOC Member
I've got lots of queries just lately - Egli very very nearly back on the road again, and my brain is getting back into being a Vincent owner (ok half Vincent).

Question - How did the Vincent works measure the power of the bikes? Did they have their own dyno? Did they measure at the wheel or crank? etc

55 bhp is not a lot of power to push a heavy, unfaired bike to nearly 130 mph (probably wearing a Barbour jacket) when my 125 bhp lighter, faired Fireblade is only good for 165 mph. I know all (some of) the theory about diminishing returns, and the faster you go the more power you need to go a bit faster, but even so, there seems a big dicrepancy.

H
 

Albervin

Well Known and Active Website User
VOC Member
Power

Brighter lights than me can give more detail but I believe the answer is Torque. A Vincent develops similar torque figures to my BMW R1100RT (but at lower rpm than the BMW). Given BHP is a figure derived from torque & rpm I have no doubt that those raised on 15,000 rpm Jap machines find it hard to comprehend a Vincent was/is capable of 120 mph. Some road going Vincents I know of have been dyno tested at well in excess of 60 bhp (at the rear wheel) so I am sure the original bikes were in the ball park of 55 bhp at the rear wheel. For day to day riding though, it is the torque you use as ultimate BHP only comes into play as you approach 5,500+ rpm.
My little Aprilia RS250 has a claimed max bhp of over 50 but that is at 11,000 rpm & below 6,000 it won't pull the skin off a rice pudding! It will pull close to 115 mph though!;)
 

ogrilp400

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VOC Member
Power Measuring

Torque is what does the work. Yes Vincent did have a Dynamometer test house In it was a Heenan and Froude water brake that measured torque directly off the crankshaft. Quite a simple apparatus actually that could do these measurements for hours or days at a time.

Phelps.
 

david bowen

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VOC Member
water brake

Yes Ken you are correct on the same brake they run the MOD marine engine for weeks, the test house was at the top of the yard at vincents Great North road factory
 

Howard

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VOC Member
Ok, first part answered, Vincent had a Heenan Froud dyno, I suspect it was probably chain driven from the final drive sprocket, not the crank, so Albervin's thoughts that 55 bhp is a rear wheel power is probably right. Probably around 60 at the crank allowing for losses in the gearbox, primary chain etc.

55 bhp = 125 mph but 125 bhp = 165 mph is still a puzzle for me. Like other subscribers to this thread I used to tell myself that it's because of the torque, but by definition torque cannot do the work, because there's no time factor involved in torque measurement. It's got to be power measured in ft.lbs/sec which determines the speed in ft/sec not the torque which is only measured in ft.lbs (Sorry if ft and lbs are the wrong way round, I use metric units these days).

Torque may be part of the answer, but I don't think it's engine torque. If more torque is needed at the rear wheel we change down a gear and rev the engine more, the engine produces more power, and the gearbox converts it to more torque at the wheel.

I've worked for a long time with industrial electic drives including 0.25 kW electric motors geared down so far they produce 100,000 Nm of torque, but they turn so slowly you can't see any movement.

Any more for any more? My brain must be missing something.

H
 

ogrilp400

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VOC Member
The dynamometer was driven directly off the crankshaft. That is, there was a double universal jointed shaft between the drive end of the crankshaft and the dynamometer. No gearbox.
100,000 Nm of torque!!!, strewth, that is impressive.

Phelps.
 

Tom Gaynor

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VOC Member
Power and speed

The answer is that the power required increases +/- with the square of speed, given a constant Cd - aerodynamic drag factor. To go from 100 to 120 mph (120/100 = 20% increase in speed) requires a 44% increase in power (120 x 120 / 100 x 100).
About 36 bhp is enough to push an unfaired bike to 100 mph, and 55 bhp to take an unfaired bike to 125 mph or so. The speeds (110 and 125) claimed for Rapides and Shadows suggest that PEI and PCV knew that.
However if the 55 bhp bike has a Peel fairing, it'll clock 145 mph. Peel faired Manx Nortons (about 55 bhp...) were pulling over 150 mph at the NW 200 30-odd years ago. And a full dustbin fairing was the reason the 70 bhp Moto Guzzi V8 was clocked at 178 mph in 1956.
 

