Can anyone tell me how to read this dyno chart?

[kaineb]

I know it sounds stupid but i have never read a dyno before so trying to make sense of it. Even though this is on a E60 i really doesn't matter. Also wondering why it is showing only 285 hp on an engine that produces 367?

Trying to figure out the difference before and after as well.

Thanks!

[Justin517]

it most likely measured horsepower at the wheels.

Cars have what is called "drivetrain loss" sending the power through the transmission, drive shaft, and differential soaks up some of the power the engine is making. Manual transmissions are usually around 15-20% loss and automatics are usually 20-25% loss... I assume your car is automatic? Looks like you lost the widely accepted 22% through the automatic.

[rf900rkw]

One of them pulled stronger up to about 6K before a restriction choked it off. YOU will have to tell us which was before, and which was after.... and what changes were made between runs.

[kaineb]

Just realized i had a few responses. This is a dyno chart from RPI showing before and after their muffler install.

So was trying to make sense of it. The one side looks like a drastic change. again i cant imagine the 367hp at the crank = 285hp at the wheels. That seems like an immense loss.

[rf900rkw]

Ah, so in other words it's not even a real dyno chart.

First, that massive flat spot between 2K and 2.5K. I don't know the 550 platform very well, but I have doubts that BMW would release such a thing to the public. So from right there we have to assume either the dyno or the car isn't correct.

Now, one of the graphs pulls stronger than the other at lower revs, then starts running into a wall about 5200. And at 5900 it just falls off a cliff.
The other one is flatter and more consistent with more usable high rev power, but less in the normal ranges you'll be in most of the time. Remember the forum manta... I lost a bit of mid range torques but it pulls strong up top.

So which of the two is this marketing fluff claiming is for their product? I can't tell.



Oh, and don't worry about the actual numbers. Everyone knows dyno dynamics gives unrealistlc low readings.

[Justin517]

I want to know why peak torque is below 2000 RPM... seems very fishy...

[Cyrix2k]

I want to know why peak torque is below 2000 RPM... seems very fishy...

probably an auto. The torque converter multiplies torque output until it hits its stall speed.

[Justin517]

probably an auto. The torque converter multiplies torque output until it hits its stall speed.

I forgot about that... I don't see many dyno charts of automatic cars.

[rf900rkw]

Once you are at stall speed (slip across the converter) then it will stay at stall until you lift. And torque converters don't really multiply torque. Not in the way people think of ree torque out of thin air. Torque converter CONVERT torque into heat. While doing this they "rearrange" the horsepower to slower speed and more twist.
So the a converter does not explain that bump in the horsepower and derived torque map. Most likely, it's just a large ring from the initial start of the run. They didn't let the system settle under load before starting the recording.

[granlund]

it most likely measured horsepower at the wheels.

Cars have what is called "drivetrain loss" sending the power through the transmission, drive shaft, and differential soaks up some of the power the engine is making. Manual transmissions are usually around 15-20% loss and automatics are usually 20-25% loss... I assume your car is automatic? Looks like you lost the widely accepted 22% through the automatic.

~20% loss in transmissions? You do realize that 20% loss in a transmission on a car that produces 367hp on the crank is 55kW (367hp=275kW) of generated heat. A house range burner or space heater produces 1-2kW of heat.

Even if some of the lost power is in the diff, both the diff- and transmission cases would be glowing red after a longer full-power run if the total loss was ~20%.

Most likely that engine was nowhere near it's stated 367hp during the dyno run.

[Justin517]

~20% loss in transmissions? You do realize that 20% loss in a transmission on a car that produces 367hp on the crank is 55kW (367hp=275kW) of generated heat. A house range burner or space heater produces 1-2kW of heat.

Even if some of the lost power is in the diff, both the diff- and transmission cases would be glowing red after a longer full-power run if the total loss was ~20%.

Most likely that engine was nowhere near it's stated 367hp during the dyno run.

BMW is held to very strict horsepower ratings, they can't just say an engine makes X horsepower without being held to it and facing suit if they "lied". Plus it is pretty well known that automatic drivetrains lose around that much power through them.

Between the torque converter, clutches, bearings, flex in the guibo, movement in the CSB and center U-joint, rear CV joint, the rear diff, axles with inner and outer CV joints that chnage angle while going over road surfaces, and then you have brake rotors, wheels and tires...

The torque converter when unlocked is a fluid connection and you are correct in that it generates heat, why do you think automatic transmissions have coolers?

