A10 horsepower ratings

[Housewiz]

From what I have read, the Folden Flash has 34hp.  I'm not sure what the Road Rocket HP is - did I read somewhere it's 40?  And the RGS is 50?

I'm trying to determine how much improvement the hot cams, improved intake & exhaust ports, and upgraded carbs made.

Thanks

[orabanda]

Hi Housewiz,
Here are results I have obtained at the rear wheel:

1951 plunger
356 cam, 7.25: 1 pistons


51 Rigid
334 cam, 7.25:1 pistons


'54 S/A
356 cam, 7.25 pistons


'55 S/A
356 cam, 7.25 pistons


'60 SR
357 cam, 8,5:1 pistons, big valve head

[Rocket Racer]

You have to consider that the 1960 golden Flash hp is quoted at just over 5150rpm, whereas the the road rocket 40hp is at 6k, the super rocket and finally RGS is 46hp at 6250rpm.

If you looked at the power curves the humble flash would be very comparable up to 5000 if not better than the sports models and only above that would a sports model start walking away.

The catch is few people actually ride these bikes regularly in those higher rev ranges so the advantages are practically only in bragging rights.

A cooking motor will typically be much sweeter to ride and stomp up hills where a sports motor might be changing down to keep up.

For road use, a modest compression with a stock carb matched to a 356 or 357 cam makes for a lovely motor.

I see any comparison of model performance as academic for the road.

[iansoady]

Thoroughly agree with Rocket Racer. Many people buy things like Thruxton Venoms, Goldies, RGS etc then find them pigs to ride under normal circumstances. There's a road test of a Golden Flash in one of the old Motor Cycle magazines which effectively says the same thing, and suggests that the "seasoned enthusiast" (read most of us I expect) will actually get much the same performance as would be obtained from the sportier models, and with far less drama. Twin carbs, lumpy cams and close ratio gearboxes are all a pain at low and mid-range revs.

It is very much about image and far less about usability and common sense.

[A10Boy]

I am a fan of the lower comp cooking engines for road use. Apart from my iron A10 I have a 650 twin AJS CSR which has [relatively] high compression etc. I was reading a review on this model from the early nineties edition of a classic mag, the owner said he had "taken the advice of the owners club" and fitted lower comp pistons from the standard model 31. He went on to say that it made it a much more "tractable and rider friendly" machine. I plan to do this at my next rebuild.

BTW, that figure of 34 BHP was for the very early small fin model wasn't it? I thought the later iron head D A10s with the 356 cam produced around 40hp at the crank?

[Rocket Racer]

From what I've read BSA only ever claimed 35hp from the Flash in spite of changes to cams, pistons and carbs over time. I recall the revs they claimed this at did change slightly.

My opinion is that whereas the road rockets were selectively assembled and dyno'd to meet the high performance expectation, the Flash's were mass assembled so the HP claim was conservative.

[Rocket Racer]

Housewiz,
the main benefit of the larger carbs was improved fuel economy. 29mm is acknowledged as the biggest for road use, although on the track 30mm is considered the maximum.

The 356 was a nice sports cam so allows more revs than the cooking cam
The 357 was the final sports cam (excepting the race only 358) that was slightly hotter.
Both are nice all rounders, but the 357 has more lift and in some earlier motors, the cam tunnel needs machining out.
Either cam would be fine, although on a small fin/thin flange I would personally stick to a 356.

compression ratios above 8:1 are largely at the expense of a sweet engine. My race engine is at 8:1 and pulls 7500 readily.

Valve sizes also differed across models but I would suggest leaving well alone (as I would carb size) as the smaller valves and inlet ports have faster gas velocity producing more bottom end torque.
Increases to carbs/ports valves all reduce gas velocity so only provide benefits over stock at full throttle. How often will you practically be holding your engine at full throttle?

Has this better answered your questions?

[orabanda]

Housewiz,
A friend loaned me the factory delivery sheet for his Road Rocket; note the dyno results, and engine specifications.



This is how it looked , bought new.



This is how it looked, after catching up with a car in Perth, Western Australia.





Both he and the bike were repaired!

Richard