[Hint] Notes on Cars

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Index

Part 1

  • Horsepower Disambiguation
  • Relationship between Power, Torque, RPM
  • General Guidelines on the Engine Choice
  • On the “Perfect Shift”
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Horsepower Disambiguation

Two common definitions of horsepower:

Relationship between Power, Torque, RPM

  • P = 2πTn/60/1000 = Tn/(30000/π) ≈ T*n/9549.3
    where:
  • P: Power (kW)
  • T: Torque (N·m)
  • n: RPM

General Guidelines on the Engine Choice

  • High power
  • Moderate torque *
  • Low boost (NA to be best **)
    And high RPM would be the implication. (as shown in Relationship between Power, Torque, RPM)

* There’s no definite standard on how moderate is moderate… It’s all up to the driver’s preference. At times that “excessive” torque might be desirable, to achieve specific driving techniques. (that’s where Ferrari’s early days’ approach (“Racing V12”) doesn’t seem to work very well…)
** At the same PTn (Power, Torque, RPM) ratings, naturally aspirated (NA) engine would outperform all other force induction types, for no “boost lag” at all (thus superior throttle response). Though the very engine with force induction would certainly have its ratings boosted to another level…

Side note: What with tons of horsepower doesn’t necessarily go fast, but what without doesn’t for sure.

On the “Perfect Shift”

The rationality of multiple gears

As you have realized, the engine’s output power may vary greatly with the RPM; its peak power is only reachable within a certain RPM range (i.e. the optimal RPM).

Thus for optimal performance, it’s important to have the engine maintained at the optimal RPM whenever necessary.

“Perfect Shift”

Shift that approximates the “perfect power delivery”: equivalent * output power from the engine, before/after the shift.

* Which may not always be possible, depending on the specific gearing and engine.

Worth noticing, the “perfect shifting RPM” for a certain car may vary, depending on the 2 factors:

  • Gearing design. (certain designs may have sacrificed the ease (and/or effectiveness) of power delivery, for other goals like: emphasized torque (on wheel), higher top speed, improved “engine brake” efficiency, etc.)
  • Resistance on the car. (e.g. sloped road, “boost lag”, etc.)