Relative merits of 60s race bikes

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Om thinking about the Aermacchi thread, I have come to realise that I have taken many guys knowledge for granted. My knowledge of 60's race bikes has come because I lived and raced in that era. In the early 60s, the top race bike was the 500cc short stroke Manx Norton, - Gileras and MVs were way beyond the reach of most of us. In the lower capacity classes, the 1958 AJS 7R, the short stroke 350cc Manx and the 350cc DBD 32 BSA were tops. The Aermacchi Ala D'Oro 350 came along a little bit too late. But most of the 350cc bikes were good for about 44 BHP compared with a top 500cc Manx which had 50 BHP. The Aermacchi 350 is much lighter than a 500cc Manx. Today, a good guy on a 350 Aermacchi would give the average guy on a 500cc Manx a bad fright. Usually you find the idiots who write the historic racing rules, stop the two from racing against each other. Dave Roper riding the Aermacchi on the IOM is interesting - a very good combination.
 

Fast Eddie

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Dave Degens loved the ‘macchi. His first Dresda frames came about because he loved the macchi handling, but could get more power out of a 500 Triumph twin.

So he copied the macchi geometry and set this as his design perimeter, inserted a Triumph 500 unit motor, and connected it all together with the fewest, simplest, smallest tubes possible.

A little while later, used the same design, but shoehorned in a 906cc NRE equipped Bonnie motor.
 
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Another old mag image I snapped at Daytona; looks like early Astrodome short track. I believe this is Randy Goss' Sprint tracker.

 
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Dave Degens loved the ‘macchi. His first Dresda frames came about because he loved the macchi handling, but could get more power out of a 500 Triumph twin.

So he copied the macchi geometry and set this as his design perimeter, inserted a Triumph 500 unit motor, and connected it all together with the fewest, simplest, smallest tubes possible.

A little while later, used the same design, but shoehorned in a 906cc NRE equipped Bonnie motor.
The trouble with the 500cc Triumph unit motor is that they did not have a real bearing in the timing side until about 1973, and the gearbox is different to that which is used in a 650. So it is always very expensive to play with one. That 906 cc NRE motor is pointless when there are capacity limits and racing without capacity limits is pointless.
 

Fast Eddie

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A lot of things seem pointless to you Al!

But you’re wrong about the 500 Triumph, I can’t remember when they got decent main bearings, but it was way before ‘73.

Regarding the gearbox, Quaife 5 speed clusters were popular as the engine was so inclined to rev. Many had a powerband of between 8,000 and 10,000.

Don’t think you’d have liked one.
 
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Another old mag image I snapped at Daytona; looks like early Astrodome short track. I believe this is Randy Goss' Sprint tracker.

Love the bike and I wish I could afford one. It would be a lovely thing to own. I think it is pretty obvious that the good guys in racing were much smarter than us average punters. In the old days, I would never have thought of buying an Aermacchi. In the 1960s, they were around when the Japanese two-strokes arrived and beat everything. Campaigning an Aermacchi would have been more expensive, but to my mind it would be a much better option. A Japanese two-stroke is easier to ride than most other bikes, but I can see where an Aermacchi would have an advantage. On Phillip Island, it would be unbeatable when raced against similar capacity bikes.
 
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A lot of things seem pointless to you Al!

But you’re wrong about the 500 Triumph, I can’t remember when they got decent main bearings, but it was way before ‘73.

Regarding the gearbox, Quaife 5 speed clusters were popular as the engine was so inclined to rev. Many had a powerband of between 8,000 and 10,000.

Don’t think you’d have liked one.
The 500cc Triumph had the plain timing side bearing at least until 1970. If I bought a Quaife 5 speed cluster for one, how many guys would want to buy it after I had finished with it ? With the unit Triumph, I would have been in the same situation I was in with my converted 650 motor. A very nasty power band. I looked at one of those bikes at a swap meet a few years back. It was on sale for $3000. It would have ended up costing about 4 times that by the time it got raced, and would never have been as good as a featherbed Jawa.
 
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I think the Geoff Monty bike was a 500cc unit Triumph motor in a 250 Ducati frame - might have been good ? Anything in a featherbed frame is too heavy.
 
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My own 500cc short stroke Triumph had a power band from 6000 RPM to 10,000 RPM. But if it dropped below 6000 RPM, it had nothing - above that it gave you a big kick in the bum. On some race circuits 6000 RPM in first gear of a close box, is about 70 MPH. If you have got nothing to bring you out of a corner at 70 MPH, what do you do - slip the clutch and go sideways ? It is all too difficult. With a torquey motor, you just get stuck into it. I once rode a good 500cc Manx - slower down the straights, but much faster around the corners.
 
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In flat track, max horsepower doesn't necessarily make you the fastest guy, even on the straights. Anything over 110 bhp is kinda wasted as it becomes impossible to use because the back tire just spins.

