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shift points

Subject: shift points
From: (Phil Bates)
Date: Wed, 11 Dec 1996 20:53:56 -0700
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:

                ------ x 4800rpm = 8000rpm

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:

                ------ x 4800rpm = 6960rpm

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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