You need to carefully look at the cost and benefits of the following suggestions. There are many examples where it doesn't make economic sense to do the mods. There are others where it does.
To begin:
When thinking of how do increase mpg remember that, gas used is determined by load and RPM. Decreasing load and decreasing RPM are how you will improve mileage.
1) Drive less aggressively, and just plain drive less. Keep RPMs down when accelerating, acceleration is where most of your gas is used. If you maintain a constant speed and accelerate tot hat speed at a slower rate your mpg will improve in a direct proportion to how much your driving style improves.
2) Maintain your car. Worn out 02 sensors (BIG ONE HERE), plugs, dirty trans fluid, dirty oil, etc are all bad for mpg. That rough idle and miss from a bad IAC and torn plug boots aren't helping either. Check and clear codes as they can affect this as well.
3) Buy a car that gets decent mpg. Guess what? Your Chrysler 300C SRT-8 isn't ever gonna get 30mpg around town. Or 20. Buy something that will.
4)Minimize engine accessory use. There are mods to help with this as covered later, but most people underestimate the amount of engine load that goes into turning your A/C, alternator, water pump, and power steering pump. Again I will cover modifications to reduce or eliminate the use of these items later.
5)Weight reduction, take out that spare tire, back seat, passenger seat, rear speakers, stereo system, and anything else that you can. Buying a car with manual items like manual door locks and crank windows will help with this as well. Serious mods to improve this are covered later. Often replacing you chrome wheels (either stock or otherwise) with 15" (or 16" if you have large brakes, and don't wnatt o grind the calipers) OEM/Aftermarket alloys can work wonders for this.
6) Run the lightest weight synthetic oil you can get away with. Change over to a synthetic oil (Not fake synthetic, real synthetic, like amsoil or royal purple. A PAO synthetic) in both your engine and trans. This will improve parts life, acceleration, everything. Running 5W20 engine oil will net you a noticeable mpg increase over say 5w30 or 5W40. Although if your car burns oil you should run the lightest weight you can to prevent it from burning oil.
7) Keep tires inflated, this could even be moved up as it is very important. Over inflating can be dangerous and cause poor tread wear, but I do it on the rear tires of FWD cars. Keep the front of FWD and all of RWD at the correct spec as stated on the sidewall.
8) Run harder or low rolling resistance tires. This is an easy thing to do, however how well it works is questionable. There are conflicting opinions that you can judge for yourself and your situation. There are some safety concerns with this, reading up on them and weighting the cost and benefits of your decisions are the best way to make a logical choice. Some Info:
http://www.tirerack.com/tires/tirete....jsp?techid=29
9) (Automatic transmissions) Shift into neutral and rolling up to stop lights. CAUTION: Shifting into neutral at high speeds (and low speeds) for any distance can be very bad as in automatic transmissions a drum inside will no longer receive lubrication and can explode causing VERY costly and time consuming repairs. Although it is fine at like 10-15 mph for a few feet, or while at a stop light. Do NOT do this at a substantial speed. I know this from drag racing experience where people have blown up their transmissions by shifting into neutral after a pass.
10) Air dam blocking, I do not know much about this, obviously it is made to improve aerodynamics and therefore engine load. This can have some horrible effects, especially for your transmission. If you are going to do this you NEED to add a transmission cooler. A transmission cooler is a good idea anyway as it adds more fluid to the system, (and therefore more heat absorbing capacity) and will GREATLY increase transmission life in cars that do not have them from the factory. Obviously also if your cooling system isn't up to snuff this can cause decreased reliability, overheating engine knock leading to blown head gaskets, new engines, and new transmissions. I would strongly consider the potential costs that you could incur as a result of this mod for making a logical decision. However a hotter car will get better gas milage while it runs.
11) Drafting. No explanation needed here, but maybe your life isn't worth the extra 2-3 mpg? Again cost and benefits, if you are a ******* with no children and the world doesn't need you, draft all the semis you want.
12) Gas mileage indicator, some cars come with them now, adding one helps add consciousness, as well as lets you see what brands of gasoline work best with your car and how well your mods are working. For sure one of the better mods out there.
