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General E46 Forum
This is the place to get answers, opinions and everything you need related to your E46 (sedan, coupe, convertible and wagon) BMW!

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Old 09-09-2010, 10:08 AM   #1
TiAg2247
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Who says shorter gears give poor mileage?

I respectfully disagree.



364km = 226mi. And for those curious Americans, my odometer is sitting at 156k miles and counting

This is on my 3.62 LSD with only a 5spd Granted, I did a lot of HWY driving in this time, but normally I average around 520 km (~323mi) per tank which is nothing to scoff at considering the HUGE performance gains from the shorter gearing and limited-slip capabilities.

I see people here hesitant about doing even the 3.46 gearing or even more conservative swaps because you're worried they're worried about poor mileage, DO IT! You'll be fine.
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Last edited by TiAg2247; 09-09-2010 at 11:06 AM. Reason: sp.
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Old 09-09-2010, 10:47 AM   #2
Toxic0n
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Actually logic and basic math say that with shorter gears you will be at higher RPM at a given speed and hence will have worse mileage. Your particular example does not disprove anything but congrats.
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Old 09-09-2010, 11:05 AM   #3
TiAg2247
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Clearly my post wasn't intent on disproving simple physics, but, it seems the message flew right over your head: the purpose of the post was to show real-life implications of the modification in question.

Cheers.
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Old 09-09-2010, 11:20 AM   #4
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and I typically get about a hundred more miles per tank with my 3.07 and sixth gear...
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Old 09-09-2010, 11:25 AM   #5
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In your case that's a sampling problem. No way in hell shorter gears will improve mileage. This reminds me of the joke when scientists keep ripping the legs off of a cockroach one by one, then upon whistling loudly the cockroach runs away, until no more legs are left and the cockroach does not run away, the scientists conclude that a cockroach can't hear without its legs.
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Old 09-09-2010, 11:29 AM   #6
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Originally Posted by Toxic0n View Post
Actually logic and basic math say that with shorter gears you will be at higher RPM at a given speed and hence will have worse mileage. Your particular example does not disprove anything but congrats.
This.
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Old 09-09-2010, 12:38 PM   #7
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it's good to see that this mod can be done without a harsh penalty in terms of fuel economy.
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Old 09-09-2010, 12:40 PM   #8
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2.93 to 3.38

23.0 MPG to 23.5 MPG

lol don't ask haha... i have no idea
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Old 09-09-2010, 12:50 PM   #9
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Quote:
Originally Posted by JJR4884 View Post
2.93 to 3.38

23.0 MPG to 23.5 MPG

lol don't ask haha... i have no idea
mileage or MPG's are all relative.

I believe in the case of the OP, his driving conditions, other variables and 3.46 have offered him comparable MPG's to that of his old setup. Does that mean you will experience the same thing? Impossible. Why? because nobody can reproduce OP's exact driving conditions, mechanical properties of his engine/drivetrain, climate, tire condition, driving behavior or road conditions exactly.

In JJR's case, same thing. There very well may be an MPG gain in using a higher diff for city driving. You could experience the same. You could experience better MPG's.

However, in the case of normal highway driving, scientifically your chances of experiencing higher MPG's are highly unlikely. The engine is less efficient on a normal flat highway with a 3.46 compared to a lower differential.
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Old 09-09-2010, 01:15 PM   #10
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I always when someone speaks of "miles per tank"

Unless we all fill our gas tanks until they overflow and drive until we run out of gas, this is a highly inaccurate way of calculating your mileage.
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Old 09-09-2010, 02:05 PM   #11
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Originally Posted by spage View Post
I always when someone speaks of "miles per tank"

Unless we all fill our gas tanks until they overflow and drive until we run out of gas, this is a highly inaccurate way of calculating your mileage.


i always fill my car up when it is between a quarter and a half... usually thats after 230-300 miles of driving
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Old 09-09-2010, 02:22 PM   #12
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Too bad 100% flat and straight highways dont exist in the real world

My uncle claims he gets better milage by running the engine in its most-efficient-power-range.

