Heidi Rose, my oldest girl, is taking her motorcycle training course this weekend. She is on the little red Suzuki. This afternoon we will go to the Kawasaki shop and look at the 250 Ninja.
The jetting is done and I have a torque curve for the new build. This curve gives me a lot of useful information. The torque peaks at 5,800 rpm and it drops off rapidly. My target rpm, and this is the engine speed I try to run at through the measured mile, is 7,500 rpm. The new build and the old one have the same torque at this rpm.
First, a look at sprocket sizes for this year's BUB meet. Last year I ran 127.14 mph at 7,450 rpm using 19 and 43 tooth engine and wheel sprockets, respectively. The new build has the same torque at that engine speed as the old motor. It is likely that I will not go faster with the old 19/43 combo. This year I will use 19/42 chainwheels. The engine will be turning less rpm when I get to top speed. The peak torque for the new build is at lower RPM, too, so this gearing change is a better match for the new build.
Will I go faster? All of the gears, sprockets, wheels, etc. in the bike are levers, and the 19/42 gearing will give the pistons less leverage to move the bike across the salt. This may offset the greater torque and result in speeds similar to last year's. I hope for more speed, but the reality is, I probably will not get it.
The second thing I see in this dyno printout is the need to do more work. Torque should fall off after 7,000 rpm, rather than 6,000 rpm. More torque at higher rpm = increased horsepower = greater speed. Less restrictive carbs and tuned intakes and exhausts will do this. This will be next winter's project.
The dyno work took 7 hours at $80 per. Big dollars, and is it worth it? The bike I brought into the shop had a power band like a Kawasaki triple and made a trifling 42 horsepower. It was thrilling to ride and it felt fast, but in reality, it was not. It came out of the shop correctly jetted with 70 horsepower. I have the info I need to set my gearing for next year, and I know what changes I need to do to the torque curve to go faster. Money well spent.
This engine build has cost a lot of money and it required some very special parts and a lot of good advice. We got a break on some part costs, a few things were given to us, and there was a donation of many hours of dyno time. The team Go Dog, Go mutts would be sleeping under the porch all summer if it was not for this help. Special thanks to Cascade Moto Classics of Beaverton, Oregon, South Bay Triumph of Lomita, California, and folks on this forum. We are ready to go!