cold air

Assuming everything is at normal operating temperature:
Is there a limit regarding how cold air increases hp? I figure that colder
air (denser air) feeds the intakes better, so does that mean driving in -15
degree weather gives a lot more HP than driving at 90 degree weather? what
about driving at -30 vs. driving at 110? any numbers?

-sachin

 

Everything is NOT normal at "cold" temps. Yes, density and thus O2 content
increases as temperature decreases, however...

The efficiency of vehicles operating in cold temps decreases. I notice this
when it gets colder than -20C (about 0F) here in the middle of Canada. Last
week it was -41C (about -43F) and my vehicles were burning a lot more gasoline
than normal.

Driving in cold weather causes more wear on my vehicles than driving in summer.
The CV boot rubber always seem to crack and break in winter. Coincidence?? I
don't think so.

Ken
Winnipeg

 

And he knows of what he speaks, winter-wise.

I think all immigrants to Canada should have to land in Winnipeg in
February, then decide if they really want to stay.

Wind starts in Calgary and just keeps going till it hits Winnipeg!.

The best way to see Winnipeg is from 30,000 feet at midnight!

(only kidding, i know lots of people who now live elsewhere that think
its the greatest place to leave) (that doesn't sound right |>)))

Dan

 

Well, are you talking theoretical vs. practical?

Theoretically, the highest heat engine efficiency is found when the
exhaust temp is absolute zero - 2nd lawof thermodynamics at work.

However, for auto engines, if the intake air is so cold that the fuel
doesn't atomize well (in the combustion chamber or intake manifold),
then things start to go bad due to unburned fuel. Modern engines
depend more upon the injector spray to atomize the fuel, however,
so the limit is lower, I'm sure.

Pontiac advertised 15-20hp for their ram-air system on the Firebird.

IIRC, intercoolers for turbocharged engines do up to 50hp.

Floyd

 

I remember from college physics that as the temperature drops, more energy
is expended in keeping the engine block at operating temperature, so the
benefits of the denser, cooler air are offset (and ultimately lost as the
temp goes down.)

Seat of the pants experience would suggest that about 50F and slightly humid
is good "makin' horsepower" weather -- at least in a vehicle for which no
special measures have been taken to collect cool air (i.e. stock induction.)
The effect is noticeable.

--Geoff

 

Additional point. No one does any drag racing here (nor at Brainerd, Minnesota) in
the winter. Removing any snow from the track is simple, so the snow is not the
problem. I don't think it is because the increased density causes increased air
drag resulting in poorer time results ;-)

Perhaps it is because there is just so much snow mibile racing going on.....

 

I may be because even a guy that will strap himself into one of those
things and accelerate to 300+ mph in less than 5 seconds has "some"
brains and wants to stay out of the cold. |>)))


Dan

 

If you think about what you are suggesting, Canadian cars would be
infinitely more powerful than their US counterparts, and people in the
Southern US states would be fitting refrigeration units to the intakes
rather than swapping headers and fitting dual 4 barrel carbs..

 

Haven't you ever heard of an intercooler? Lowering intake temps is a
good way to get more power.

Didn't Ford have some luck hooking their supercharger up to the air
conditioner? I can't find any references to it but I vaguely recall
reading about it.

 

But in the case of the intercooler, you are attempting to lower the
temperature of the intake are only, after you have increased its
temperature by compressing it.

Whole different thing from cold, un-compressed air entering a vehicle
system that is surrounded by cold.

Dan

 

The air is still colder and will generate more power. It may not be
all that significant, and it may also be contaminated by engine heat
under the hood, but it still will make a small difference.

 

Yes, but the inefficiencies of having the rest of the vehicle in system
cold (including the fuel) negate the advantage.

As someone said earlier, around 50 deg F, with some humidity in the air,
seems to be where the two lines cross for most vehicles.

Also, in cold, wintery weather, there is a lot of "zero mpg" time |>))

Dan

 

Here's a real world observation. When the temperature is in the 80's,
my race car will hit 130-132 mph at the end of the back straight at
Mid Ohio. When temperature is in the 50's it will hit 135-137 mph.

Jim C.

 

What are you driving . . . a Camry? -Dave

 

At -41 C I haven't seen any car racers here in Winnipeg. My own vehicles (84
Voyager and 83 Volvo) don't accelerate as well as when it is warmer- like today
when it was -9C. These vehicles work much better in the summer than in the winter
even though they are "warmed up" to operating temps.

In theory it may make a difference. However, cold temps increases "the drag"
hugely, especially in the drive train beyond the engine

 

What will it do below zero F, or warmer, say zero C? Let us know. That will
basically nail down everything about this thread. I should talk with some of the
"stockers" here for their observations.

Ken

 

Not quite. Its a stock class Porsche 968.

Jim C.

 

The only time I ever drove it there below 40 degrees F it was
raining/sleeting, which obviously slowed things down. Frankly, I hope
never to be there when its that cold again

Jim C.

 

My car, with intercoolers and two smallish blow driers, has noticably
more punch in cool temps and noticably less punch when it's over 100
degrees.

 

What, it only does ~130??? You sure it's not a camry? -Dave