[Deveray]

For the past few days driving around town I've been trying a new strategy - changing gear very early to keep the revs at 1200 RPM or less [1000 RPM or less on the flat]. The car pulls from 600 rpm so this isn't that difficult - and above ~32mph in 6th obviously you go over, but around my town that doesn't happen often.
This has yielded about 4mpg more than I usually get on the same routes [dropping kids off at school]. That's 28mpg instead of 24 [I drove gently before but let the revs rise 'cause it sounds nice].
I know in theory, wide open throttle [WOT] at low revs is most economical but WOT is hard to do in practice around town, but merely by aiming to keep the revs so low, you do end up with quite wide throttle openings even in traffic at low speed.
It's also quite entertainining in situations where yo can't be entertained by the other end of the performance envelope, and another tribute to the N54 engine that it is so immensely flexible and economical

[retlod]

Why not go for 30 extra and get a Prius? You just *might* be driving the wrong kind of car.

[runnerx]

driving at such low RPM is actually harmful to your engine.

[darkphantom]

I keep my shifts at 1.5k-2k RPMs...but again, I have the ZF auto.....but I need to shift myself during normal driving because the tranny thinks I'm Micheal Schumacher

[TiAg335i]

I shift at like 2.5K-3K

[darkphantom]

hehe, it just puts a smile on my face though when I'm in just rolling around in parking lots in first, just tap it a little to scare people walking slow....

[Haywire]

Originally Posted by retlod

Why not go for 30 extra and get a Prius? You just *might* be driving the wrong kind of car.

being economical doesnt mean someone is driving the wrong car, it simply means he's aware... thats a good thing.

I too shift at low rpm, i would say around 2-3...at higher speeds, a lot closer to 2 than three. I get much better mileage in doing so.

its amazing the small changes you can make to your driving habits to maximize fuel economy.

[noro]

Originally Posted by runnerx

driving at such low RPM is actually harmful to your engine.

+1 .. you're putting extra stress on the combustion chamber that way. The good news is that all those dollars you will save on gas you will have to spend fixing the engine!

[Dmitriy@AUTOcouture]

I shift at 3/3500k and redline the car at least once a day. I get roughly 20MPG average between City and Highway on my 6MT.

Oh and I also don't use my brakes that much, downshifting FTW! I'm not sure if that helps out gas milage though.

[F32Fleet]

Originally Posted by runnerx

driving at such low RPM is actually harmful to your engine.

My rpms are ~ 1,500 while driving 55 mph (A/T). That's fairly low.

[darkphantom]

Originally Posted by shpuntik

I shift at 3/3500k and redline the car at least once a day. I get roughly 20MPG average between City and Highway on my 6MT.

Oh and I also don't use my brakes that much, downshifting FTW! I'm not sure if that helps out gas milage though.

whaa?! shifting around 3-3.5k gives me like less than 20mpg...and I don't brake w/ the tranny b/c supposedly you stress it more. It's good if you do both though, tranny + brake, simultaneously.

[Haywire]

yeah, at 3-3.5 im surprised youre doing so well on fuel and i dont find downshifting that effective with my coupe, personally...altho i continue to use both to slow down as well.

[epiphone3]

Originally Posted by runnerx

driving at such low RPM is actually harmful to your engine.

this should only be harmful to the engine if it makes it lug or struggle in any way. Otherwise, all is fine... especially with variable valve timing and direct injection!

To the guy who said driving the engine at low speed "stresses the combustion chamber," you are wayyyyyyyyyy out to lunch. If you lug the engine (run it way too slow), it puts excessive load on the crank shaft in the direction perpendicular to its axis. This is hard on the crank and on the bearings. Nothing to do with combustion chamber. You can generally cruise with the engine at low speed and it will be fine but will start to lug once you add load. Best thing to do is to down-shift at this point to raise revs and avoid lugging.

