Gearbox swap = 17% FE boost - so far.

[D.O.G.]

Gearbox swap for older Datsun / Nissan autos.

I've mentioned a couple of times in other topics that I've done an auto gearbox swap in my '81 Datsun 280ZX.
For those interested in details, my Datsun is a 12/1981 (series 2), 2+2, automatic, with the original L28e, 2.8 litre fuel injected straight six, in the S130 body, (with a targa roof).
In Australia, we didn't get the Turbo version (sniff) or the two seater version (sniff, sniff).

As with many cars of the 70's and 80's, my Datsun came with a Jatco 3N71B three speed auto gearbox (no TC lock).
These are a popular box with amateur drag racing types, but not so good for fuel economy due to the lack of an overdrive gear.

Most people in Datsun circles go with an auto to 5 speed manual conversion to remedy this lack, while gaining that "sporty" feel.
I look on the S130 (in 4 seater guise at least) as more of a "grand tourer", with it's greater focus on comfort over the earlier S30 (240Z, 260Z) models. With this in mind, I chose to keep it as an automatic.

The most practical donor vehicle was the series 2, MR30 Skyline (Maxima in the U.S.).
It uses the L24e engine, so no bell housing adapter is needed and the L4N71B gearbox with no electronic controller to mess about with.

So, how is it performing in regards to fuel economy?
When I first got the car, I averaged about 11.5 L/100km (20.5 MPG)
With hypermiling and the 3N71B, I averaged about 10.6 L/100km (22.2 MPG)
With the L4N71B, my three tank average is 9 L/100km (26 MPG).

Around 17% increase - so far - just from the extra gear and locking torque converter.
Plus, it's so much nicer to drive at 110 kph with the motor at 2300 rpm, as opposed to 3400 rpm with the 3 speed.

[mcrews]

what a gREat write up!!!!
I had listed gear box change as one of my dream items on the kia sportage. Just dont have the tools!!

well done!!!!

[MetroMPG]

Congrats on the improvement, D.O.G.

Could you post a pic of your car? I'd like to add this to the front page.

[cRiPpLe_rOoStEr]

The right gearing really does miracles mileage-wise

[D.O.G.]

Originally Posted by cRiPpLe_rOoStEr

The right gearing really does miracles mileage-wise

Actually, I think that I can get better FE by lowering my overall gearing a bit.

This L4N71B box has no external controls for the torque converter lock-up, it's mostly determined by vehicle speed (oil pressure from the governor on the output shaft).

Because I'm still using the standard 3.54:1 ratio diff, the torque converter lock-up is at nearly 90kph in 4th gear, fine on the motorway, no use on the highway where the limit is only 80 kph.
I have a 3.9:1 ratio diff that should drop lock-up down to about 80 kph and only increase motorway (110 kph) engine speed to about 2500 rpm.

[cRiPpLe_rOoStEr]

Originally Posted by D.O.G.

Actually, I think that I can get better FE by lowering my overall gearing a bit.

I said the RIGHT, not necessarily high, gearing