Hi... if the post looks familiar I've posted it a another forum.

I've done quite a bit of reading on the CAI issue of whether or not after market kits make a difference. It sounds like there are believers and non believers. (Seems like some are quite passionate about the topic).

One line of reasoning has been bothering me and I would like to run it by the group. Without starting a long drawn out argument, does anyone have any thoughts on the following logic?

Is it safe to say that a dirty stock air filter will affect gas mileage in a negative way? If so, what causes it? Less flow, less efficiency? Does installing a clean filter improve the situation? i.e. more mileage.

If the above is true, then doesn't it make sense that a change from the stock intake system to a more efficient intake system is much like "cleaning" an air filter? i.e improving flow etc? If so, shouldn't it result in an improvement in HP and or gas mileage?

Some of the arguments against the effects of an aftermarket intake system seem to imply that the MAF and computer take care of "whatever" air flow is produced regardless of the filter/system. If this is true, why should anyone bother cleaning their airfilter?

Thanks...

2001 F-150 SuperCrew 4x4
5.4

 

Good question... I've been thinking of posting the same question. Along with the MAF, the O2 sensors job is to keep the air/fuel mixture the same all the time.

My thoughts are... if going 60 mph down the highway with a dirty air filter, your throttle opening might be 20%. Now put a new K&N filter in there and at 60mph you migh have 15% throttle opening (just using those throttle opening numbers to show a point, I have no idea what they typically would be). So, at 60mph, the same amount of air is going to the engine and the propper fuel is being added to that air to produce the horse power to go 60mph. In other words, you restrict the air flow with the air cleaner and intake as well as you do with the throttle plate.

My opinion is this and feel free to flame me on this, it is only an opinion. A new air cleaner or a free flowing K&N will NOT give you better mileage. It can't because the truck is going to add the propper fuel to get you to the perfect mixture (there's a name for this). But... a K&N will allow more air to enter you engine at wide open throttle at which point the truck will add more fuel to compensate giving you more horse power.

Let's hear it boys !

 

I would present this fact. The stock air intake has improper bends and is very restrictive, so the engine has to work harder to breathe and pull the air in. On an aftermarket CAI, typically it is alot more free flowing, less restriction. The engine may or may not take in more air (not sure if pcm adjusts accordingly), but it is definately taking air in easier, breathing more free. An abstract example: take a straw and suck in on it. You breathe in ok. Take same straw and bend it in a few places. Takes alot more energy for you to breathe in same amount of air (you get winded). This results in more power going to drivetrain, it's not using so much to breathe. But we also have tuners to allow more air to enter The stock intake is a restrictive design, and my guess simply enough is that anything over the stock system would allow more air in, regardless of what the pcm "wants". Hope this helps?

 

Jester...thanks for the reply.

Do you know if the throttle open is directly proportionally to the amount of Air Flow. Example: More Flow = Less Opening. Does the MAF also affect the amount of time the throttle is open? or is it directly dependent on the gas pedal, cruise control etc?

 

Swap the intake with a good aftermarket set up - your going to gain on an average about 4 HP - maybe more depending on the exhaust. .

Your always in control of the throttle body (Throttle Plate) in the 97 - 03 models. The stock intake runs thru a 2" silencer for the most part.

Keep the stock filter housed in the cold air return and upgrade the intake pipe - Look at "AIR FX" . There cheaper and you can get the kits that use your stock Filter set up - IMO - best kit out there - they make a killer filter as -well..

All these truck can use better flow over stock as well an upgraded exhaust - That combination works well with each other = better performance and economy .

They need to breath..


Any Time you change up the air flow - or replace something that is air metering - You need to reboot your computer to take advantage of it.

 

Gingo,
Your throttle plate/throttle opening is as jbrew states, connected to your gas peddle.

jbrew,
Follow me on this.... I'm courious as to what your reply is.
Say I have a dirty air filter on a stock intake system. I drive 60mph and have the ability to see that my throttle opening is 20%. Now I put on a new CAI, and a better air filter or even a clean stock air filter. I agree with you, the new filter and intake will be less restrictive. So... I go 60mph again, I would see that the throttle opening is less than 60%. This is because I moved the air restriction from the intake to the throttle plate itself.

