MPG and the M3

[T Bone]

Originally Posted by godot

There's another big factor that I didn't see anyone mention: The Corvette's manual tranny has a magnetic gate that forces you to skip from 1st to 4th gear, except when accelerating hard. So in casual driving, you physically cannot enter 2nd or 3rd. (Of course, a lot of people find this massively obnoxious and disable it with an aftermarket wiring harness.) Presumably, the software for the automatic tranny does something similar.

As to highway mileage, coeff of drag is <0.29 in the Vette vs. 0.32 in the M3. Part of the tradeoff of having more passenger and cargo room, I suppose.

Didn't know that about the Z06....that would suck not having control over what gear to choose!! That would suck in city traffic.

Another misleading thing is the drag coefficient actually, the Cd is calculated after determining total drag forces. What is most important is the frontal area X Cd.




BTW, in my 335xi, I often shift from 4-6 or 3-5 regularly..... I often accelerate briskly then cruise, I read somewhere this was the most efficient way to conserve fuel...fun way too.

[T Bone]

Originally Posted by Samifumi

Congratulations. As you said, only real world numbers matter. Different individuals, different driving styles, different numbers. Thank you for affording me the opportunity to make my own assessment.

Why don't you report in after awhile?

Look below at the E46 M3 numbers, we are all very close to each other.

Good luck saving fuel with the MDCT.....maybe the tooth fairy will visit you soon too.

[Samifumi]

Originally Posted by T Bone

Why don't you report in after awhile?

Look below at the E46 M3 numbers, we are all very close to each other.

Good luck saving fuel with the MDCT.....maybe the tooth fairy will visit you soon too.

Trust me. I'll be here, if only to raz you about you about your omniscient Tom Cruise-like "you dont know the history of DCT, I do, I did the research" point-of-view because you've driven past SMGs. Part of the problem with this transmission is that it is wildly speculated about (the "magical, mystical" description was intended for a reason), and there is little to no public real world experience with it. Before you start spouting off as the all-knowing developer of the transmission, why don't you let me talk about what I've also read without suggesting that it's totally asinine or without plausibility (the "smoking crack" comment really sets me off here). I don't know for sure. That has been admitted in everyone of my posts. But without real world numbers on the actual transmission itself, your guess is exactly that: a guess.

[GarryF]

The figures you referred to btw were comparing DCT to a normal auto, which tends to be 10-15% less efficent than a manual.

Don't buy DCT as an excuse to save fuel !!!

[MelsM3]

It's sad, that a 2006 Dodge 1500 [5.7 V8, Auto] gets better EPA figures and a $0 gas guzzler tax.

I saw a 2008 $98,200 M5 the other day...

It has a $3,000 gas guzzler tax!

[e46e92love]

Originally Posted by kishg

agree. i don't believe in garage queens. none of my cars are. But i have 4 cars, the M will be stored from end of Nov thru April. Don't want salt and snow on it.

damn, I got one now, my wife to be has one, and I'm looking to add the M3......your way ahead of me brother, but giving me the goal to shoot for. You sound like my buddy, he leases a X5 4.8i and drives the sh*t out of it from November to March, then in April it gets put away (he just drives occasionally) and brings out his Dinan SC e46M3. But again, he is in a totally different income bracket as me, as in a lot more 0's

[T Bone]

Originally Posted by Samifumi

Trust me. I'll be here, if only to raz you about you about your omniscient Tom Cruise-like "you dont know the history of DCT, I do, I did the research" point-of-view because you've driven past SMGs. Part of the problem with this transmission is that it is wildly speculated about (the "magical, mystical" description was intended for a reason), and there is little to no public real world experience with it. Before you start spouting off as the all-knowing developer of the transmission, why don't you let me talk about what I've also read without suggesting that it's totally asinine or without plausibility (the "smoking crack" comment really sets me off here). I don't know for sure. That has been admitted in everyone of my posts. But without real world numbers on the actual transmission itself, your guess is exactly that: a guess.

If people can honestly get a 3 mpg increase, I will gladly eat humble pie.

Want to make a non-monetary wager on fuel economy? Just a little humilation to the loser of the bet?

How about....

• If the M3 DCT gets 2.5 mpg better than the 6MT, T-Bone will put a Hybrid Sticker and a Honda Type R Sticker on his M6 and take some photos and post.
• If the M3 DCT doesn't yield a 2.5 mpg improvement over the 6MT, Samifumi will join the 6MT club as Mascot and will need to put the 6MT club logo in his sig and "Club Mascot" for 1 month.

Data will be derived by 10 people with DCT from this forum after 3,000 km.

Deal?

