[Neill222]

Here is also something interesting I think I get better mileage when I use 89 octane instead of 91 octane but the car is not quite as quick on the pedal

[Mavus]

Originally Posted by mike-y

while weight and rotating mass is are big enemies of acceleration and braking, it's not the biggest enemy in terms of fuel mileage. once you are moving at a steady speed, it's not harmful. in fact, it will help the car coast longer because of the higher inertia. Aerodynamics makes much more of a difference at speed than overall weight does.

but in all other aspects of performance, excess weight is bad, yes.

This is not true unless you are disputing physics laws:

******
In physics, a force is said to do work when it acts on a body, and there is a displacement of the point of application in the direction of the force. For example, when you lift a suitcase from the floor, the work done on the suitcase is the force it takes to lift it (its weight) times the height that it is lifted.

The term work was introduced in 1826 by the French mathematician Gaspard-Gustave Coriolis[1][2] as "weight lifted through a height", which is based on the use of early steam engines to lift buckets of water out of flooded ore mines. The SI unit of work is the newton-metre or joule (J).

The work done by a constant force of magnitude F on a point that moves a displacement (not distance) s in the direction of the force is the product,

W = Fs.

For example, if a force of 10 newtons (F = 10 N) acts along a point that travels 2 metres (s = 2 m), then it does the work W = (10 N)(2 m) = 20 N m = 20 J. This is approximately the work done lifting a 1 kg weight from ground to over a person's head against the force of gravity. Notice that the work is doubled either by lifting twice the weight the same distance or by lifting the same weight twice the distance.

http://en.wikipedia.org/wiki/Work_%28physics%29
*****

Every time the engine has to do the work it is using gas. Although the inertia of a havier wheel will keep the car rolling longer on a flat surface (0 deg), once the desired speed is achieved, the work performed by the engine to accelarate (reach) and maintain the speed will be larger as the weight increases.

If you are going down the hill you can put the car in N and use brakes only. Your engine will not be doing much work. If you are going up the hill the sprung and unsprung weight is your enemy.

The aerodynamics does not become a major player until 60-70+ mph.

There are some ways to improve efficiency or "ask the engine to work less":

1. turn off your lights and AC
2. drive with 1/2 tank or less (not practical for most folks)
3. decrease the sprung and unsprung weight as much as possible (light wheels, 205 tires, no RFT, light weight battery, all unnecessary items removed from the car).
4. rate at which you apply the throttle (light foot - less gas)
5. route optimization (commonly done with airtraffic to identify routes with less headwind). Avoid hills, the engine will need to do more work. Consequently, going downhill you will be wasting energy and burning brake pads.
6. when you park your car during summer try to find shaded spot. The higher the interior temp the more work engine will need to do to cool the cabin temp.

Do not run higher psi in your tires than what is specified on your door jamb. You will alter vehicle handling and may become a safety issue. There is a very good reason OEM provides that info right on your door jamb. Check your pressures every week. As you drive the tire pressure will increse 5-9 psi usually based on conditions and speed.

Hope this helps!

[smithf80]

Here are something to try besides just driving differently.

If your car is high mileage and hasn't had this done yet:

Spark Plugs
Coils
Engine Air Filter
Fuel System Cleaning
Charcoal Filter Delete

[AdamN52]

Why would you spend money on mods to save money on gas? Seems redundant to me - unless your motive isn't money, and you just want to make the world a better place. My guess is you wish to save money though. lol

I can't think of any mods that would give you a reasonable return on gas savings...

I'd suggest using cruise control when you can, and if it's really a huge deal then probably best to look at getting a commuter car.

I know that's not really what you were asking... but my vulcan-like brain wants to be logical :-p

[fravel]

Originally Posted by AdamN52

I can't think of any mods that would give you a reasonable return on gas savings...

I actually noticed an average increase of 1 MPG after I installed a set of the Cyba Scoops. Considering how cheap they were ($40) and how early into my ownership I installed them, I'm fairly confident that they've paid for themselves at this point.

[cuco]

Installing a software tune usually helps since it leans out the mixture while increasing timing advance. I got at least 2 more mpgs after installing my AA tune. The K&N with charcoal delete help a LOT.

[mike-y]

Originally Posted by Smooth 330i

This is not true unless you are disputing physics laws:

Hope this helps!

