"83 280ZX close ratio box and 3:90 differential

[bertvorgon]

If it was me, my last word...15" tires are kinda tall from what our 510's came with, they are going to be 23.5" or so tall.

If you have a line on a 4:11, you will really benefit from that, Guaranteed. Unless you spend all day, 5 days a week, at 70 MPH on the freeway, you will enjoy the slightly shorter gearing in the real world of stoplights and general day to day driving. Having a 'snappy" car is what makes our 510's fun and 3:9's will just be a bit lame IMHO. I drive with a group that runs from 4:11, 4:3, and of course my 4:6's and they are all pretty zippy cars.

[funwithmonkeys]

I agree with Keith. Don't think twice about it. Go with the 4.11's. I have 4.44's and a second diff with 4.6's that is going in next month. With the .74 OD it makes the short gears totally bearable for hwy driving. It is also the cheapest HP you can buy.

[datzenmike]

Not everyone who has a Datsun has a 'true' close ratio box, would even know about them, where to find one, could afford one, and if they did they probably wouldn't like them anyway for their predominantly street driven cars. The 'close ratio' box is simply too esoteric for a street car. So that leaves the 71B 5 speeds that actually came in the cars sold and can be found relatively easy in the three ratios mentioned. For want of a better way to identify them they are (relative to each other) wide, mid and close. That there are even closer ratios is splitting hairs. No one is going to find one in a wrecking yard and outside of a NISMO parts catalogue they almost don't exist.

[Gereed75]

Realize that this thread is a bit old and most know this, but the 84-85 200SX non turbo 5 speed is very close to the NISMO N3130 ratio's at 3.321/1.9/1.308/1/.833. These things are readily available in junk yards for cheap. They do require a fairly simple adaptation of an L series bell housing. It is a 71B tranny some times called a "near C". IMHO, a much better choice than the ZX tranny.

[datzenmike]

The "close ratio" ZX box - close ratio being a standard misnomer as it really isn't - but it's slightly closer ratio than the early box. However the ZX 'close ratio' nothing like what Bert posted above, which is a true close ratio box. There were three close ration comp boxes from what I understand in the 71B's, wide, middle and ultra close. The ZX "close ratio" box isn't any of the above, but has been widely called a "close ratio" box by people who obviously don't know better and it's now become main stream in the Datsun circles.

That aside, the late ZX box works very well (for me) with the 4:375 and 4:44 gear sets as a compromise for those that are weekend warriors and actually drive the car to events for any distance. I'm in the 150 HP/Torque range with a 2.2 L/Z frankenmotor. The .74 OD is nice on the highway, as my car also runs in the 4K range at 70mph/120KPH.
The lower rear gears help with the tall 1st - which is much taller than the 510 4spd ever had, and the gears do get a bit closer as the 2-3 jump isn't as much of a killer. For auto X, I should have run a lower rear gear if it was available to me, as I often found I needed to be somewhere between 1st and 2nd. Maybe Keith did get it right as I spent more time hunting/shifting which wastes precious time on the course. Keith also had twice the HP/Torque -0 which is obviously the game!
My thoughts anyways, pretty hard to go wrong with the low gear. It equals instant HP under all circumstances and is by far the cheapest way to get 60 ft times and 1/8 mile if that's your thing! Definitely a winner at the stop light GP! And the tall ZX OD helps on the highways side to make the compromise.

Byron

Close ratio is what I call it as all the other'real close ratios' are not commonly available to the average Datsun owner. Of the three that are found commonly the '80-'83 ZX are closer than the other two. It's all relative.

If you don't mind mixing a few parts put the input and counter drive input set from a 720 wide ratio transmission into a zx close ratio and you can make a (for lack of a better word) ultra close ratio box with a 2.90 first and a 0.68 something over drive. Of little to no use on a street car unless with some tall gears.