[Rosseau]

You folks may know all about this. Data is from 2017-19 M240i xdrive. Not sure if I attached their chart properly...

"As far as the numbers go--- its easiest to visualize with the attached power chart. BMW rates the stock vehicle at 335HP but we measured it on the dyno at 369HP. MAX HP Gain is the largest gain over stock at any given point. In the case of the M240 that occurs art 6500RPM where there is a 47 HP gain over stock. Peak HP gain is the difference in stock to Dinan at the highest measured point on the stock curve. This occurs at 6000 RPM where there is a 32 HP gain."

Nathan Fette
E: nathan.fette@dinancars.com
URL: www.dinancars.com

[Rosseau]

The oft-quoted 0-60 for M240i xdrive/auto is 4.2, whatever the dyno says, unless users have experienced better runs.

[XutvJet]

Ever since BMW went with turbos in the mid 2000s, they've all been quite underrated. That goes for the N54, N55, S55, B58, etc. For example, the M235 is rated at 320hp and 330tq but it actually makes about 310whp and 330wtq on the Dynojet with a 6MT. Assuming a 15% drivetrain loss, the 320hp M235 is making more like 365hp and 390tq. The M240 is making more like 390hp and 390tq.

[Rosseau]

Yes, I think I will delete this thread as it's been done to death.

[B58togo]

Dinan cracks me up, misleading the public into thinking they can precisely and "officially" measure brake horsepower using a chassis dyno. They're extrapolating BHP from chassis dyno numbers, which can't be done with any real precision. The "369" figure sounds more genuine than say, "370". That said, the reality is, the B58 most likely is somewhere in the range of 360-375 at the crank. BMW has been underrating their turbo cars (to varying degrees) for the past 12 years.

[aerobod]

Typically BMW has been conservative in it’s power ratings. It used to be that a variation of 10% in engine output was normal from engine to engine due to manufacturing tolerances, this may be tighter now, but it has been postulated in the past that the BMW quoted figures will always ensure any car produced will meet the quoted spec and on average will exceed the spec.

In the past, it has typically been non-European manufacturers who have been taken to task for quoting power outputs that some of their vehicles have not been able to meet.

[stevenvillatoro]

Originally Posted by Rosseau

Not sure if I attached their chart properly...

I don't see a chart in the app forum. Try again?

[Rosseau]

Sorry Steve. It's a little too big, and I can figure out how to re-size it in Paint. But I'd be happy to email it to you or put it on dropbox.

[stevenvillatoro]

Originally Posted by Rosseau

Sorry Steve. It's a little too big... I'd be happy to email it to you or put it on dropbox.

Sent you a message.

[aerobod]

One way to estimate power output and how accurate it is, is to look at the kinetic energy profile of the car over a reasonable acceleration interval, a 1/4 mile run is reasonable for this.

From online quoted 1/4 mile sea-level times for stock M240i xDrive cars, 12.7 seconds at 171 km/h (106 mph, 47.5 m/s) seems to be fairly typical, with 12.3 at 174 km/h (108 mph, 48.3 m/s) being about the best.

Assuming a weight with driver and tank of fuel of 1700 kg (3747 lbs), drivetrain efficiency of 85% (15% loss), gearing effect allowing 90% of power to be used across rev range in each gear and power available after accounting for tyre rolling resistance and drag of 80%.

Kinetic energy at the end of 12.7s 1/4 mile will be 0.5 x 1700 x 47.5^2 = 1918 kJ
Energy input per second (power) will be 1918000 / 12.7 = 151kW
Power available for acceleration will be 0.85 x 0.9 x 0.80 = 0.612 (61.2%)
Consequently engine crank power required will be 151 / 0.612 = 247kW (331bhp)

If the 1/4 mile is managed in 12.3s @ 48.3 m/s, then the engine crank power equates to 263kW (353bhp).

Off the line acceleration and consequential wheel spin will tend to add a fraction of a second to the time and waste power in heating the tyres, so the power values will be a bit underrated, but these basic calculations point to BMW nominal rating (250kW / 335bhp) to nominal plus 10% (275kW / 369bhp) as being a reasonable range for the power output at the crank.

[stevenvillatoro]

Here is Rosseau's resized comparison graph...

[Rosseau]

Originally Posted by aerobod

One way to estimate power output and how accurate it is, is to look at the kinetic energy profile of the car over a reasonable acceleration interval, a 1/4 mile run is reasonable for this.

From online quoted 1/4 mile sea-level times for stock M240i xDrive cars, 12.7 seconds at 171 km/h (106 mph, 47.5 m/s) seems to be fairly typical, with 12.3 at 174 km/h (108 mph, 48.3 m/s) being about the best.

Assuming a weight with driver and tank of fuel of 1700 kg (3747 lbs), drivetrain efficiency of 85% (15% loss), gearing effect allowing 90% of power to be used across rev range in each gear and power available after accounting for tyre rolling resistance and drag of 80%.

