racing a s2000
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Joined: Jan 2003
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From: Wylie, TX
Sorry, but I believe your logic is all wrong.
First of all, my equation:
HP = Torque * Engine Speed
is actually correct. The only reason that your 5252 constant is required is because you choose to use ft-lbs as your unit of torque and RPMs as your unit for engine speed. Different units would require a different constant. Likewise, if I had used a different unit for power (like Kw instead of horsepower), the necessary constants would be different still. Technically, I should've made the equation even more generic by simply using power instead of horsepower, but whatever.
I'm not exactly sure what you're talking about with the rest of your statement, though. In the end, if you're running 1/4 mile race, you want to be accellerating as much as possible from the time you cross the start line to the time you cross the finish line. To do that, you need to maximize torque, which will subsequently maximize horsepower (since the two correlate). If you do this, then you will end up with the optimal trap speed and ET for your car. While it's possible for car A to have a lower trap speed but still have a better ET than car B, it's not possible for car A to have two seperate runs where his ET is the best his car can produce but his trap speeds are different, simply because he chose different shift points (assuming you disregard traction issues, etc). It's just not possible.
First of all, my equation:
HP = Torque * Engine Speed
is actually correct. The only reason that your 5252 constant is required is because you choose to use ft-lbs as your unit of torque and RPMs as your unit for engine speed. Different units would require a different constant. Likewise, if I had used a different unit for power (like Kw instead of horsepower), the necessary constants would be different still. Technically, I should've made the equation even more generic by simply using power instead of horsepower, but whatever.
I'm not exactly sure what you're talking about with the rest of your statement, though. In the end, if you're running 1/4 mile race, you want to be accellerating as much as possible from the time you cross the start line to the time you cross the finish line. To do that, you need to maximize torque, which will subsequently maximize horsepower (since the two correlate). If you do this, then you will end up with the optimal trap speed and ET for your car. While it's possible for car A to have a lower trap speed but still have a better ET than car B, it's not possible for car A to have two seperate runs where his ET is the best his car can produce but his trap speeds are different, simply because he chose different shift points (assuming you disregard traction issues, etc). It's just not possible.
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From: UCF Knights!
Think about it this way. We'll use arbitrary numbers, since I haven't clocked it to give you exacts...
Say I'm accelerating in 3rd gear from a redline 2nd gear shift. As I'm climbing thru the revs, the MPH are obviously increasing...but...at around 8300 rpm, the rate at which I'm still accelerating is now decreasing...I'm losing torque.
We'll say for arguements sake it takes me a total of 8 seconds to reach 90 if I wind out 3rd gear. If I shift to 4th at 8300 though instead, my torque is higher when I land in 4th than if I'd have stayed in 3rd, and I get to that same 90mph in 7 seconds instead because my rate of acceleration is now faster (more torque).
Since my acceleration was at a higher rate by staying in my torque band, I covered more ground by the time I hit 90...I'd have hit 90 in more time by keeping it in 3rd, but I'd be slightly farther from the end of the 1/4. ...so by the time I do cross the 1320, my speed will be greater if I wind out each gear, but it took me more time to get there. I didn't have the optimal acceleration.
See my point now?
*edit* I just re-read your last post, and your last statement "it's not possible for car A to have two seperate runs where his ET is the best his car can produce but his trap speeds are different" and you are right. That's not the point I'm arguing. I'm saying that your quickets ET run isnt necessarily going to be the same as your fastest MPH run. Winding out you may get 14.1 @101, or shifting early you may get 13.8 @ 98.
Say I'm accelerating in 3rd gear from a redline 2nd gear shift. As I'm climbing thru the revs, the MPH are obviously increasing...but...at around 8300 rpm, the rate at which I'm still accelerating is now decreasing...I'm losing torque.
We'll say for arguements sake it takes me a total of 8 seconds to reach 90 if I wind out 3rd gear. If I shift to 4th at 8300 though instead, my torque is higher when I land in 4th than if I'd have stayed in 3rd, and I get to that same 90mph in 7 seconds instead because my rate of acceleration is now faster (more torque).
Since my acceleration was at a higher rate by staying in my torque band, I covered more ground by the time I hit 90...I'd have hit 90 in more time by keeping it in 3rd, but I'd be slightly farther from the end of the 1/4. ...so by the time I do cross the 1320, my speed will be greater if I wind out each gear, but it took me more time to get there. I didn't have the optimal acceleration.
See my point now?
*edit* I just re-read your last post, and your last statement "it's not possible for car A to have two seperate runs where his ET is the best his car can produce but his trap speeds are different" and you are right. That's not the point I'm arguing. I'm saying that your quickets ET run isnt necessarily going to be the same as your fastest MPH run. Winding out you may get 14.1 @101, or shifting early you may get 13.8 @ 98.
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From: Scatterbrainia
Wow, you guys are over-complicating things!!
I'm pretty sure the correct answer for the OP's original question of "Racing a s2000, what's the right way?" is:
For pinks. On a public street. Lined up with an SRT-4, with lots of spectators around.
I'm pretty sure the correct answer for the OP's original question of "Racing a s2000, what's the right way?" is:
For pinks. On a public street. Lined up with an SRT-4, with lots of spectators around.
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Joined: Jan 2003
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From: Wylie, TX
You're forgetting the multiplier of the transmission gearing. When you shift into a higher gear, the torque multiplier at the transmission is smaller. That's why you don't accelerate as quickly in 4th as you do in 3rd. Even if you have 160lb-ft (at the engine) at 6000RPM and only 120lb-ft (at the engine) at 9000RPM, it may still be better to stay in 3rd gear all the way to redline, instead of shifting to 4th, even though the engine torque is lower. The reason for that is because you have to take into account the gearing factor.
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From: Wylie, TX
Originally Posted by wildcardtrd,Aug 27 2007, 12:33 PM
I'm saying that your quickets ET run isnt necessarily going to be the same as your fastest MPH run. Winding out you may get 14.1 @101, or shifting early you may get 13.8 @ 98.
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From: UCF Knights!
A good point. 3rd gear ratio is 1.481 vs 4th gears ratio of 1.161. Since my dyno was run in 4th gear, the graph shows actual rear wheel torque in 4th. If you acount for the multiplier difference, there may be very little difference between the 2 results...
Ugh. This is what happens when I've got my brain all fired up to do homework and leave s2ki on in visible sight
Ugh. This is what happens when I've got my brain all fired up to do homework and leave s2ki on in visible sight