Different way to say this... if instead of going 60mph with the new intake and filter, let's say I put my throttle and 20%. More air in the engine is good. But it would be lean if the computer didn't add more fuel to it ( you said i had to reboot the system for it to learn again). Now with more air and fuel at 20% throttle opening, I will be doing over 60mph.

I'm convinced that the better intakes and air cleaners allow more air in the motor allowing more peak horse power. I'm not convinced that I gain mileage because the truck computer is going to keep the air/fuel mixture a constant.

Gingo,
I hope you don't think I'm stealing this thread. I think I'm helping you by asking more questions on the subject.

 

Woops... the "60%" in the above post should be 20%. I don't know how to edit and fix that.

Here is something on fuel mixtures I grabbed from Wikipedia: The part in bold is what I'm talking about when i say the truck compensates for the increase in intake air.

Air-fuel ratio (AFR) is the mass ratio of air to fuel present during combustion. When all the fuel is combined with all the free oxygen, typically within a vehicle's combustion chamber, the mixture is chemically balanced and this AFR is called the stoichiometric mixture (often abbreviated to stoich). AFR is an important measure for anti-pollution and performance tuning reasons. Lambda (λ) is an alternative way to represent AFR.

A mixture is the working point that modern engine management systems employing fuel injection attempt to achieve in light load cruise situations. For gasoline fuel, the stoichiometric air/fuel mixture is approximately 14.7 times the mass of air to fuel. Any mixture less than 14.7 to 1 is considered to be a rich mixture, any more than 14.7 to 1 is a lean mixture - given perfect (ideal) "test" fuel (gasoline consisting of solely n-heptane and iso-octane). In reality, most fuels consist of a combination of heptane, octane, a handful of other alkanes, plus additives including detergents, and possibly oxygenators such as MTBE (Methyl tertiary-butyl ether) or ethanol/methanol. These compounds all alter the stoichiometric ratio, with most of the additives pushing the ratio downward (oxygenators bring extra oxygen to the combustion event in liquid form that is released at time of combustions; for MTBE-laden fuel, a stoichiometric ratio can be as low as 14.1:1). Vehicles using an oxygen sensor(s) or other feedback-loop to control fuel to air ratios (usually by controlling fuel volume) will usually compensate automatically for this change in the fuel's stoichiometric rate by measuring the exhaust gas composition, while vehicles without such controls (such as most motorcycles, and cars predating the mid-1970's) may have difficulties running certain boutique blends of fuels (esp. winter fuels used in some areas) and may need to be rejetted (or otherwise have the fueling ratios altered) to compensate for special boutique fuel mixes. Vehicle manufacturers do not provide a means of altering predefined fuel maps making such alterations impossible without replacing the stock ECU with a customizable system. Vehicles using oxygen sensors enable the air-fuel ratio to be monitored by means of an air fuel ratio meter.

 

I'm not sure what your trying to figure out - Maybe just an understanding.

Anyway,

Dirty Filter - Computer will adjust on its own - Keep in mind you have programed parameters (tolerances) - With a dirty filter - The computer works the motor harder to pic up the slack.

This continue as long as your inbetween margins - Once you fall out side of parameters a MIL will appear (Check Engine Light will illuminate) and store code.

Then , of course , scan and service.

 

Thanks for the good responses.

What I was trying to figure out is effect of more/better air flow on the engine and what is the "real" effect of a CAI intake kit like an Outlaw or K&N etc.

As JBrew mentioned a dirty filter "works motor harder to pic up the slack".
If this is true, shouldn't an after market intake kit that allows more/better flow make the engine work less than a stock system?

The logic seams sound.

Thanks Again,

 

only to a certain extent because your enginie wants to keep an air/fuel ratio of about 14.7:1. So your computer will compensate by opening the injectors a little longer than it would with the same throttle position with a different intake. The thing that the intake will do is run your truck on the leaner side, say into the 15.x:1 which is giving better mileage but your computer may and probably will eventually learn and compensate for it by opening the injectors longer and you are right back where you started

 

And I would put in my .02..

As someone using an aftermarket intake I've noticed no increase in my mpg. No decrease either. I have experienced noticeably better throttle response at mid to high rpm..