Why would BMW ever under rate their horse power on an engine especially an M3/4

[Drift Master]

Can any one think of a reason since HP sells cars and its would be to their advantage to say higher numbers!! I am sick of all this talk about under rated engines!!!!

[A418t81]

Originally Posted by Drift Master

Can any one think of a reason since HP sells cars and its would be to their advantage to say higher numbers!! I am sick of all this talk about under rated engines!!!!

So far, every *single* one of BMW's turbo powerplants has been significantly underrated versus what chassis dynos show the engine to actually be producing. While I'm not saying I expect the S55 to be the same, I certainly wouldn't be shocked to see it putting down somewhere around 400 whp stock, which is well above 425 hp at the crank.

[Sapper_M3]

Something interesting to throw into the discussion:

http://www.gminsidenews.com/forums/f...sepower-90543/

[swamp2]

^ Lower losses are a factor but those alone can not explain the achieved performance of many cars, specifically their trap speeds. Cars like the GT-R (1st year), 335i and F10 M5 all outperform what their stated hp achieves even assuming a low loss like 10-12%, which would be a quite efficient drive train.

That being said the US and the SAE "Certified Power" (SAE J1349 and J1995) are exactly the type of specification I would expect out of the typically more formal and more regulated EU. Unfortunately, even in the US, adherence to SAE Certified Power (each car being within 1% of stated) is entirely voluntary.

[Zoli007]

Is it possibly something to do with regulations based on power numbers? Totally talking out of my arse here. But I know some countries have increased road tax based on displacement of engine in the car. Perhaps there is something similar to this?

Or they prefer to under rate it to allow for a larger variance in output for mass produced engines?

[aus]

Because if you state you make X HP but really only man x HP, you get sued and have to pay owners a boat load of money or buy the car back.
It also helps insurance premuims to have a lower listed HP reading.

.

[M3ryder55]

see my other thread

they are not claiming these figures to be whp, just previous trends have shown less of a power train loss from crank to wheel. Whether that "under-rated" number stems from less of a power train to wheel loss or the way they are evaluating their engines is something I do not know. Regardless, more wheel hp is a good thing and nothing to get upset over IMO.

We live in an era now, where the HP wars are over. Its all about power to weight ratio and engineering the way the power is delivered to the wheels rather than just making bigger higher output engines. I think BMW prides itself in "engineering" and I'm assuming by giving these types of figures it would make them look even better, but i could be wrong. just my .02

[hadeed]

Should we assume that 0-60 numbers are underrated too? :P

[swamp2]

Originally Posted by jFran

Should we assume that 0-60 numbers are underrated too? :P

Those always are. Perhaps it's better to just call them extremely conservative.

[Mako]

Originally Posted by swamp2

Those always are. Perhaps it's better to just call them extremely conservative.

actually not ALWAYS, lately BMW has been right on with their 0-60 numbers, at least with a few non M cars, the 335i xdrive is stated at 4.7 by BMW, I highly doubt that is under rated. X3 35i is rated at 5.5 by BMW, and car and driver tested it exactly at that 5.5 seconds...

BMW is saying 3.9 for the M3, I bet that is a number the average owner could get, while magazines and pro drivers can probably get ~3.6

[ixse]

why r u bitchin at something thats for our advantage? if they overrated the figures than we have a problem.

[mkoesel]

Originally Posted by Drift Master

Can any one think of a reason since HP sells cars and its would be to their advantage to say higher numbers!! I am sick of all this talk about under rated engines!!!!

One reason would be to establish a proper hierarchical relationship among products with respect to their position in the lineup. For example, perhaps BMW has good reason to want the M3/M4 to sit below the 550i/650i (especially the latter) when you compare the horsepower on their spec-sheets. It may be that research tells them that a 650i buyer values this. Remember, marketing is not about being forthright or forthcoming, its about telling people what they want to hear. On a side-note, I would make a terrible marketer.

[ASAP]

From my experience it seems that the NA bmw motors are about right. The turbo ones are all underrated, N54, S63tu and the like all dyno'd a bit more than claimed. If I had my guess for the S55, I would put it at 390 WHP, which would be incredible for a stock car w that weight and dct. If it touches 400 whp, i may cry.

[m3ct]

Originally Posted by mkoesel

One reason would be to establish a proper hierarchical relationship among products with respect to their position in the lineup. For example, perhaps BMW has good reason to want the M3/M4 to sit below the 550i/650i (especially the latter) when you compare the horsepower on their spec-sheets. It may be that research tells them that a 650i buyer values this. Remember, marketing is not about being forthright or forthcoming, its about telling people what they want to hear. On a side-note, I would make a terrible marketer.

That seems very plausible to me. It wouldn't make sense if the M3 on paper was better than the M5, what would the incentive be to pay more for less?

