Manufacturers underrating power numbers

[Amaru]

Why the fuck do some manufacturers publish underrated horsepower/torque figures on their cars?

I have been pondering this for a while, and I still can't come up with a good reason for doing so... except perhaps if they're worried about disappointing owners who put the car on a dyno and see lower-than-expected power numbers?

It's not just 1 or 2 car brands doing this, either... I have a 2009 335i, which BMW claims to have 300bhp, and most car mag tests put the real number around 325-330bhp. Nissan has also done so with the GTR, Chev with the Z06, Audi with the RS5, etc.

Why?!?!

[PandaDog]

Reminds me of the good old days of the 276HP Pact...
...I didn't understand why when I bought cars in Gran Turismo the horsepower figures went up after I bought them

Perhaps in the real world, dynos may be set up differently so results may not be consistent from one dyno to another?

[GS8]

I don't know about now but back in the muscle car era, it was to keep insurance costs down.

[Amaru]

Originally Posted by RoughEntity

Perhaps in the real world, dynos may be set up differently so results may not be consistent from one dyno to another?

True, but the manufacturer power stats are flywheel numbers anyway, so that would apply to every car, no?

Plus, the type of owner who actually puts their car on a dyno will presumably also know enough about cars to understand that wheel horsepower can fluctuate and will be lower than the published manufacturer power specs. I don't think manufacturers like BMW or Audi really care about the tiny % of their customers who will put their car on a dyno.

[thumper]

i always thought that they did this so that when the next year's model comes up they can claim they made changes and there was a bump in hp but in fact nothing had been done except on paper...

[BoostedBB6]

First off, the manufacturers measure horsepower on a stand, strictly from the engine (bhp) when you measure hp in your car you do it on a dyno (whp).

A dyno is not a truly accurate measure of power as I can go in with a few clicks and make a B16 look like it makes 600whp. There are loads of variables with a chassis dyno compared to an engine dyno.

Its also not the manufacturers who are providing these numbers, its the SAE with there new certified power standards. Some manufactures had all there vehicles tested (Toyota and Honda I think) but others are only doing new engines as they come out. So the idea that the manufacturers are out to up them on paper and not in the actually world is false....at least now it is.

[Traum]

It probably has to do with liability. As extensive as automation gets used at the factory, you are still going to get production variance. On top of that, bear in mind that real world testing conditions are never the same. Do it on a hotter day, assuming that the idiot testers / owners will put in 87 octane gas instead of the 91 it needs, owners / testers continuing to use old engine oil beyond the manufacturer recommendation, yada yada yada. If the owners / testers can't reproduce the results claimed by the manufacturer, today's prevalence of information sharing pretty much guarantees a PR disaster.

It's the same deal as published gas mileage and 0-60 times. You use a conservative number because you don't want to get sued / penalized (it happens with published gas mileage), and you most definitely do not want any PR disasters.

[Amaru]

Originally Posted by thumper

i always thought that they did this so that when the next year's model comes up they can claim they made changes and there was a bump in hp but in fact nothing had been done except on paper...

Dude, great point.

It may be that, but also it could be to ensure no lower models have power numbers close to their more expensive cousins... Ie. ensuring the M3 power #'s are well above the 335i, Z06 above the standard Vette, etc.

[tiger_handheld]

OR under promise and over deliver?

[StylinRed]

Yeah figured it was all part of marketing, so the potential customers go 'omg whoa I already thought it was cool before but now!!'

[320icar]

my personal experience was very different with my focus on the dyno. put down 186whp when the specs are supposed to be 252crank hp

[toyota86]

I have a suspicion they test the engines under less than ideal conditions using lowest grade gas for the region. They then list the hp value on the lower end of allowable range. I think its done mostly for liability reasons. There will be complaints if their car reads low on a dyno. I don't anyone will complain if their higher than advertised.

[Amaru]

Originally Posted by Traum

It probably has to do with liability. As extensive as automation gets used at the factory, you are still going to get production variance. On top of that, bear in mind that real world testing conditions are never the same. Do it on a hotter day, assuming that the idiot testers / owners will put in 87 octane gas instead of the 91 it needs, owners / testers continuing to use old engine oil beyond the manufacturer recommendation, yada yada yada. If the owners / testers can't reproduce the results claimed by the manufacturer, today's prevalence of information sharing pretty much guarantees a PR disaster.

Yeah, and that all makes sense... but wouldn't that suggest ALL cars have underrated power numbers? That may be the case but generally speaking, based on tests results I've seen in car mags and auto blogs, most cars generally produce power numbers within 5-10bhp of the advertised specs. But there are some cars (BMW 335, Z06, GTR, certain porsches, etc) that seem to consistently put up power figures that are well above (ie. >10%) the manufacturer's advertised numbers.

Surely, if the 335 is posting 320-330bhp on average when tested, BMW would be safe (liability wise) advertising 315bhp.... especially if a competitor car, like the G37, is rated by Nissan at 330bhp and producing roughly that number when tested.

Originally Posted by StylinRed

Yeah figured it was all part of marketing, so the potential customers go 'omg whoa I already thought it was cool before but now!!'

Could be, but wouldn't the manufacturer rather post the highest possible power numbers so that they appear to be in line with competing cars?

Most car buyers won't know the "real" power numbers when they're car shopping, so it wouldn't influence their buying decision. And if I'm a carmaker with a car that puts out 210hp, while my competitor's car in the same market segment is making 220hp, you can be damn sure I'd be advertising it as having 210hp... definitely don't want potential buyers who are comparing models to think that mine is underpowered compared to its direct competitor.

[underscore]

I know the testing done by SAE has changed within the last while so the listed HP is now lower than what it would have been under the old testing procedure (so some cars "dropped" in HP during their production even though nothing changed on the engine). I'm not familiar with the tests they do but I'm guessing the new procedures may cause higher-powered engines to spit out artificially low numbers. And don't forget 5% on a 200HP car is 10HP, but on a 600HP car it's 30HP.

Not to mention chassis dynos are hardly accurate (really they're only good for bragging rights and tuning) and some spit out artificially high numbers, I know of one that said my friends 10 year old car makes more WHP now than it made in BHP new. Unless the mags are following the SAE procedures the numbers they get will always be different.

If it is the mfr's intentionally doing it though I'd guess it's either to drum up hype when the mags find higher-than-listed HP, or because of where the car lands in their lineup. I know Porsche hold back on the Carrera because they don't want it to be too good compared to the 911.

[white rocket]

I thought it was an insurance thing but I'm liking thumpers idea. That would be a very smart move to save on costs.