So I recently did some research on cold air intakes for my Dodge Dakota, and was pretty let down by the products that were available, what they actually seemed to do in comparison to the stock air intake, and how much they cost for how little they were. I got to thinking about a great alternative design for a cold air intake system that would beat the current aftermarket systems, but I wanted to get a bit more information first. My questions are pretty general, and not really dodge Dakota specific, but I'd appreciate some help.

On the airaid design, the cold air intake doesn't appear to be placed anywhere that would actually decrease the temperature of the air received, infact it's right above one of the exhaust manifolds, probably resulting in higher temperatures over the stock intake that takes air from closer to the wheel well. It does however claim to deliver increases in horsepower, which from what I can tell, is the result of increased air flow, espescially since the stock air intake takes a 90 degree turn at the end, that dead ends right into one of the quarter panels..

My questions are:

-How do air flow and actual air temperature affect engine performance?
-Will high airflow with a higher temperature outperform lower airflow with a lower temperature?


I'm interested to see what everyone has to say about these two factors, and how the balance between the two would work out. If airflow outweighs air temperature, then the design I have in mind just may not outperform the airaid intake design without some alteration, although it will surely surpass the stock intake.


Oh and another quick and easy question... why not just remove the plastic piece leaving the stock air intake, and get a sawsall and just open up the stock air intake box a bit more? That will vastly improve airflow that the engine can receive, along with reduce the amount of 90 degree turns.

 

i have the airaid cai in my truck. it gives me a little more power than the stock but i love the sound it makes when you punch the gas. my gas mileage has gotten a little better almost 1 mpg. it mounts into the stock box where the air filter is and has a heat shield. i think it is the best for the money.

 

Are we not thinking of the same airaid one? It's this one below correct?



The airaid one I've seen goes right above the intake, removes the stock box, and is just a big old filter in the middle of the engine bay. Airaid's design undeniably improves airflow, as it reduces the amount of turns the air has to take in the intake, and also allows for puling in more air. While the tubing is sort of shielded...it's still pulling air form inside of the motor bay, like the stock intake.

Hence my questions.

I like the look of the CAI you have though, and I am quite familiar with the sound those intakes make, which is quite nice. I just can't seem to stomache the $220 price for... a short piece of aluminum tubing and a big old air filter that K+N sells for $60.

 

for the first question, cooler air is denser, so with denser air entering the engine means more fuel is injected into the cylinders which creates more horsepower, and the flow of air through the system determines the resistance, example: a simple straight intake tube with no bends has little to no air restriction where as a system with sharp bends will cause a an air restriction, sort of a reverse back pressure, where on an an exhaust system, the more bends in the pipe the more back pressure you create, straighter the pipe less back pressure... for your second question... IMO, high airflow w/ a higher temprature is better since the air flow can pass through the intake system quickly versus the lower airflow lower temprature. with the lower/lower, in my theory, the air will heat up quicker since it will take more time to pass through the hot intake ducts of the engine, warming up the air, also a more restrict intake system requires more vaccum pull in that cylinder, causing more strain on the motor, not the kind of strain to harm it, just to rob maybe 1hp... i hope this makes sense

 

owns,
you are asking the right questions

Page 415 of the Bosch Automotive Handbook, 5th edition

http://tinyurl.com/yplr3d

has the two equations you need
to see how horsepower and torque change
when either temperature or pressure change.

For temperature the offical equation
used by Americans (SAE) Europeans (ISO) and Japanese (JIN)
is:

{ Temperature Before + 460/Temperature After +460} raised to 0.6 power

you need a scientific calculator to do this
but there is one built into every Windows computer
under Start...All Programs....Accessories

As an example,
say that your re-locate your air inlet to a spot where the air temperature
drops to 80 degrees
when before the air coming in had been 100 degrees.

{100 +460 divided by 80 + 460} raised to exponent 0.6

={560/540} raised to exponent 0.6

= {1.037} raised to exponent 0.6

= 1.022

You mulitply this number times your horsepower or torque
so if your engine.
If your engine makes 230 hp at peak
1.022 times 230 = 235 horsepower with the 20 degree lower air temperature.

You may have heard the 'Rule of Thumb' that each 10 degree F reduction in air temperature improves horsepower by 'about' 1% and the equation above is where that comes from, but is more accurate. The rule of thumb gives inaccurate estimates when the temperature changes a lot.

For corrections when the pressure changes
the following equation is used:

{absolute pressure after/absolute pressure before} raised to exponent 1.2

As an example
say that the weather is changing where you live
and one day the weatherman says the pressure is
29.5 inches of Mercury as a stormy "Low" passes over
then the next day a clear sky "High Pressure Area" passes over
and the pressure rises to 30 inches of Mercury

{30/29.5} raised to exponent 1.2
{1.0169} raised to exponent 1.2
= 1.0204

It is important to realize
that built right into your engine
are IAT (intake air temperature)
and MAP (manifold air pressure)
sensors.