Maybe thats whats happening here? Op's short gearing runs his engine at a more efficient rpm where it developes more power, versus pushing it 80% throttle to get up a hill at 1700 rpm.

The germans dont cruise at 65-75, they can go much faster on the autobahn, so maybe thats where the 6sp& 2.93 is best.
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Old 09-09-2010, 03:07 PM   #13
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Quote:
Originally Posted by NOVAbimmer View Post
and I typically get about a hundred more miles per tank with my 3.07 and sixth gear...
I wish I had 6th.
Quote:
Originally Posted by nk_zhp View Post
In your case that's a sampling problem. No way in hell shorter gears will improve mileage.
And no way in hell did I ever claim to improve mileage. Where the hell are you drawing this statement from?
Quote:
Originally Posted by SLVR JDM View Post
This.
See previous reply, as quoted below.
Quote:
Originally Posted by dbworld4k View Post
Clearly my post wasn't intent on disproving simple physics, but, it seems the message flew right over your head: the purpose of the post was to show real-life implications of the modification in question.

Cheers.
In other words: changing to a shorter geared differential doesn't kill fuel economy as severely as some people fear.
Quote:
Originally Posted by blk04zhpcpe View Post
it's good to see that this mod can be done without a harsh penalty in terms of fuel economy.
It seems like at least one person understood my post.
Quote:
Originally Posted by JJR4884 View Post
2.93 to 3.38

23.0 MPG to 23.5 MPG

lol don't ask haha... i have no idea
LOL now there's a strange situation.
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Old 09-09-2010, 03:25 PM   #14
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LOL now there's a strange situation.
I drive slower on the highway because I don't like the idea of cruising at 3000 rpms... i know it isn't doing any harm, but for the peace of mind, i'll chill at 70 at 2700
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Old 09-09-2010, 03:35 PM   #15
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Quote:
Originally Posted by NOVAbimmer View Post
and I typically get about a hundred more miles per tank with my 3.07 and sixth gear...
I get about 200 more... 450/tank!
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Old 09-09-2010, 04:44 PM   #16
eric_waltrip
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I get between 26-30 highway mpg with 3.46 ever around 4k


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I road in my buddies with 350hp and he switched highways at wot scared tge piss out of me felt as fast other bodies 500hp supra awesome car they are rare hopefully they will bring them back rx8s r ok but I don't like tge rear doors and odd shape and lackbof turbos
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Old 09-09-2010, 04:59 PM   #17
MachRc
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my supercharged 330 with 10psi with 3.07 gearing got me honest 19-23 mpg

The m3 now with 6psi with 3.62 gets me an honest 15-20mpg.

only if I could slap a 3.07 LSD in the M, then I would get alot better gas milage and be able to hit 90 in second gear.

If only


I just bumped luask thread..

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Old 09-09-2010, 08:14 PM   #18
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mehh i average about 250 miles to one half tank of gas and 440 to a full tank mixed highway and street driving. stock 323ci steppy

440 is more city than highway too :p
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Old 09-09-2010, 08:18 PM   #19
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Back in the Day,
I had an 86 M535i with an M30 motor, 5 speed and 3;73lsd...
at 85mph I was turning around 4K but got 27mpg on the highway...
every motor has it's own sweet spot where it prefers to run
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Old 09-10-2010, 04:29 PM   #20
Minnoe07
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I say that shorter gears give poorER gas mileage.

Shorter gears are probably the biggest MPG hit you will take with any mod on your car. I lost more mpg with the differential swap from a 2.93 to a 3.38 than I did with the supercharger. I remember getting around 400 miles to a tank before the differential. Now I'm lucky if I get 320 miles. 80 miles is a lot to some people. That's about 4 gallons of gas on my current mpg.

Personally, I think it is worth it, but not everybody is willing to sacrifice that much for a mod.
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