Part of the reason for the XR Harley's dominance of flat track for so many years is the shape of the power curve produced. They were able to make the torque continue to rise as the horsepower fell off. Most dyno charts will show horsepower continuing to rise as torque falls off and this is the unusable part of the powerband on a tracker. At current weight limit (325 lbs) anything over 110 horsepower is unusable.

Several years ago, the AMA changed the rules to allow over-750cc engines to compete if they were production-based. Suzuki, Ducati, Aprilia and KTM all have engines that fit the "Supertrackers" rule, but despite superior horsepower, none have ever dominated, even though some scattered wins are in the books. The XR, the Indian FTR, and the lone RS750 Honda still competing are restricted to their displacement due to having race-only powerplants. Production-based twins are allowed up to 1000cc, but it hasn't done them much good. The 650 Kawasaki twins punched out to 740cc showed you didn't need 1000cc and 140 bhp to win races. Bill Werner took what he learned tuning all those championship XRs and applied it to the Kawi and did what no Supertracker was able to do-win the #1 plate.
 

robs ss

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They were able to make the torque continue to rise as the horsepower fell off.
Not sure what to make of this Danno - Horsepower is actually torque X RPM (in radians) so it impossible for horsepower to drop while torque is increasing.
It's actually the reason why sometimes horsepower appears (falsely) to indicate an increase in engine performance when torque has flatlined (or dropped) but only RPM contributes to raising horsepower figures.
 
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Not sure what to make of this Danno - Horsepower is actually torque X RPM (in radians) so it impossible for horsepower to drop while torque is increasing.
It's actually the reason why sometimes horsepower appears (falsely) to indicate an increase in engine performance when torque has flatlined (or dropped) but only RPM contributes to raising horsepower figures.
It's a little more complex than that. Torque and horsepower are equal at 5252 rpm, but the relationship is not a direct proportion.

Combustion tuning (see the thread on the harley XR ports we'd all like to have in our Nortons) flow, carburetion, cam profiles and timing all contribute to the shape of the powerband. Engines that make their torque peak at relatively low rpm do not rely on astronomical revs to make power.

The torque of an XR does not surpass the bhp, which would be impossible, as you have discerned, but continues to rise as the bhp falls off the table at higher rpm. The lines of the graph will intersect at 5252 rpm, but what happens after that is fluid.
 

grandpaul

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One of the relative merits that's gotten little (if any) mention, is FUN.

60s race bikes are FUN.
 

lcrken

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It's a little more complex than that. Torque and horsepower are equal at 5252 rpm, but the relationship is not a direct proportion.

Combustion tuning (see the thread on the harley XR ports we'd all like to have in our Nortons) flow, carburetion, cam profiles and timing all contribute to the shape of the powerband. Engines that make their torque peak at relatively low rpm do not rely on astronomical revs to make power.

The torque of an XR does not surpass the bhp, which would be impossible, as you have discerned, but continues to rise as the bhp falls off the table at higher rpm. The lines of the graph will intersect at 5252 rpm, but what happens after that is fluid.

Not so, Danno. The relaltionship is a direct proportion, as rob ss said. By definition, horsepower equals torque (in pound-ft) times rpm divided by 5252. That's why they are equal at 5252 rpm. In other units the constant will be different, but the linear relationship is the same. You can't have a situation as rpm increases where horsepower is decreasing while torque is increasing. When you hit the point in rpm where horsepower has peaked and started to drop, torque must also be decreasing.

Ken
 
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These days, there are guys riding four cylinder MVs at Goodwood Revival. In the old days, only factory riders had them. The most FUN that can be had is when the bikes are all of the same TYPE and evenly matched. The Lansdowne Series probably provides better racing (MORE FUN) than the Barry Sheene Memorial Trophy. If you are riding a Manx and get beaten by a guy on an MV, it means as little as if you were beaten by a guy on an RG500. If the guy is on another Manx or G50, that is a different story.



 
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Not so, Danno. The relaltionship is a direct proportion, as rob ss said. By definition, horsepower equals torque (in pound-ft) times rpm divided by 5252. That's why they are equal at 5252 rpm. In other units the constant will be different, but the linear relationship is the same. You can't have a situation as rpm increases where horsepower is decreasing while torque is increasing. When you hit the point in rpm where horsepower has peaked and started to drop, torque must also be decreasing.

Ken

You have a choice - you can make your motor either pull or rev to get power. In the two cases, the inlet ports and exhaust systems are usually different and different gearing is used. When you make a Commando motor rev, it can become very expensive. A high revving motor usually produces more horsepower at the expense of torque, so it depends on which types of circuits you normally race on, as to which way you choose to go. For Daytona, short stroke and big ports and open exhaust are probably better, but then you have to also ride the bike in the infield. On which part of the circuit can you make up the most time ?
 
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