[///MFrankie]

This is something that always has me confused and I notice it a lot on this forum.

For instance, an M2 Comp will be dyno'd in the US and the horsepower will read at 405, the tuner will say this is WHP, so the car at the crank is making 450+.

I've seen owners claim healthy engines making 415-420whp so like 480bhp at the crank.

I noticed this mostly in the latest IND thread on the new M2 where the guy said it's making 547bhp at the crank...

Then, we come to the UK, which I know is much harsher on the results but the same car will be dyno'd here and get similar, if not the same numbers, yet they will be crank BHP so a 405bhp M2 Comp will be like 360 at the wheels.

What is going on here?

[G30M]

every dyno is different
every dyno operator will use different math
nothing is comparable unless you use the same dyno and the same operator's fuzzy logic

[G30M]

there are also different dyno methods

from my understanding if you use friction dyno you are measuring torque and then calculating the HP using a simple math formula

measuring the torque is where the problems lie

you have to overcome the inertia of the friction bed before you get accurate torque

problem is all your gears are torque multiplies, you also have a final drive gear which is another torque multiplier

so the 2 torque multipliers x inertial loss just to measure the torque already introduces a lot of mistakes

then you have to calculate HP

then you still want to guestimate crank HP? forget it!

[G30M]

[G30M]

[///MFrankie]

Originally Posted by g21

there are also different dyno methods

from my understanding if you use friction dyno you are measuring torque and then calculating the HP using a simple math formula

measuring the torque is where the problems lie

you have to overcome the inertia of the friction bed before you get accurate torque

problem is all your gears are torque multiplies, you also have a final drive gear which is another torque multiplier

so the 2 torque multipliers x inertial loss just to measure the torque already introduces a lot of mistakes

then you have to calculate HP

then you still want to guestimate crank HP? forget it!

I think I'll go back to not paying any attention to dyno numbers

I'll give them videos a watch though.

[G30M]

Originally Posted by ///MFrankie

This is something that always has me confused and I notice it a lot on this forum.

For instance, an M2 Comp will be dyno'd in the US and the horsepower will read at 405, the tuner will say this is WHP, so the car at the crank is making 450+.

I've seen owners claim healthy engines making 415-420whp so like 480bhp at the crank.

I noticed this mostly in the latest IND thread on the new M2 where the guy said it's making 547bhp at the crank...

Then, we come to the UK, which I know is much harsher on the results but the same car will be dyno'd here and get similar, if not the same numbers, yet they will be crank BHP so a 405bhp M2 Comp will be like 360 at the wheels.

What is going on here?

the more you know, the less they know

i don't believe any of these numbers

drag race and show me real life straight line, locked in gear, turbo lag, etc

still doesn't tell you how it drives etc etc

[///MFrankie]

Originally Posted by g21

the more you know, the less they know

i don't believe any of these numbers

drag race and show me real life straight line, locked in gear, turbo lag, etc

still doesn't tell you how it drives etc etc

I agree, the numbers don't add up at all. Especially as the times they run 1/4 mile make no sense to the power claimed.

I would bet my life the new M2 is not making 550bhp from factory lol but that's why I found it weird it comes up and no one questions it.

[G30M]

Originally Posted by ///MFrankie

I agree, the numbers don't add up at all. Especially as the times they run 1/4 mile make no sense to the power claimed.

I would bet my life the new M2 is not making 550bhp from factory lol but that's why I found it weird it comes up and no one questions it.

regarding your signature

HP is what you want
Torque is what the engine makes
HP is just Torque x RPM

hence you need the torque curve vs RPM so you can see where the HP is
unfortunately in real life i don't know how they add up

on my M340i torque is 500nm 1800-5000 rpm

but i swear the car doesn't push me into the seat until i get to 3000rpm at low speed, and not until 4000 rpm at high speed. despite the NM bar on my car showing max torque at 1800rpm as expected.

[XutvJet]

A dyno measures torque to the wheels vs rpm over a span of time to calculate HP. Most dynos used in the US are either a Dynojet model or some version of a brake dyno, typically known as a "Mustang" dyno.

Dynojets are simple in operation and can't be manipulated by the operator, thus they have a level of consistency when it comes to comparing dynos runs of cars run on a Dynojet. The numbers are typically within 2-3% or less assuming the same car, mods, and atmospheric conditions. The Dynojet simply takes the amount of time it takes for the car's wheels to spin a weighted drum for the span of the measured rpm. From there, the Dynojet calculates the torque to the wheels and the theoretical HP.

The Mustang dyno has a drum with a brake to create load. This is the ideal tuning dyno as the dyno operator can manipulate the load on the engine to simulate hills and other driving situations other than full throttle. Mustang dynos calculate their data in a similar way to the Dynojet, but the data in a sense can be and is manipulated by the dyno operator. A Mustang dyno will show about 10% lower numbers than a Dynojet due the way the power is measured and influenced by the brake on the dyno.

It's well known that BMW underrates their turbo motors. Typically the quoted HP/TQ of a BMW motor is what the car makes to the wheels. In many other makes, the quoted HP/TQ is what the motor makes at the crank, not to the wheels. Typically, there is a 12% to 20% drivetrain loss.

Stock M2 Comps typically make around 375-385whp and 395-405wtq on a Dynojet. Assuming a 12% drivetrain loss and that means the S55 in those cars is making more like 425-435hp and 445-460tq.

In the UK, I've seen countless dynos over the years where they report only in crank HP which is bonkers, IMO. For whatever reason, the dyno takes the wtq and corrects it to crank tq and hp. Dumb. I don't get why they do this. Who cares about crank numbers, it's what makes it to the ground that matters.