Kinetic energy at the end of 12.7s 1/4 mile will be 0.5 x 1700 x 47.5^2 = 1918 kJ
Energy input per second (power) will be 1918000 / 12.7 = 151kW
Power available for acceleration will be 0.85 x 0.9 x 0.80 = 0.612 (61.2%)
Consequently engine crank power required will be 151 / 0.612 = 247kW (331bhp)

If the 1/4 mile is managed in 12.3s @ 48.3 m/s, then the engine crank power equates to 263kW (353bhp).

Off the line acceleration and consequential wheel spin will tend to add a fraction of a second to the time and waste power in heating the tyres, so the power values will be a bit underrated, but these basic calculations point to BMW nominal rating (250kW / 335bhp) to nominal plus 10% (275kW / 369bhp) as being a reasonable range for the power output at the crank.

Using your formula, is there a way to determine approx 1/4 improvement using Dinan's MAX HP Gain of 47 WHP at 6,500 (Stage 1 tune is $1,400 for an M240i).

From a simplistic perspective, like the audiophile, we are facing the law of diminishing returns on performance vs. cost. It takes a lot more HP to get a car from 4.2 sec-to-60 down to 3.7, versus getting a 5.8 sec car down to 5.3.

[USA-RET]

This has been discussed on other forums also. Taking Dinan out of the equation, I believe the German manufacturers published HP and Torque numbers are closer to @ the wheel numbers rather than the normal U.S. standard of @ the crank HP/torque.

A reason many feel the German cars are under-rated when perhaps their published numbers are the true numbers one gets @ the wheels

My Mini S is rated by BMW @189 HP. Car dyno's @ 188 @ the wheels. IMO opinion WHP should be the published HP/torque numbers rather than an inflated flywheel number.

[aerobod]

I think it is more a case that many manufacturer engine outputs are optimistic, perhaps meeting the stated spec at the best end of the manufacturing tolerance scale, BMW being an exception here. Most dyno plots are wildly optimistic due to the correction factors applied - designed to give more of a feel good factor more than an accurate representation of true power output.

The effect of power imparted to the vehicle vs the actual engine power output is the most important thing to measure. Taking the non-linear and less predictable loses in getting off the line with the M240i xDrive by subtracting the 0-60 mph typical values (4.4s) and allowing 0.2s for each of 2 gear changes in the ZF8 transmission between 60 and 106 mph in the 1/4 mile (3-4, 4-5), then a typical B58 will put out about 269kW (360bhp). This is based on the following parameters, which may be contentious:

- Weight 1700kg / 3747lb (on the high side, heavy driver with full tank of fuel)
- Transmission & driveline losses 15% (on the low side, could be up to 20%)
- Non-optimum power output due to rev point on power curve of 90% on average for a given gear( low for the B58 with ZF8, off dyno plots could be as high as 98% due to flat power curve at higher revs)
- Losses due to tyre rolling resistance and drag 11kW required at 27m/s (60mph), 49kW at 47.5m/s (106mph) (this is slightly on the high side at 20% loss, biased towards the losses at higher speeds)
- Outcome of above factors is 0.612 (61.2%) of engine power available to accelerate the car from 27 to 47.5 m/s (60-106 mph, 96 to 171 km/h) in 7.9s (12.7s - 4.4s - 0.4s for gear changes)

If anyone wants to propose different parameters and additional losses, please do and the calculations can be re-run.

[Zwei]

German law requires their manufacturers to state power outputs that all the engines meet or exceed as manufactured. Power is lower before break-in and there are tolerances to be accounted for, these could account for 10% increase above rating.

[XutvJet]

Another thing to keep in mind about the impressive performance of these motors in relation to peak power numbers is the overall powerband and power under the curve compared to something naturally aspirated. These turbos motors have very wide and thick powerbands. In the same car, a turbo motor making 350 peak hp will undoubtedly be a bit quicker/faster than a naturally aspirated motor making 350 peak hp. The turbo will simply have more power under the curve, thus will sustain a longer and stronger acceleration throughout the rev range.

The power is also so linear and robust that they sometimes don't feel all that quick compared to something naturally aspirated which is a bit more peaky and gives a climbing sensation in power as the revs climb. What your butt dyno says compared to what the time slip can be at odds with a well sorted turbo motor.

[XutvJet]

Originally Posted by Rosseau

Using your formula, is there a way to determine approx 1/4 improvement using Dinan's MAX HP Gain of 47 WHP at 6,500 (Stage 1 tune is $1,400 for an M240i).

From a simplistic perspective, like the audiophile, we are facing the law of diminishing returns on performance vs. cost. It takes a lot more HP to get a car from 4.2 sec-to-60 down to 3.7, versus getting a 5.8 sec car down to 5.3.

I wouldn't concern yourself so much with 0-60 and 1/4 mile and you seem a bit obsessed with it (I too was that way years ago ). There's not much on the street that going to hang with a turbo 6 X-drive 2 series. With that said, just enjoy what you have and come to terms with the fact that there will always be someone faster. Always.

