Its a juggling session, no doubt of that. CAI also helps by being less restrictive than most stock intake systems. If your engine builds more power faster (lower in the RPM range.) you do indeed use less gas. What you are doing there is increasing the efficiency of the motor. More bang for the buck, as it were..... so you are getting more power from the gas you do burn. Thus, better fuel economy.

That said, here, you are working with a heavy friggin' truck. It isn't ever going to rival any car in the fuel economy department. If you can average 15 MPG or so, consider yourself fortunate.

 

I get 8 in the city, but I think that's due to my 2 mile drives, 33" tires with 3.55 gear ratio, 500 pound toolbox, and heavy foot.

 

That's the primary mechanism right there. Intake restriction is a parasitic loss, forcing the engine to expend energy to overcome the restriction. (Try running a mile breathing through a dive snorkel.)

 

To heyyou and unregistered user..... I no the more restrictive the intake is the worse mpg and response will be but if cold air doesn't help then wouldn't a 14x3 be the best thing since it would pull the most air and it would be warm air? Not being a smartass this is a serious curiosity...

 

That's my theory on the 14x3 and one of the reasons why I run one.

I have witnessed a tuner get a f150 3 mpg but it didn't have much to do with the tune, 90% was the driver. The tuner is a bullydog, it has a setting where you put in your desired fuel economy and it has a status bar that gives you feedback on your driving to help coach you to the fuel economy you set. Obviously it only works if you set it at a obtainable MPG but if used correctly its a great tool for training yourself to drive as efficiently as possible.

Its about time for tires, I have 275s now, when I replace them I will go with something skinnier. A e-fan will be after that.

 

Whether the air enters the throttle body as a laminar flow or a turbulent mess is also important, but fluid dynamics is a big subject so I'll summarize rather than writing a stinking treatise on the subject.

Once upon a time when big-inch street machines were more common, the hot ticket was the tunnel ram intake -- that tall dude that stuck up out of a hole cut in the hood, with one or two carburetors parked on top. All other things being equal, the tunnel ram made more gross horsepower than the same setup on a low-rise manifold. This was common knowledge way back then, but in these days of fuel injection and so on I suspect it might not be. So, gosh, same engine, same carb(s), same RPM, same quantity of air in the same time, same amount of fuel delivered, same everything except the length of the run from the venturis to the intake ports of the heads. So why more horsepower?

Laminar air flow. In a nutshell, anyway.

On the drag strip or any other time a guy wanted to squeeze every last bit of power out, instead of just removing the air cleaner and tossing it aside he'd stuff on velocity stacks. Again, same engine, same everything, but more power than running with nothing at all. Again, thanks to laminar air flow.

A CAI with a nice long tube will always provide more laminar air flow than will an open element 14x3 living in a turbulent environment and bringing all of that turbulence very close to the throttle body. But fluid dynamics is something I'm trying to avoid talking about...

This stuff gets downright tricky if you keep on going until you've got your head fully wrapped around it all. If you don't really care to grok fluid dynamics and become intimately familiar with the Richardson number, don't sweat it. We're not operating at the margins where piddly little 5h17 like this is going to make a big difference -- for us, CAI vs. 14x3 is a holy war rather than an intellectual debate. Just put whatever air intake on your truck you think is somehow the coolest and be happy because it ain't all that important.

But if you're going to be doing stream crossing or mud playing you'll be better off with a CAI and a filter sock (K&N calls 'em "dry chargers") to keep the water outside where it belongs. Other than that, run what ya like and be happy.

All ya really need on a NA gasser is a vacuum gauge. Drive to keep the needle high and you'll get better fuel economy.

 

I dont think you misspoke.... better to add to this thread than start another mpg thread... there's likely 500 MPG threads here all with close to the same info in them already....(if only the search option allowed 3 letter searches without using google...)
Regardless of what it comes down to on paper things like weaker winter blend gas and running rich during longer warm up times generally cause the gas mileage to suffer in the winter....I have a company Camry and the leasing company keeps very strict records tied to my gas card showing bar graphs for MPG and such and it does dip in the winter....
and as far as cali goes its practically its own country with its own added restrictions to everything...with us in new york being second... cali has different emissions laws different vehicles and likely modified gas because of it.... And I've never been but isnt it hilly? that would certainly add to gas consumption..

