Pardon me for butting in here, but let's take your stock, run-of-the-mill
360. Let's give it an 85% volumetric efficiency ratio. Therefore, every 2
revolutions, it's moving 85% of 360 cubic inches of air, or 306 cubic
inches. Round that off to 300 cubic inches.
Typical highway cruising RPM is about 2,000RPM, so we're moving 300,000
cubic inches of air per minute.
Now - here's where it's going to get a little tricky, but let's assume a
K&N-style cold air intake. That tube is about, what, 4" in diameter, and
about, oh... 4 feet long? Calculating the volume of that cylinder, we get
about 603 cubic inches? (Pi * 2" squared * 48"). That means we have to
empty that cylinder about 498 times over per minute to feed the engine's
demand for air. Therefore, each molocule of air has to make the 48" journey
in .12 seconds (60 seconds/498). That works out to about 22.7MPH.
So... how much heat do you think the cool, 70-ish degree outside air is
going to soak up from a thermoplastic tube, going almost 23MPH, and sitting
in there for just over a tenth of a second?
I'm betting... not too much.
I'm on vacation this week and there's no way I'm going to the shop to get a
scanner but if one of you guys with a scanner in your back pocket would
check the reading of the intake air temp sensor you'd have an answer to the
question. I'm betting its hotter than you think..
I'm sure that it is with a stock setup but lets not forget that the factory
CAI is not normally the most efficient on the planet. The plastics that they
use are based more on a cost / endurance ratio with the main influence being
on the cost. That same cost factor also sometimes leads to a fairly
restrictive setup and in most of the factory setups, the filter is contained
in a box on or near the engine where it is subjected to much more heat
If at first you don't succeed, you're not cut out for skydiving
Go the head of the class! Also, what must be considered is that when
traveling down the road, the underhood air is not a stagnant mass of hot
air, but is pretty well ventilated from air incursion through the wheel
The formula for any four stroke engine is:
CFM = (CID x RPM x VE) /3456
where: CFM = Cubic feet/minute
CID = Cubic inch displacement
RPM= Revolutions per minute
VE = Volumetric efficiency
To calculate velocity thru the air intake system:
CFM/intake area in square feet
This does not take into account the very minor loses due to friction.
More fuel to the fire.....
It is already hot from the air that it surrounds it.
You would be correct for some of the
I'm talking about the air in the engine compartment, under the hood where
the tube is surrounded by air which is well over 120 degrees.
WTF is this thing part of the space shuttle? <G>If the tube is under the
hood for a hour at at normal operating temp are you trying to tell me the
inside of the tube is cool?
And at the filter the air is slowed down.
Okay, for the sake of this mindnumbing exercise let's say it is 80 degrees
outside, you have been rideing around for 45 minutes with a/c on driving at
35-45 mph, the engine compartment is well over 120 degrees, what would you
figure the air temp is when this 80 degree air upon entery to the filter is
when it hit's the tb?
Tom your talking nothing but bs here. It is a stock truck, with stock tb,
stock cam, stock 'putor all stock. The "less restiction" means nada to it.
as does this so called "cold air". If it was a race car modified to handle a
fater mix then everything matters. But it isn't.
Answer the question. Is there or is there not heat transfer?
From experience with a bunch of hi performance cars, street and drag cars.
At the entrance of the tube, in it's box is a pretty restrictive filter,
slowing things down. Does the air somehow get sped up after it goes through
the filter? Or does the noise tell you something?
While we are at it go to a few of sites, you can buy a cai used all day
long. I wonder why? Could it be that it doesn't work all that well on a
also did a whole bunch of jet and heat range changing to handle the cold
air. So it wasn't all with the scoop and stack, which I hope you would agree
is a much better system, although not for street use, than the current cai
being offered for a truck. But since you think that 1/2 second gain is huge.
What do you think the gain would be in a stock truck with a cai?
Thinking about this does a stock putor note the change if you somehow
managed to get cooler air to the tb? I think it would require a reflash.
Also wouldn't you need a to go to a different heat range plug to accomodate
all this cold air you and miles are stuffing into the fuel/air mixture?
On a stock truck at operating temp I think I am. But if I'm wrong then you
must have one of these performance delivering, gas saveing toys on your
Are you trying to tell me that the air coming from outside the engine
compartment through the tube is the same temp as the air outside the
tube? That would only be true if the air sat still in the tube for that
hour you are talking about.
80-90 depending on the vehicle and duct used. Measure it if you feel
thats not possible.
What you are missing Roy is the rate of heat transfer. Ok, lets say
that tube sat at 120 for an hour and the inside is also 120. Now start
a constant flow of 80 degree air through it. The inside of the tube will
cool which does mean heat was transferred to the air....but only for the
first few minutes. Plastic does not conduct heat very well. It won't
be able to continue heating that air significantly.
I never said that it would give huge improvements in every truck but you
cannot validly say that no improvements would be made in any stock truck
either. And then again, there is the bling factor that to some people, is
worth every penny that these things cost.
Let me explain it then. In order for K&N or any of them to legally make
those claims, they have to have done it. They could have found that in one
model and year of truck A that they were getting a 12 HP increase (factory
filter was way too small) and in completely different truck 'B' that they
managed a 3 MPG gain (highly restrictive ducting). Now they can say that
with their product you could get up to 12 HP and up to 3 MPG gains because
they have seen it but nothing in the wording claims any specific vehicle and
in most cases, you will not get close to either one of these increases while
Probably because their HP increases did not occur with the Vette, especially
since it is a sports car and probably already has enough air flow capability
because HP is the name of the game for a car like that but for most
passenger cars and trucks, max HP at any cost is not exactly a priority for
Fair enough but for a while the group had some life in it again.
If at first you don't succeed, you're not cut out for skydiving
They make no such legally binding claims. Read the way they word it. It is
very misleading. Here is an example copied from the K&N website describing
their "High Performance Intake Kits".
"Designed to increase horsepower and acceleration by as much as 10% ..."
Even if it results in a huge power loss they are only claiming they
/designed/ it for an increase. What happens after you install it has no
bearing on this "claim". The only way you could bring legal action is if you
can prove it increases horsepower and acceleration MORE than 10%, and that
they /designed/ it for more than a 10% increase. I suspect that will never
happen. I bet K&N's lawyers suspect that will never happen either.
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