How much does a torque converter full of fluid weigh? 30 lbs? the clutchs in the drums and related planetaries and shafts? another 30-40 lbs?, drive shaft? 15-20 lbs?, axles? say 16 lbs for the pair? brake rotors? 25 lbs? wheels and tires? 80+ lbs?... that is 200-230 lbs of rotating mass before the power even gets to the ground and then there is the slight rolling resistance of all the bearings throught the transmission, in the CSB, the rear diff and the rear wheel bearings... does physiscs not apply to that stuff?

[granlund]

Physics does apply. How much power is lost in 200-230lbs of rotating mass at constant angular velocity? The answer is none!

The biggest loss is in the torque converter when unlocked. This is why we have a transmission fluid cooler. The other losses are in the hypoid gears in the diff and the planetary gears in the gearbox. The friction loss in the bearings are small compared to the aforementioned losses.

For the transmission cooler to convect away the power from the torque converter at theses power levels, there needs to be a significant airflow across the radiator. The velocity needs to be similar to the road velocity according to this power level. If not, power is probably reduced with the electronic throttle. Was there a fan in front of the radiator, and if so, did it produce enough airflow?

[Jesus Freak]

This is a pretty good article

http://www.modified.com/tech/modp-10...s/viewall.html

[Justin517]

Physics does apply. How much power is lost in 200-230lbs of rotating mass at constant angular velocity? The answer is none!

The biggest loss is in the torque converter when unlocked. This is why we have a transmission fluid cooler. The other losses are in the hypoid gears in the diff and the planetary gears in the gearbox. The friction loss in the bearings are small compared to the aforementioned losses.

For the transmission cooler to convect away the power from the torque converter at theses power levels, there needs to be a significant airflow across the radiator. The velocity needs to be similar to the road velocity according to this power level. If not, power is probably reduced with the electronic throttle. Was there a fan in front of the radiator, and if so, did it produce enough airflow?

That is fine when you are not accelerating... I'm pretty sure it is impossible to not accelerate during a dyno run so the lack of loss at a CONSTANT angular velocity is a moot point.

From the above posted article:

"steady-state losses occur while the vehicle is cruising at a steady or constant speed, where average angular acceleration is zero because no additional torque is being called upon to accelerate the drivetrain's rotational mass. Within the drivetrain, steady-state power losses occur from the following components: the transmission torque converter (in the case of automatic transmissions), the transmission oil pump, clutch pack drag, one-way clutch drag, seal and bearing drag, gear windage and friction, and final drive losses."

Read more: http://www.modified.com/tech/modp-10...#ixzz23AJvZoTG

And...

"Dynamic drivetrain losses, on the other hand, include the rotational inertial losses from angular acceleration occurring within the drivetrain while accelerating. In fact, during acceleration there are losses from the rotational inertia of spinning transmission and differential internals as well as driveline components like driveshafts and prop shafts, but also from the increased load and friction being generated between the gears within the transmission and differential(s). And as you already know, with increased friction comes increased heat"

Read more: http://www.modified.com/tech/modp-10...#ixzz23AKdufzT

so... between the steady state and dynamic losses... that is how you get a 20-25% loss through an auto.

I recommend you read the entire article before you claim that a long known loss is BS and that the manufacturer is simply inflating hp numbers.

[kaineb]

Wow, lots of info. For those who asked the chart is showing a stock run versus when the muffler was replaced with aftermarket. If I am not mistaken one of the runs show a massive difference in torque? I am not sure as I dont know how to read this correctly.

FYI, this is RPI. Right from their website.

[granlund]

...I recommend you read the entire article before you claim that a long known loss is BS and that the manufacturer is simply inflating hp numbers.

I was not saying that BMW inflated the numbers. My point was that at this power output, with those loss figures, there is a significant heat that needs to be convected away through the radiator. Since BMW have a history of electronically compensating for various known and unknown ambient parameters on engines already in the 90's, it is not inconcievable to think that their engineers assumed that for a sustained +350hp output, the car has to be traveling at >200km/h, and producing an air inflow at that speed cooling the radiator to keep the transmission and coolant temperature stable. Without that airflow, temperature rises and the ECU automatically dials power back until the temperature stays within limits.

Of course, this is merely a plausible assumption, but it could explain for the lower wheel power numbers if the radiator did not have a powerful enough shop fan infront of it.