Im swapping a "new" tranny (-77 5speed) and im thinking of changin the differential too. Which one is better ?

Are you gonna cruise or track the car?

Better for what???

Chuck

There's a 4.5% difference in gearing between the two. I bet that if the tach was covered you wouldn't be able to tell which gear was installed.

I have a 3.54 with five speed. It makes for quite a lazy cruisin' ride, but still has enough go for me. I seldom use fifth gear. Fourth at 100 km/60 mph is 3000 rpm.which is in good zone for passing. Down shift to third and it goes really well.

Fifth at 100km/60 mph is around 2600 rpm.

I'm doing a 5 speed swap as well (82-280zx) and moving to the 3.9 diff - I like more spirited driving. I will put the 4 speed and my 3.5 diff in storage like the other stuff I have been collecting (or should I say "swapping"). Just for record my 4 speed with the 3.5 diff is very spirited!

I suspect I have the 3.54.

In my car, what I find is for coming OUT of a corner, 3rd gear is too high. If I downshift to second coming INTO the corner, I have to rev it too high to match rpm's, and my 200k mile synchros just aren't up to the task. So what I've BEEN doing is stomping on the brake AND the gas and leaving it in 3rd. But my RPM's are too low to pull away quickly.

I SUSPECT I'd like the 3.7 or even a 3.9 simply because of where 2nd and 3rd would end up, range-wise. (Higher RPM's in 3rd at the same speed)

I find for passing, I really have to go down to third. Fourth just doesn't give me the accelration to get the job quick enough, not up here at 6000' altitude, with appx. 15% power loss. With the 3.7 I might be able to "only" go down to 4th.

So do you want a quiet, comfy cruiser, or a hells-bells cornering and passing machine.

I probably have it all backwards, but you get the gist of what I'd prefer the gearing to be. A few hours going back and forth between two cars, one equipped with each ratio, and you'd instantly know which you'd prefer.

Edited September 10, 201212 yr by Wade Nelson

Im swapping a "new" tranny (-77 5speed) and im thinking of changin the differential too. Which one is better ?

What do you have now? The 3.36 was standard equipment in North America, but I believe the 3.9 was stock in Europe. Did your car come to you from the U.S. or Canada, or was it originally sold in Europe? If it has a 3.9 now, I can not imagine dropping down to a numerically lower ratio unless you have a lot of high speed long distance crusing to do. Most people here want to find a 3.9 when they drop in a 5 speed.

The early 4 speed, the later 4 speed and early 5 speed, and the later 5 speed all have different 1st gear ratios. This will affect the quickness from a stop. Something to consider. You can see how the 240Z got away with a 3.36 final ratio.

3.592 240Z 4 speed

3.321 280Z 4 speed to 79 5 speed

3.062 80-83 5 speed

Looks like the factory tried to stick around 12:1 for first gear overall ratio, in general. The 260Z and 79 ZX are oddballs.

240Z - 3.36 x 3.592 = 12.06 (if this is what they had, the FSM says 3.9, still confused on that. Looking at the numbers it looks like they just got 3.36 and 3.9 swapped in the FSM since the 5 speed has a 2.906 1 st gear)

280Z - 3.54 x 3.321 = 11.76

80-83 ZX - 3.9 x 3.062 = 11.94

Edited September 11, 201212 yr by Zed Head

My z is California import, so it has 3:36. I dont do tracks, only cruising + occasional bimmer harrassing in traffic lights. I've been offered 3:54 and 4:11, that would be quite the hasty differential i suppose.

In a stock 4 speed moving to a 3.54 would be a noticeable difference with acceleration - the only challenge is with 60mph your taching in the 3K mark. If you don't do much interstate driving is not too big of a deal -

It sounds like a 3.54 is the way to go.

Chuck