what would a 4.10 do to my M20?

[Todd Black 88]

No, not really.

What I said was switching from a 3.73 to a 4.10 is only a couple hundred rpm difference, it's negligible. Doesn't matter if the car was an auto 3.73 getting a 4.10, or a manual 3.73 getting a 4.10, the difference will be a couple hundred revs.

[JinormusJ]

That's what I stated in my previous posts

[QUKBMER]

It is about a 500 rpm difference not acouple of rpm's using a 3:73 vs 4:10 rear diff. I track my car and daily my car 6 days a week.Driving at 80 to 85 mph you will be right at 4000 rpm's. 70 to 75 mph you will be turning around 3400/3500 rpm's . I drive 36 miles one way to work with freeway and side streets, 72 miles round trip and i fill up about every 4 days at about 300 miles on a tank. Stock m20 2.5 k&n filter/Markd chip 91 oct w/17.5 lb injectors/ billet 272 cam.

[goldenbb]

EatsHondas, I have a 5spd. with a 3.73 and I have a similar feeling when I drive--even around town I just zip up through the gears. Highway cruising, I can't remember the exact rpm, but it seems high for a stock 325is. I've been considering trying to find a 3.53 or whatever the next taller gearing available is and trying that. The car is fun, but it's almost annoying at times. A 4.10 for me would be un-driveable.

[Ether-D]

I'd have to agree with most on this thread. I have the 4.10lsd in my 5-speed m20. I love how fast it feels, but I hate the lost mpg. I went from 26mpg to about 21-22mpg. Bear in mind that that's partially from the higher revs at speed and partially because it's sooooo much fun to stomp the shit out of it now. For what it's worth, I'm going back to the 3.73. You wanna buy a 4.10 viscous LS ix diff? I'll have one in a week or so...

[EatsHondas]

EatsHondas, I have a 5spd. with a 3.73 and I have a similar feeling when I drive--even around town I just zip up through the gears. Highway cruising, I can't remember the exact rpm, but it seems high for a stock 325is. I've been considering trying to find a 3.53 or whatever the next taller gearing available is and trying that. The car is fun, but it's almost annoying at times. A 4.10 for me would be un-driveable.

Oh man, sounds like you're describing a 4.10! I thought the 3.73 would make you lose a little giddyup in exchange for a little better MPG on the highway and making 1st gear a little more usable. I guess the ratios are just too similar to make much of a difference either way.

[nando]

it will turn 1st gear almost useless when trying to drag race.. it will lower your top speed and ruin your mpg at speed. supercharge it if you want to boost acceleration off the line...

it's not going to lower your top speed. no stock E30 is gear limited - they run out of breath long before that point.

as far as the MPG difference, it will be negligible. in city driving you can actually use 4th and 5th gear while cruising.

as far as the RPM difference - it's not anywhere near 500rpm. it's only about 300rpm at 70mph. at 100mph it's 450rpm difference. at 50mph, it's less than 200rpm.

people like to exaggerate the difference. these aren't buicks - they aren't supposed to accelerate like slugs and chug along at 60mph/1500rpm. if anything, the engine is more efficient when its in it's torque band, which starts between 3000-4000rpm.

[CabbE30]

^Usually I'd agree w Nando, but you WILL see reduced MPG. I went from 4.10 to 3.73 and saw a gain in 4-5 mpg w mixed driving.

[goldenbb]

Yes, I guess a little too similar. I will double-check that I really have a 3.73, but that's what would come stock on a '90 325is and I'm pretty sure the PO didn't change it (it certainly looks the same age as the rest of the undercarriage).

I really want to rebuild the whole rearend and find a taller geared lsd and it should be a kick ass daily driver for me.

[Killacortes]

I agree with nando. He is on point at 3k going 70mph. I still get pretty damn good mpg compared to a 3.73 I think that it's because of my new cap and rotor, plug wires, and o2 sensor

[digger]

you cant have your cake and eat it to sometimes.....

[nando]

^Usually I'd agree w Nando, but you WILL see reduced MPG. I went from 4.10 to 3.73 and saw a gain in 4-5 mpg w mixed driving.

A 20% change in fuel economy from a 9% change in gearing seems like a stretch.

[digger]

i run a 3.91 but was using a 3.46 at one point for several months. cant say i noticed anything dramatic with economy maybe 10%

[SmokeE30]

Tire Size also needs to be taken into consideration, you could run a 4:10 with a taller tire and have your cruising rpm the same as a 3.73 running a shorter tire.

[Ether-D]

A 20% change in fuel economy from a 9% change in gearing seems like a stretch.

Well, for me, the 4.10 makes me wanna hawg down on the throttle more often cause it's more fun. That could easily make up my extra 11%...