I have a 1990 Toyota Supra Turbo 4 speed auto. I've done some research about automatic transmissions and manual transmissions and what are the positives and negatives of each. (For example, MT is said to have better fuel economy by having the wheels roll without any influx of air.) A topic that I came across is that AT loose more HP, around 15% to 20% of the HP created at the wheels when translated from the engine (aka the crank HP), as opposed to MT loosing <15% at the wheels.

• What contributes to the AT loosing more of the HP generated at the wheels?

• What should one do to reduce the HP lost at the wheels without compromising the efficiency of the car? (Exhaust mods/manifold mods/ straight-piped via CAI reduces low-end torque [obtained info from a plethora of automotive sites].

• If the above answer is impossible to obtain, what should one do to decrease the amount of HP lost in an AT at the wheels?

Since I have a AT, I'm not necessarily going to do any modifications. I'm just using my car as a reference.

Thanks, Branden

  • Short version: There is nothing you can do. Autos are inherently less efficient than a manual. Your choices are to 1. Accept it. 2 Get a manual. 3 try and acheive some power/efficiency gains elsewhere so you can sleep at night. If youre not prepared to make any changes to your car then option 1 is going to be your only option. Jan 3 '16 at 2:00
  • Are you certain CVT Automatic is less-efficient?
    – NoBugs
    Jan 3 '16 at 8:27

The power losses in a MT are primarily do to friction. Everything in a MT is positively locked together, meaning there is no slip anywhere. Beyond friction at least one of the rotating assemblies is partially submerged in the gear lube to provide splash lube for everything else. Stirring the fluid looses power.

In an automatic everything I just mentioned applies(ish). The additional power loss comes from the need to produce line pressure to operate the transmissions systems. Also before the torque converter clutch engages to lock the torque converter 1:1 there is substantial thermal loss inside the torque converter from just churning the fluid inside.

As far as improving lost horsepower well there's nothing you can do. Friction is a bitch we all have to live with. Every bearing from the back of the crank shaft all the way to the wheels contribute to these losses.

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