[Nagakilo]

So in the past I've found myself wondering how I can get the best mileage out of my mustang, so I’ve asked around the forums and did a little research myself. Well the other day I realized that there is a Fuel Economy section of the forums, so I stumbled my way on in to see if there was a guide like what I’m about to write up and there was not one. So I decided to write one up. Note that this is a simple guide, I am not getting into the science of any of this (As if I would even understand what I was saying if I tried) but just simply stating how to get your best economy. A good chunk of it is just me consolidating information from other places into one place.
Driving Habits
Uncle Sam says save fuel, so let’s just take his word for it that he knows what he’s talking about
Drive Sensibly
Aggressive driving (speeding, rapid acceleration and braking) wastes gas. It can lower your gas mileage by 33 percent at highway speeds and by 5 percent around town. Sensible driving is also safer for you and others, so you may save more than gas money.
Observe the Speed Limit
While each vehicle reaches its optimal fuel economy at a different speed (or range of speeds), gas mileage usually decreases rapidly at speeds above 60 mph.
You can assume that each 5 mph you drive over 60 mph is like paying an additional $0.24 per gallon for gas.
Observing the speed limit is also safer.
Fuel Economy Benefit:

7-23%

Equivalent Gasoline Savings:

$0.17-$0.56/gallon

Remove Excess Weight
Avoid keeping unnecessary items in your vehicle, especially heavy ones. An extra 100 pounds in your vehicle could reduce your MPG by up to 2 percent. The reduction is based on the percentage of extra weight relative to the vehicle's weight and affects smaller vehicles more than larger ones.
Fuel Economy Benefit:

1-2%/100 lbs

Equivalent Gasoline Savings:

$0.02-$0.05/gallon

Avoid Excessive Idling
Idling gets 0 miles per gallon. Cars with larger engines typically waste more gas at idle than do cars with smaller engines.

Use Cruise Control
Using cruise control on the highway helps you maintain a constant speed and, in most cases, will save gas.

Use Overdrive Gears
When you use overdrive gearing, your car's engine speed goes down. This saves gas and reduces engine wear.

[Nagakilo]

It's my bed time, so tommorow I'll add in the fun stuff about air intakes, exhaust, and the other bolt's ons that give your more MPG. I'll be editing this post for that just to make it easier on the eyes.

[Nagakilo]

And now for my favorite part of owning a mustang, customizing it! Beleive it or not that GT rumbling by you that sounds like a beast on wheels may actually get better gas mileage than your V6 does. It's kinda fun how some of these modifications go.

Exhaust

The exhaust system is a great way to get better mpg. From a simple muffler swap, to a full on high flow dual exhaust kit, you can net anywhere from 1-2 mpg. Most muffler companies advertise how much power you gain, but on the vehicles I've done an exhaust mod to I've noticed about a 5% gain in mpg. Don't forget about the headers! While there is the big debate about long tubes vs short tubes, either way you go as long as you don't "Enjoy" your new found power too much you'll still find a 2-3% gain in mileage.

Intake

Now in life you have to be just as concerned about what goes into the body as what comes out, and while exhaust can help your mpg's a fair amount, your intake can really get you going well. Adding a cold air intake, a ram air, or any other induction system (No sorry a turbo/supercharger doesn't count though we can all dream of a supercharger that improves our mileage) helps the engine breath better and thus gets more out of it. I've seen companies claim an upwards of 10% increase in MPG for a Cold Air Intake system, but realistically that rarely holds true. Personally with the mods I have (See forum signature) I get about 4 mpg better than stock ratings and I'm a "spirited" driver.

Electronic Modification

I've don't claim to have experience with these things, but the theory behind them is that by taking less electric or running a system that is more efficient you free up more energy to be used to turn into engine power instead of electronic power. You free this up by adding things like Underdrive Pulleys, Ignition Coils, and Spark Plugs. While I can prattle on for hours on things you can add, I'm just listing off those three because they can be easily found at Americanmuscle.com or Auto Zone.

Tuners

I r lazy that why I gots computers to do work 4 me. All modern cars have computers in them, they have been programmed to work around exactly what you have in your car stock. Well the makers of our wonderful mustangs tend to go conservative when it comes to dealing with our computers, but we wouldn't all be driving mustangs if we all where big on the "Slow" thing. So by getting a Flash Tuner from a company like SCT, you can reprogram your computer to be faster, more fuel effecient, blah bah. It's just like any other computer you can make it do just about anything but sprout wings and fly if you try hard enough. SCT's new EcoTuner advertises a 10% gain on stock engines, so you can estimate 15-20% overall with modifications.


Fuel Catalyst

For those of you venturing to the extreme side of watching your MPG's, reviews have sided that the APSI company and their Fuel Catalyst product can net you an extra 1-2 mpg. Never tried it, I don't like tampering with my gas lines, but if your more confident than I, this is their website Fitch Fuel Catalyst - Home

[mwd]

All good stuff. On your CAI math, I think you were getting better than the company claimed 10%. If you went in at 20 mpg and came out at 24 (as an example), that's a 20% gain.

Anyway, I put a C&L CAI on my 2006 V6 and it works great. In my tune though, I asked for performance over economy and in the end, my mpg lost 4. Car feels/sounds great though. Noticeable power increase. Sound resonable or do you think something's not right?

[mwd]

Also, I've been reading a bit on underdrive pulleys as another fuel saving/pwr increasing modification. May be worth a try.

[Nagakilo]

I've not gotten a tuner personally (YET) so I wouldn't know for sure, but it seems reasonable that a more tune that would produce more power would decrease fuel economy because I think the tuners just make your car use your things more efficiently which makes the car work a bit harder.

[kosa.vixen]

+1 for all the tips. for me is to watch my right foot coz this is my reason why my MPG dropped from 16 t0 12 when i replaced my stock muffler to ATflowmaster. i love the noise and drone

[TomTom64]

very helpful, thanks for the post