[FC4]

Europeans love to report BHP which is absolutely meaningless. Measuring WHP on a dyno then adding an arbitrary percentage for "drivetrain loss" to get an estimated BHP accomplishes nothing.

I was going to type more, then realized it would just mimic what XutvJet posted above as it's spot on.

[Redd]

The actual term is brake horse power (BHP) which is the unit of measurement for power. Whp means 'wheel hp' or hp measured at the wheels on a dyno.

Manufacturer numbers always state engine power at the crank, ie with the engine out of the car, with no drive train or frictional losses.

When you dyno the car it is not practical to remove the engine from the car. Most dynos use rollers to measure power which is measured at the tires. Hence the term wheel hp. Wheel hp includes drive train losses which can differ from car to car. Typically they are 15% for Fwd, 18-20% for rwd, and up to 25% for awd.

It's important to understand also that dynos usually can also show engine (crank) power but this is an estimate by the dyno computer only and calculated from the whp. This estimated engine hp is usually quite inaccurate, so most people will quote whp which is more consistent.

Dyno numbers will also differ greatly from dyno brand to dyno brand, and slightly from temperature and SAE smoothing methods. For all intents and purposes, dynos are most useful for comparing differences a mod has made on the same car, on the same dyno, preferably at around the same ambient conditions.

[///MFrankie]

Originally Posted by XutvJet

A dyno measures torque to the wheels vs rpm over a span of time to calculate HP. Most dynos used in the US are either a Dynojet model or some version of a brake dyno, typically known as a "Mustang" dyno.

Dynojets are simple in operation and can't be manipulated by the operator, thus they have a level of consistency when it comes to comparing dynos runs of cars run on a Dynojet. The numbers are typically within 2-3% or less assuming the same car, mods, and atmospheric conditions. The Dynojet simply takes the amount of time it takes for the car's wheels to spin a weighted drum for the span of the measured rpm. From there, the Dynojet calculates the torque to the wheels and the theoretical HP.

The Mustang dyno has a drum with a brake to create load. This is the ideal tuning dyno as the dyno operator can manipulate the load on the engine to simulate hills and other driving situations other than full throttle. Mustang dynos calculate their data in a similar way to the Dynojet, but the data in a sense can be and is manipulated by the dyno operator. A Mustang dyno will show about 10% lower numbers than a Dynojet due the way the power is measured and influenced by the brake on the dyno.

It's well known that BMW underrates their turbo motors. Typically the quoted HP/TQ of a BMW motor is what the car makes to the wheels. In many other makes, the quoted HP/TQ is what the motor makes at the crank, not to the wheels. Typically, there is a 12% to 20% drivetrain loss.

Stock M2 Comps typically make around 375-385whp and 395-405wtq on a Dynojet. Assuming a 12% drivetrain loss and that means the S55 in those cars is making more like 425-435hp and 445-460tq.

In the UK, I've seen countless dynos over the years where they report only in crank HP which is bonkers, IMO. For whatever reason, the dyno takes the wtq and corrects it to crank tq and hp. Dumb. I don't get why they do this. Who cares about crank numbers, it's what makes it to the ground that matters.

Originally Posted by FC4

Europeans love to report BHP which is absolutely meaningless. Measuring WHP on a dyno then adding an arbitrary percentage for "drivetrain loss" to get an estimated BHP accomplishes nothing.

I was going to type more, then realized it would just mimic what XutvJet posted above as it's spot on.

I agree that the crank figures are pointless but that is beside my point.

What I was asking is why US wheel figures are often the same as UK crank figures. This would make the cars way more powerful than they actually are.

[chad86tsi]

Break horsepower is what the engine actually makes at the back of the crank.

wheel horsepower it what is leftover to apply to the road after break horsepower is applied to/through drivetrain losses. Rotational inertia and friction are the main sources of HP loss. Even something like changing to larger(heavier) rims will reduce your WHP.

Wheel horsepower is more useful to determine acceleration of a set mass (weight) because it's measured where that force ultimately apples and is converted to motion on that mass.

You can't determine BHP from WHP because no two drivetrains are the same. You also can't determine wheel WHP from BHP for the same reason.

BHP will always be a higher number, so it's useful for advertising.

Torque is a more useful number for determining how it will drive. A 600 HP honda 1.8 liter motor will haul a 10,000 pound load up a steep hill about the same as a 600 HP 6.7 liter diesel. They will however have a very different acceleration personality under load. The diesel will probably get the job done quicker because it has torque throughout the power band, and the little Honda will have to stay at peak RPM to get the job done, which is difficult to do as you go through the gears.

[lens]

Originally Posted by ///MFrankie

This is something that always has me confused and I notice it a lot on this forum.

For instance, an M2 Comp will be dyno'd in the US and the horsepower will read at 405, the tuner will say this is WHP, so the car at the crank is making 450+.

I've seen owners claim healthy engines making 415-420whp so like 480bhp at the crank.

I noticed this mostly in the latest IND thread on the new M2 where the guy said it's making 547bhp at the crank...

Then, we come to the UK, which I know is much harsher on the results but the same car will be dyno'd here and get similar, if not the same numbers, yet they will be crank BHP so a 405bhp M2 Comp will be like 360 at the wheels.

What is going on here?

I mean, you guys do drive on the wrong side of the road

[Redd]

Originally Posted by ///MFrankie

What I was asking is why US wheel figures are often the same as UK crank figures. This would make the cars way more powerful than they actually are.

Show me an example. I doubt this is common if comparing apples to apples.