[goldminer]

Originally Posted by 1960apache

I know, I just dont understand how a 4 litre motor can use so much fuel compared to much bigger motors that have more horsepower and get better milage. I guess I just expect too much from BMW after all these years of buying their products!!

It probably has to do with gearing and the rpm the car turns at while going 60 mph. I believe that in the Corvette both 5th and 6th gears are overdrive with 6th being a very tall cruising gear (something like 0.65:1). The Vette engine has a lot of low end torque and the car is very light (hundreds of pounds less than the M3) and so can turn a tall gear like this. The result is it is loafing along turning way under 2,000 rpm on the highway. Can someone answer what the M3 turns at 60 mph? I suspect that there will be your answer.

[swamp2]

Originally Posted by T Bone

....improved fuel economy would have absolutely nothing to do with the gear switching mechanism.

The efficiency gains for the DCT Vert have been released. Sure we all know the EU testing cycle is not the US one and not the CAFE one neither. Either way you are right - no way in hell +3 mpg. 3/20 (20 just for the sake of an reasonable/easy number) is 15%. Not going to happen. However the numbers I discuss here have shown about 5%. If the DCT can be run in auto mode with low rpm shifting as enigma suggested the gains will be repsectable and will likely at least knock us down a step on the GGT ladder.

I definitely disagree with you though on where the benefits come from. It comes from 3 key areas. Not sure I am willing to rank them in order of importance but all will contribute.

1. Gearing
2. Shift pattern (auto mode?)
3. Shift times

The first two are obvious. The reason shift times are important: A relaxed shift (not when trying to boogie) is about .75 s. During this time the engine has to decrease its rpm leaving an efficient steady state. The car then coasts AND decelerates from rolling losses and air resistance, losing a good couple mpg depending on condiditons. Then the engine is brought back up to rpm, wasting more fuel to shift smoothly, then you waste fuel regaining all of the speed you lost shifting. These effects, although not enormous are repeated over and over again and do waste a significant amount of fuel. We are only talking in single digit percentages here! DCT should drastically reduce this part of the waste.

[Samifumi]

Originally Posted by T Bone

If people can honestly get a 3 mpg increase, I will gladly eat humble pie.

Want to make a non-monetary wager on fuel economy? Just a little humilation to the loser of the bet?

How about....

• If the M3 DCT gets 2.5 mpg better than the 6MT, T-Bone will put a Hybrid Sticker and a Honda Type R Sticker on his M6 and take some photos and post.
• If the M3 DCT doesn't yield a 2.5 mpg improvement over the 6MT, Samifumi will join the 6MT club as Mascot and will need to put the 6MT club logo in his sig and "Club Mascot" for 1 month.

Data will be derived by 10 people with DCT from this forum after 3,000 km.

Deal?

No problem. I'm ok with having a little fun with it. Admittedly, I'll probably lose this one. Also, I'm not really familiar with the DCT vs 6MT club competition (not sure I can even participate without an M3 on order), but whatever gives the winner the spoils of victory. The problem is you'd have to run it by the leader of the DCT club, and let their members participate in establishing this. I cannot unilaterally hold myself as a representative/agent of the club.

[skierman64]

Originally Posted by T Bone

If people can honestly get a 3 mpg increase, I will gladly eat humble pie.

Want to make a non-monetary wager on fuel economy? Just a little humilation to the loser of the bet?

How about....

• If the M3 DCT gets 2.5 mpg better than the 6MT, T-Bone will put a Hybrid Sticker and a Honda Type R Sticker on his M6 and take some photos and post.
• If the M3 DCT doesn't yield a 2.5 mpg improvement over the 6MT, Samifumi will join the 6MT club as Mascot and will need to put the 6MT club logo in his sig and "Club Mascot" for 1 month.

Data will be derived by 10 people with DCT from this forum after 3,000 km.

Deal?

I wouldn't want to drive around for a month with my new car doing everything I could to get good gas mileage. I'm going to vary throttle position and rpm in order to break it in properly, which doesn't necessarily equate to good mileage.

I doubt we'll get a 3 mpg increase over the 6MT. But we only need an increase of 1 mpg to save $300 on GGT and a 2 mpg increase to pay zero GGT. Any increase in MPG will help with the amount of GGT the DCT owners will pay.

[GS997S]

Originally Posted by MelsM3

It's sad, that a 2006 Dodge 1500 [5.7 V8, Auto] gets better EPA figures and a $0 gas guzzler tax.

I saw a 2008 $98,200 M5 the other day...

It has a $3,000 gas guzzler tax!

I am not sure what a Dodge 1500 is, but it sounds like it might be a truck. If so, gas guzzler tax does not apply to trucks, regardless of how poor the mileage is. It should apply, but it doesn't.

