I figured someone would. Here's the deal. The rate of airflow going into the cylinders at a given RPM is a function of total intake tract restriction. For a given airflow (and thus power output) at a particular RPM, any method of achieving the total intake restriction is equivalent. So changing an air filter out for a clean one, or a lower restriction one, or none at all is compensated for by an increase in the throttle restriction (for the same power generation.) Ah!, you say, I get more power out at the same throttle position then. Exactly, you get more airflow at the same throttle position, and therefore more fuel flow, and more power. Of course, you could just press the throttle a little more with the dirty, restricted filter for the same effect. The only place this matters at all is when the throttle is all the way open, and the lower restriction filter can pass more air.

Thus, a claim of more power from a low restriction intake is probably legitimate. A claim of more fuel mileage would only be legitimate if it were achieved in the new possible range of airflow, a dubious proposition (i.e. my truck does not achieve its best mileage with the throttle floored.)

In very very very old cars, an air filter could have an effect on mileage as a restricted filter would richen the air-fuel mixture. This was mitigated long ago by referencing all the carburetor settings to the absolute pressure at the carb input (the most visible of these is the float bowl vents in the intake stream.) In a modern, closed loop controlled engine, the fuel air ratio is set by the computer, measuring exhaust by-products, mass airflow, and other engine operating parameters.

So here is a quick mental exercise summarizing the above. Imagine taking your truck around a course with a restrictive air filter. Now imagine taking your truck around the course again with a clean air filter, but making sure that the velocity and acceleration were identical at each and every point along the way. In order for this to occur, the amount of power generated by the engine would have to be the same along each point. In order for the power to be the same, the amount of air/fuel mixture going into the engine would have to be the same along each point. Thus, the combined restriction of the air filter and throttle position would be the same along each point. Since the filter is less restrictive, the throttle position would be more restrictive at each and every point (i.e. you would be giving it slightly less throttle around the course.) Since the fuel flow is dependent on the total airflow, not the pressure between the air filter and the throttle body, the fuel consumption is the same along each and every point of the course. Thus, no difference in gas consumption is possible (given the same driving style.)

So for more maximum power, a low restriction air filter can help. For better gas mileage, look elsewhere (regardless of any anecdotal evidence.)

The same situation does not hold with respect to low restriction exhaust systems. The exhaust pressure is not used as a control mechanism for the engine (like intake pressure is) so any exhaust pressure that the engine must overcome is just a pumping loss, and represents waste. Reducing exhaust restriction should increase fuel mileage. Note that I have not done this since I do not think that the payback is effective. But if you want a different exhaust sound, you might as well enjoy the mileage boost that comes with it.

 

If you did not recalibrate the speedometer, your mileage may not have suffered as much as you think. When you change to bigger diameter tires, your speedometer and odometer read low. You are traveling further than is indicated, and your actual gas mileage is better than you have calculated. Your mileage may have decreased though since you may be driving faster than you used to.

 

I agree with that entire analogy, and add this to it.

If you've been around here for any length of time, and read through posts on air filters, oil filters, and oil, you'll see testimonys both pro and con. Some say this and that helped, and others say no change. I spent the bucks on K&N for my PowerStroke, and my dad's 02 F150 SCrew with the 5.4 2valve. In both motors, fuel milage was unchanged. I even made sure not to change any driving habits for me, and my dad rarely if ever stands on the throttle. No change at all.

I've also done some thinking here, and tinkering too. The new tray filter that our 5.4s use is hardly a restrictive unit. It's a vast improvement over previous designs. What's more, is that with the goofy CAFE standards that car makers have to live up too, (which is why you are asked to use 5W 20 oil)does anyone think that Ford would actually sabotage the mileage by placing an inadequate filter in the intake if they thought that mileage could be gained otherwise? Sounds illogical to me. These filters have an engineered flow rate, and like myst pointed out, the engine uses aquired live time from a variety of inputs to manage the engine, and it's highly unlikely that air restriction is happening, or playing a performance changing role.

There are also, those who have declared that the "less restrictive filters" do not filter down the the micron levels needed for good protection. I've seen one motor personally that was destroyed at 80K because of improper filtration.

It's just like the oil stuff. If a company is willing to pay the money, a big name will say anything about their product that they want. K&N is a waste on these trucks.

Now, the 69 Mach 1, that's a completely different story.

 

Your assumptions in your post are what are called theoretic perfection in technical discussions. They do not include real world considerations. We used to get this a lot from the engineers, when I worked on design and cooling in computer hardware. They could go on forever about how this or that would not improve the cooling on a CPU. Then, when we would violate the theory, they would get very angry, explain it was impossible, and stomp out. After the product went into production, they would come back with another theory that explained the results, and say that we had originally given them the wrong input data. This overlooks that we were working from their specifications from the beginning...

