BMW M3: "The optimal speed for fuel economy in this car seems to be around 80mph"

[dremd]

I'd average $500~$600 a month on parts when I daily drove a Supra. If it aint Broke, Fix it. I couldn't tell you where all that money went to save my life, but it was always a ton of $. When I started driving the Golf I couldn't believe how much less I spent on stuff.

[sickpuppy318]

total oppo of my Z. I bought a new slave once, but for whatever reason, it never held fluid. I leard to rev match. when i tryed to fix it again, the syncros were so shot i had to match anyway. other than that, maintenance free for two years, amature drifting, a few races topped out at a very floaty (no shocks) 130.

now i drive about 5-10 under and worry "lugging" my engine!

[WhenGrantAttacks]

I believe it, my old 5 series got its best gas mileage around 76mph

[RPM]

You might also want to see this funny video where Top Gear compares the fuel economy of an M3 and a Prius. The Prius goes flat out around a circuit, with the M3 following in hot pursuit.

YouTube - Top Gear - Toyota Prius Vs BMW M3

[Yahma]

I believe it!

According to the Top Gear segment, it would seem that the BMW is more efficient than the Prius at Autobahn speeds (100 mph), where the little prius engine is seriously struggling just to maintain that speed.

I drive a BMW 325i (2006 model), and have been keeping close tabs on my fuel economy while commuting. I have a long highway commute everyday (Hollywood to San Diego) of about 125 miles. Over the course of many tanks, my trip computer says I have averaged ~38.4 mpg @ 76.8 miles per hour. The MPG figure is verified by calculations done at the pump.

This morning I got 40.6 mpg for my 125 mile commute, but my average speed was 69.5 miles per hour.

The best gas mileage for my 325i is between 68-75 mph. Going slower does not improve economy, while going faster reduces economy. BMW's were designed for the Autobahn, and based upon my informal testing, it seems the numbers posted for the M3 are legit, considering the M3 has significantly more power than a 325.

[aerohead]

I'd be reluctant to burn him at the stake.I ran the T-100 on the stretch of 80-mph interstate out in W.Texas between Monahans and Van Horn.She was still pulling over 31-mpg,and that was with hilly terrain. And at 100-mph airspeeds at 80-mph road speed she only dropped to 28.The Bimmer may be hitting it's stride there at 80.Don't know.BSFC is a funny thing!If someone can get the max.torque rpm and the gearing for that car,we could probably learn something.

[tjts1]

The S54 engine in the E46 M3 has individual throttle bodies mounted near the injector. The whole intake plenum (there is no traditional manifold) is tuned to be an efficient air pump at extremely high RPMs (8000rpm red line). Newer BMWs like the 325i described by yahman don't have a throttle plate at all. They utilize gasoline direct injection in conjunction with infinitely variable intake valve lift and timing to eliminate all pumping losses. Because of the direct injection, these engines can also run ultra lean fuel mixture while cruising at constant speed without running into the NOx problems honda had with its VTECe engines. A lot of the traditional preconceptions about these cars no longer apply. Last winter I drove a BMW 335xi (4wd automatic twin turbo 300hp) while visiting relatives on the east coast. Over 2 weeks of stop light races and triple digit sprints I managed 23mpg. Not bad at all in the dead of winter with 4 people in the car.

More on direct injection.
Browser Warning

BMW N52 engine.
Inside the N52 Engine

[aerohead]

In a dated article,they said BMW would like to dispense with the whole valve gear and end up with solenoids actuating the valves.Glad someones really thinking!Great info,thanks!

[greenitup]

Originally Posted by JJW

He says "90mph" in one of his comments, so that's not kph. I'd still like to know where, honestly, traffic "cruises" at 80 anywhere in the northeast. I think its a psychological effect of traveling that speed, noticing other cars staying in your group, and assuming everyone is going that fast while you disregard all the people you are flying by.

What he means by "gears use more fuel at any speed" is that if you change the final drive gearing higher for better acceleration your fuel mileage will go down. That's why its under mods.

the highway, people are hauling @$$ on the highways in CT (65 mph speed limit), they just figure out the places, in my area police get very spotty so they figure out where to slow and where not to, 80 mph isn't that fast on the highways in my area. ive seen 80 mph on main roads too, 65 is more common though, still kinda above the posted 45

[obioban]

Hey, hey, I made that post that was linked to in the OP. Sorry I didn't post two years ago... just got linked to this.

For the test I was always fully up to speed at the beginning of the route, so those average MPGs don't include the acceleration to that speed.

Originally Posted by JJW

He says "90mph" in one of his comments, so that's not kph. I'd still like to know where, honestly, traffic "cruises" at 80 anywhere in the northeast. I think its a psychological effect of traveling that speed, noticing other cars staying in your group, and assuming everyone is going that fast while you disregard all the people you are flying by.

What he means by "gears use more fuel at any speed" is that if you change the final drive gearing higher for better acceleration your fuel mileage will go down. That's why its under mods.

The M3 come stock with 3.62s. People like to switch to 3.91s or 4.10s-- those are the gear swaps that I meant result in worse economy. Nobody ever goes the other way.

Originally Posted by diesel_john

that must be 80 kilometers, the data would almost make sense then.

... it was MPH

Originally Posted by kevlar

It would be quite a kick in the pride, but I'll bet it would do good around fifty in fifth

I was doing this plan for a rally I was going on-- comparing the speed vs MPG to figure out what rate of speed would result in the shortest possible driving time with fuel stops factored in (as in, at what speed would I be using so much gas that the extra stops would make my net time slower).

... but you're right, I didn't try anything below 70. I should have tried 50 in 5th, as that's right around the same RPM as 80 in 6th. It would honestly just be for testing sake, though... I can't actually stomach driving that speed...

[QUOTE=RPM;41155]You might also want to see this funny video where Top Gear compares the fuel economy of an M3 and a Prius. The Prius goes flat out around a circuit, with the M3 following in hot pursuit.

YouTube - Top Gear - Toyota Prius Vs BMW M3

Hmm... by that logic, and the way I normally drive, the M3 should always be more efficient for me than a Prius.



I'd be happy to redo testing with someone from this forum if there's interest, though my MPGs are probably going to be worse these days-- I've running 285s on all 4 corners now.