[JoeFromPA]

First off, haven't you ever heard you can't compare dynos across different machines? A normal dyno to dyno comparison may be 10% different.

Now we are comparing expected wheel dyno output to BMW benchmarked engine dyno? This is getting ridiculous.

Turbo engines are very volatile to external factors. Heat soak, fuel grade, air flow to the engine. They are more likely to have larger swings on a dyno.

BMW MAY not be under-rating, but instead be producing an engine dyno rating that can be consistently achieved using lower quality fuel, some heat soak, and non-ideal air flow or air density (i.e. providing a dyno that's accurate at 4000 feet elevation)

But hey, let's all ignore the actual science and possibilities here and claim "under-rating compared to my sea level, Joe's mustang dyno + massive fans dyno which measured the output at a completely different part of the car and applied an unscientific adjustment for parasitic loss!"

[MKE_M3]

Originally Posted by JoeFromPA

First off, haven't you ever heard you can't compare dynos across different machines? A normal dyno to dyno comparison may be 10% different.

Now we are comparing expected wheel dyno output to BMW benchmarked engine dyno? This is getting ridiculous.

Turbo engines are very volatile to external factors. Heat soak, fuel grade, air flow to the engine. They are more likely to have larger swings on a dyno.

BMW MAY not be under-rating, but instead be producing an engine dyno rating that can be consistently achieved using lower quality fuel, some heat soak, and non-ideal air flow or air density (i.e. providing a dyno that's accurate at 4000 feet elevation)

But hey, let's all ignore the actual science and possibilities here and claim "under-rating compared to my sea level, Joe's mustang dyno + massive fans dyno which measured the output at a completely different part of the car and applied an unscientific adjustment for parasitic loss!"

Well said

[tallshortguy]

Originally Posted by Mako

actually not ALWAYS, lately BMW has been right on with their 0-60 numbers, at least with a few non M cars, the 335i xdrive is stated at 4.7 by BMW, I highly doubt that is under rated. X3 35i is rated at 5.5 by BMW, and car and driver tested it exactly at that 5.5 seconds...

BMW is saying 3.9 for the M3, I bet that is a number the average owner could get, while magazines and pro drivers can probably get ~3.6

I feel like it's largely always been like that though, the stated 60 time is what your average owner or even enthusiast can get while more experienced drivers can get the real 60 time.

[miiipilot]

Originally Posted by mkoesel

One reason would be to establish a proper hierarchical relationship among products with respect to their position in the lineup.

This

I feel this b/c when manufacturers stagger their performance hierarchical cars, the higher end outgoing model looks less appealing. So you underrate it as not to upstage their bigger older brother and hurt sales of the more expensive car.

I remember this in all the magazines when I was a kid reading about the Buick Grand National/GNX vs the corvette. The lunch box car killed its more sporty cousin.

[ZGM3]

Can someone from Europe chime in on this.
I often thought that due the extremely high cost of insurance in Europe (especially the UK) that rates have a correlation to the HP of the vehicle.
I could be wrong, but if you talk to anyone from the UK and ask them what their insurance on their car is compared to the US, you will see that we have it extremely good and cheap.

[tognettiza]

It also helps insurance premuims to have a lower listed HP reading.

[coloradoe92m3]

Someone hit nail on head. If it were from other reasons listed like keeping hierarchy in check, then the NA motors would have also been "underrates" it is solely due to turbos extreme variance and susceptibility to heavy soak, fuel quality etc. Running cars in cool inside dyno with fans and 93 octane will give you numbers rarely seen on hard driving or other days where heat a factor. Whereas although NA motors are effected by same variables, its much less dramatic.

So listed HP is usually a minimum value that assumed bad factors being present to a degree. Or a middle ground. Prob are quite accurate if it was possible to dyno real world driving after 10-15 mins of hard driving in summer, the numbers would probably seem overrated

[JS919]

Originally Posted by JoeFromPA

First off, haven't you ever heard you can't compare dynos across different machines? A normal dyno to dyno comparison may be 10% different.

Now we are comparing expected wheel dyno output to BMW benchmarked engine dyno? This is getting ridiculous.

Turbo engines are very volatile to external factors. Heat soak, fuel grade, air flow to the engine. They are more likely to have larger swings on a dyno.

BMW MAY not be under-rating, but instead be producing an engine dyno rating that can be consistently achieved using lower quality fuel, some heat soak, and non-ideal airflow or air density (i.e. providing a dyno that's accurate at 4000 feet elevation)

But hey, let's all ignore the actual science and possibilities here and claim "under-rating compared to my sea level, Joe's mustang dyno + massive fans dyno which measured the output at a completely different part of the car and applied an unscientific adjustment for parasitic loss!"

I think you are on the right track.

My guess is BMW is using worst case scenario environmental conditions for their HP ratings. An engine will have substantially more HP at sea level on a 50 degree day than at 5000 ft on a 100 degree day.