I'm not, read my post again. I'm saying it won't make that much of a difference from a pure mileage standpoint. why spend $1600+ on wheels and tires for minimal gains in gas mileage (if that's what he is trying to do)? That's ~400+ gallons of gas!

when I got aftermarket wheels and tires (wheels were 19lbs vs 26lbs for the stock wheels) I saw ZERO change in gas mileage. Acceleration and braking felt slightly better, but that was felt mostly at lower speeds, like 1st and 2nd gear. At highway speeds the difference isn't nearly as noticeable.


Newton's first law of motion covers inertia, which is a lot of what we are dealing with when it comes to cruising on the highway at steady speeds. When you are going for good MPG, controlling engine load trumps everything else, requiring you to severely limit your throttle inputs. And when you are dealing with very small throttle inputs to minimize engine load, wheel weight matters even less.

[Kevin52]

I have noticed an increase in my highway mileage since I installed my eurobox with pipe cross filter and Cyba scoops. When I'm driving 72 my computer regularly shows me 30+ mpg

[jc_bmw]

The best tune is still driving skills....

getting 8.6L/100km

[MBP0202]

Just as a data point...

2007 328xi

Did a 200 mile highway drive today, computer showed average speed of 73 and 28.6mpg

Having the primary cats out helps a bit to improve the mpg but ultimately speed is the critical factor.

If there were no traffic, I'd stay in 5th gear, 65mph and I think I would see 30mpg. It seems like the n52 engine likes the higher rpms because it just hates to be lugged and if I were at 3k in 6th gear then I'd be going 80+mph and it would definitely decrease my mpg.

Just my .02

[nelsonvr6]

1. If you aren't already, Use a bmw approved ll-01 0w-30 instead of a 0w-40 or 5w-40.
2. Depending on your mileage change the transmission and rear end fluid to a good synthetic (amsoil, redline).
3. New plugs
4. Chevron techron every 4-5k miles, also google top tier fuels
5. Already mentioned but put an extra psi or two in the tires
Your driving habit will make the biggest difference
I bought my 06 330i 6spd with 88k on the clock and it was averaging roughly 25 mpg. After doing the stuff I listed above I've been averaging close to 30

[Greyfox]

I drive 255 miles to work on Mondays and the same later in the week to get back home. I can average 30 mpg normally.

A couple of things...

Keep check on your air pressures. Absolutely critical. Also, keep track of the wear pattern. If you start "feathering" edges, you might want to get an alignment.

Get on the Interstate and lock in your cruise control. I've tried to beat the cruise on mileage. I can't get within 2 mpg using my foot.

Oil change will cause your mpg to go up temporarily.

[AdamN52]

I drove ~300km round trip today in my '07 328xi auto
All hwy with low to medium traffic and got 7.8L/100km (30mpg) average. Just used cruise control. Had the AC on.

Around the city/short trips I get between like 10-13L/100km (18-23mpg), which isn't great.

[Casca]

Originally Posted by lightsareout

I've been trying to keep my driving consistent issue is there is only a 2 lane road for 21 miles to the highway and many of the 5000 employes all travel it at the same time. One slow person who doesn't know how to use cruise control kills my gas mileage plans.

Leave for work before they do. Most people have to be at work 8am where I am. The difference between cars on the road at 6am and 6:30am is huge. Before 6am, it's pretty wide open of other drivers.

I use to wake up and be on the road by 4:30am. Very stress free driving as the highway is like my own personal use at that time. Stop at a gym pretty much next door to where I work, run a couple miles, lift some weights, shower up and go to work. Of course the drive home after work is not as enjoyable. But I don't really live that far away.

[tboudre]

Originally Posted by lightsareout

I have a 328xi and recently started a new job and drive 80 miles round trip each day. What mods can be done to improve the gas mileage of my car? I'm already looking at a k&n drop in filter and the charcoal delete.