Your IAT and MAP sensor outputs can tell you whether an aftermarket air intake has helped or hurt your power output. You can read these sensors
yourself by using an OBD-II scanner, or a cheap electrical multimeter.

You are correct to suspect that most CAI's
only make more noise and have flashy colored parts.

Want confirmation about this from a CAI manufacturer?

Well right now KN Filters is running an advertisement in the various hot rod magazine saying that a typical paper air filter from the factory creates a restriction of about 2.8 inches of water....and when this filter gets really dirty the restriction rises to about 12 inches of water restriction. The KN advertisement has a dyno graph showing that this can cause about 11 hp power loss on a high horsepower engine.

The pressure of the air around us is about 404 inches of water
so KN Filter Company is saying that the pressure is changing from
404 - 2.8 = 401.2
to a new pressure of
404 - 12 = 392 inches of water

Play around with the equations above
and you can find out what the actual horsepower of the engine KN was using was....and then confirm it by looking at the dyno graph in the advertisement.

 

The Airaid is worth every penny......but on the note if you are having issues about cost of some simple upgrades you should not be worried about having a truck and go get a neon and be done with it.....next will be the cost of gas vs mpg and it just goes down hill from there

 

I'm quite fine with the cost, I just don't like shelling out so much money for what seems like an inferior design. The airaid design simply removes a few turns, and has a wider air path, thus increasing airflow, or decreasing restriction. At the same time it increases air temperature since it's still pulling from right inside of the engine bay. Yes it's shielded, but it's still pulling air from directly inside of the motor bay. Airaid also makes those fake throttle body spacers that don't do anything and are completely bogus on the dakota motors... so I don't have much faith in them.


This part interestes me a whole lot:

"Your IAT and MAP sensor outputs can tell you whether an aftermarket air intake has helped or hurt your power output. You can read these sensors yourself by using an OBD-II scanner, or a cheap electrical multimeter."

I'm an electrician and sound system technician, so getting in there with a multimeter doesn't scare me in the least bit. OBD2 readers are relatively affordable as well though. Could you get me some more information about what I'd be doing with either the multimeter or OBD2?



The design I have in mind for an air intake would surely surpass an aftermarket intake right now for temperature acheived. The real question however, is how would it influence restriction, in comparison to the airaid designs. I've got two designs in mind, one of which goes directly from the stock box to the outside of the motor bay, via a short S curve. The other design would be more akin to the current cold air intakes, only it would place a large cone filter a bit more outside of the motor bay.

I'll try both when I can get some help designing this stuff, and bring some real world numbers back here. I'm going to apply for a patent first though if I get some really good results. I'm surprised no one else has attempted this design. It just seems so sensible.

 

With a multimeter
most times what you want to do when the engine is running
is splice into a sensor output wire
and read the milliamps flowing.
Then use Ohm's Law to convert to the resistance the sensor is providing.

The Dodge Field Service Manual (FSM) has tables showing the IAT resistance (it is a thermistor).

The MAP sensor can be read with the key on but ignition off.
This engine off pressure will be the barometric pressure that the weatherman also gives for that day...typically around
30 inches Hg
or 1018 millibars
or 404 inches of water.

The OBD-II scanners do all this conversion for you so once you start using one you get addicted.
Good scanners to look at are the Scangauge, or cheapest is the CarChip.

When thinking of the air flow of your intake
don't think of it as a gently flowing stream of water.

It is more like the air flow out of a machine gun barrel behind the bullets.

The 8 cylinders are creating big pulses each time the intake valve opens.

This is why there is so much noise
on an aftermarket air intake
when they do away with the engineering to silence the noise.

 

Very well said! I've never quite heard the comparison, but it makes sense.

I ran into a nice guy who owns a machine shop today at an event where I was providing sound reinforcement. I explained my theory to him, and he gave me his number to call him sometime. I'm going to try and fashion something, and see what kind of results I get. I'll also look into those OBD2 scanners you mentioned. I believe my dad recently purchased a OBD2 to usb converter, and a program that works with a laptop. Do you know anything about this?

 

I believe there are programs and cables
to use both laptops and PDA's
to read OBD-II data

http://www.bowserelectronics.com/

http://www.obd-2.com/

http://www.autotap.com/product.asp?sku=AutoGuide

In Sears stores, they usually have in stock a 'CarChip'
unit for about $100 that records data for awhile
then you remove it and read the data with a laptop.