Why did BMW do this?

[Earendil]

Very interesting!/nice computations. So a 4.1 is quicker to 60 mph than a 3.73 rear-end. But, is it quicker to 60 mph than an e30 M3?


MAXELHOFF

Since the American M3 had almost 20 more torque, and 200+ fewer pounds, I'm going to go with "no" :)

That said, what makes a good drag car is a far cry from what makes a good road racing car, which is what the M3 was built for. In a straight line the 325i may look like it comes close, but that S14 was designed for high revving power delivery and had a perfectly matched transmission and diff compared to the 325i.

Interestingly enough, I read a review a little while back of the 325i, written when it first came out, by car and driver I think. One of the things they loved about the car was how wonderfully the transmission had been designed for the engine. You could go from gear to gear and stay inside the engines primary power band. Making our fun little family sedan drive completely different when pushed "aggressively" than when mommy is sitting copilot :)

[Earendil]

You can short shift the 4.10 and get almost the same effect as the 3.73
will give you, so any advantage the 3.73 had, is really not going to help
with acceleration.

do you mean short shift the 373 and make it act like a 410 (but with less torque)? Short shifting the 4.10 will make it lose any advantage it might have over the 3.73. You'd never short shift in a drag race for example, only on a track for strategic purposes, or if it's snow :D

In a car with not a lot of torque (e.g. 4 cylinder or even a small 6 cyl)
you need to spend time in the area where the motor makes horsepower.
Driveability is where the the higher gear ratio (3.73) is an advantage.
A daily driver that is constantly needing to be shifted is more work
to drive. The 4.10 will require you to shift more often, and will sound
and feel more "buzzy" at highway speeds.

quite right. I prefer daily driving my e46 because all the gears are longer, meaning each gear has more "room" before I either have to shift, or feel like I'm "winding her up".

Drag racers run low gear ratios (larger rear end numbers) for high acceleration.
If you want faster 0-60 times, 4.56 ratio, (if it's available - I'm new to BMWs)
4.88 or even 5.39 ratio would make 0-60 faster, depending on how fast you can shift.

I'd maintain that a high diff ratio only helps if it doesn't add an extra shift to your run, and leaves you crossing the line at the bottom of a gear. Just like a 3.73 will be faster to 53mph then the 4.10 ever will.

There's a lot more to it than the basic numbers can show though.

http://www.wallaceracing.com/reargear.htm

http://www.wallaceracing.com/calcrgr.php

http://forums.corvetteforum.com/c4-z...ear-ratio.html

Thanks for the links!

I'm need to go find gear ratios for the M3 getrag 265 now. I'm curious where it's shift points are... Or course this also means finding the stock tire size too...

[Mark 42]

I'm saying short shifting a 4.10 makes it feel like a 3.73.

3.73 will be slower to 50, 53 or 60 mph. The 4.10 lets you spend more
time with the engine where it makes power. That's just the way it works
in the real world. You have to drive them rather than look at numeric speeds
at gear ratios.

You can make up the time it takes to do one extra shift in the advantage
gained by better acceleration. Most people who practice can shift gears
pretty fast - I would guess it's about about 1/4 second. I'll see if I can find
a real number.

[Mark 42]

Looks like my 1/4 second estimate is pretty realistic:

Quote from a 2006 Cayman S brochure

"In manual mode, the driver can change gears by hand using rocker controls located on the steering wheel. Gearshifts are completed in about 0.2 seconds with virtually no interruption in drive—very comparable to a well executed gearshift in a manual transmission car."

That probably would just about even them out, I suspect.
Other than running a car, changing the diff gears & running it again,
I don't think there would be a way to conclusively determine it.
Even two otherwise similar cars with 3.73 and 4.10 diffs would leave
me wondering whether it was the gear ratio, or something else.

But, drag racers have been running larger rear end ratios for many years,
even with engines that have a lot more torque than what we drive, so
I'd put my money on the 4.10 beating the 3.73 in a drag race, especially
a short drag race. It's a gut call, I guess, but I've been around awhile,
and have a lot of non scientific (experiential) data.

There are other ways to accelerate faster...

http://www.rcramer.com/fun/econobox/

60 mph = 88 ft/sec
88ft/sec x .25 sec = 22 ft.

So, if the car that had to do one extra shift STOPPED MOVING during
the time it takes to shift, it would lose about 2 car lengths.

Coasting, while the other car is still accelerating, you'd probably lose 5 ft.
So, if you could gain enough acceleration to have a 1 car lead at 60 mph
(about 6 seconds) you would win the race.

But first across the line is not the same as first to a certain speed, and
that is a difficult number to measure accurately.

So I'm back to what my gut instinct says from experience - which is the 4.10
still gets there first.

