Torque curves

At the Broadford Bonanza a couple of years ago, there was a guy with a Commando with megaphones. I wouldn't have tried to ride it like that. You could hear the cam to start working as he revved it. Commandos have got to much torque to not be smooth in their power delivery. You can tie yourself in a knot in a corner if there is a large bump in the way power is delivered, especially if you get in really hot. One thing I have noticed about my bike, is the way it never creates any anxiety. I just ride it and let it do it's thing.

With my 500cc Triton, if you could not ride it around a 50 MPH corner at 70 MPH in first or second gear, the motor would drop almost dead - and if you slipped the clutch to get it going again, the bike would go sideways. Some guys have the theory that what you need is max horsepower and do everything to get it. The result can be a bike which tries to kill you. I used to like that bike, it was like a pussy-cat which has been badly mistreated. You could love it, but it would bite or scratch you regularly. There was a kid at a meeting a while back who has a short stroke 500cc Nourish Weslake - same deal, he was a nervous wreck. I think a Paton might be scary.

acotrel said:

If you have a fixed rev limit of 7000 rpm and over-port the motor, the bike would go backwards. What you take out of the port is almost impossible to put back. If all becomes top end, the bike can become very difficult to ride well. If it only pulls from 5 to 9. that is the usable power band with which you and the gearbox must cope.

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My A65 has a C/ratio 5speed and makes over 55lbft between 4,400 and 8000 it peaks at 6000 with just over 65lbft. The article you quote on the high torque Triumph are they quoting rear wheel hp and torque? Manufacturers almost always use engine hp not rear wheel. If that's the case the A65 power would translate to around 72lbft and 97hp at the crank. The dyno operator had it on full throttle with the dyno holding it around 3,500 before initiating each run, full throttle on the thing doesn't work at that rpm. It drives better with less throttle till about 4,400. If you were racing it and limited rpm to 7,000 it would still be making over 80hp at the wheel. You are right about over porting, even if you get more flow from a better shaped port of the same volume, although it shouldn't lose down low it's going to want to rev higher and make more power higher up. Why its worth dynoing and seeing where the curves are going over, because that tells you when it's running out of breath, if its peak hp is at 6500 and you rev it to 7,000 a better shaped port could extend the peak hp to 7,000 without loss lower down. When they do keep making power its hard not to use the higher rpm because it feels like it likes it.

The 2 into 1 pipe makes things deceptive. From what I developed to make my Triton sane, I went straight to what I now have on my 850. Then I used a bit of judgement when setting the cam up. It all seems to work very well. But I think that with that pipe, ANY cam would work well. When I did the pipe for my Triton, the first thing that happened was I cut 2000 rpm off the top end. That dropped the top of the rev range to 8000 rpm. Then I started cutting back the collector and fitting bigger tail pipes until I regained about 1000 rpm. Ant restriction at the end of the collector and you lose too much power. The result of the exercise was that my lap times dramatically improved.
He pipe on my 850 is too loud, but it performs well. There is no internal step anywhere in the exhaust system. The ID of the header pipes is the ID of the exhaust port where the aluminium ends. I made threaded stubs which screw into the ports onto a heat resistant gasket. The pipe is held on with sleeves and springs. With the cam timing I use, the paint is burned off the exhaust for about 18 inches, even when using methanol fuel.
I usually race-change up from just below 7000 rpm, which seems to give excellent acceleration with the close box and the heavy crank. But I still do not know where my motor would stop pulling. It is extremely easy to over-rev it.

I think the figures quoted for the new Triumph motor would be at the rear wheel. I don't think they would bother to connect the dyno to the end of the crank, these days.

It's what the factory claim so my guess would be at the crank. Factories use engine dynos as well as rear wheel type.