Power band

[Walter F.]

Can someone explain to me what they mean when they say and engine makes its best power band between certain RPMs ? Does that mean running and engine to its peek red line is wastfull for power.

[Robert D.]

Re: Power band

Walter
Power band is the range from peak torque to peak horsepower (or sometimes to redline). For example: combustion engines typically generate maximum torque at perhaps 2500 RPM. The peak horsepower might be 5000 RPM. Such an engine would have a power band of 2500 to 5000 RPM, in which the engine would be very efficient. The power band is usually determined by the camshaft specifications and can be altered as long as the bottom end of the engine heads fuel and air flow can tolerate the changes. hope this helps
Bob

[Duke W.]

Re: Power band

The term can be defined in many ways. For example the rev band that the engine makes 80 or 90 percent of peak power.

What's more important for a road engine is torque bandwidth. A road engine should make at least 80 percent of peak torque by 2000 or it will feel "torque shy" or "peaky". For an automatic trans my criterion is 90 percent of peak torque at 2000. All Corvette engines make at least 80 percent of peak torque at 2000 except small blocks with the 30-30 cam.

The power bandwidth can also be defined by gear ratio spacing. For example, with a CR four speed, if you shift at 6500 revs drop to about 5000, so 5000 to 6500 would be the useable maximum power bandwidth.

For a racing engine you generally want to maximize average power in the top 25-30 percent of the rev range, assuming the intergear ratios average about 1.25.

Duke

[Mark E.]

Re: Power band

This is an example of how there's a difference in understanding about a seemingly simple question...

I think of the power band as the RPM range in an engine's power curve (the plot of HP vs. RPM) that uses the most horsepower as you shift through the gears. One method is to shift when HP before the shift equals HP after the shift.

Example for an engine with a peak HP at 5,000 RPM, a 26% RPM drop between the 1-2 shift, and a symmetric power curve above and below 5,000 RPM: Stay in 1st until 5,750 RPM (750 RPM above peak), then shift into second which will drop RPM to 4,255 RPM (~750 RPM below peak).

HP often drops more quickly after the peak in the power curve; in this case, adjust the shift speed down so HP is equal before and after the shift.