Which diff ratio for M42?

[KenC]

I downshift a lot less with the 4.45 too

[Hick]

3.73 works great with the M42. Frankly, its all down to how you want to drive it. Ive run my chipped, M20 flywheel and 3.73LS M42 car at the autocross for a few years now, its quick enough, i liked it more than the 410 because i could stay in 2nd longer.

The M42 is slow no matter what diff you put in it. But from experience ive found that the car likes to pull out of a corner in 2nd, 4.10 or 3.73. If you go higher you may end up stuck in an ineffective RPM range somewhere in between 2nd and 3rd (ie too high for 2nd, too low for 3rd)

Sure, go hunt down a LS 4.27 or 4.45, GOOOOOOOOD LUCK! Finding a 3.73 LS is as simple as it gets.

Unless your swapping out an open diff for a LS unit dont bother.

[carnurd]

Well, I'm a huge fan of the 4.10 I do think the highway rpm is a little nuts(almost 4k @ 80mph). However in AutoX I like it, as I have plenty of power where I need it(I have big cams and a 7.5k rpm limit). And as far as road racing, the gearing is nearly perfects for buttonwillow CW13. One thing is I did replace my open 4.10small case with a LSD 4.10 med case. Yes I know it weighs more and will make my car actually slower, however I intend to beat the crap out of this car(track whore'n) so I like the durability. I hear the 4.45 diff is great for road racing mainly, but not worth it to drive on the street. My lightweight flywheel slightly offsets the heavier diff..

[KenC]

I love the 4.45 for the street. Our highway speed limits here are 55, so I'm usually cruising around 65-70mph.

I have a 323i 13lb flywheel in mine too. Revs up pretty quickly.

I stumbled upon the diff with 110k miles for a killer price so I couldn't pass it up. You're right though, they are super rare.

[Cal]

honestly, with the stock motor, a 4.10 is about right.

This is what I decided in the end and got a medium case 4.1 and will order a Mark D chip shortly.

[M-technik-3]

I love the 4.45 for the street. Our highway speed limits here are 55, so I'm usually cruising around 65-70mph.

I have a 323i 13lb flywheel in mine too. Revs up pretty quickly.

I stumbled upon the diff with 110k miles for a killer price so I couldn't pass it up. You're right though, they are super rare.

I did not need anymore spare metal in my garage. It was sold at rock bottom pricing as I knew it would head out the door at that price.

Ti's are where the small case 4.45lsd are at. Look for an automatic 95 model if you need one.

[freedomrabbit]

3.73, Up or Down?

What kind of gas mileage you getting with the 2.93 rear end. Of course, tell me what kind of mods you got, and how much power you're putting down when you answer me. Thank you.

freedom rabbit

[Ryann]

I think for the m42 a 4.10 is too tall around town, about right for country back road high rpm thrashing, and too short on the freeway.

[Bearmw]

What about the 3.90 small lsd from a late 320i ? Seems like a good choice and BTW I have one I may sell ;)

[RadioRon]

I'm running a 4.27 LSD in my '91 318is, along with 13lb flywheel, 13lb wheels, MarkD chip (7200rpm). The focus of this car is autocross and it all works very well.

[///digitalme]

im running a 4.10 open diff, i just purchased a 3.91vlsd
and see how that goes

[Ian Bowers]

I really like the 3.73 in the car. It isn't much slower to 60 than the 4.1, and I improved my MPG by 7 the last time I checked. (28 was my average on fill-up with the 4.1, 35 was my average when I filled it up last.)

[Hey-U]

I'm running a 4.27 lsd in my 92 vert with Mark D 93 chip. It tops out at 200k and 6k rmp. I like the diff for city driving but wish the trani had a sixth gear for highway. My thoughts are to add more hp, in that case I think I would want to change to something lower, so this thread is very interesting.

[expressfish]

same here, 4.27's. at highway speeds (bout 60mph) I'm buzzing in the 3 grand range. I hate it for fuel mileage but its oh so good when accelerating. How do you like you Markd chip?

[tjts1]

I downshift a lot less with the 4.45 too

Sort of defeats the purpose of driving a car with a manual transmission.