Britbike forum Forums British Motorcycle specific Brands Bsa bulletin board horsepower from a A65

Hello

Is there anyone who have tested their BSA A65 for power ?
could be interesting to konw what horsepower a 650 ccm gives on the backwheel as standard and also bigger bores with different kind of setups, porting, valves..

and also topspeed achived.

I also achieved over a ton from a Thunderbolt (OK it's a Smith speedo but it looked very exciting to see it go to 160 kph, touch it and go over it for a bit).

One ride later this happened.



Than I grew up, bought a modern machine to hit the ton and kept the T-bolt for quiet rides.

So you had blowbye on both sides.

I do not know how a BSA head is fitted but check there is no raised area around the stud holes. Make sure the gasket is a good fit. Anneal the gasket properly. Use copper coat on the gasket. Clean the threads and use a torque wrench. Run the bike a few minutes, let it cool overnight and retorque and then retorque a couple of times again in the first 1000 miles.

Retorquing is usually more important with composite gaskets not copper gaskets.

I beleive a good solid Brit 650 gives around 40 to max 45 rear wheel BHP.

Its a good street Commando that gives more than about 48 bhp. Combat trim I dont know.

A65, modified, Megacycle X1 race cam, flowed head, 32 mm AMAL Concentrics, lightened valve gear, EV engineering slash cut pistons 9.2:1 compression ratio:


(HP scale, sorry it's cut off but it's plotted on the same scale as torque). And yes, it's an intertial dyno so take the numbers with a grain of salt.

Hello guys thanks for answers.

Alex:
what is a inertia dyno ? can you comment more on the results true figures.

I assume its a 650 ccm you had tested.
what kind of lightening of the valve gears are we talking about, was the valves increased ? how big valves ?

is the pistons lighter than stock ?

Do you know the cam profile figures ? duration, lift .. @..
do you have experinece with other cams ?

Inertia or drum dynos are the most common dynos around because they are substantially cheaper than brake dynos. They work by measuring the angular acceleration your bike can produce on a drum and therefore have to make some compensation for the inertia in your drivetrain. This can give errors up to 5%. Brake dynos actually use a large brake (can be fluid, friction, or electromagnetic) and can essentially measure power at any fixed rpm without the impact of inertia in the drive system. There aren't a lot of brake dynamometers around for us normal folk so we make do with the inertia dyno.

Anyway, yes, it's 650 cc. The pistons are slightly lighter than stock but I don't remember how much right off hand. It does also have a substantially lightened flywheel and carillo rods. The valves are stock size.

The cam specs: 542-x1 Road race profile. Mid-range and top-end
Lift: .400" Duration: 280° 103° power. Use racing springs and pistons. Intake open/close: 37 btc/63 abc exhaust open/close: 63 bbc/37 atc.

I have only run BSA stock cams beside this one. This cam has really nice midrange and keeps the torque broad and in a manageable range while continuing to produce power past 8000 rpm. Not sure I'd wanna run it on the street.

hers my BSA last summer, 2010 before I started to modify the enine, all are in pices now, bur soon it will be assembled

machined for Norton Commando crank and bearings

this will be a 883 ccm

Norton Commando crank, machined to fit BSA A65

alu cylinder made in Germany, not my engine

BSA A65 with aluminium cylinders and Triumph T 140 pistons. bore around 76 - 77mm. (this is not my engine)
Cylinder made and engine assembled by Rainer Traupel in Germany.

My own experience with a bike set up for lsr trials has been a best of 52+ hp and 115.5 mph on a standing start mile with official timers. The motor uses 74.5 mm pistons to meet the 650 class. Stock cam, stock valves, flowed head, 32mm Mk1 carbs, 10.4 cr, mufflers. 20/47 gears. Pazon ignition. I have also used 2 different 'racing' cams and was surprised to find that the Beezer cam was best with mufflers. With Megacycle X-8 and megaphones running 11.8 cr the bike did 121.5 at the same track. PRT

Norton Commando 89 mm stroke crank, machined for BSA A65

Hello Pushrod Tom

52 + horsepower seems like a high number for me on a fairly stock A65. Was it measured on the back wheel or on the cranc ?

Still not as much as a stock Trident.

David, Tom's talking rear wheel, a stock trident might not get that. It would be interesting to compare rear wheel power on different bikes.

Oleandreas, how did you menage to install a Norton bearing on the timing side of the engine ?
My impression was their outside diameter is much larger than space available.
By the way Norton engine is another design with a crank floating in the cases ( rollers both sides ) and somehow it works ???
It means BSA engine should work as well with this bearing configuration.

If you look at the photograph, it has a needle bearing on the timing side, not a Superblend roller. What I would be interested in knowing is why he used a needle bearing for the intermediate gear shaft? And not even a full compliment needle at that. A bush has a very high load capacity and I do not remember when I had to replace one due to wear. Also, why change from the two front inner bolts to one central one? It appears to be right at the back end of the rocker support.

DM, it has the threads there for the other bolts, maybe its an extra, I've never looked where it would come out but maybe it would be useful. With an alloy block esp with smaller studs and bolts the head cannot be pulled down to the std bolts 33ftlb, not that that seems a problem from my experience, but it may help stop oil leaking up the front where A65s sometimes seep. Some dowls on the oil drain holes would probably help that.

P.S. I forgot to mention that my Hornet had 38-40 hp when I started out on the Speed adventure that is still ongoing and still driving me crazy! PRT

needle bearing for "intermediate gearshaft" idler wheel or what its called, I dont see it as any important upgrade. I had to replace the weared bushing, and I decided to change for a roller. I dont see any special benefit in this, probably much more useful on the camshaft....