I was in your shoes a couple years ago, driving a new Infinti G37 about 150 miles/day round trip and spending $500/month on premium fuel and I tried just about anything, aside from a tune, as that would have cost over $500 and tunes are designed for power, not economy, though some report increased gas mileage. One trick was to put 3-4 oz of acetone per 10 gallons into the tank. It was supposed to help atomize the fuel better. I couldn't see any recognizable gains in MPG. I bought some of these vortex things to put in the air intake that were supposed to swirl the air and mix it better. All it did was created a restriction in the intake and made the car very sluggish to respond. Perhaps after the computer adjusted to starving the air from the car I may have had some mpg gains, but who wants to choke a 300hp card down to 200hp? The best thing I could do was keep my foot out of it, I'd allow myself one or two WOT accelerations per day, but keep it on cruise control. I was adamant about putting pure gas in the car, as the 10% ethanol would give me lower mileage. But it was to the point that I could have cheaper gas and get lower mileage or get better mileage with more expensive pure gas, and it would be about the same either way. All the while putting premium fuel. I ran across an article recently. It proposed that E10 (what is available at most pumps, up to 10% ethanol) is the absolute worst mix that you can run for mileage. They found that certain cars, with no modifications, could run E30, E50, or sometimes straight E85. They also found that a mix of E20 or E30 in some vehicles resulted in the same mileage as pure gas or sometimes better. Of course, the main thing isn't the MPGs, it's saving money. What if I told you that instead of paying $3.79/gallon for 93 octane that you could buy 5 gallons of E85 at 105 octane for $2.89.gallon, and mix it with 10 gallons of 87 octane at $3.14/gallon and end up with a mix of about 30% ethanol and 93 octane? You just saved $11 on a tank. Of course, I do this now, since I no longer have a long commute, and I have the 335i and the JB4 tuner, and I get a buttload more horsepower from this setup for a couple of different reasons that are not relevant to this discussion. Any car should be able to do this, but YMMV, and, as I understand, if you start getting into higher E%, a tune may be necessary, and possibly some other mods.

[Clammy]

Originally Posted by tboudre

I was in your shoes a couple years ago, driving a new Infinti G37 about 150 miles/day round trip and spending $500/month on premium fuel and I tried just about anything, aside from a tune, as that would have cost over $500 and tunes are designed for power, not economy, though some report increased gas mileage. One trick was to put 3-4 oz of acetone per 10 gallons into the tank. It was supposed to help atomize the fuel better. I couldn't see any recognizable gains in MPG. I bought some of these vortex things to put in the air intake that were supposed to swirl the air and mix it better. All it did was created a restriction in the intake and made the car very sluggish to respond. Perhaps after the computer adjusted to starving the air from the car I may have had some mpg gains, but who wants to choke a 300hp card down to 200hp? The best thing I could do was keep my foot out of it, I'd allow myself one or two WOT accelerations per day, but keep it on cruise control. I was adamant about putting pure gas in the car, as the 10% ethanol would give me lower mileage. But it was to the point that I could have cheaper gas and get lower mileage or get better mileage with more expensive pure gas, and it would be about the same either way. All the while putting premium fuel. I ran across an article recently. It proposed that E10 (what is available at most pumps, up to 10% ethanol) is the absolute worst mix that you can run for mileage. They found that certain cars, with no modifications, could run E30, E50, or sometimes straight E85. They also found that a mix of E20 or E30 in some vehicles resulted in the same mileage as pure gas or sometimes better. Of course, the main thing isn't the MPGs, it's saving money. What if I told you that instead of paying $3.79/gallon for 93 octane that you could buy 5 gallons of E85 at 105 octane for $2.89.gallon, and mix it with 10 gallons of 87 octane at $3.14/gallon and end up with a mix of about 30% ethanol and 93 octane? You just saved $11 on a tank. Of course, I do this now, since I no longer have a long commute, and I have the 335i and the JB4 tuner, and I get a buttload more horsepower from this setup for a couple of different reasons that are not relevant to this discussion. Any car should be able to do this, but YMMV, and, as I understand, if you start getting into higher E%, a tune may be necessary, and possibly some other mods.

I'd be ecstatic to be able to get 93 octane for $3.79/ US gallon. Up here, it's almost $6.00/ US gallon...

[Taskmaster]

Driving better will help the most. Acclerate brisk up to speed, and hit cruise - let off the gas and reapply gently. Coast whenever you can, be smart about braking and you too can hit high 20s and low 30s.

[spuntyb]

I've found that a light foot around the city and using cruise control as soon as I hit the highway helps to the tune of about 2 mpgs, versus what I was getting before. Not huge, but it's also not much work and it's free (vs a tune or mod). I'm running completely stock.

I found I had a slight boost in mpgs, although transient (a few thousand miles), from a fuel injector clean and spark plug change as well.