Shifting at RPM or horsepower

[Interested Observer]

Tauruck:  TE = Tractive Effort    That is, the thrust imparted to the vehicle by the driven wheel(s) interacting with the ground, or, the salt surface.


It is unfortunate that so many people are so attached to the notion of the torque curve and/or the torque peak in connection with performance evaluations.  There are really only two things torque information is useful for:  calculating the horsepower curve, which is most often done as a matter of course by the dynamometer facility; and for use in sizing driveline components.  Vehicular performance is effected by the application of POWER.  Torque is for rod bolts, lug nuts, etc.

So the opening question was how to best apply the available power.  The accompanying graph would seem to provide a straightforward and graphic example of how to do that.  The power curve, once obtained, is manipulated by the driveline characteristics--gear ratios, tire size, etc.--to determine the vehicle speed at each point of the power curve in each of the gear ratios.  This is then plotted as shown in the graph.  The horsepower required curve can also be plotted, with the vertical distance between the available and required curves representing the power available for acceleration (if the surface traction will support it).

In the example shown, the power available in the lower gears is probably well in excess of what can be used, and part-throttle operation is most likely required for those lower speeds.  However, this example clearly shows that third gear is too short for optimal operation.  Running the engine to redline will incur a drop in power in third and at the shift to fourth a further drop will be experienced.  Again, assuming traction is sufficient that third can be operated at wide open throttle.

The fourth-fifth shift is nicely arranged, with minimal disruption of power, and the information shows that the shift should occur at 8100-8200 rpm.  Further, fifth gear is likely arranged to provide maximum power at the point of maximum velocity--which is the point of the exercise.

Hopefully the "image" will appear.  If not, it is in the attached document file.


 

[Sumner]

The accompanying graph would seem to provide a straightforward and graphic example of how to do that.  

....In the example shown, the power available in the lower gears is probably well in excess of what can be used, and part-throttle operation is most likely required for those lower speeds.  However, this example clearly shows that third gear is too short for optimal operation.  Running the engine to redline will incur a drop in power in third and at the shift to fourth a further drop will be experienced.  Again, assuming traction is sufficient that third can be operated at wide open throttle.

The fourth-fifth shift is nicely arranged, with minimal disruption of power, and the information shows that the shift should occur at 8100-8200 rpm.  Further, fifth gear is likely arranged to provide maximum power at the point of maximum velocity--which is the point of the exercise..

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Hope that helps,

Sum

[SPARKY]

Love the Graph---this is what I work with so I can trade off my variables as to gearing and tire size----I can only get away with such a wide split low to direct because I run larger eng. class

I run a PG/GV set up  as a 3 speed low/direct/ OD

The first column is RPM 2nd TQ from dyno
3rd & 4th 1st      speed and   TE calculation (TQ x FDR)
5th & 6th 1st/od speed and TE   
7th & 8th Direct speed and TE
 9th   & 10  OD   speed and TE


I didn't put the lower RPMs on this copy---to see how I use I shift at 8000 low falls all the way back to around 4300 but I am going slow enough if pulls ok  .  It really starts to pull at  4700 and is full on above 4950.  the reason I love this set up so much look at the final shift at 256 mph into OD   It falls back to 6250 which is above peak TQ of 5875 and pulls right on up to and a little past peak HP.  With the new car I may need new components as I need to move my HP UP the RPM range.   ymmv          `                      
RPM   TQ   1st   1.76   Tire 23"   1 od 1.37       2nd 1.00       OD 0 .78       gear 5       gear 6   
      FDR 3.76   TC   .93   FDR   2.93   TC   .93   FDR 2.14   TC  .93   FDR 1.66   TC  .93               
      Speed   Tra. Eff.   Speed   Tra. Eff.   Speed   Tra. Eff.   Speed   Tra. Eff.   Speed   Tra. Eff.   Spred   Tra. Eff
         
5,100    707    93    2,637    155    2,058    163    1,499    210    1,170             
5,200    713    95    2,659    158    2,075    166    1,512    214    1,180             
5,300    717    96    2,674    162    2,087    170    1,520    219    1,187             
5,400    719    98    2,681    165    2,093    173    1,525    223    1,190             
5,500    724    100    2,700    168    2,107    176    1,535    227    1,199             
5,600    721    102    2,689    171    2,099    179    1,529    231    1,194             
5,700    720    104    2,685    174    2,096    182    1,527    235    1,192             
5,800    717    106    2,674    177    2,087    186    1,520    239    1,187             
5,900    718    107    2,678    180    2,090    189    1,522    243    1,189             
6,000    718    109    2,678    183    2,090    192    1,522    247    1,189             
6,100    713    111    2,659    186    2,075    195    1,512    252    1,180             
6,200    715    113    2,666    189    2,081    198    1,516    256    1,184             
6,300    722    115    2,693    192    2,102    202    1,531    260    1,195             
6,400    717    117    2,674    195    2,087    205    1,520    264    1,187             
6,500    719    118    2,681    198    2,093    208    1,525    268    1,190             
6,600    716    120    2,670    201    2,084    211    1,518    272    1,185             
6,700    710    122    2,648    204    2,067    214    1,505    276    1,175             
6,800    706    124    2,633    207    2,055    218    1,497    280    1,169             
6,900    706    126    2,633    210    2,055    221    1,497    285    1,169             
7,000    701    127    2,614    213    2,041    224    1,486    289    1,160             
7,100    698    129    2,603    216    2,032    227    1,480    293    1,155             
7,200    694    131    2,588    219    2,020    230    1,472    297    1,149             
7,300    690    133    2,573    222    2,009    234    1,463    301    1,142             
7,400    682    135    2,543    225    1,985    237    1,446    305    1,129             
7,500    673    137    2,510    229    1,959    240    1,427    309    1,114             
7,600    660    138    2,461    232    1,921    243    1,399    313    1,093             
7,700    650    140    2,424    235    1,892    246    1,378    318    1,076             
7,800    640    142    2,387    238    1,863    249    1,357    322    1,059             
7,900    630    144    2,349    241    1,834    253    1,336    326    1,043             
8,000    620    146    2,312    244    1,805    256    1,315    330    1,026