you would want you next up shift IE 3-4)to hit close to or just b4 peek tq and ready to shit about peak hp
Crower Billet Crankshaft?
- Thread starter SIKDMAX
- Start date
you would want you next up shift IE 3-4)to hit close to or just b4 peek tq and ready to shit about peak hp
Neither, it is the shape of the torque curve in the rev range you will be running in.
OK, let me put this out there using a Dyno chart from my engine a few years ago.
This first graph is of the rear wheel torque that would be produced in each gear. (I had to add some additional data by hand for the higher RPM levels)
This next graph shows the same data but has been adjusted to show the torque at the rear wheels as a function of MPH. I assumed 33" tires. Note how the torque curves intersect. That is where it pays to shift to the next higher gear.
This first graph is of the rear wheel torque that would be produced in each gear. (I had to add some additional data by hand for the higher RPM levels)
This next graph shows the same data but has been adjusted to show the torque at the rear wheels as a function of MPH. I assumed 33" tires. Note how the torque curves intersect. That is where it pays to shift to the next higher gear.
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so with this data one could ,make thier truck faster my extenting the
2-3
3-4
4-5
shifts to make them similar to the 1-2 shift.
2-3
3-4
4-5
shifts to make them similar to the 1-2 shift.
Fingers stuff is pretty close. Notice the torque is falling the whole time. That's because as soon as you put speed (rpm) into the formula, it becomes HP again. If you started with the HP curve and did the same math (torque at the tires vs. speed), the points would be the same RPM.
Here's what I know from real life drag racing late model cars and trucks:
You are going to shift after the HP peak if RPM limitations don't bite you. Experimentation will be necessary, because doing it on paper only gets you so far. The point falls between the HP peak and the "matching point" on the HP curve.
The matching point is where the HP in the gear you are in (falling), equals the HP in the next gear (rising). I used to think the matching point was always the answer, but it isn't the best. Could be due to tach lag, but it's all you have.
Here's what I know from real life drag racing late model cars and trucks:
You are going to shift after the HP peak if RPM limitations don't bite you. Experimentation will be necessary, because doing it on paper only gets you so far. The point falls between the HP peak and the "matching point" on the HP curve.
The matching point is where the HP in the gear you are in (falling), equals the HP in the next gear (rising). I used to think the matching point was always the answer, but it isn't the best. Could be due to tach lag, but it's all you have.
Thank you!OK, let me put this out there using a Dyno chart from my engine a few years ago.
This first graph is of the rear wheel torque that would be produced in each gear. (I had to add some additional data by hand for the higher RPM levels)
This next graph shows the same data but has been adjusted to show the torque at the rear wheels as a function of MPH. I assumed 33" tires. Note how the torque curves intersect. That is where it pays to shift to the next higher gear.
And thank you!
I guess I need to get on a dyno and see what my torque/HP curves look like in each gear.
Nope, just one gear, either 4th or 5th, and run it out past the HP peak. Start from 2200 and go perhaps to 4000.
FWIW, I found the G-tech to be a good tool at the track. You can plot acceleration and see how it tapers off. Looking at the shift points, you will want to look at the acceleration before and after the shift. You want at least the same acceleration after a shift.
It is strictly trial and error, but works.
It is strictly trial and error, but works.
And as a side note, this what all of this boils down to:
Say at 3000 RPM you are producing 500HP at the flywheel in 4th gear (1:1). This shows the the engine is producing 875 FtLbs (Torque=(HP*5252)/RPM). We're gonna ignore losses in the driveline for this. Going through the differential (say we're using a 4.00:1 ring and pinion), the 875 FtLbs at 3000 RPM gets changed to 3500 FtLbs at 750 RPM at the tires. If you've got 32 inch tall tires (2.67ft diameter or 1.33ft radius), that means you've got 2625 pounds of "push" at the contact point. Force(lbs.)=Torque(FtLbs.)/Distance(Ft.radius)
So the higher in RPM band you can make torque, the more "push" you have at higher wheel speeds. This is why big HP motors show big trap speeds.
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