My nephew who is an actual rocket scientist (very tiny rockets, he works in research for guidance/stabilization systems for geostationary satellites) says it is worse now. They listen to the scientists, nod a lot, then go try things till it works...

The flaw is in the assumptions of a perfect heat pump formula. You present the air flow/density/temperature and fuel flow/density/temperature, etc. to be considered a constant.
It is not, thus invalidating the statistical universe you are working within.

One of the flaws is that the system is not static. If you get a slight increase in boost, you need less time to reach the desired velocity, and thus need less mass to get there.

The theory that the vehicle will accelerate at the same Delta V over T is faulty. If it makes more aggregate power during the Delta V maneuver, you will use less total mass to accelerate to the desired velocity because of the decrease in T. Do the math. The main loss of fuel is in the acceleration phase, not the steady state phase as your hypothesis suggests.

It also neglects the feedback loop aspect. The system refreshes a nominal 30 cycles a second. Thus there is not a steady state analysis by the CPU of fuel/air needs. It may give the suggestion of such, to a human observer, but the actual needs/usage varies far more than the human sees.

With the increase in air available, and the built in time delay in the system to increase the fuel to air mixture, a leaner air input equals less use of fuel.

Side issue, test this for yourself. Take plastic wrap and decrease your air intake on your regular filter by 50%. You can do that in two minutes. Then drive the vehicle. Watch your readout on fuel consumption. Notice the increase.
In theory the computer will 'compensate' for this. Sorry, the system is 'less than perfect'.

These observations are supported by every study done, by manufacturers, to the Government. Even the silly Consumer Reports suggests using less restrictive airflow.

This is fun, maybe we can continue this away from the truck boards.
Do you hang out on any of the technical newsgroups? I am on a few, mostly computer, but two on more technical stuff.
I don't use IRC or any of those as my server has rather too many barriers to direct communication. And nine times out of ten I am next to the server when I get a chance to read and answer post. As you can tell from my usual lack of spell checking, or any useful formatting tools.
I hate Windows, but I think I hate Linux even more...
Chris

 

Boy, there's always some smart-aces out there with some kind of dumb comment. I don't like being told to "read threads" either or else we wouldn't be writing and asking a specific question. There's not a whole lot you can do to get a lot better mileage. I have a bone stock '04 f150 supercab 4x4, 5.4L, and I have been getting 18-20 mpg consistently lately. I have 5700 miles on it, I broke it in properly, I don't get into the gas pedal very often, and I still don't drive like a grandma either. You can get aftermarket exhaust system and expect 1-2 mpg increase, and maybe get another 1 mpg from an Airraid system or something. Other than that, I hate to tell you, but the only way to get better mileage is to stay off the pedal so hard. We don't always have to go 0-45 in just a couple of seconds, and once I realized that and the fact that gas prices will not be dropping any time soon, I slowed my roll down to the speed limit mostly. It works! I was getting 15-17 mpg tops consistently before, and now that I drive an easy 55 mph most places except the interstate, I get 18 or better consistently on a stock truck with no mods whatsoever.

 

Man I'm in over my head now!!!
I love to read a good techinical discussion though, especially one about the best trucks ever made!!

BTW,
My speedo read high with the 17" wheels, and just about right with the 18" wheels (per GPS). I do realize this contributes to the MPG "difference". No need for blueprints or schematics, I think I have a handle on the big wheel little wheel concept. I just wish I could find some 13" low profile tires on 6 hole rims, I'd get 30 MPG!!!

 

That's the problem with the real world, too many ignored considerations for a good understanding. Someone makes a change, like an air filter, and measures the results, which change, and comes to a conclusion, ignoring everything else that changed like driving a completely different route under different conditions, different loading, different atmospheric conditions, even different vehicles. But they have experienced it for themselves, so it must be true. I saw a great example of this on Mythbusters when they tried to figure out if running with their air conditioner on or with the windows down was better for mileage. Unbelieveably poor experimental setups.

The basic gist of my argument seems to have not been clear. None of the conditions you mention are at all effected by whether the throttling is done at the throttle body, or at the air filter. No more air is available unless you are exceeding the airflow potential of the original setup (i.e. punching it.)

Unfortunately, it would take a lot more than 2 minutes to figure out if gas mileage was influenced by the test you propose. A person would have to set up instumented runs of steady state and acceleration conditions at various vehicle speeds and carefully chart the results. It's pretty difficult to construct experiments that compare apples to apples. Casual observations are what lead to the wildfire spread of urban myths.

One thing I am very confident of is that if changing to a bigger, less restrictive air filter consistantly made a 2mpg difference in fuel consumption on these trucks, Ford would have put it in.

 

You were kind of making sense up till this comment

 

It may not regularly show, but sometimes I'm an optimist.

