Curious about HP...

[rscupper]

Auto manufacturers, tuners, mechanics, and my fellow board members often quote horse power numbers related to a particular power plant.

I'm curious to know if one took, say, a hundred 3.2L stock engines - as identical as a Porsche line would turn out in regular production - how much (if any) would the ACTUAL HP vary from those published? To what HP 'tolerance' were such engines engineered & produced?

Anyone know?

[Rick Lee]

Straight from the factory, they probably would all match. But as 95 of that group will customize their cars, and all will wear away clutch components, build up soot in the air filter, cook the cat, etc., HP can and does decrease.

[Kurt B]

That's a good question. I think we can infer that number from the numbers that Porsche publishes and the 'real' numbers.

My car supposedly had originally 207 HP. This is apparently an average; let's assume it is. But the book says '200' (one that came with the car).

They probably concentrate much more on a lower bound number rather than a tolerance per se which skews the distribution a bit, but let's assume it's normally dist'd.

I'm sure Porsche is compliant and uses the 3 sigma rule.
(or 99.97 % production within x1 and x2 HP numbers)

If we assume Porsche is using this rule, and my car on average really has 207 HP, then the 200 given in my book represents 3 sigma below the mean of 207.
7/3 = 2.3 HP

{But I'm not satisfied with that because the 200 appears to be much more conservative than really necessary. This is because in 1984, 200 was more than adequate for a sportscar. Nowadays, you really need to milk every HP to sell a car. }

Continuing on, let's just state it with the 2.3
68% will be between 204.7 and 209.3
95% will be between 202.4 and 211.6
99% between 200 and 213.9

Unfortunately, this is all poppycock, because HP isn't going to be distributed like that.

This assumes the engines are built and not tuned; that the process is normal (which it probably isn't), that 2.3 is the actual SD, which I'm sure it's not, and it assumes the target HP is 207, which, although it could be, would be terrible for us! Who knows though...if the target WERE the mean (or very near it), then you might be able to apply this if we could get a good estimate of the SD.


In fact, there's probably upper bound far below my 213 HP estimate for 3sigma high. But still, it's fun making this crap up.

[rscupper]

Caught you in thinking mode at work, huh Kurt?

[Bill Douglas]

Porsche built the engines then tuned them on a dyno. This is part of the running in/burn in process. Any engines that weren't up to spec, and being Porsche the specification would be pretty high, were rejected and torn down to see what the fault was.

So there would not have been "floating" ranges of HP.

Hhe reason for lower than actual HP being stated is so some d1ckhead doesn't own the car for 6 months then get a HP test done on it and return it to the dealer because it has been miss-represented to him as a "something" HP car.

[Brian993]

Hey Kurt,

Wanna say that in english (brain cramp).

[speeder]

It is a good question w/ a 2-part answer. Porsche used to claim in their advertising that they dyno every motor and roadtest every car to ensure power-output and performance figures. Haven't seen that claim in print lately- probably no time for this as they sell Boxsters and 996's like proverbial hotcakes. They never did tell us exactly how close to spec the dyno-reading had to be to pass, but other part of answer is that they were always known for being on the conservative side, (as opposed to liberal side), when putting out HP #'s, (understating slightly). Hope that helps.

[Kurt B]

They really are very conservative. Think about it, my buddy bought a Honda S2000 which claimed a 5.9 as opposed to Porsche's claim of 6.2 on my car (stock)

Using my accelerometer, he never even got close to that 5.9. However, I had no trouble doing 6.3 when I first got the car and it was running poorly and unmodified.

Also, Porsche numbers are at half-load capacity. Do other manufacturers put the same restrictions, or do they do the test with a 110 lb japanese jockey doing the test?

....
Porsche's goal is not to just sell, but to deliver. You should always be pleasantly surprised I think, is their hope.

[makaio]

Noah,
They probably thought you were a spy from GM or Ford.

[Mike the mechanic]

My 86 Carrera is suppossed to make 207hp @ the flywheel. With only a Racing Dynamics chip upgrade, I got 202hp @ the wheels which tranlates. That is over 230 flywheel horsepower.

Mike
86 Carrera t

[Yargk]

I remember Ruf talking about this very subject when referring to using the 996 motor in their Boxster based 3400s in Excellence. Basically what was said is that Porsche motors used to be more consistent in the hp department. Before modifying the 996 motor, they have to make sure it makes the right stock hp because they apparently are encountering "weak" motors more often. This problem isn't really an issue with the GT-3 or Turbo motors, if I remember the article correctly.