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## Re: shift points

 To: jello@dns.ida.net Re: shift points "Thomas James Pokrefke" Thu, 12 Dec 1996 00:18:31 -0600 (CST)
 ```I used the same formula to calculate shift points for my MGB. Save yourself the time: 1st->2nd 4800rpm 2nd->3rd 4700 3rd->4th 4100 Thomas James Pokrefke 1970 MGB pokrefke@ocean.st.usm.edu http://ocean.st.usm.edu/~pokrefke > > Someone asked for the shift points. I assume that you want them for optimum > acceleration. I have looked up some information - it is available in the > July 1988 issue of Road and Track, and the October 1993 issue of road and > track. Basically, it says: > > a car will accelerate most quickly if each shift drops the revs back to the > torque peak, regardless of where the horsepower peak may be. Often, this > means going all the way to redline - and still the revs may be too low in > the next gear. > > For example, the '85 Toyota MR2 (sorry for the non british example) has a > redline at 7700rpm, peak horsepower at 6600 rpm, and peak torque at 4800 > rpm. First and second gear ratios are 3.17 and 1.90. So to shift from 1 to > two and get the maximum acceleration: > > 3.17 > ------ x 4800rpm = 8000rpm > 1.90 > > but you really shouldn't exceed redline, so shift at 7700. The third gear > ratio is 1.31, so for the 2 to 3 shift: > > 1.90 > ------ x 4800rpm = 6960rpm > 1.31 > > > They also mention that things get kind of screwy when you have a very flat > torque curve. As (the example they have) when you have a turbocharged car > such as a Saab turbo. For this car, the shift points are at 1 to 2 at > 3745rpm and 2 to 3 at 2908rpm, as the peak torque occurs at 1950rpm. With > the flat torque curve, the shift point is definitely less important. > Phil Bates > 58 MGA > 67 MGB > 75 Jaguar XJ12C > 52 MG TD replicar (VW) > ```
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