 

2004 Supercrew 5.4l/3.73 ratio. When new was getting 15.5 - 16.0 mpg. after Magnaflow SISO exaust, airaid intake, Superchips tuner, Soft tonneau cover getting 16.5 - 17 mpg. never do more than 65 on highway which is 70% of my driving. Was getting better mileage after exaust install and then lost .5 mpg after airaid install which was my last mod.

 

If they did put a low restriction filter in, then there would be a whole lot of people beating down the dealership's doors for repairs due to the "excessive intake noise." In addition, there would be 600 threads on this website talking about the newest intake system that's "6db quieter" than all the other ones...It's not just fuel economy that the manufacturers have to contend with...it's also NVH, reliability, and the all important planned life cycle for parts breakdowns. You have to remember, that most people want their truck to act, sound, and drive like a luxury car...

 

Just figured my MPG...I got 11.9 all city driving...not to happy with that. It only has 500 miles on it though so I hope it will improve. It has the airaid intake, dual exhaust, and retrax. This was all city driving...Never getting above 2K rpm and no jack rabbit starts. Is this the avg. for such few miles and can I expect it to increase the more the engine gets broken in?

Thanks,

Brian

 

That sums that argument up nicely. Also, the air filters that are used are good off road, long duration no maintenance, and on dusty job sites. I wouldn't recommend the K&N there, unless ponies are more important than longevity.


And Myst two things wrong here, at least, in your quote;
First, it is a straw dog argument. Nobody, but nobody said anything about 2 mpg. On my light truck with the improved exhaust, tuner, etc. it gave me on the close order of .5 mpg. This is on my lighter truck. I know how to drive for mileage, and I understand flashpoints, free-wheeling, vacuum draw, etc. This is probably on the high side of actual improvement.

Second argument, is cost over return. There are a dozen ways these trucks could get slightly better mileage. They all return less bottom line to the Ford Motor Company.
Thus they are not used.

Example, putting lower gears in the rear, but adding a higher gear on top. You could increase the mileage by at least three miles per gallon. And you could not recoup the costs in sales, thus giving less return to the manufacturer.

That is how all manufacturing is done. It's always a cost vs. return basis.
You analyze the market, then build the unit that returns the best margin for the least cost.

A good example, if you made more money from attacking the other maker rather than promoting your make, you would do that.
See political commercials for an easy example. Without a doubt, there is more 'return' in an attack ad than in a self promotion ad. This is known/proven/accepted.

Fortunately this doesn’t yet apply to car ads. Yet.

CAFE is not relevant, as ALL trucks in this category get about the same miles per gallon...thus no competition. Now one or two years from now that might vary. I doubt it.
If you want miles per gallon, you don't buy a big truck.
Also, in the same principle as the attack ad, there is the fleet loophole.
If you have a selection of vehicles that you want to sell, and you want to increase the Corporate Average Fuel Efficiency, you don't have to improve your miles per gallon on a given truck, you just have to sell a percentage of vehicles that get good mileage.
Example;
Go to a Cadillac dealership. Notice they sell little imports badged as Cadillacs. Wonder why? Because when they sell an Opal, or whatever, as a 'Caddy' the CAFE for the manufacturer goes up. Biggest loophole in the law. There are others.
Your turn.
Chris

 

RUNNERBL,

Let that truck get about 3000-4000 miles on it and you'll start to see increases in fuel mileage. Be easy on it for a while, like it sounds like you are already. If you keep it below 2k rpm's most of the time, you'll start getting great mileage after the engine is more broken in. If you drive so much in the city, go on the freeway once in a while and let it run down the road for 10+ miles without having to slow down or stop, like once or twice a week, and it will help to level your mileage out also. It just needs to do something besides constant stop and go.

 

Whole bunch of common sense in that post Myst.
Couple of things- The torque converter locks right away with the cruise on. Regular driving and it will lock at about 45 mph, but with cruise on at 40 it locks.
This is going to **** people off, but I would'nt put a K&N (or any other oiled gauze) filter on my truck on a bet.
-Given equal surface are most filters gain airflow only by sacrificing efficiency. Through personnal experience with oiled gauze (motorcycle and heavy equipment) I found they Don't work well (enough). I am not alone. Do a web search and you should find some studies conducted in the field a few years back. If I remember right using them voided the warranty on some equipment. I believe there are also lab studies (SAE?) indicating the same.
-Even if they do provide a little better airflow (they might), this wouldn't impprove fuel milage. These are electroniclly injected motors and compensate for airflow. They probably don't even care how far the throttle plate is open, only the amount of air coming in and the percentage of oxygen going out. Changing the filter ,all other things being equal, will have no effect. It is possible that some filters could change airflow (not volume) in such a way so as to alter the airflow readings that the engine recieves, but I doubt it.
LOL- While pecking this out, I went back to the thread and saw that there is already a bunch debate on the same. Oh well, I'm too lazy too start over