Howard

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VOC Member
Tom

I think you must be the same generation as me, what you write is what I always understood to be the case.
BUT
By your (our) calcs 98 bhp should be good enough for 165 mph (unfaired) and the 125 Fireblade horses should take it to 185+mph. I'm sure things like rolling resistance change with speed, but 27 lost bhp seems a lot to account for - not including the fairing, and about 80 lbs less weight.

Is this what I've suspected, Vincents work on horses big enough to carry Knights into battle, but the Japanese industry use racehorses.

Phelps

Oh well, I suppose in top gear, we'd only lose about 5% on the way to the rear wheel.

As an aside, the biggest gearbox we built would transmit 500,000 Nm and was used to turn a swing bridge. Our fitter was big on attention to detail, and liked to despatch all his drive units with the keyway on the output shaft vertical (at 12 o'clock) - he went for a coffee break while it was turning into position, when he got back the keyway had turned too far, so he watched it for an hour to make sure it didn't overrun next time. He said it was because he had pride in his work, but I have my suspicions.

H
 

Tom Gaynor

Well Known and Active Website User
VOC Member
Horsepower at crank vs horsepower at rear wheel

The common assumption is that 50 at the rear wheel is 55 at the crank - or at least it is in classic racing circles. Seems a lot in top gear, as has been remarked. However since all I and other racers are only interested in maximising bhp, rather than establishing an absolute number, I don't know of anyone who has investigated the assumption. It wouldn't be terribly easy to do, since all dynos (even of the same basic design) give different results. Stories abound of people seeking the dyno that over-reads most so as to sell their 190 bhp GSX-R for a higher price than a 180 bhp ditto would fetch.
(In passing, "my" dyno man had never tested anything with "only" 50 bhp at the rear wheel, and we had to develop a technique to get the drum up to speed without burning out the clutch. I had to accelerate the Norton through the gears into 6th. A big Japanese bike just does it in top!)
I've always assumed that Vincent did enough brake testing to establish that a reasonable Rapide should put out 45, and a reasonable Shadow 55, and those were the numbers attached to all. I expect that in reality Rapides varied either side of 45, and Shadows either side of 55, and that there must have been "good Rapides" and "poor Shadows" that were indistinguishable in performance.

Tom

Tom

I think you must be the same generation as me, what you write is what I always understood to be the case.
BUT
By your (our) calcs 98 bhp should be good enough for 165 mph (unfaired) and the 125 Fireblade horses should take it to 185+mph. I'm sure things like rolling resistance change with speed, but 27 lost bhp seems a lot to account for - not including the fairing, and about 80 lbs less weight.

Is this what I've suspected, Vincents work on horses big enough to carry Knights into battle, but the Japanese industry use racehorses.

Phelps

Oh well, I suppose in top gear, we'd only lose about 5% on the way to the rear wheel.

As an aside, the biggest gearbox we built would transmit 500,000 Nm and was used to turn a swing bridge. Our fitter was big on attention to detail, and liked to despatch all his drive units with the keyway on the output shaft vertical (at 12 o'clock) - he went for a coffee break while it was turning into position, when he got back the keyway had turned too far, so he watched it for an hour to make sure it didn't overrun next time. He said it was because he had pride in his work, but I have my suspicions.

H
 

Tnecniv Edipar

Well Known and Active Website User
Non-VOC Member
55 bhp = 125 mph but 125 bhp = 165 mph is still a puzzle for me. Like other subscribers to this thread I used to tell myself that it's because of the torque, but by definition torque cannot do the work, because there's no time factor involved in torque measurement. It's got to be power measured in ft.lbs/sec which determines the speed in ft/sec not the torque which is only measured in ft.lbs (Sorry if ft and lbs are the wrong way round, I use metric units these days).

Torque may be part of the answer, but I don't think it's engine torque. If more torque is needed at the rear wheel we change down a gear and rev the engine more, the engine produces more power, and the gearbox converts it to more torque at the wheel.

Any more for any more? My brain must be missing something.

