eli5: Can horsepower be added to each other or is there overlap? Example: If Ferrari says that an electric motor on each front wheel can produce 100hp each, and the combustion engine produces 750hp. Is it actually 950hp exactly? Or is there overlap or less hp etc?



In: 103

It depends

In the case of the Ferrari SF90 it seems the answer is yes. 3 electric motors providing 217 hp combine with a 769 hp combustion engine to make 986

It’s not always true for hybrids. If the electric motor and combustion engine are both tied into the same transmission you could end up limited by the transmission’s ratings.

A Honda Accord hybrid gets 146 hp from the gas engine, 181 from the electric motor, but combined to just 204 hp because the CVT can’t handle the torque

Sometimes it doesn’t add up. For example, the combustion engine will have max hp at 5500 rpm and electric motor will also have max hp around 5500 rpm. Except the combustion engine will have max rpm around 7000 and the electric motor will have max rpm around 12000. So the two motors will be geared different. And they probably won’t both hit max power at the exact same time. So probably electric motor will hit peak power first and then start dropping off by the time combustion motor hits peak power.

It should be noted that there are no laws regarding how power is reported, so some companies may just be adding them up. New standard SAE J2908 will make rules on how to report power, and it must be measured at the wheels.


So, engine peak power will happen at a certain RPM – this goes for the gas engine and the electric motors.

The speed at which the electric motors give you peak power from may or may not line up with the RPMs the gas engine hits peak power at. So even without any other limitations it probably won’t match up perfectly.

Yes it can if it’s measured at the WHEELS.

Modern marketing (the race to the highest horsepower) means HP is measured at the CRANK of an engine. Measuring the engine’s horsepower but not necessary the “car’s” horse power.

The crank is the bit that sticks out of the engine, that spins the transmission and then the transmission spins the wheels. Horsepower gets lost along the way due to friction/heat and other inefficiencies. But what do you do if there’s an electric engine per wheel driving each wheel?

Best way to find out is to measure the end result (rubber hitting the road) and determine the horsepower there.

torque can be additive. horsepower might not be unless it’s on a separate axle.

in the case of most hybrid drivetrains, just because a motor can put down 200hp and the engine puts down 250 doesn’t mean the car has 450hp.

you’d have to plot the torque curves and add them up, then calculate the resulting horsepower. or you could measure output directly on a chassis dyno.

the problem with a measurement on a chassis dyno is that the output is lower than at the engine. and bigger numbers make for better bragging rights. which is why manufacturers will claim separate numbers for gas engine and electric motor for bigger overall numbers.