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Re: Horsepower Vs. Torque



Hey guys,
 Just thought I would forward this to the list-- someone on the A2 16V list
asked a really good question, and I gave him a good answer. :)  And some of
you
might also be wondering the same thing, so I thought I'd cc my response here.

For the record, this post will *not* start an 8v/16v war.  Thank you. :)

Jason



At 02:11 PM 4/3/99 , you wrote: 
>
> I have heard a lot about the question of whether torque or horsepower is
more
> important.  For instance the VTEC engine produces 190 hp but only 130 lb/ft
> of torque, whereas for instance the VR6 produces 172 hp and if I am correct
> around 170 lb/ft of torque as well.  It seems to me the VR6 would be a
> stronger engine because of these more even numbers.  My question is for all
> you techies:  What are benefits of this torque and does the bigh VTEC
> horsepower number mean nothing without acompanying torque to match? 



Hi Michael,
That's a loaded question you ask there. :)  But it's a great question, and as
such, deserving of a great answer.  <ahem>  I will try my best.

The "evenness" of the numbers doesn't mean a thing, really, because the
numbers
themselves are arbitrary-- an engine might put out 170hp and 170lb-ft
torque...
but you measure that engine with a German standing above it, and he'd say it
had 168hp and 225 Nm of torque.

I'm going to refer you go a great page to look up what's important in the
horsepower / torque wars... have a look at:
http://www.vettenet.org/torquehp.html

The real benefit of VTEC is that it allows and engine to rev to ungodly speeds
while still making some power.  You know how a stock 1.8 16v kinda feels like
it's running out of breath at 7200rpm?  Well, VTEC changes the valve timing at
around 5000, so this doesn't happen.  It keeps a steady pace of acceleration
all the way until it smacks into the rev limiter.

So, for example, let's take Honda's 1.6l 16v 4-cylinder.  In normal form, it
makes about 106hp and redlines at 6000rpm or so. (Don't quote me on that). 
The
VTEC 1.6 in the EX makes 125hp, redlines at 7000rpm, but doesn't make any more
torque than the non-VTEC.  Now, there's the Si VTEC that makes 160hp, redlines
at 8000, and still doesn't make any more torque than the base 1.6.

The result?  Driving all of these cars "normally", you won't notice any
difference between the three of them. Why?  Because it's the *torque* of an
engine that you feel accelerating you, and they all have the same torque. 
However, if you look at 0-60 times, the 160hp car is faster than the 125hp
car,
which is faster than the 106hp car.  Why?  Well, because of how high they can
rev.  Let's say they have the same gearing,  right?  The 106-hp car
redlines at
6000, let's say that's 25mph in 1st gear.  Well, the 125-hp car can go another
full 1000rpm before you need to shift.  So, while the 106-hp car is already in
2nd (and therefore not accelerating as fast, because of gearing), the 125hp
car
zooms to 30mph before it needs to shift into 2nd.  And the 160-hp car can get
all the way to 33mph before it needs to shift, so it is even "quicker" to 60. 
It's "quicker", but it doesn't accelerate any faster.  

If you plotted any car's acceleration on a graph versus speed, you'd see a
gradual downward trends (shut up, I know there are spikes. :)  The difference
between the 106, 125, and 160 cars is not how high the curve will peak, but
how
slowly it descends.  

Driving impression?  I've driven a Civic LX with the 106hp motor, extensively
in an EX 125hp, and drove a Del Sol Si with the 160hp engine.  All of them
feel
like slugs compared to the Scirocco.  They all feel the same speed,
too...Sure,
they're fast on paper.. the Del Sol is almost as quick on paper as my
Scirocco-- it weighs about the same, but has 37 more hp! The difference was
amazing, though felt like night and day. 

On the other side of the spectrum, go and rent a Buick Century with the 3300
V6.  Approach about 15mph and then slam on the gas.  You'll feel a rush of
acceleration that thrusts you back into your seat like no VW you've
driven.  It
just screams "I do 0-60 in 7 seconds."  With a shocking smile on your face,
pull over on the side of the road and pull out the stopwatch.  Gun it, and get
dazed look on your face when you see consistent 0-60 times in the mid 10s.
Wha?!
It's easy.  That big ol' V6 is a torque monster.  Remember, you feel torque,
not hp.  However, it runs outta breath at like 4000rpm.  So, it accelerates
like a bat out of hell until 4000rpm, and then has to shift into a higher
gear.  Of course, the next higher gear won't have the torque multiplication
that 1st does, so acceleration really drops off.

So what happens in a stoplight drag (no clutch drop, ok? just full
throttle) in
a Civic Si with 160hp and a Buick Century 3.3?  Well, by the top of 1st gear,
it's probably dead even.  The Buick squirted off the line, leaving the
Honda in
it's disgusting exhaust fumes.  But, as they say, slow and steady wins the
race.  The Buick redlines and shifts into a much longer 2nd gear.  Meanwhile,
the Honda's still mozying towards redline in 1st gear, and gradually pulls
away
from the Buick, leaving it far in the dust as it trounces it in top speed.  

Why is it faster in top speed?  Well, the Buick can only rev to 4000 (I think
they're redlined at 5000, but it's useless above 4k, and I don't think I've
gotten one of those cars to shift higher than 4500 anyways).  Since it can
only
rev to 4000, you're talking a *long* ass gear to get high speeds-- let's say
that car can do 120mph, just for argument's sake.  120 mph would need to be no
higher than 4000rpm, right?  Well, let's say the Honda could do 120mph, too. 
But it redlines at 8000rpm.  So the engineers throw in a gear that makes
120mph=8000rpm.  That gear is TWICE as short as the Buick's top gear!!  So the
engine's torque (the little there is) is multiplied by the transmission TWICE
as much as it would be with the Buick's top gear!  Suddenly the little 1.6
liter 4 cylinder can outdo a 3.3 liter V6 with 200hp and 200lb-ft of torque!

Not to be outdone, I will illustrate another point.

Volkswagen debuted the 1.8 16v in the Scirocco in 1986.  Our engines are 
*old*
technology, k?  Honda gets 125hp and 110lb-ft of torque out of their EX VTEC
1.6 liter.  Sure, that's a technical achievement and all, but 13 years ago, VW
got 125hp and 120lb-ft out of the 1.8 16v... and got it to rev happily to
7200rpm *without* VTEC.  The 1.8 16v might be criticized for its lack of
low-end torque, but I disagree.  Yes, I agree that there is a serious
deficiency in torque under 2000rpm, but that is moot to begin with.  If you
have any disagreements about the 1.8's torque curve, take it up with the Dyno
sheet that's printed on my website (under PRESS).

My point is, our VWs have the best of both worlds.  They rev like VTEC Hondas,
to take full advantage of gearing... and they have a lot of torque so that
*while* you're taking advantage of geaing like that, you're accelerating
like a
bat out of hell.

And that, my friends, is why our cars have Fahrvergnuegen and their cars are
just langweilig.

Jason







----------
jason@scirocco.org
1987 Scirocco 16v
60,000 original miles.
<http://members.aol.com/rocco16v>http://members.aol.com/rocco16v  

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