vange_c4s

So i was reading my owners manual and in the back were some charts. One is for horsepower/torque vs rpm, and another is speed vs rpm vs gear. I wanted to look at rpm drop for each gear change, minimum hp after gear change, and minimum torque after gear change. New car and trying to figure out best shifting. Data was plotted by eye and the following charts were generated. I lined up rpm in both charts so you can look from gear/speed chart onto hp/tq graph. I assume shifting at redline (7200rpm) into next gear. Observations - torque is always on the flat part - 270lbft or so - and the 3/4, 4/5, and 5/6 shifts are on 302hp peak!! I think I have this right? No wonder why there is always power. Love it.

himself

HP is the critical elelment, not TQ. Besides, the TQ will typically appear relatively flat for a rising HP curve. [Because of the equation: HP=TQXspeed/5250. That also means at 5250 RPM TQ=HP (always)]. To know where you should shift, you also need to look at your gear ratios so you will know what the wheels are seeing. Put another way, all you need to know is the HP and RPM and gear ratio and you can determine where to shift.

In a 996 it looks something like this (actual dyno data, not factory claim):



The bold numbers show where you will end up when you shift. As you can see, the wheels see much more tq at HP increases up to redline. And when you shift, the wheel tq drops significantly. There is no place you can short shift with your engine and benefit - even where the HP starts to drop off. That is, even where the HP dips, due to gearing, you still have much more tq at the wheels than the next lower gear will provide.

The short answer is: for the 996 3.4/3.6L motor is shift at redline. Of course, this is a "rule" for driving in a straight line.
-td

vange_c4s

Hi td,
I think this makes sense. I did not consider the transmission multiplication of engine torque to the wheels. I should have skipped to the short answer for the easy explantion. thanks

Millemiglia

Interesting reading, I have been thinking about this myself.

vange_c4s

i like your words of understanding:

"Understeer is when you hit the wall with your front end. Oversteer is when you hit the wall with your rearend. Horsepower is how hard you hit the wall. Torque is how far you move the wall."