that aside from electric direct-drive cars like the GM EV1, most cars do not have engine drive the wheels directly. Instantaneous acclearation at given vehicle velocity is determined by engine power, not engine torque: P = F * V. Power rating is conserved through engergy conservation, whereas wheel torque can be anything depending on the gear set design and seleciton.

The advantage of high torque rating lies in "load factor." A car with planetary gears can not be staying put at peak output and continue acclearation at the same time, necessitating gear shifts. Assuming perfectly flat torque curves (a reasonably good approximation for modern engines), when you upshift an engine that makes 200hp at 7500rpm and drops the RPM to 2500, you are getting only 67hp when the new gear is engaged; whereas in a car that makes 200hp at 5000rpm, the same drop to 2500rpm would still provide you with 100hp. As you go through the gears, you have to average the engine output over the time it spends churning out 67/100 to 200 horsepowers to get the total amount of work done by the engine; ie. the distance covered by the car. Of course, if the car is well designed and the driver is skilled to keep the 7500rpm engine boiling at 3750rpm or above, both cars will have the same output over time. How realistic is it to stay at 3750rpm or higher on high ways all the time is a different story altogether. That's why all race cars have high revving engines; the drivers and driving condition allows high rpm's all the time.

The original poster made a very good point in that with CVT, there will be little advantage performance-wise in having a turbo engine. With a CVT, "load factor" is irrelevent because CVT can put the engine at precisely peak horsepower point throughout a long stretch of accelearation. It's a bit weird to see the tachometer pegged at 7500rpm for minutes while the car gets faster and faster, but that is the way to achieve the best accelearation; there's no gear shift delay to boot!

posted by 24.218....

• Q: if the engine is designed to give a flat torque..., TB, Fri, 1 Mar 2002 13:20:31
  • power vs torque, Thomas L, Fri, 1 Mar 2002 19:02:30
    • Wait a minute!, PatO, Fri, 1 Mar 2002 22:05:43
      • But you forgot . ., Jim, Fri, 1 Mar 2002 23:09:53 <-- Viewing This Message
        • Excellent post n/m, Thomas L, Sat, 2 Mar 2002 14:55:42
          • Re: Thanks. n/m, Jim, Sun, 3 Mar 2002 21:54:55
        • Re: But you forgot . ., Eli5, Sat, 2 Mar 2002 13:04:55
        • Re: But you forgot . ., PatO, Sat, 2 Mar 2002 09:20:42
          • "in a given gear" is irrelevent, Jim, Sun, 3 Mar 2002 11:41:44
          • Really????, Thomas L, Sat, 2 Mar 2002 15:01:24
            • Re: Really????, PatO, Sat, 2 Mar 2002 18:30:44
              • Typo, PatO, Sat, 2 Mar 2002 18:33:28
                • Re: Typo, 2Slow, Mon, 4 Mar 2002 09:10:46
                  • My own typo..., 2Slow, Mon, 4 Mar 2002 12:07:42
                  • Didn't the M1 have a serious design flaw..., zeke, Mon, 4 Mar 2002 10:17:47
                • Clarification, Thomas L, Sun, 3 Mar 2002 04:48:38
        • I may be wrong-, Dennis, Fri, 1 Mar 2002 23:30:34
          • Re: I may be wrong-, Jim, Sat, 2 Mar 2002 00:46:29
  • Re: Q: if the engine is designed to give a flat torque., Al, Fri, 1 Mar 2002 16:07:54
    • experimental data:, Eli5, Sat, 2 Mar 2002 12:52:29
    • Re: Q: if the engine is designed to give a flat torque., BrooksG, Fri, 1 Mar 2002 16:55:26
      • I don't consider 5th an overdrive..., Bob M, Sat, 2 Mar 2002 11:21:00
  • lower rpms for same speed?..., bob m, Fri, 1 Mar 2002 14:00:00
    • darn enter button..., bob m, Fri, 1 Mar 2002 14:00:50
      • Faster as in 160+ mph? n/m, Eli5, Fri, 1 Mar 2002 16:01:15
        • Yep -- 150 anyway. n/m, Bob M, Sat, 2 Mar 2002 11:13:54

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