With my 323i, I can cruise it at 1750 - 2000 rpms then give it throttle and the engine will pull very smoothly. If I try lower engine speeds in the higher gears (say, 1500 rpms in 4th gear), you can tell from the sound the engine makes that it is struggling a bit with that load at that speed and the onset of lugging is there. I avoid this at all times as lugging is tough on the bearings. There are two components to lugging... engine speed and engine load. Hence why you can cruise at certain low rpms and can't just step on the gas and pull smoothly without lugging (as the load increases).

with regards to the combustion chamber... In the old days, running the engines slow could cause excess carbon build up, however, with direct injection and variable valve timing on both cams, these problems should be prevalent. Just make sure you warm up the car really well and drive it like you stole it once in a while. You need to enjoy it... you did buy a BMW after all!

[MrClean]

Originally Posted by runnerx

driving at such low RPM is actually harmful to your engine.

+10000000

I guess if you're driving in a relaxed manner on flat ground, then no big deal. But if you're doing this under other circumstances, you're putting a lot of stress on the "expensive parts" (bearings, upper cylinder) of the engine by doing this. Think how much fun you would have trying to pedal up a steep hill in the highest gear on your bike. Sure, you're only pedaling a tenth as much as if you were in the lowest gear, but the strain on your joints would stop you quickly. Unfortunately, your car cannot cry "uncle" or shift on its own if you are in manual. The closest thing to that is "lugging", and if you're doing that, downshift.

That's why cars have more than one gear, folks. Use 'em.

J

[Haywire]

You would have to be extremely hard on the engine for you to do any damage with this. My car is brand new, so of course im getting used to the gears and so forth.... every once in a while, not so much anymore... i would get a lug... learning the ropes of my new ride. now of course this isnt GREAT for the engine, but this would have to be a common practice before you fu@ked anything up.

I dont suggest you try and pop it from first to 4th lol... but if you keep it reasonable, theres no immediate worry....

and like clean said, NEVER on a hill... jesus, just gear down lol.

[Gig103]

Hypermiling and a twin-turbo 6cyl engine seem to contradict each other....

[Couch]

I'm confused as all hell. How do you WOT at low revs?

[742]

This not new; the practice goes back to at least Charles Lindbergh. And high BMEP/ low RPM was used in WW II to extend the range of airplanes in the Pacific theater. But there is a point where this becomes very destructive, and not even BMW can overcome the laws of physics and the limits of metallurgy.

I suppose this is another one of those "do you lease or own?" issues.

[KWA VaTech]

Originally Posted by Gig103

Hypermiling and a twin-turbo 6cyl engine seem to contradict each other....

The TT-6 is a replacement for a V-8 due to gas worries, how are these posters not making sense by trying to get more out of it? I expect to see many boosted I-4 and I/V-6s in the future with increasing MPG.

Overall, I think just because someone has a TT car they don’t have to abandon all sense of economic responsibility.

On a separate note, does the WOT concept still hold true for booster cars?

[Deveray]

As the OP I'm surprised to see comments about stressing the engine, as at such low RPM the torque is way below maximum so the size of the explosions in the cylinders [even on the rare occasion that you get to wide open throttle] is going to be far less stressful to anything [con rods, cylinder heads, cylinders] than when the engine is working at peak torque when the explosions are biggest or peak power when the dynamic stresses are highest. Sure, if the ECU didn't adjust the timing correctly and the firing was happening too early then you'd get knocking, but I would assume BMW thought of that and retards the timing sufficiently.

[galahad05]

Nope, epiphone3 is correct: lugging the engine puts extra stress on the crankshaft and main bearings. Plus, I'd add a bit of side-thrust on the cylinder walls, piston pins, etc....

But, the kind of driving you do should be quite okay: you aren't lugging the engine. You'd KNOW if you were lugging it.

[kefler]

Originally Posted by Haywire

being economical doesnt mean someone is driving the wrong car, it simply means he's aware... thats a good thing.

I too shift at low rpm, i would say around 2-3...at higher speeds, a lot closer to 2 than three. I get much better mileage in doing so.

its amazing the small changes you can make to your driving habits to maximize fuel economy.

How about going 6MT instead of Auto? A few extra MPG + 30 tanks of gas!