Horse Power / Torque vs MPG

This article explains how that HP and TQ affects Fuel mileage.

First, let’s figure out what decreases fuel mileage.  Opening the throttle wider uses more fuel.  Turning higher RPMs uses more fuel.  So the goal is to turn less RPMs and to open the throttle as little as possible to get better fuel mileage.

Here is where I will prove that increasing HP will consume more fuel than by increasing TQ.  The way to make more HP is to move the TQ band further up the RPM range.  The SAE formula to calculate HP on a dynamometer is TQ multiplied by the RPM divided by 5252.  So if looking you are looking at a dyno graph, you should be able to take the TQ and multiply it by the RPM that the TQ reading is located, then divide it by 5252 and it should give you the correct HP at that RPM. Example:  You have a graph showing peak TQ of 100 @ 3500 RPM.  Using the formula TQ x RPM / 5252, the HP will be 66.64 HP.

Now move the peak TQ of 100 up the RPM band to 5000 RPM.  The formula will be 100tq x 5000 rpm / 5252 = 95.20 HP.

So basically you have to be in the higher RPMs to make HP.  So if you are riding your Bagger and start up a hill or go to pass another vehicle, you will usually have to gear down.  The reason that you have to gear down is because you have to get in a gear that puts the engine in a RPM range where the TQ is located (torque band).  This should tell you something.  If you were already in the TQ band, there would be no reason to gear down.

If the engine’s TQ band is in the lower RPMs, you don’t have to open the throttle as much during cruising or under load. 

If you build the engine with the torque band in the lower RPM range, you use less throttle because you are already in the power of the engine which saves fuel.  Since the power is in the lower RPM range, you turn less RPMs which saves fuel.

Conclusion:  A high TQ engine with the TQ in the lower RPM range, turns less RPMs and uses less throttle.

A high HP engine with the TQ band in the high RPMs uses more fuel due to more throttle application and running in a higher RPM range to stay in the power band.