[DML] Horsepower vs Torque

["content22207" <brobertson@xxxxxxxxxxxx>]

I think you've fallen into the same HP trap that gets so many people.
Horsepower (by itself) is NOT a measure of power transmitted through
the crankshaft -- torque is. A higher HP number does NOT automatically
translate into higher torque (your sportscar examples are roughly
equivalent to the HP rating of a semi tractor -- which one produces
more torque?). HP does indicate how fast a particular class of engine
can rev and still produce power before it starts to stumble all over
itself.

Remember: Horsepower is calculated: Torque x RPM's / 5252. This is the
exact same formula used by every engine manufacturer (has to be, or
else you couldn't compare one to another).

Notice that Torque can be measured idependently of HP. RPM's can be
measured independently of HP. Horsepower can not be calculated without
both Torque and RPM's.

In other words: a HP rating without either the RPM's or Torque at
which it was calculated is relatively useless.

The highest PRV HP rating I've found to date is a non-consumer Renault
Le Mans racing application. (I should have clarified my HP statement:
You're going to be hard pressed to get much more than 250 HP in a 3
liter production engine). It did put out something like 400 HP at 7000
RPM. But do the math -- that's only 300 Ft Lbs of Torque. Production
American big blocks have always exerted more.

The common misconception is that "horsepwer" somehow translates into a
an imaginary "number of horses" hitched to the front of your car
pulling it like a wagon. The obvious flaw with that vision is it
neither tells you how big the horses are nor how fast they are moving.
6 Clydesdales at a steady gait will outperform a dozen galloping
circus ponies every time. I guarantee it.

I like to raise uninitiated eyebrows with the locomotives my employer
used for many decades (electric traction motors I know, but the shock
value is the same). 600 max HP. Doesn't sound like much, does it? But
they produced that at 700 RPM's. In other words, they exerted more
than 4,500 Ft Lbs of Torque. That generates more than enough
electricity to pull 5 1/4 *MILLION* lbs of freight. Could your
similarly rated Lambourgini Diablo (550 HP) do the same? Of course it
couldn't, but a person comparing only Horsepower numbers would never
know that, would he? (Our railroad now uses bigger 1,500 HP units that
spin closer to 900 RPM)

Bill Robertson
#5939

>--- In dmcnews@xxxxxxxxxxxxxxx, Martin Gutkowski <webmaster@xxxx> wrote:
> Ok, I'm not going to go beyond this message. Bill, You can believe what 
> you like. I _have_ an "Alpine" engine to fit into my DeLorean. I write 
> that in inverted commas because what I have is a Renault 25 turbo 
> engine, which has a slightly different crank case (interchangable
with a 
> DMC's) and different intake pipework (which is nothing more than a 
> couple of pipes which are a different shape on the Alpine).
> 
> You have clearly had very little experience with after-market tuning. I 
> won't pretend I do, however I have several friends who have, and I'm 
> learning as much as I can at the moment, and I'll begin by replying to 
> your last point. Quote "250 HP is the more reliable number. You're
going 
> to be very hard pressed to get much more than that from a 3 liter 
> gasoline engine, even turbocharged." - this is complete and utter 
> nonsense. I've ridden in several fast cars - a Subaru Impreza Turbo
(WRC 
> champion several years running) which has a twin turbo 2-litre flat 4 
> and my friend's puts out over 330hp. Another friend's Nissan Skyline 
> with a single turbo 2 litre strait 6 putting out nearly 400hp. (and the 
> modern 2.6 litre twin turbo equivalent can be tuned to over 600hp).
I've 
> also got a friend with a 550 hp 6 litre V12 normally aspirated 
> Lambourgini Diablo, who also took me out in the Gallardo he had as a 
> loan car recently..... and the Skyline is quicker than all of them.
> 
> Just because Renault tuned these cars to 250hp out of the factory, 
> doesn't mean they aren't capable of a lot more. The top end that should 
> be considered for boost is 20psi. Purely in air flow alone, you're 
> talking equivalent displacement of over 7 litres (rough maths) - in an 
> engine capable of 7000rpm. It doesn't matter how much torque you put 
> through the gearbox, as long as the ratio is such that the tyres let go 
> before you reach the limit of the gearbox, you won't break anything 
> apart from traction.
> 
> I've also delved into the engine management on the Z7U and suffice to 
> say that this is one area where Renault really were the envy of the 
> world, in the mid 80's they were mapping these engines to a level of 
> detail that even Cosworth could only dream of. And that's my final word 
> on the subject: I was taken for a spin in a Sierra Cosworth last week. 
> That's about 300hp from a 2 litre single turbo inline 4.
> 
> Martin
> 





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