Regearing the rear end for HWY use
 

To start off I must say that I have no idea what the final drive ratio on my car is or how exactly to go about figuring it out. What I can say is that at 70mph the engine is right at 3k rpms. I know that over the years there were several different rear end options that came from the factory on the ZX. I'd like to switch mine to something that doesn't cause the engine to hover around 4k rpms when I'm driving 90+ on the interstate. I can't imagine that those kinds of engine speeds for an extended amount of time are doing any favors for the l28. Are there taller gears I can buy or would I have to find a diff to swap in at a junkyard? How can you tell what gears are installed in a rear end without pulling it apart (assuming that the stock rear end is on the car)?

I'm quite a noob at this so any help at all is appreciated.

Thanks Nismo!

Something isn't right here though, that page tells me that with the factory 5spd and r180 with 3.545 gears I should be at ~2600 rpms @70mph. Hmmm, time to borrow my dad's GPS to see if the new speedo is accurate. I did measure it against my GF's car and it seemed that we were right on par at 50mph...

ya, I found that my speedo was slowly getting slower readings. So when I thought I was going 70, I was really going 78!! Not cool when I'm driving 75 thinking I'm only going 5 over. :)

I replaced the speedo and found I got 'much better gas milage' hehe...

3.54 rear with either the T5 or late ZX 5-speed seems tall enough to me

Tested the speedo against a GPS unit today and found that it is telling me that I am going 2-3 mph faster than I really am across the board. This means that I'm hitting 3k rmp at just under 70mph. Putting in all my car's specs on the calculator page tells me that at 70mph the motor should be at 2594rpm. Something tells me the PO swapped out either the stock transmission or rear end for something else :017:

most likely a 3.9 rear

You're right, going back to the calculator page I see that 1980 GL models came with the r200 with 3.9 gearing. Is there a way to tell the r180 from the r200 without opening it up? Are gears interchangeable between r180 and r200 differentials?

Looking at the outside of the diff you can tell just by the basic size of it. Its hard to explain in text though. I don't have any pics.

The gears are not interchangable.

R200 on the left ... R180 on the right.

http://zhome.com/rnt/L28conversion/Diff.jpg

I love you guys!

:icon_super:

Actually, a better shot would be from the top where the input shaft offset on the R200 is blatantly obvious compared to the relatively centered input shaft on the R180.

P.S.
I can barely tell that's an R180 with all the crud build-up on the one in Nismo's photo! ;)

I can't take credit for that... I just typed in "R200" in Google images. :D

So based on that picture I do in fact have an r200 in the rear. I see that the lowest gear ratio used in a Z with the r200 is 3.364, which I think will be ample for my needs. Is there anyone making taller gears for this rear end or do I have to get one from a junkyard?

Many thanks for all the answers :)

It's a lot easier & cheaper to get the entire diff w/ the gearing you want... then you can switch it back out if needed. I think someone sells a set of 4:11's... but that's really not necessary unless it's a pure track car.

The smaller numbers (numerically) are actually 'taller' gears.
3.36 is the tallest gearing I have heard of. That ratio in a R200 is harder to find an a R200 LSD now. SUPER rare so I don't usually even mention it as a possibility.

R200 3.54 is still fairly tall and easy to find. :D so my suggestion still stands. Get the 3.54 and call it good

I got 32mpg highway with my NA L28, T5 5-speed, and 3.54 rear

I've gotten over 30mph as well and thats with the 3.9 in there :icon_super:

I'll look for 3.36 gears but if I can't find any 3.54 it will be. I do know a good all Nissan junkyard in Phoenix so I'll look around while I'm there. Is there any way to check what the ratios are inside the diff without pulling it apart?

Nismo, 4.11s aren't exactly what I'm looking for, well maybe for the Tacoma :042:

I got 32mpg highway with my NA L28, T5 5-speed, and 3.54 rear
__________________
I've gotten over 30mph as well and thats with the 3.9 in there

MPG with out MPH is useless Info.

I got 30 mpg ONCE! just to see if doable, the most boring commuting day of my life (55 mph, cruise control) suicide came to mind more that once..whoever is concern with MPG in this category is playing with the wrong toys..Peace

Driving 70-75 I got the 32 miles per gallon over a couple tanks of gas on a trip down the west coast. :)
The same type of driving with a 3.9 got me about 28-29mpg
Also, I had a 2+2 if it makes a difference at all.

i got 26mpg all the way down and back again to cali, i have a 3.9 ratio diff. the only way to tell the ratio, is to pull the back cover off the diff, it says it right on the ring gear. find yourself a turbo car, they had the 3.54 ratio, or at least its more common in those, if you find a 4.11 in one, ill buy it from you, and if you find a lsd in one, ill buy that too!! just pull every diff ya see, then go thru them, heck its only time.

this just in....
 

I can add to the selections.... well, the stiffer end of the spectrum anyway.

Earlier (pre 98ish?) Subaru's share the R-180/160 platform.
you unbolt the axle "stubbies".and bolt the Z piece in..and slam the diffy in place! The driveshaft yoke is the same pattern.

The "Ruby" pieces come with a wide assortment of ratios. 3:54, 3:70 (usually LSD's), 3:91's, 4:11 and the killer 4:444's !!! (talk about a tire ripper!)
The ratio is almost always on a sticker (clearly visible) on the rear cover.

I've used the 4:11's and 3:9's with great success. I'm still looking for a set of "44's" (Yahoooo.....)

The subaru LSD's are plentiful, and strong enough to take some heavy abuse (just ask me!) . many many 3:70 units are unmarked LSD's ! watch for these.

Happy hunting

Todd/BC240Z

Shady... theres still 2 4:11 sets in the pick an Pull here in kelowna.. we're just a couple hours from you. there's prolly several of 'em, in your local yard as I speak. go man GO!!
are 'ya gone yet?
Todd/BC240Z

When looking for gas mileage, remember, these engines were designed to operate most efficiently between 3000 and 3500 rpm and were geared appropriately.

Putting the 3.364's in a Z with an '80-'83 tranny is gonna bog the engine down at anything less than about 85mph...

I'm running a 3.7 R200 with an '83 5-speed and that's about as low as I would go and I'm considering putting the 3.9R&P in the 3.7 case. I would use the 3.545's if that's the best I had to choose from since it came in so many Z's, all the automatic first and second gen Z's and the turbo 280ZX's.

4.11 R200 is what Shady wants. Only found in 84-85 200sx turbo

that one is for the race car tho, i got a 3.7, a 3.9 and i want the 4.11 for it, that way i can swap it out as per the track or conditions!! my street car is very happy with its 3.9. dont forget to grab the speedo gear on the side of the tranny that way at least its more accurate. hey b.c. can you grab one for me, the local yards here crush everything under 1990, so leaving me wizzing into the wind. if you can also grab me a lsd unit thatd be great. umm you said r180? does that lsd fit into the r200? i thought not.

Naw.. no such luck.
the LSD's will swap from R180 to the 160. but not the R-2hunnerd. sorry bud.

I guess the different Z-bar from 200 to 180 makes it a pain. bummer fer you. lol

Lemme tell ya though. since I discovered this swap.. the drag times have been falling like a stone! I cant wait to find some "44's"