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All Right , I'll play your silly game .

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Re: All Right , I'll play your silly game .

Postby Rohan » Sat Feb 11, 2017 9:11 pm

Danno wrote:
Years ago it was discovered that increasing horsepower in a flat-track engine did not go hand in hand with a reduction of lap times. It was postulated that any more than around 100-105 bhp was useless because it could not be put down on the track and only brought on excess wheelspin.


Wellllll, there is that famous story of Kenny Roberts on a TZ700 (TZ750 ?), where he cruised with the pack and really opened the throttle on the last lap, and BLITZED em !
And reportedly parked it and quipped "they don't pay me enough to ride that thing" and never rode it again.
And they (multicylinder roadracing strokers) were banned.

But it did show that all the perceived wisdom about hp and torque and traction was just talk.
A good rider can use as much hp as possible...

Danno wrote:Then, someone out of the inner circle took a look at a dyno graph of an XR 750 and discovered something curious: We all know the hp and torque graphs intersect at 5250? rpm, but most graphs show hp continuing to rise while torque maxes out and starts falling off. The XR 750 chart showed the lines intersecting and crossing the opposite way; as the hp fell off, torque continued to rise.


Technically, we'd need to see those graphs.

The torque curve is merely a reflection of how well the engine breathes.
It is not impossible for the most efficient/effective breathing to happen at higher rpms,
to or even beyond redline in some cases.

However, the hp curve is CALCULATED from the torque curve, so if torque keeps rising,
then the hp HAS to keep rising as the rpms increase - its a strict mathematical relationship.

You can't have torque with no power, or power with no torque - they are rather solidly bolted together...

5252 rpms is significant only because its part of the formula twixt torque and hp.
At those particular rpms, the torque in ft-lbs is numerically the same as the hp.
Thats why the graph lines cross (providing the ft-lbs and hp scales are drawn the same).

Rohan
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Re: All Right , I'll play your silly game .

Postby jaydee75 » Sun Feb 12, 2017 6:33 am

Regarding speedway bikes on AMA dirt tracks:
I was at the Daytona flat track in the early 70's and one of the top Euro speedway riders was there for a demonstration. Probably the most impressive display of riding I have ever seen. He sprayed dirt several rows up into the stands. I don't remember who it was.
Then for fun, after the races, they ran a match race of him against the AMA winner that night. I believe the speedway bike won, too long ago to remember.
It was impressive I know. Great night I will never forget.

Jaydee
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1975MK3 BoughtNew,SN329404,TriSpark,HarlyStartr,Decibels,NinjaBrake,TM34Flatslide
1959 AJS 650 Twin
1973 Yamaha RD350
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Re: All Right , I'll play your silly game .

Postby Danno » Sun Feb 12, 2017 9:55 am

jaydee75 wrote:Regarding speedway bikes on AMA dirt tracks:
I was at the Daytona flat track in the early 70's and one of the top Euro speedway riders was there for a demonstration. Probably the most impressive display of riding I have ever seen. He sprayed dirt several rows up into the stands. I don't remember who it was.
Then for fun, after the races, they ran a match race of him against the AMA winner that night. I believe the speedway bike won, too long ago to remember.
It was impressive I know. Great night I will never forget.

Jaydee


That could happen on a short track like the old one at Daytona, but a Mile is a lot different. Short track races are all but gone from AMA GNC Flat Track, with only one on the 2017 schedule. This years Daytona race will be a TT on a purpose-built track inside the Speedway. Twins are the top class with singles a support class. Even on a half-mile, a speedway engine would likely overheat and seize.

A buddy once tried to run an air-cooled 2-stroke motocross engine (no tuning changes) in his flat tracker and it repeatedly seized. The problem was that motocross bikes are designed to run at full power in short bursts. not a continual long stretch, Different porting and lower compression cured the seizing.

Danno
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Re: All Right , I'll play your silly game .

Postby Danno » Sun Feb 12, 2017 10:06 am

Rohan wrote:
Danno wrote:
Years ago it was discovered that increasing horsepower in a flat-track engine did not go hand in hand with a reduction of lap times. It was postulated that any more than around 100-105 bhp was useless because it could not be put down on the track and only brought on excess wheelspin.


Wellllll, there is that famous story of Kenny Roberts on a TZ700 (TZ750 ?), where he cruised with the pack and really opened the throttle on the last lap, and BLITZED em !
And reportedly parked it and quipped "they don't pay me enough to ride that thing" and never rode it again.
And they (multicylinder roadracing strokers) were banned.

But it did show that all the perceived wisdom about hp and torque and traction was just talk.
A good rider can use as much hp as possible...

Danno wrote:Then, someone out of the inner circle took a look at a dyno graph of an XR 750 and discovered something curious: We all know the hp and torque graphs intersect at 5250? rpm, but most graphs show hp continuing to rise while torque maxes out and starts falling off. The XR 750 chart showed the lines intersecting and crossing the opposite way; as the hp fell off, torque continued to rise.


Technically, we'd need to see those graphs.

The torque curve is merely a reflection of how well the engine breathes.
It is not impossible for the most efficient/effective breathing to happen at higher rpms,
to or even beyond redline in some cases.

However, the hp curve is CALCULATED from the torque curve, so if torque keeps rising,
then the hp HAS to keep rising as the rpms increase - its a strict mathematical relationship.

You can't have torque with no power, or power with no torque - they are rather solidly bolted together...

5252 rpms is significant only because its part of the formula twixt torque and hp.
At those particular rpms, the torque in ft-lbs is numerically the same as the hp.
Thats why the graph lines cross (providing the ft-lbs and hp scales are drawn the same).


Actually, Kenny DID ride that bike (or an exact replica) again at Indy several years ago. And his comments were to the effect if he had had today's tires back in the day, it would have been much easier to get the TZ tracker to hook up, which was it's biggest bugaboo, and highly evident in film of that particular race. The only way he was able to win was by the fact that the TZ had a full 40 horsepower on the Harleys. And it was still practically a photo finish.

The strict mathematical relationship between torque and horsepower is that they are both the same in ANY engine at 5252 rpm. How else would torque fall off while hp continued to rise? (see the vast majority of torque/horsepower graphs) According to your logic, torque would have to continue to rise as horsepower rises. it never does.

And since torque and horsepower are measured in different units, any graph is just an overlay of two different graphs with the intersection at 5252. Are you saying there's no way the graphs could intersect and then diverge one way but not the other? Please show YOUR graphs to illustrate torque and horsepower curves in parallel.

Danno
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Location: Southwestern Illinois

Re: All Right , I'll play your silly game .

Postby Rohan » Sun Feb 12, 2017 3:19 pm

Danno wrote:
The strict mathematical relationship between torque and horsepower is that they are both the same in ANY engine at 5252 rpm. How else would torque fall off while hp continued to rise? (see the vast majority of torque/horsepower graphs) According to your logic, torque would have to continue to rise as horsepower rises. it never does.


My "logic" doesn't come into it, its the mathematical formula that defines hp from torque that controls it !
It doesn't just apply at 5252 rpms, it applies right across the WHOLE rpm range.

And as long as torque falls at a lesser % than the % that rpms are rising, then hp will keep climbing.
If the torque falls at more % than the rpms are rising, then the hp curve starts falling...

Have you never graphed a hp curve from the torque curve. ?
I'd agree completely, the 2 graphs are quite separate, but often shown overlaid for convenience.
But that XR750 engine can't defy the laws of torque/hp curves....

Rohan
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