Differential gearing?

[boxy02]

I recently pulled this LSD unit from a 79? 320. The #'s on the bottom were:

HH8

12015510-GGG50

F

In that configuration. Anyone know what gearing it is?

Thanks,

Mike

[Mike Self]

'79 with a four speed, it's most likely a 3.64. I think the marking would be "11/40." The 1.8 liter engines with 5 speeds started in 1980; they had 3.91 diffs.

cheers

mike

[boxy02]

Thanks! Yup, it was a 4 spd....3.64, that's good right?

[BarryA]

Personal opinion, but for anyone whose car is primarily driven on the street and who is staying with a tire/wheel combo in the general area of 185/70x13 a 3.64 diff may be preferable to a 3.91 - even with an E21 OD 5 speed installed.

Running that combination (185/70x13 tires, 3.64 diff and 5 speed), I pull about 3500 rpm at 75 mph - about as high an engine speed as I want to see (and hear) for long freeway drives.

[boxy02]

This will be a track car and I'll most likely be running a 15" wheel. I'd like to keep the motor stock, but maybe add a header, mild cam and a Weber......I must do more research......

[peteinjp]

on the street with a 5 speed. The taller gears will not be so great on the track probably. I'd never run the 3:64 unless I was spending all the time on the highway.

[BarryA]

This will be a track car and I'll most likely be running a 15" wheel. I'd like to keep the motor stock, but maybe add a header, mild cam and a Weber......I must do more research......

wheels with fairly tall tires (185/60 on 6" Alpina replicas front, 205/60's on 7's rear - its a pure street/commuter car) - swapping the stock 3.64 diff for an iS 3.91 lsd kept me right at 3500 rpm @ an indicated 80 mph (speedo looks to be about 5% fast, so it's really pulling about 76 mph @ 3500 - about the same as the '02 on 185/70x13's and a 3.64 diff).

You'll probably find a 3.91 combined with 15" wheels and short sidewall tires will move you up the rpm range a useful amount for a track car.