H
You are correct , torque is effort , the push down the road , but power which is torque x RPM is work done , is the factor that allows the bike to develop speed. There is another factor though , power band. Any engine can produce an impressive PEAK power at a given RPM but if that is only a spike a few hundred RPM wide the vehicle is unuseable unless it has a 20 speed gearbox ! Vincents have a wide power band , that is , if the torque and power graphs are examined you would see alot of area under the curve instead of a tall mountain as tends to be the case with modern multi's. This means there is a constant thrust at the drive wheel to develop and maintain velocity.
 

Howard

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VOC Member
You are correct , torque is effort , the push down the road , but power which is torque x RPM is work done , is the factor that allows the bike to develop speed. There is another factor though , power band. Any engine can produce an impressive PEAK power at a given RPM but if that is only a spike a few hundred RPM wide the vehicle is unuseable unless it has a 20 speed gearbox ! Vincents have a wide power band , that is , if the torque and power graphs are examined you would see alot of area under the curve instead of a tall mountain as tends to be the case with modern multi's. This means there is a constant thrust at the drive wheel to develop and maintain velocity.
Yes I'll go along with that, I've never seen the need for more than 4 gears on the Vin, and the Fireblade has 6 - I think - as Mike Hailwood famously said about one of his Hondas - I just keep changing until there are no more.
One minor problem - the Fireblade pulls quite happily from 30 mph in top (2000 rpm), not stunning acceleration, but smooth and far from sluggish.

H
 

Robert Watson

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VOC Member
You are right about the Dyno
Heenan and Froude DXP3 I believe. I have one in my carport, and most of the gear to make it run. We had it mocked up at the 2003 Int Rally with a drive connected to the final drive of a Vin, however they were direct coupled to the crank in the test house. There are pictures floating around that show it. We have toyed with setting it up here and are only lacking the Lightning or Picador engine donation to make it a reality. We even have a 1000 gal water tank standing by. Anyone?

Robert
 

Tom Gaynor

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VOC Member
Power and speed

If 55 bhp gives 125 mph (personally I doubt that many Shadows ever did 125 mph, so I'll settle for 120 mph) then to get 165 mph, you need 165/120 squared, x 55 = 103 bhp. The Vin is naked, the modern bike isn't, so 95 bhp would seem more reasonable for a faired bike. However, from my own experience of publishing power figures on oilfield downhole motors, knowing that drilling "engineers" were uneducated nerds, more testosterone than brains, who were impressed by numbers they didn't understand, bhp became an abbreviation for "brochure horse power". We always looked to see what the opposition were claiming, then fiddled the numbers to get more. A flash reading of 125 on the brake, miraculously survived, became "delivers a reliable 125 bhp". Who would ever know? It's capitalism, baby. Caveat emptor. As many bankers - some, but not enough, busted - would tell you.
The doyen of UK Aermacchi tuners, Dick Linton, quotes an American tuner (sorry, forgotten his name) who said that horsepower sells bikes, but torque wins races, and this is true. When the torque falls off a cliff (on the Manx, about 7200) the speed is still increasing, but now more slowly. Knowing this, I shifted at about 7000, and only let it run (to about 8300) in top. This works. One of the highlights of my racing career was out-accelerating a 55 bhp Gilera four replica on a 50 bhp Norton at about 110 mph. He had the power, but I had the torque IN THE RIGHT PLACE. (Noisewise there's no comparison. I got the full Doppler as I eased past him. Orgasmic.)
I've never put the Vin on a brake, but it would be interesting. Meantime, it goes from 30 to 100 in top, at which point I need to deploy the Vulcan Death Grip to stay on board, and I'm too old for any undignified lying on tanks. Would it do 125 mph? Doubtful, but WTF cares? Not me.
However 103 bhp (and now you know what bhp means) is close enough to a claimed 125 bhp to bear out the rule. The horsepower to reach any speed has a square law relationship with the speed difference, starting from about 36 bhp to see 100 mph on a naked bike.
And if you want to check the veracity of brochure claims, try weighing your Fireblade or whatever. Most of the claimed weights are only true if the bike is without oil, petrol - and crankshaft. Would-be customers are known to look particularly at weight. So lie. Who'll ever know?
Thought for the day: a "cynic" is what an idealist calls a realist.


