andy levy <andy-dml@levyclan.us> wrote:
: J Wynia wrote:
:> I have a question about the effective gains from a cold-air intake. I'm
:> asking because I read over and over about how much the gains are for a few
:> degrees difference (as the cooling of the air is passive rather than
:> actively cooled). I've always wondered about this because I live in MN. In
:> the next 3-4 weeks, I will likely be starting my truck in the morning
:> during temps of -20F. If cold-air intake means more horsepower, shouldn't
:> pulling in air that's 100F cooler than summer air make a difference? I
:> guess the fact that I don't really notice a "January boost" is making me
:> wonder if cold-air intake is just another example of automotive snake oil.
: There is a difference. Bob Tom's 13s run back in November was partly
: due to the weather I think. And my trucks have both felt stronger in
: the winter. It's just not a huge difference.
Yep, cold air definitely does make a difference. Here is some
misc info and points to consider:
I have read that power fluctuates approximately 1% per every
10 degrees F of temperature. So, in theory, in the 100 degree
cooler winter air, if your engine is rated at 220hp, it would be
making around 22hp more in the winter than in the summer.
During the winter months, most gas stations switch to a
"winter" blend. I don't recall the exact differences except
that the winter fuel is no friend to making horsepower. So,
it is possible that the winter cold air boost is being offset
by a power loss from the fuel.
Even though the ambient temperature is cooler, your engine
might not be seeing the exact same drop in temperature. (This
depends on where it is drawing the air from, how insulated the
engine compartment is, etc.) For example, on an 80 degree day,
due to heating of the engine compartment, a non-insulated intake
system, etc. your engine might be drawing in air which is around
100 degrees by the time it gets into the combustion chamber. If
the outside temp drops to 60 degrees, the combustion chamber might
be seeing air which is 85 or 90 degrees, not 80 degrees, as you
might expect. The drop in combustion chamber intake air
temperature does not necessarily exactly duplicate the drop in
outside air temp. (BTW, the numbers above are not accurate
examples, I just made them up.)
Another factor is the general tune-up of your engine.
Without properly functioning oxygen and IAT sensors, your engine's
computer may have difficulty determining that there is additional
oxygen and cold air being introduced, and it might not be
adding enough fuel to burn the extra oxygen.
Like Andy, I have also noticed a power increase during the
winter months (or on a crisp fall day). It isn't always as large
an increase as one might expect, due to some of the above factors,
but it is usually quite noticable. Also, when I used a cold-air
intake at the dragstrip, my ETs dropped by 2-3 tenths. (That
equates to around 10-15hp, certainly nothing to sneeze at!)
BTW, the reason cold air equals more power is because the
various molecules that make up "air" vibrate less as you cool
the air down, which means that a given mass of air will take
up less volume - it becomes more dense, which for our purposes
means that a given volume of air will contain more oxygen
molecules when it is cold. (It will contain more of all of the
different types of molecules that make up air, but the engine is
only concerned with the oxygen.) Your engine is capable of drawing
in a given volume of air at a given RPM. When the air is cooler,
although the volume of air being drawn into the engine doesn't
change, the increased density and therefore, increased number of
oxygen molecules per volume means that more fuel can be burned
per stroke and therefore more power is realized. This is actually
the primary principle behind adding power with nitrous oxide;
broken down to its base theory, nitrous oxide is essentially a
way to cram more oxygen into the motor so that more fuel can be
burned. Using cold air does the same thing as nitrous oxide -
it puts more oxygen into the motor. However, the cold air does
this because the air is slightly more dense than normal whereas
the nitrous oxide can inject a large volume of oxygen - obviously
the nitrous oxide is a lot more effective, but the basic principle
is the same.
So I guess the point of all this rambling is, "no, cold air
intakes are not automotive snake oil". :-)
--
-Jon-
.-- Jon Steiger ---- jon@dakota-truck.net or jon@jonsteiger.com --.
| 1970 Barracuda - 1990 Dakota 'vert - 1992 Ram 4x4 - 1996 Dakota |
| 1996 Intruder 1400 - 1996 Kolb FireFly - 2001 Ram QC 3500 CTD |
`------------------------------------ http://www.jonsteiger.com --'
This archive was generated by hypermail 2b29 : Fri Feb 06 2004 - 11:47:13 EST