HP as it relates directly to each car......

adrean8j

adrean8j

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I have a question for all of you gearheads about exactly how the "advertised" HP of a car relates to what the car is actually putting out(RWHP). For example BMW advertises that the '99 323i has 170hp...is that at the wheels? If not how much is lost before it gets to the wheels? If it is at the wheels how much HP does the engine put out? Is there an industry standard as far as telling the ratings? Or does each manufacturer do it differently? I mean Amplifier manufacturers(not the good ones mind you) will say an Amp is 1000w but in small print will be the words Peak wattage output...which means that the amp could have a totally different wattage than you would first think...is it the same way with HP? If anyone can school me that would be cool!
 
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epj3

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Dan is right - I think they usually use around 20% drivetrain loss. That 170 crank hp is probably around 130-140 wheel hp (probably being optimistic). Typically an automatic is less efficient than manual unless you have a high stall converter (in a muscle car for instance). Cars with all wheel drive have even higher drivetrain loss - so that 170 crank hp might mean 110-120 wheel horsepower. Drivetrains are worlds more efficient now-a-days though, especially with the carbon fiber driveshafts and other advancements.
 
bahnstormer

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it used to be done at the wheels way back when

now its almost always at the crank unless its some small
company

there are varying schools of thought on this topic so here goes

rwd cars lose approx 20% through the drivetrain before hp hits
the wheels

fwd lose 15%

awd lose 25% or more


industry standards vary. great sentence right? lol
europe, japan, usa all have differnet stuff and it even
varies manufac to manufac

and the worst part is each dyno vaires too
mustang dynos are believed to be the most
pessimistic (iirc)

so yah u can google for more indepth stuff =]
 
MrElussive

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The advertised horsepower you read is horsepower at the crank. But this horsepower is the maximum horsepower produced at a certain rpm, which is always close to -or at- redline. So if we take the new BMW 330i for example, which has the 3.0 liter 255hp I6, it is producing the 255hp at 6,600rpm (according to the BMWUSA website). When you are idling at 800rpm or so, the engine is not producing anywhere near that 255hp. Most, if not all gasoline engines work in the way that the higher the rpm's, the more power (horsepower) they are producing. This is NOT the case with torque, though.
 
adrean8j

adrean8j

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Ok well one of the reasons I ask is that my car is a 523i...advertised as 170hp(or ps)....so if what you say is true that is 170hp at the crank.....so counting for roughly 20% loss in a RWD vehicle I should be sitting around 136RWHP? Is that what a Dyno should read give or take a few hp?
 
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epj3

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adrean8j said:
Ok well one of the reasons I ask is that my car is a 523i...advertised as 170hp(or ps)....so if what you say is true that is 170hp at the crank.....so counting for roughly 20% loss in a RWD vehicle I should be sitting around 136RWHP? Is that what a Dyno should read give or take a few hp?
Click to expand...
If they dont factor in estimated drivetrain loss, then yes.
 
MrElussive

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Well do not forget that not all dynos are created equal (which almost makes dynos in general worthless). Some dynos are more conservative than others and some are just wacky. Your best bet would have been to take your stock car and dyno it...then after you do some mods, take it to that same dyno and see how much your horsepower has improved. I believe that is the most accurate way to measure actual gains from your modifications. [:)]
 
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epj3

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adrean8j said:
Interesting because i dynoed my car a couple of weeks ago and it dynoed at 171.3ps.....modifications i have are ChipTuning(www.digit-power.de), Sport Exhaust(Remus Romulus), and a BMC Carbon Dynamic Airbox........
Click to expand...
Did it dyno at 171.3 RWHP? Or did the slip just say "171.3"? They might have factored in drivetrain loss.
 
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epj3

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MrElussive said:
Well do not forget that not all dynos are created equal (which almost makes dynos in general worthless). Some dynos are more conservative than others and some are just wacky. Your best bet would have been to take your stock car and dyno it...then after you do some mods, take it to that same dyno and see how much your horsepower has improved. I believe that is the most accurate way to measure actual gains from your modifications. [:)]
Click to expand...
YOU DONT KNOW WHAT YOUR TALKING ABOUT YOUDONT EVEN HAVE A Bmw!!!1!!
 
MrElussive

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epj3 said:
YOU DONT KNOW WHAT YOUR TALKING ABOUT YOUDONT EVEN HAVE A Bmw!!!1!!
Click to expand...
Dude...I HAVE JUST AS MUCH RIGHT TO BE HERE AS ANYONE ELSE>>>MY JAP CAR DYNOS 480HP AT THE WHEELS SO I ROXORS YOUR SOXORS IN YOUR BOX0RS!111111111111111!!!!!!1111
 
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