[T Bone]

Originally Posted by Samifumi

No problem. I'm ok with having a little fun with it. Admittedly, I'll probably lose this one. Also, I'm not really familiar with the DCT vs 6MT club competition (not sure I can even participate without an M3 on order), but whatever gives the winner the spoils of victory. The problem is you'd have to run it by the leader of the DCT club, and let their members participate in establishing this. I cannot unilaterally hold myself as a representative/agent of the club.

There is no leadership on MDCT. I will make it more fair for you. If MDCT gives 2 mpg+, you win, else I win.

No worries, people will particpate.

Just to be exact:

• If the M3 DCT gets 2 mpg better than the 6MT, T-Bone will put a Hybrid Sticker and a Honda Type R Sticker on his M6 and take some photos and post.
• If the M3 DCT doesn't yield at least a 2 mpg improvement over the 6MT, Samifumi will join the 6MT club as Mascot and will need to put the 6MT club logo in his sig and "Club Mascot" for 1 month.

[!Xoible]

how the hell does tranny give 2+ mpg?!

[T Bone]

Originally Posted by skierman64

I wouldn't want to drive around for a month with my new car doing everything I could to get good gas mileage. I'm going to vary throttle position and rpm in order to break it in properly, which doesn't necessarily equate to good mileage.

I doubt we'll get a 3 mpg increase over the 6MT. But we only need an increase of 1 mpg to save $300 on GGT and a 2 mpg increase to pay zero GGT. Any increase in MPG will help with the amount of GGT the DCT owners will pay.

Above would roughly be offset by babying the car abit for the first 1000 kms.

Originally Posted by swamp2

The efficiency gains for the DCT Vert have been released. Sure we all know the EU testing cycle is not the US one and not the CAFE one neither. Either way you are right - no way in hell +3 mpg. 3/20 (20 just for the sake of an reasonable/easy number) is 15%. Not going to happen. However the numbers I discuss here have shown about 5%. If the DCT can be run in auto mode with low rpm shifting as enigma suggested the gains will be repsectable and will likely at least knock us down a step on the GGT ladder.

I definitely disagree with you though on where the benefits come from. It comes from 3 key areas. Not sure I am willing to rank them in order of importance but all will contribute.

1. Gearing
2. Shift pattern (auto mode?)
3. Shift times

The first two are obvious. The reason shift times are important: A relaxed shift (not when trying to boogie) is about .75 s. During this time the engine has to decrease its rpm leaving an efficient steady state. The car then coasts AND decelerates from rolling losses and air resistance, losing a good couple mpg depending on condiditons. Then the engine is brought back up to rpm, wasting more fuel to shift smoothly, then you waste fuel regaining all of the speed you lost shifting. These effects, although not enormous are repeated over and over again and do waste a significant amount of fuel. We are only talking in single digit percentages here! DCT should drastically reduce this part of the waste.

We are not really disagreeing. Gearing is the most important consideration. I just don't place too much weight on the shift times and the shifting algorithms.

In a rare defence of the 6MT, if I wanted to drive for max fuel economy, I would push the car hard in 1st and shift at 6000 rpm and 2nd to the desire cruise speed and then shift right to 5th or even 6th.....this meat algorithm will be as good as any computer algorithm.

[swamp2]

Originally Posted by T Bone

We are not really disagreeing. Gearing is the most important consideration. I just don't place too much weight on the shift times and the shifting algorithms.

In a rare defence of the 6MT, if I wanted to drive for max fuel economy, I would push the car hard in 1st and shift at 6000 rpm and 2nd to the desire cruise speed and then shift right to 5th or even 6th.....this meat algorithm will be as good as any computer algorithm.

Well I think we are disagreeing. My point is that the entire shift system, most notably the shift time will noticeably contribute to the efficiency gains had by M-DCT. You clearly stated nearly the exact opposite to that. Do note again my list abouve WAS NOT in order of importance. I am not prepared to speculate on the proper order.

I have also heard about the high rpm in 1st then shift to a very high gear for the best fuel economy. Sounds possible but also a bit counter intuitive. If that is true it would also seem to strongly support my theory that the shift time is a critical piece of the mpg gains of M-DCT. Do you have some references/actual test data on this topic, I would be keenly interested? Also, don't you think it would make sense for one of the automatic modes of M-DCT to be an efficiency mode, and if a driving method like you mention really does work, this mode could implement something along those lines? Sure it probably would not be best to implement it absolutely literally if it requires always shifting at 6k rpm from 1st then over to 5th or 6th, but the algorithm could apply lessons/results from the method to improve mpg and to let the silicon computer do the work. Surely your contention was not that you (i.e. the meat computer) can best silicon in a pure contest of mpg? That is a bit contradictory...

