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Actual BHP of a Vincent Twin ?

Tom Gaynor

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VOC Member
Horsepower

The original figures were taken on a Heenan and Froude type dyno, probably at the crank. It isn't unreasonable to subtract 10% for gearbox losses, so I'd expect a really good Shadow to show 50 on a rolling road. The club Shadow when first built showed 37 I think, boosted to the mid-forties by some tweaking.
 

Glenliman

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VOC Member
Tom, I recall reading in MPH that the club did do some dyno work when designing the current version of the spiral baffle muffler. The bike used was said to be a somewhat below average performer, according to observations from riding. The horsepower figures were quite low, mid thirties, but then the testers only ran the RPM up to something like 3200 RPM for some reason. A full RPM test up to 5500 RPM would have provided more info. Torque was very high at the tested speed, especially with the spiral baffle muffler installed. Torque was in the 65 foot pound range at about 3200 RPM, which explains why Vincents hold 70 MPH in top gear so easily, even when loaded right down on a fairly steep hill. It also explains in part why they are so pleasant to ride, the high torque at low RPM means you are not struggling to find the power band.

I know of one local bike which has been dynoed at 65 RWHP, (John McDougall's Shadow) but it is quite modified.
 

Tnecniv Edipar

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Non-VOC Member
Those power characteristics are typical of a low compression , small port , mild cam , big displacement motor.
I reckon 70-75 bhp should be easily achievable with higher compression and friskier cam , some port work & larger carbs . Still with a good torque band though.
 

TouringComet

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VOC Member
VOC Forum Administrator
VOC Forum Moderator
How about 115+ HP at the rear wheel? Steve Hamel is getting that much from a modified 1000cc Vin on petrol, good for 155+ MPH at Bonneville. You can see what he did to the ports here. This is the sweetest sounding twin I've ever heard.
 

Tnecniv Edipar

Well Known and Active Website User
Non-VOC Member
Cool !!
What lubrication system does it run ? Can't imaging the standard arrangement being adequate for that power !

My interest was more what could be reasonably obtained from a more or less standard motor though , with slightly less radical mods !!

Great to see this type of development occuring to a design more than half a century old !!
 

johncrispin

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VOC Member
power output

Paul Packman's Rapide, well put together and moderately tweaked is, if I remember correctly, giving over 60 BHP possibly 65. It is quite the most desirable Vin I know of and has sensible but unobtrusive mods done by Paul, a highly knowledgeable engineer.
He has done it this way so that he can keep up with his son on a Ducati ! Pictures of the machine distinctive with homemade 2ls front brakes is on www.thevincent.co.uk.
 

Upstreeter

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VOC Member
My Shadow shortly after running in after an engine rebuild was put on John Renwick's brake and Lambda equipment. He did an excellent and highly accurate job, but it was found to deliver a measly 46bhp. it goes ok though...strange things, horses, everyone seems to have a different breed.
 
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Tnecniv Edipar

Well Known and Active Website User
Non-VOC Member
Torque is the important thing for how any vehicle feels to drive or ride. I've never seen a torque curve for Vincent but I suspect it would be high and wide relative to the BHP curve.
Thats why Ducati's have been so dominant in World Super bike & Moto GP.

If you have the dyno graphs I would be very interested to see them ?
 

clevtrev

Well Known and Active Website User
VOC Member
Just been done by a Portsmouth section member 40BHP.
Basically to find out the size of the main jet required. 140 rear 145 front.
 

clevtrev

Well Known and Active Website User
VOC Member
How about 115+ HP at the rear wheel? Steve Hamel is getting that much from a modified 1000cc Vin on petrol, good for 155+ MPH at Bonneville. You can see what he did to the ports here. This is the sweetest sounding twin I've ever heard.
You should mention that it is a brand new everything engine.
 

Robert Watson

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VOC Member
Not long before it was driven to South America, we ran Dan Smith's Rapide on a rolling road, with a couple of diferent silencers. I don't recall all the details but I think it made about 48 with one and 50-51 with another, on the rear wheel. This with Mk 11 cams, 1 1/8 carbs, and magneto ignition. I do know that I ran it as Dan was recovering from his accident in NZ, and I also know I got blamed for the broken cam spindle boss when he next got on the bike!!

Cheers
 

Diogenes

Well Known and Active Website User
Non-VOC Member
Actual BHP of a Vincent Twin

"Would be interested to know if anyone has had a post war twin on a dyno and the power figure it produced ?"
Some info in Fig.23 page 52 of Paul Richardson book 2nd ed.
You can easily calculate torque from the bhp versus RPM 'maximum engine life' curve given.
Stops at 87 mph.
 

Albervin

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VOC Member
Bhp

I understand that Reg Bolton is putting his racing Rapide back on the road. He has owned the bike since the 50s & made several mods to it. Last I heard it was putting out close to 100 bhp but not sure if that was at the crank or back wheel. John Renwick was responsible for this figure.:)
 

Albervin

Well Known and Active Website User
VOC Member
Bhp

I understand that Reg Bolton is putting his racing Rapide back on the road. He has owned the bike since the 50s & made several mods to it. Last I heard it was putting out close to 100 bhp but not sure if that was at the crank or back wheel. John Renwick was responsible for this figure.:)
 

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