4.45 diff for M42 manual - fun or annoying?

[Jay-Vee]

Hi Everyone,

Just picked up a 4.45 diff and thinking of using it with my M42 and Getrag240.

I wanted to add some 'spice' and a bit quicker acceleration, but now worrying that it might just be annoying if its way to short a ratio.

The car is mainly a restoration project and will be only used occasionally for days out, maybe some light track or auto-x, and maybe highway use once a year to my beach house (1.5hr drive).

What do you all think?

[bmwman91]

[TobyB]

It will be both- fun until you get up to 65, annoying cruising thereafter.

Also, 1st becomes truly useless, 2nd is not much better, but third is still too tall.
Once you're at revs in 3rd, however, the 3-4-5 gearshifting is fun.

I stuck one into a street 2002 once, for troubleshooting.

t

[Wanganstyle]

Install it.

Then you’ll need to install a f20c with 9krpm and 6 gears for optimization


Sent from my iPhone using Tapatalk

[roguetoaster]

I have run one in my 318 for 2.5 years or so. It hurts mileage, but it really does make the car more fun, and in my opinion, the highway revs are not a big deal.

Remember, we are talking less than a 10% change in ratio here, so all of the gears are still quite useful, and you gain a new gear mostly for spinning tires, as well as no longer needing to drop a gear to pass on the highway.

[brads2002]

M42's love to rev. I bet it will be fun!

[Chuck C]

Got a 4.27 in my M42 track car--pretty buzzy on the highway, but fewer shifts at the track. 1st gear is only to get rolling, but 3,4 and 5 are nice.

[e30davie]

If i it was 4.1 and now its going to be 4.45 thats an change of ~8%, So if you were say 2900 on the highway before, you will be ~3100rpm with it. I don't think it would be an issue. you will lose approximately 8% in fuel economy as the engine is physically spinning faster all the time.

I once put a shorter ratio diff in a car and it made life nicer on the highway cause the exhaust was quieter at the higher rpm!

I too should buy a beach house.

[e30s50dan]

Got a 4.27 in my M42 track car--pretty buzzy on the highway, but fewer shifts at the track. 1st gear is only to get rolling, but 3,4 and 5 are nice.

I also have a 4.27 in my soon to be track car.Im excited to see how it will be

[Jay-Vee]

Thanks for the advice guys, maybe ill put it in and see how i go - the car is mainly for some fun (although not interested in spinning tires), and ill still keep the original one anyway.

[roguetoaster]

Blah, blah (not interested in spinning tires)

What?!? Unacceptable.

At the very least do the Australian burnout with the back end in a shed.

[Jay-Vee]

ok ok... Even though its not my usual interest, I cant lie... that does sound tempting haha...

[Bmwdayz]

I've run 4.44 diffs in m42 cars and 4.45 in s14 cars. If it's not your daily Hwy cruiser and more for fun do it. It's a lot of fun! Even on the Hwy it's not to bad at all

[varg]

The I4 droning away will get old fast imo. I didn't even like the 4.10 when I had my M42, I can't imagine a 4.45.

M42's love to rev. I bet it will be fun!

Love to rev? I'd say "has to rev but not very high." An engine that taps out past 6,500 even if you set the rev limiter to 7,500rpm (speaking from personal experience) may be rev happy by old iron V8 standards but for a 1.8L 16V I4 it's... unimpressive. It needs some cams to be any good past the stock limiter but they're $$$$

[Wanganstyle]

The I4 droning away will get old fast imo. I didn't even like the 4.10 when I had my M42, I can't imagine a 4.45.



Love to rev? I'd say "has to rev but not very high." An engine that taps out past 6,500 even if you set the rev limiter to 7,500rpm (speaking from personal experience) may be rev happy by old iron V8 standards but for a 1.8L 16V I4 it's... unimpressive. It needs some cams to be any good past the stock limiter but they're $$$$

Ive got a 4,56 in my car with 6 gears and 9200rpm. its not that fun all the time; the original 4,10 would be more ideal for most