Even for those people who don’t understand how horsepower works, it probably makes sense to you that a sports car, like a $90,000 Corvette, has more horsepower than the SUV you drive to work every day. You can probably deduce that since the Corvette is a sports car, and your SUV isn’t, the Corvette is faster, and therefore, has more horsepower.
A quick Google search comparing the horsepower of a new Corvette to whatever SUV you have will probably confirm your suspicions that the Corvette actually has more horsepower. What you may not realize is that the numbers you see may not be entirely correct.
The numbers that each manufacturer releases is the crank horsepower. That is the horsepower being made at the crankshaft, right where the power number is the greatest.
Because the wheels of a vehicle aren’t connected directly to the crankshaft, there will always be a net loss of power as it has to travel through the entire drivetrain of the car. The more complicated the drivetrain is, the more loss of horsepower there is.
Let’s go to your SUV.
For example’s sake, you have a 2008 Honda CR-V. The advertised engine horsepower from its 2.4 liter engine is 166 horsepower at 58000 rpm. As a general rule, a vehicle will lose anywhere from 15 to 25 percent of its crank horsepower through the drivetrain components, before it reaches the wheels.
If your CR-V really makes 166 horsepower, the actual amount of power reaching your wheels is more like 140 horsepower, perhaps even a little less. This number could still be high, given that the CR-V is an all-wheel drive vehicle. All-wheel drive vehicles have more drivetrain components and generally lose more power.
Notice, before I go farther, that I said “if” your CR-V makes 166 horsepower in the last paragraph. In 2008, when your CR-V was new, it may have made that much at the crankshaft. Machines wear out. Engines lose power over time because wear and tear causes decreased efficiency.
In 2018, your CR-V may have 10 or 20 horsepower less than when it was new. This loss of efficiency will vary from engine to engine.
All of this sounds a bit depressing doesn’t it?
Well… never fear. There’s another factor that plays into horsepower as well.
So far, we’ve talked about horsepower loss. There is a fairly common practice among manufacturers of underrating their engines’ outputs. It may not be everywhere, but there are a good number of vehicles that have had engines with higher horsepower numbers than advertised.
Now, let’s go back to our Corvette Z06.
Officially, from General Motors, the 2015 Corvette Z06 has 650 horsepower. Some have called their bluff. Having tested their own 2015 Corvette Z06 on the dyno, Vengeance Racing recorded a horsepower number of 585 horsepower at the wheel (Source).
Though it is a loss of horsepower from advertised, it isn’t a loss of nearly as much as it should be. Even if the Corvette lost 15% of its power through the drivetrain, it should be producing a number closer to 550 horsepower. That’s on the low end of what’s normal.
If the Corvette did lose the expected 15% of its crank horsepower, it means that the engine is producing close to 700 horsepower rather than 650! That’s a significant difference, and it shows where manufacturers can work the numbers.
Another classic example of this is the “Gentleman’s Agreement” held by Japanese automakers, primarily in the 1990’s. This agreement held numerous iconic Japanese performance cars to 276 horsepower in an attempt to prevent horsepower competitions back in the 1990’s.
In short, it worked on paper. Also in short, Japanese automakers knew that they could put whatever they wanted to on paper. Cars like the Toyota Supra, Subaru WRX Sti, and Honda NSX were all affected by this agreement. Most produced different power numbers than advertised. The most notorious offender was the Nissan Skyline GT-R.
One of the most coveted enthusiast cars ever produced, these now decades old Nissans have been put on dynos all over the world and have consistently produced 300 or more horsepower… at the wheels. Some have recorded numbers as high as 330 wheel horsepower.
After 20 years, if a car with an advertised horsepower output of 276 horsepower produces that much at the wheels, you can only begin to imagine what the engine actually produced when it was new. It goes without saying that there were some lies being told.
Now, back to your car. It probably isn’t a Corvette, and it probably isn’t a 20 year old Nissan sports car. That doesn’t mean that the numbers you see on the window sticker or on your favorite car review website are always accurate.
The best way to determine the truth is to put your car on a dyno.
Of course, you probably won’t do that either, and that’s ok. Most likely, there’s somebody on the internet who already has. You can just use the power of Google and see the actual numbers your car produces if you really are that curious.
Whether you drive a 2008 Honda CR-V or a 2015 Corvette Z06, the numbers will only tell some of the story. Most of the time, none of what we just talked about matters. But, isn’t it kind of interesting knowing that you may just have a hot rod sitting inside the body of your minivan sitting out front?