 

I'm not a ninja, nor a cagey old dude.. but I'll offer this:

the 14x3 DOES breath better than a CAI.. the restriction with a 14x3 is the filter, which are most often paper.. get a cloth one? it will out perform the CAI.. the problem with CAI's, is they aren't true CAI but instead a bunch of marketing.. if they were marketed 'LRI' for less restrictive intakes, well, that would be more accurate..

the thing about your cold air: it's not that it's 'cold', exactly.. it's that it's denser, aka MORE air.. more air means more ponies.. more air needs more fuel.. you get a bump in power with a true CAI, but you use a matching increase in fuel to feed it..

RPM's are directly related to overall gear ratio.. that is a science that can't be argued.. for instance, @ 1900RPM, through the 46RE, through the 4.56:1 ratio rear end ratio, and over 35" skins, I'm running just over 60MPH.. If I want to see 60MPH, that is the RPM range the truck will be in.. the exception to this is coasting, or a loaded engine.. the trick to fuel economy is UNLOADING the engine and only using as little go foot as you need to get the job at hand done..

that is the crux of it all.. if your engine is tuned correctly, and you've eliminated, within reason, the restrictions/burdens, there is no reason these trucks can't get 13~15MPG..

 

Paper is more restrictive but with the amount of area you have a 14x3 IMO a paper filter is the way to go. Changed every oil change for $2.99 it takes a while for a cloth filter to be cheaper after buying the filter and cleaning kit and your not getting a better filter with the cloth.

I drive dirt roads often, I'll stick with the paper filter changed at every oil change. The cloth filters just don't keep as much dirt out.

I've calculated mine at 16 driving mostly highway with a refrigerator in the bed.

 

Just a clarification since it's implied in your post that the engine runs richer to generate combustion heat, although your conclusion is right on.

Richer mixtures burn cooler than lean mixtures ... unburnt gas has a cooling effect while fully burned gas generates more heat energy (you exploit all the energy available in the fuel).

There will be a rich A/F ratio, but not to generate heat. Cold fuel resists atomization ... instead of evenly mixing with air it tends to drop out into droplets which can not burn ... gasoline only burns in a very narrow range of fully atomized A/F ratios. The ECM will therefore increase fuel to compensate for the fuel that falls out of suspension and will not burn.

Since a computer-controlled FI engine adjusts idle speed in steps from cold start to warm idle, RPMs can be higher than necessary at closed throttle cruise, waiting at stop lights, etc.

Higher RPM tends to improve atomization (via increased intake velocity), so both will be used during cold engine operation. The catalytic converter needs to work at a certain minimum temperature so much of the ECM actions that improve fuel economy won't be available until the engine is fully warmed up and the ECM can use all it's available engine management options.

No catalytic converter is 100% efficient when operating under ideal conditions; when it is too cool it is much worse. Unburned fuel tends to clog the cat so prolonged operation under this condition leads to premature cat failure.

Although 180F is probably warm enough to properly atomize fuel, the needs of the catalytic converter are part of the ECM's map. So, the ECM may be mapped in such a way to work to get the engine warmer while the 180F thermostat prevents it.

This can result in a rich A/F mixture going into the combustion chamber, a lean burn condition within it, and unburnt fuel in the exhaust at the same time.

You are literally paying to throw perfectly good gas out the tailpipe to perform the job of degrading the catalytic converter.

Unburnt fuel also has the tendency to wet the cylinder walls and dilute the engine oil since fuel can pass the oil control ring on the piston. This results in increased cylinder wear and requires more frequent oil changes. In severe cases (mercifully, something that is more common on carbureted engines with a manual choke, not a FI engine) oil dilution causes premature main bearing failure due to an inability to maintain a high pressure oil film.

Because a forum like this one has members from all kinds of operating environments, it's possible for some drivers to benefit from a 180F thermostat ... say, if they drive in Death Valley and the earlier opening helps cooling but the water temp still climbs to 195 or higher. But for most drivers it's not going to be an advantage for MPG.