If you've ever been to the 1/4 mile strip with your own car, you'd know 1/4 mile times are HIGHLY variable and the calculation provided isn't very reflective of what you'll see. Density altitude conditions (i.e., air temp, humidity, baro pressure, elevation) and wind (tail, cross, head) have huge effect on the ET/MPH, even turbo cars which can compensate to some extent by making more boost when the oxygen content is less (i.e., hot, humid air, high elevation). Running on a 100 degree humid day vs a crisp 50 degree low humidity day could mean the difference between running a 12.5@112mph vs a 13.0@108mph. In my prior naturally aspirated cars, a summer day would usually mean my car would be running 0.5-0.7 seconds and 5mph+ slower, no changes to the car, just crappy conditions.

Lastly, some tracks are simply quicker for no apparent reason. I've run 0.3 seconds and 3 mph faster at certain "fast" tracks with absolutely no changes to the car, driver, fuel grade, 60 foot, and similar density altitude conditions. 3mph would suggest the car is making 30whp more power. That was certainly not the case at all.

IMO, magazine times are pretty accurate for what a good driver will run at a typical track in sea level conditions. Magazines typically post the average ET/mph of 10 runs (5 in each direction) and the ET/mph corrected to sea level conditions. It's been my personal experience that a good driver can beat mag times by about .3 seconds and 2 mph in good conditions because we're not averaging our times. With that said, it takes a TON of runs at the strip to learn how to launch and drive a car to it's full ability on the street tires; automatic, manual, AWD, RWD, and FWD. I've ran them all. It took well over 100 passes to understand the science and skill of drag racing. 9 out of 10 street drivers are clueless as to how to drag race their own car, though they all think they're stellar drivers

[TajoMan]

Originally Posted by XutvJet

If you've ever been to the 1/4 mile strip with your own car, you'd know 1/4 mile times are HIGHLY variable and the calculation provided isn't very reflective of what you'll see.

My times were super consistent.
(Same day but 15F difference from first to last run)

It was boringly consistent. lol

[dradernh]

Originally Posted by XutvJet

The power is also so linear and robust that they sometimes don't feel all that quick compared to something naturally aspirated which is a bit more peaky and gives a climbing sensation in power as the revs climb.

What I noticed at the track is that my M240i also doesn't sound very quick. I can, however, see that it's quick by the rate at which the scenery is going by. The rheostat-like delivery of this car's torque is truly wonderful.

Compared to the S50B32 I had in a stripped E36 race car, there's little going on aurally to tell me either how fast I'm accelerating or whether my heel-and-toe efforts are doing a satisfactory job of rev-matching. Since I use comfort mode on the street, I'm looking to get rev-matching coded for DSC OFF.

[XutvJet]

Originally Posted by dradernh

What I noticed at the track is that my M240i also doesn't sound very quick. I can, however, see that it's quick by the rate at which the scenery is going by. The rheostat-like delivery of this car's torque is truly wonderful.

Compared to the S50B32 I had in a stripped E36 race car, there's little going on aurally to tell me either how fast I'm accelerating or whether my heel-and-toe efforts are doing a satisfactory job of rev-matching. Since I use comfort mode on the street, I'm looking to get rev-matching coded for DSC OFF.

My friend has a turbo Miata that weighs 2,300lbs. The car makes 210whp and 190wtq and usable power is from 3500rpms to 6500rpms. Under boost, power is shockingly linear. That car is lowered on coilovers. I drove the Miata for 30 minutes and it was an utter blast. The Miata has a slightly lower power to weight ratio than my M235 and not as fat a powerband, but the aural drama under power and the fact that you're in a tiny, low riding car makes it feel quite quick and fast. My M235 felt numb and slow when I drove home.

[dradernh]

Originally Posted by XutvJet

My friend has a turbo Miata that weighs 2,300lbs. The car makes 210whp and 190wtq and usable power is from 3500rpms to 6500rpms. Under boost, power is shockingly linear. That car is lowered on coilovers. I drove the Miata for 30 minutes and it was an utter blast. The Miata has a slightly lower power to weight ratio than my M235 and not as fat a powerband, but the aural drama under power and the fact that you're in a tiny, low riding car makes it feel quite quick and fast. My M235 felt numb and slow when I drove home.

Miata - THE answer to so many questions!

I drove a well-built Spec Miata for a day at Watkins Glen, a very high-speed track, and I never did stop adjusting to what that car wanted - which was for me to stay flat almost everywhere. Like you, I found the combination of noise and its nearness to the surface made even that slow-ish car feel quick. It was fun in the corners, and that's pretty much what it's all about for me.

[USA-RET]

Originally Posted by XutvJet

My friend has a turbo Miata that weighs 2,300lbs. The car makes 210whp and 190wtq and usable power is from 3500rpms to 6500rpms. Under boost, power is shockingly linear. That car is lowered on coilovers. I drove the Miata for 30 minutes and it was an utter blast. The Miata has a slightly lower power to weight ratio than my M235 and not as fat a powerband, but the aural drama under power and the fact that you're in a tiny, low riding car makes it feel quite quick and fast. My M235 felt numb and slow when I drove home.

I have to say my tuned Cooper S provides a similar amount of enjoyment. Switching between the MCS and the M240i I fancy the one I happen to be driving over the other one.

If I had to choose just one car, it would be the tuned Cooper S. A bit more utility, 37MPG and a blast to drive around town.