13) Change to a hotter thermostat. Only do this if your cooling system is up to snuff and properly maintained. Switching form the stock (usually to 170-180) costs little, is easy on most cars, and can net some real world increases. Of course detonation can occur if it gets too hot which will lead to shortened engine life or engine failure.
14) You can add on taller tires to drop cruising RPM.
The following are a little more advanced and require your own research into the cost and benefits. Generally if you cannot perform your own labor, they will not be worth it.
15) BIG ONE HERE. A simple mail order tune and SCT XCal 2 (or whatever is out there for your vehicle) can often net a few mpg (depending on how "on the edge" you're willing to go) This can work well in conjunction with many of the below listed mods. If you have an OBD-II ford vehicle, the Xcal/Xcal2 can be a simply reasonably priced way to have significant long term benefits. There is even a company out there using it to offer a plug and play switch to E85 if its available in your area. The xcal2 has data logging, as well as use in tuning and is a OBD-II code reader.
16) Getting under drive pulleys for your accessories will decrease engine load, although it will adversely affect things like your water pump efficiency and alternator charging ability, this shouldn't really be a problem as long as your cooling system is at factory specs and you don't have a 10 billion watt stereo system. To get maximum fuel economy, Delete AC (Lots of weight removed as well as not using it freeing up engine load), if your car has a version with a manual steering rack or its offered in the aftermarket, delete power steering. Install an electric water pump such as one from Meziere, and run an underdrive pulley on your alternator. This will net a noticeable mpg gain as well as power gain. Lets also not forget those of you who still have a smog pump thats belt driven. Most people here have FWD cars but if you have a RWD car that has a clutched fan for god sakes switch to electric. A Lincoln Mark VIII fan(best) or Ford Taurus fan(still very good) will provide better cooling that many aftermarket fans. Get one from a junk yard.
17) If you have a RWD car, change the rear gear ratio for your type of driving. If you only drive in the city and have a heavy car with 3.08 gears, you can greatly up your mpg (and transmission life) by switching to a more city friendly gear in the range of 3.55s or 3.73s. This will also greatly help acceleration of course. Conversely if you drive mostly on the highway and have 3.27s or 3.55s in your car switching to 3.08s (using ford 8.8 gears in this example) or 2.73s will drop cruising RPM.
18) If you have a car that asks for high octane gas or want to run a ragged on the edge type tune, a methanol kit can be built in your garage easily for less than $200 installed. You can run isopropal alky, washer fluid, straight meth, or straight water, either way this will increase octane, decrease detonation, and allow you to lean out your gas use and A/F even more in the upper RPMs. Great for sue in conjunction with a dyno tune.
19) Weight reduction that requires commitment. This goes beyond removing seats and spare tires that you don't need. Take out everything, make a sheet metal dash, A/C, heater core, smaller battery, aluminum radiator, remove all sound deadening, switch to super light weight aluminum wheels, there is a long list. Aluminum heads, aluminum blocks, etc. Heres just a short list with some expected gains.:
http://www.theturboforums.com/smf/in...?topic=21593.0
20) Weight reduction/aerodynamic body kits. The only time this is worth it is if you car has body damage that needs to be replaced anyway. Having said that replacing steel components with fiber glass, and you glass side windows with lexan can shave off some extra weight.. You can get full fiberglass front ends from places like harryglass and others. For aerodynamic body kits, many if not most of them are actually worse for aerodynamics. Weigh the cost and benefits for your situation carefully here. This is more race car stuff, if youre trying to have a fast car that also achieves good mpg,
21) Got boost? Turbocharging and supercharging will allot you a significant increase in gas mileage. I have seen up to 8mpg increases when properly tuned. I myself had a supercharger on my 1998 Mark VIII and picked up 2mpg on AVERAGE and that was with a heavier foot in a 4000+lb full weight car. We're talking 150mph+ highway blasts and drag racing factored in.
22) Simple cold air intake and higher flowing exhaust. Make your engines job easier and you will net a small mileage increase and HP increase.
23) Engine/Transmission swaps. Obviously a more fuel efficient engine or one that isn't a worn out piece of crap, will get you better mpg. A manual transmission not only offers you more control but also reduces drivetrain losses.
