flyingtoaster

You can use the ideal gas law to figure out the differences in air density, which corresponds to power.

Croc

do you mind to explain in a few words?

not only i would appreciate but i think it would be worthwile for "future generations" to have all info in one thread.

flyingtoaster

density = (pressure) / (R x Temperature)

R (specific gas constant) = 287.058 J/(kg·K)
Temperature (Kelvin) = degrees in Celcius + 273
Pressure at sea level = 101325 Pa

I have no idea what a good intake air temperature would be, but let's say we have a car with a ram air intake on a cold day. By the time the air reaches the intake manifold, it has warmed to 34 degrees C. If we follow the equation, the density is 1.15 kg per cubic meter. Now let's say we have an S2000 with a stock intake. Once the engine heats up, the intake air temperature stabilizes to around 60 C. With the equation, we have a density of 1.06 kg per cubic meter. If we install a ram air intake in my theoretical situation, we would gain 7.8% more density and therefore more fuel once the ECU catches up. With an 06+, this doesn't take long.

Croc

thx for this!!!

let's sum what do we have until now:

1. free flow intake - still no convincing explanation how it alters AFR
2. free flow exhaust - same
3. free flow intake/CAI lowers intake air temp thus increasing density of air thus bringing more oxygen particles thus alters AFR - but stock ECU adds fuel and corrects it

so - this is still open - why AFR changes?

i asume that it changes indeed as we do see reports from the owners that see their AFR changed after intake/exhaust mods.

flyingtoaster

Cars built for fuel economy have small diameter exhausts because they are meant to cruise at a certain low RPM. If their exhausts were a little narrower, their engines would have to work harder to push air through the small pipe due to too much back pressure. If their exhausts had a larger diameter, the engines would have to work harder to push out the large volume of air hanging out in the exhaust pipe. Nascar engines are designed to work at a certain high RPM, so they have large diameter exhausts that don't work well at low RPM. The best intake and exhaust would have small diameters at low RPM and large diameters at high rpm. Look up dual runner intake manifolds.

Croc

this good inside.

how it relates to AFR?

Croc

OK - we're bunch of amateurs got stuck here.

Professionals, come to help!!!

Billman and other, where are you?

H22toF20

So much misinformation in this thread and way to much to try to explain. Get a better understanding of how a motor works, then come back; 4 stroke cycle, valve timing/overlap, intake manifolds, exhaust manifolds.

But to answer a few of your questions, 99% of factory motors don't make it even close to 100% Volumetric Efficiency(VE). VE in lamest terms, is how full the cylinder is with air(in relation to ambient air). So naturally, switching intakes, exhausts ect will yield an increase in VE. This is only half of the equation though. To understand the other half, you need to know how a motor really works. The real question is "How do you get over 100% VE?".

Croc

now it looks like we're getting there......
don't be so hard on me - not everyone spent 4 years studying mechanical engineering and internal combustion engines...
this why i ask experts.

as to you last questions - IMO only FI.

punchdrunk

What is your point though

Do you need this info for a school project or something like that.