Drive both & you'll see why.
I have a 318i with an M42 that I'm pretty sure has a 4.10 diff (I'd have
to go downstairs to get the number on the diff tag - I wrote it down
last Saturday when I was under there to replace an exhaust hanger)

[Earendil]

I'm saying short shifting a 4.10 makes it feel like a 3.73.

3.73 will be slower to 50, 53 or 60 mph. The 4.10 lets you spend more
time with the engine where it makes power. That's just the way it works
in the real world. You have to drive them rather than look at numeric speeds
at gear ratios.

You can make up the time it takes to do one extra shift in the advantage
gained by better acceleration. Most people who practice can shift gears
pretty fast - I would guess it's about about 1/4 second. I'll see if I can find
a real number.

I'm aware of the practical. I own both a 3.73 and a 4.10 and have swapped them a couple times. I'd be running a 4.10 full time once I rebuild it, since right now it sucks for track use which has become the primary purpose for owning my e30. I am however no track expert.

I'll arbitrarily say that the time it takes you to shift is still more than it takes a 3,73 to pull those last 5mph at 6000rpm in second gear. It'll take the 4.1 what feels like forever to pull those last 5mph at the bottom of 3rd.

You get better acceleration, but over less time.

[Earendil]

Looks like my 1/4 second estimate is pretty realistic:

Quote from a 2006 Cayman S brochure



That probably would just about even them out, I suspect.
Other than running a car, changing the diff gears & running it again,
I don't think there would be a way to conclusively determine it.

But, drag racers have been running larger rear end ratios for many years,
even with engines that have a lot more torque than what we drive, so
I'd put my money on the 4.10 beating the 3.73 in a drag race, especially
a short drag race.

A drag race? Sure, I'd say the 4.10 would win in a quarter mile based on the average exit speed of the 325i stock in a drag race. My point was not which is faster to drag race a 1/4 mile though :)

[Mark 42]

It would be fun to do the experiments!
I think it'd be close though. When does the rev limiter cut in?

I know my FZR1000 did about 80 mph in first gear... it was scary fast,
and wouldn't stand a chance against today's version (FZR1000 became
YZF1000 which became R1)

[BergerNJ]

so I read the first post, then the entire first page. I then went to the last page, and saw an argument about differentials.

This is the definition of complete success for a troll thread. I browse the internet like its my job and to see this type of thread on r3v, disgusts me.

[Mark 42]

This is the definition of complete success for a troll thread. :hitler: I browse the internet like its my job :hitler: and to see this type of thread on r3v, disgusts me.:hitler::hitler::hitler:

So, don't read it. No one forced you. It's not your job.
Some of us found it to be an interesting discussion.

Some people hate off topic posts. I like when a thread drifts way off topic
after a few days - it makes it like a real life discussion that evolves
as real humans go with the flow of the conversation.

This thread is almost two months old, and 6 pages long (at 40 posts per page).
That's a long time to spend discussing why BMW put a 4 cylinder in the M3.

BTW, I got the number on my Diff - it's 4 10 9661

Anyone know what the specs are (can it be determined just from that number?)

[Earendil]

so I read the first post, then the entire first page. I then went to the last page, and saw an argument about differentials.

This is the definition of complete success for a troll thread. I browse the internet like its my job and to see this type of thread on r3v, disgusts me.

Didn't read the entire thread and blindly add an insult to the end and insinuate the OTHER guy is a troll... I see what you did there.

[leothedrummer]

I'm need to go find gear ratios for the M3 getrag 265 now. I'm curious where it's shift points are... Or course this also means finding the stock tire size too...

I might be able to help here. I have an E28 M535i, which as the same gearbox as the E30 M3 (Getrag 265/5, close ratio with a dogleg first and 1:1 fifth). Going by the sales brochure I have for the car:

1st - 3.72
2nd - 2.40
3rd - 1.77
4th - 1.26
5th - 1.00

Final drive - 3.46:1

Whilst my stock tire size is different (M535i's ran metric tyres...ugh), a quick look on http://felgenkatalog.auto-treff.com/ says that the E30 M3 has a stock tyre size of 225/45R16.

Hope this helps!

[reelizmpro]

Us m3 never came with dogleg.

[Mark 42]

This is the definition of complete success for a troll thread. I browse the internet like its my job and to see this type of thread on r3v, disgusts me.

So, don't read it. No one forced you. It's not your job.
Some of us found it to be an interesting discussion.

Didn't read the entire thread and blindly add an insult to the end and insinuate the OTHER guy is a troll... I see what you did there.

:stupid: :curse:

[leothedrummer]

Us m3 never came with dogleg.

Sorry, didn't realize that. My mistake