[T Bone]

Originally Posted by swamp2

Well I think we are disagreeing. My point is that the entire shift system, most notably the shift time will noticeably contribute to the efficiency gains had by M-DCT. You clearly stated nearly the exact opposite to that. Do note again my list abouve WAS NOT in order of importance. I am not prepared to speculate on the proper order.

I have also heard about the high rpm in 1st then shift to a very high gear for the best fuel economy. Sounds possible but also a bit counter intuitive. If that is true it would also seem to strongly support my theory that the shift time is a critical piece of the mpg gains of M-DCT. Do you have some references/actual test data on this topic, I would be keenly interested? Also, don't you think it would make sense for one of the automatic modes of M-DCT to be an efficiency mode, and if a driving method like you mention really does work, this mode could implement something along those lines? Sure it probably would not be best to implement it absolutely literally if it requires always shifting at 6k rpm from 1st then over to 5th or 6th, but the algorithm could apply lessons/results from the method to improve mpg and to let the silicon computer do the work. Surely your contention was not that you (i.e. the meat computer) can best silicon in a pure contest of mpg? That is a bit contradictory...

We agree on gearing

I believe shift time is irrelevant.

The last issue is the programming of the auto shifter. I think the meat computer is better in this case only because BMW will not shift from 1st or 2nd to 5th and 6th directly. Customers would never accept it, they will want the car to run through the gears. 1, 2, 3, 4, 5, 6, 7......not 1,2....5,6,7. The meat computer can shift 1st or 2nd to 5th or 6th directly (I do it all the time). So not contradictory.

[!Xoible]

how do u know how much 6MT gearing is different from mdct?

oh.. coz it's 7 speed huh?

[enigma]

Originally Posted by mantis

how do u know how much 6MT gearing is different from mdct?

oh.. coz it's 7 speed huh?

Because the pdf files released by BMW had the gear ratios in it....

I expect the shifting program for the DCT in auto mode to be completly different than what many expect. Because it can do the near zero time shifts without lifting there is no reason to hold the lower gears as long as the SMG did. I expect it to shift a lot more like a normal auto in terms of shift point selection.

[swamp2]

Originally Posted by T Bone

We agree on gearing

I believe shift time is irrelevant.

The last issue is the programming of the auto shifter. I think the meat computer is better in this case only because BMW will not shift from 1st or 2nd to 5th and 6th directly. Customers would never accept it, they will want the car to run through the gears. 1, 2, 3, 4, 5, 6, 7......not 1,2....5,6,7. The meat computer can shift 1st or 2nd to 5th or 6th directly (I do it all the time). So not contradictory.

Good about gearing.

Still about shift times? Are you positive?

What about some evidence on the driving style to promote the best mpg? I am not trying to challenge you on this I am very genuinely interested and again I have heard the same exact argument. Doesn't it make a ton of sense that if your contention about how to best obtain mph in a meat machine/MT vehicle is valid then a very likely conclusion is that shift times must be a big part of the gain?

As far as skipping gears that really should not be a problem. Gear changes to the same shaft are likely to be slightly problematic (by that I simply mean about as fast as SMG) but any changes, up or down like 1<->4, 2<->5, 3<->6 and 4<->7 should be easily possible. It just mean a different synco is moved but all clutching and other operations are identical. For instance we do know already than in D1 the car acutally starts in 2nd gear, combine that with a skip right over to 5th and that seems like a good start to a lot better mpg. As well we know on the performance side that there is a multi-shift "kick down" shift pattern that will drop as many gears as required to obtain maximum acceleration. Whether or not BMW will offer gear skipping patterns specifically to obtain improvements to mpg is entirely another question. If all it took was another D mode option accessed by the Drivelogic mode lever/button I don't see why that would not be available. Hell call it the green or hippie tranmission setting! As long as guys like us get S5/S6 I can still hope for a D=hippie setting as well.

[swamp2]

Originally Posted by enigma

Because the pdf files released by BMW had the gear ratios in it....

^

Ugh, mantis, really time to get with the program...

(in general). It seems you are always too busy posting to actually read.

[devo]

Originally Posted by skierman64

I wouldn't want to drive around for a month with my new car doing everything I could to get good gas mileage. I'm going to vary throttle position and rpm in order to break it in properly, which doesn't necessarily equate to good mileage.

I doubt we'll get a 3 mpg increase over the 6MT. But we only need an increase of 1 mpg to save $300 on GGT and a 2 mpg increase to pay zero GGT. Any increase in MPG will help with the amount of GGT the DCT owners will pay.

You may need more than 1 mpg to have M-DCT knocked down to the next ($1,000) bracket, considering these are averages of highway/city (55/45?) and each increment is 1 mpg, right?