Tom
 

Howard

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VOC Member
And if you want to check the veracity of brochure claims, try weighing your Fireblade or whatever. Most of the claimed weights are only true if the bike is without oil, petrol - and crankshaft. Would-be customers are known to look particularly at weight. So lie. Who'll ever know?

Tom
You caught me out again. I was curious about the weight claims too, so, the other night, I thought I'd try weighing the two bikes. I put the front wheel of the Egli on the bathroom scales, lots of lcd flashing but no weight! My old analogue spring scales would have weighed it.

H

ps there was no ulterior motive to this thread, just the product of my mind wandering during the boring parts of a rebuild (painting).
 

Albervin

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VOC Member
Tom, you do have a way with words! The Japs are now slowly realising that their weight claims are being questioned. We now have "kerb weight" which is probably a ready to go bike with half a tank of petrol. Look at the weight of a Vincent 1000 & it won't be a million miles from 200Kg. I wonder (or is it wander) at the speeds set 60 years ago with less than 100bhp. There are bikes out there with (supposedly) more power than 1980s BMWs & they are not doing 200 mph?! My 1985 BMW 323i weighed 1200Kg, supposedly generated 125bhp & did a genuine 120 mph ( Officer plod gave me a ticket to prove it). So why won't a 200 kg/125bhp bike do more than 165 mph?:rolleyes: On the other hand my little Aprillia has clocked 110 mph with 50 Japanese horses & weighing 140Kg (plus me).
 

Tnecniv Edipar

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Non-VOC Member
The 323i had considerably more torque & better aero.
I've noticed that contemporary Vincent road tests produced variable performance figures. The probability is , I suspect , that tolerances and quality control of the day were much inferior to today. This also applies to other British makes. Triumph in particular were known for 'exaggerated' performance claims ! Then again , so was Jaguar and many other automotive makers. Harley was a joke !
 

Howard

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VOC Member
The 323i had considerably more torque & better aero.
I've noticed that contemporary Vincent road tests produced variable performance figures. The probability is , I suspect , that tolerances and quality control of the day were much inferior to today. This also applies to other British makes. Triumph in particular were known for 'exaggerated' performance claims ! Then again , so was Jaguar and many other automotive makers. Harley was a joke !
Top Gear did an article not too long ago about 150 mph E Types and Aston Martins from the 60s, and said that only specially prepared cars ever got close to the claimed figures.

H
 

Tnecniv Edipar

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Non-VOC Member
Yes , I saw that episode but I already knew about the 'massaged' press E Type ;) Some of the worst offenders for fantasy power numbers were the American car industry. Fortunately for them , at the time , their customers knew no different.
 

lindie

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Non-VOC Member
you mean it's a real feasibility that the 19 DIN horses my MZ is claiming is a "massaged" figure? but with a combined rider and bike weight approaching 280 kg i've seen 120kph on the speedo with a correlating readout on the tacho.

should i fit a turbo or lose 40 kg?

power figures over here have been a wank for decades as well with companies strangling engines early through the seventies and still claiming the previous models output figures so as not to appear to be de evolving. and with the converse applicable in japan for a long while to adhere to an artificial limit of 280 hp from their cars. yet with newer models weight figures rising and yet acceleration figures getting sharper there had to be some wondrous H.O.G. (not the harley owners group, their passtime with the first two words "hands on") fiddling of figures or plainly detuning for dyno testing/imposed lower rev ceiling.

as long as my rapide is capable of a higher speed than my MZ(in the region of 10 kph higher is all i'll ever really require living over here anyway) and i need to ride 1600 odd miles to legally do that, then the final power output is academic and best left untested. as long as the rockers rock, the valves valve and the connecting rods decide to stay in connection, and i suspect this to be more likely for longer at moderate revs, then the big girls motor will live a fairly unstressed life in my stewardship. but i plan to sample the torque from down low with open taps on a frequent basis. revs kill engines, but it's generally torque that destroys drive components. hope i find a happy medium somewhere.
 

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