On Mon, 8 Nov 1999, Nate Johnson wrote:
> That's great and all and that's what I told my dad! "Cold air is better
> for more power." but I need something more than that to convince him! He
> thinks warm air would be better. I'm looking for a more "technical"
> answer. WHY, is it better for more power?
>
Basically, its all based on density... Superchargers, turbochargers,
nitrous oxide, ram-air, cold air intakes, cool cans, etc. are all doing
the exact same thing, if you stop and think about it. They all give you
(varying degrees of) more power by increasing the density of the oxygen
in the engine.
Consider the "stoich" A/F ratio of 14:1. This is what the computer
in your truck is trying to maintain; 14 parts of air to 1 part fuel.
My understanding is that if you can shove 14 more molecules of oxygen
into the engine, then you can burn 1 more molecule of fuel. Since
you now have one more "explosion" (or chemical reaction, whatever) than
before, you're also making more power than before.
(I'm sure the physicists and chemists amoung us will shudder when
they hear that description; but its the best I can do; I am neither
a physisist nor a chemist.) :-( (If I'm wrong, please correct me.)
I don't think your Dad will argue that a supercharger or turbocharger
doesn't increase power. What they do is to compress the oxygen, and
shove it into the engine. This means that you have more oxygen molecules
per square inch, and for every extra 14 oxygen molecules, you get to
burn 1 more fuel molecule than before.
Nitrous oxide is similar except that rather than compressing oxygen
and putting it into the engine, it replaces normal air molecules with
nitrous oxide molecules, which contain more oxygen. So you're incresing
the oxygen density there too. (Not only that, but the extreme cold of
nitrous oxide decreases the temperature of the incoming air by about
60-70 degrees.)
Cold air is more dense than warm air. The warmer the air, the
more the molecules move, and the more space they take up, which means
there is more distance between each oxygen molecule. So, the cooler
the air, the more densly packed the oxygen molecules are; you have more
oxygen per volume than warmer air. That means you can fit more oxygen
molecules into the engine, and therefore you can burn more fuel molecules,
and make more power.
According to Nitrous Oxide Systems, a 10 degree (F) reduction in
temperature is good for a 1% power increase. So, for the Dak's stock
220-230hp V8, every ten degrees you can drop the air temperature will
net you an additional 2.2-2.3hp. I don't think it'd be too crazy to
say that you could drop the temperature by 40 degrees, in which case
you'd be looking at 8-9 "free" horsepower.
-Jon-
.--- stei0302@cs.fredonia.edu ----------------------------------------.
| Jon Steiger * AOPA, DoD, EAA, MP Race Team, NMA, SPA, USUA * RP-SEL |
| '96 Dodge Dakota V8, '96 Suzuki Intruder 1400, '96 Kolb FireFly 447 |
`--------------------------- http://www.cs.fredonia.edu/~stei0302/ ---'
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