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

Anybody with an M3 want to bust/confirm this guy's "tip"? :D

http://homepage.mac.com/ianlindvig/eff.jpg

While you have to give him credit for laying out out his testing approach (details are posted in an M3 enthusiasts forum, see link below), the absense of 50 & 60 mph speeds seems to me to be a gaping hole in the data.

I'm pretty skeptical of the conclusion.

Forum thread: http://www.m3forum.net/m3forum/showthread.php?t=216328

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FYI, as a point of comparison, I tested the fuel economy of a 505 hp Corvette, and its best economy landed pretty much where I expected it would: (meaning, nowhere near 80 mph)

http://ecomodder.com/forum/showthrea...05-a-9841.html

I must confess, I would have thought he would attain better mileage ~ 50 - 55. Or right after he goes into overdrive and torque lock. But who am I? I'm trying to get 50 mpg out of a car with 199K on the clock that is in desperate need of a rebuild.
S.

The M3's engine is a high performance monster, which is why I said "skeptical" rather than jumping up and down yelling "baloney!"

But still, he's basing his conclusion on the 80 mph figure being better than the single 70 mph point.

Is it a six speed?

If you look at the "There/Back" portion of the 80 mph data set, the "Back" is significantly larger, statistically. As we know, one round-trip test generally doesn't cut it.

50 and 60 mph is indeed missing. But (GASP!) You can't drive an M3 that slow! :p

RH77

I find this tip curious: "gears mean your using more fuel at any speed"

The test course was only a totaly of 6 miles, with a turn around as well.

the back portion must have been down hill, and either way, the guy is ridiculous for trying that high of a speed

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

different engines are more efficient at different speeds, then tie that in w/ gearing and the cars areodynamics, i can see how 80mph could be the best speed for MPGs. I used to drive a 91 Camero RS V-6 and consistantly made 30mpg at 80mph, occasionaly 32mpg.

Which is why I didn't yell "baloney!" right off the bat. Still, I'm doubtful its the best speed for max mpg.

I take it nobody has an M3 at their disposal to confirm/bust this one :) I've seen a new one tooling around town lately, but I have no idea who owns it.

I'm with John on this one, 80km/h would put it at around 50mph and that would make a lot more sense for the FE to be the highest. Also, 120Km/h then would put him at around 75mph and that would be a much more reasonable speed to expect someone to drive on a public road.

I smell a fish, anyone else?

Nope, I do believe he's reporting MPH. Lots of chuckles in the thread about it, like "all runs done in mexico" etc.

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.

My mom has an '06 Jeep Cherokee and she seems to think that she gets the best mileage at 65mph. Of course, i always call B/S on that and tell her she doesn't know how to drive anywhere near reasonably. We used to live on long island, and on the LIE flow was at least 80 even though it is a posted 55. I think its a New York thing that she thinks 65 is reasonably slow and her cherokee is reasonably small!

Yeah, I get the same from my fam. People have to be willing to change or accept the Science behind the change. Meanwhile, there's nothing to do but report your own savings :thumbup: She might come around after a while...

RH77

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

I have to say that the Supra with tall gears, big tires, cold ambient temps, undertray, optimal fe speed did appear to be in the 80~90 mph zone (was 2200~2400 rpm with decent load) With the 4.30's in her now it's probably around 40mph (guess).

However I did pull several 33 mpg in town tanks on it last summer; even with 285's out back and 245's up front. Just watch the boost gauge, turn the motor off as much as I could, run lots of PSI in the tires. "Normal" driving gives 15~17 mpg in it now. I don't want to Eco-mod it nor hypermile it, as long as I burn less than 2 tanks per year (3/4 tanks burnt so far this year) I don't care.

i'm no "expert", but a little P&G with boost smells like a fried turbo. Does that supra have and oil cooler like the turbo 300zx did?

Factory oil cooler sucks, I just chunked it. M-1 Red Top Changed every 10 tanks of Fuel. (100 miles at the track, 250 "normal"and 450 in "Hypermile"

I never did P&G per say. Just let it idle down, see 1000 deg EGT and shut it down.
Just running an upgraded CT26 $400 for a new one so wasn't a big deal.

I was driving 85 miles per day in some of the worst stop and go traffic I've ever dealt with. 0-50-0-50-0-50 every 1.5~3 miles. I would run it up to speed at "0" psi idle it down, shut it off coast to stop; repeat. Sometimes I got to to not quite stop which helped out hugely. It was alot of work. But on the + side I have a vac resovoir + pump (for longer turbo Burnouts at the Track I would push through the lights and be disqualified); didn't really matter on the street.

sound cool though, i never got to take my Z to the track, but it was an N/A and i got 30+ MPG out of it. I drove the snot out of it for a couple years, couldn't kill it if I tried, and try i did. I would imagine the supra is the same way, even with a turbo.

$400 for a new turbo still sounds like quite the headach, and 1000F seems like it would still cook some oil:confused:

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.

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!

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

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

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.

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.

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.
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BMW N52 engine.
Inside the N52 Engine

http://www.mwerks.com/gallery/genera...scaled_600.jpg

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!

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

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.

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.

... it was MPH

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.

Sorry for the weird edits, the forum won't let me use links, pics, or emoticons till I'm at 5 posts :P

I've been interested in mapping the speed vs. fuel economy in my car for a while now, but I don't have the proper instrumentation. Whenever I drive on the freeway, my tank MPG seems higher than usual.

I'd be interested in seeing you test the MPG from 50+ in both 5th and 6th gears.

interesting thread, can't recall spotting this one.

My old sube is bizarre with highway too...
3600=92mph, and it is in absolute tippy toe on the throttle heaven...bouncing around 30s mpg with a sucking hole in the top of the tank (it used to be in the 40s there). I am from 87-92mph with a sucking hole... it is mythologically hilarious.

the m3 is no surprise with a deep overdive on a power to weight ratio that is quite high.

I like the route of faster and hyper mile. That is the ultimate is it not? ;)

A giant lesson is deciphering a tractor trailer...they are the same all the time, weight and speed. If the engine is content at spoeed, lean games can play and not hurt.

It would be neat to see it redone including lower speeds. Would 6th gear be too high for 50mph? I think you could at least try that as well.

Hi obioban -

I'd love to see controlled as possible testing at lower constant speeds. I'd bet a dollar fuel economy will improve as speed drops, right down to just above lugging RPM.

(Feel free to post a couple of "filler" posts to get full forum permissions. It's there so we can spot spammers and obviously you're not one.)

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Since posting this thread originally, I had a chance to take a 6-speed, 505 hp Corvette Z06 out to collect info for a speed vs. MPG chart:

http://ecomodder.com/forum/showthrea...05-a-9841.html

In a nutshell, the slower, the better.

I can confirm that it is better at 50mph in a E46 M3(2004)
 

I have achieved (over a full tank of gas) 32mpg when setting the cruise at 50mph on my trip to work and back which is ideal for gas mileage (Lancaster, CA to Edwards AFB). It is a flat stretch with no turns or stops. My tires have more drag than stock because of the size 315s in the rear and 275s up front and I am only running 35psi in them because when I jack them up to 50psi they wear in the center. Pretty remarkable because 6th gear is not really an overdrive in this car (0.85) with a 3.62 final. At 50mph I think I am taching 1750rpm. I will try 5mph increments to see what the best that I can achieve is. I can confirm the numbers at 80mph also. I get around 28mpg which is not bad at all for 333hp normally aspirated 3400lb car. I would like to note that I get some crazy looks when cruising at 50mph in an M3 when the speed limit is 70mph :)