The Difference Between BHP And WHP Explained

Do you confuse bhp with whp? Don't know what whp is? Here's everything you need to know in 1 minute!
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Image source: www.dekuyperphoto.com

Image source: www.dekuyperphoto.com

People regularly confuse the difference between brake horse power (bhp) and wheel horse power (whp), and when they do – and when they try to correct what they see as a mistake – you know they’re going to get owned in the comments section. No-one wants to be that guy…

To save you from comments ownership – and for your general knowledge – here are the differences between bhp and whp made simple:

Image source: Mustangandfords.com

Image source: Mustangandfords.com

1. Brake Horse Power (bhp)

This is the power output of any engine measured at the engine’s flywheel. (A flywheel is a disc with teeth on it. It’s connected to the rear of the engine and its purpose is for the smooth transfer of power to the transmission from the engine.)

2. Wheel Horse Power

Unlike bhp, whp is the power output measured at the wheels. This is the information a dyno run provides and usually reads around *15 per cent less than the power measured at the engine (bhp) – this is because power is lost in the driveline (including clutch and transmission).

*Four-wheel drive cars lose between 20-25 percent of their quoted bhp figure because of the increased friction.

Video

Advanced info

1. The term brake horsepower (bhp) refers to a device called ‘Prony Brake’ (invented by Gaspard de Prony), which was used to measure engine power in the early 1900s.

2. You don’t need to increase an engine’s bhp to get an increase in a vehicle’s whp. You can achieve higher whp by reducing the rotational mass in your drivetrain, such as the wheels, tyres, brakes, clutch, flywheel, etc.

And finally…

Dynoing a rear-wheel drive Miata at the front…that’ll be 0whp, then!

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  • Dennis

    That’ll be an interesting dyno run

  • This RWD guy

    Air Force Miata, requesting permission to take off. Heading nine-zero, wind in calm, next stop, the moon. :D

  • Rich

    That’ll be a fwd eunos won’t it?

  • matt

    No such thing as a fwd eunos

    • miataman28

      Actually there is such thing as a fwd eunos, the eunos 500 for example is fwd. However there are no fwd eunos ROADSTERS.

  • Dave Does Skids

    OMG this page is the biggest fail ever. BHP and WHP are the same fucking thing you idiots. Engine horsepower and Brake horse power are the two things you are trying to comment on… HAHAHAHA and you talk about not wanting to be that guy? You make a whole page about it! hahaha Brake horse power… Really? BRAKE its measured off the wheels on a dyno… Engine horse power is at the clutch or flexplate (at the engine). WOW

    • Sean Cassidy

      now who’s the idiot, they explained the. WHEEL HP is the power actually transferred to the road. BRAKE horsepower is the engines power output with nothing else attached to it, this page says get it wrong and you will get owned in the comment section, this is definitely true.

      • odd Ball performance

        Um, this site got it correctly. BHP is obtained on an engine dyno by bolting the crankshaft output, via some type of adapter, to the dyno. This said engine dyno then applies a braking force, ala Prony Brake, to the engine and measures how much force it takes to overcome the brake – which applies a known force that can be used to calculate power.

        By modern SAE standards, most manufacturers are required to state BHP of an engine with all accessories and other normal function items attached to get an accurate power reading. Unlike back in the Muscle Car days, where they would run a bare engine, say it has 400hp, and then put the alt. AC. and Power steering on which would suck up about 30-40hp.

        • Sean Cassidy

          Yeah, it was the guy I was replying to who said differently

    • Gabor Szedlak

      must.be.trolling.

      • Mark Miata

        Looks like someone was ‘that guy’ then changed his comment. Ha! noone wants to be that guy!!

        • Gabor Szedlak

          yeah :) poor Dave

  • William Berrios

    Good article.

  • Adam

    I would LOVE to see them start that Miata up and try to start a dyno run with those straps on the back wheels.

  • Dude

    You might want to correct the part that says you can increase WHP by decreasing rotational mass. You can increase the *reading*, due to shortcomings in way the number is obtained, but it doesn’t change the actual power at the wheels.

  • guest

    Yep to save everybody confusion and sometimes embarrassment, you should always talk in BHP (or WKW). Torque on the other hand should always be measured at the flywheel before it gets multiplied by the drive-train.

    • asdf

      Huh? The flywheel numbers don’t particularly matter and really don’t server any purpose other than quoting a larger number to generate sales. That’s why no one that is serious about performance and racing uses those numbers.

      Wheel horsepower to weight is what matters when it comes to acceleration, I’d happily put my 700whp car up against an original Veyron with their 1000bhp.

  • Luke

    One thing that’s never considered is nominal horsepower. I’m not sure how it works exactly, but it takes into account (I think) compression ratio, displacement of the engine and boost pressure from any forced induction devices. Basically it tells you how powerful your engine would be if there was absolutely zero friction everywhere. But because the engine has plenty of friction – piston rings against cylinders, the crankshaft on its bearings, driving the camshafts, the resistance by the valve springs and plenty more – it’s never used.

    • James Lowrey

      You’re talking more about an Otto cycle analysis, which is basically exactly you said, its a thermodynamic analysis of processes, you could also find out things like how much heat is produced, entropy generated, heat loss etc. Nominal horsepower is an equation from the 1800′s which is an approximation of horsepower based on the piston size and speed, its governed by the equation You’re talking more about an Otto cycle analysis, which is basically exactly you said, its a thermodynamic analysis of processes, you could also find out things like how much heat is produced, entropy generated, heat loss etc. Nominal horsepower is an equation from the 1800′s which is an approximation of horsepower based on the piston size and speed, its nhp = 7 x area of piston x equivalent piston speed/33,000. I imagine that you’d get a decent approximation using it but because internal energy in a fuel is a function of mass only considering the area could give you a drastically different result if you had a large displacement between TDC and BDC.

      • Luke

        You’re quite right, my mistake. Nominal horsepower is used on steam engines, but the one I was referring to I can’t remember the name of. It’s not as complicated as Otto cycle analysis like you suggested, rather it simply takes in factors like the ones I mentioned and spits out a rough horsepower estimate in the end, without giving other numbers like thermal efficiency, entropy or anything else. On the whole it’s a lot simpler than a complete analysis.

  • Ricky

    Even further disappointment to that miata.. im sure they arent going to run the dyno.. but if they for some unforseeable reason did.. the strapped rear wheels ….if put that miata in gear.. your gonna have a bad time.

  • v8vega350

    lmao they will see zero wheel h.p. hooked up like that

  • Annonnymouse

    WHEEL(Real) Horsepower vs Break(Fake) Horsepower

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