4:11 gears in '78 280z

[ComicArtist]

I've been looking around at differentials, and I'm really wanting to swap out my 3:54 to a 4:11. I don't know a lot about them, but I've been reading up and apparently they come out of an 85-86 200sx. Unfortunately, I can't find any write-ups on how exactly to do the swap.

 

Also I guess some people are doing the Subaru differential swap, but I don't know how easy that is.

 

Are they bolt ins, or do you have to modify the half shafts as well?

 

Just looking for some tips. Thank you!

[Eddie-G-Force]

I think the R200 4.11 units only came in Turbo 200SX cars. You need to do some searching on this site. If your 78Z is a MT car you'll need a R200 differential unit (bigger and different axles than R180 automatic car unit) If your car has a R200 3.54 diff. and you are lucky enough to find a R200 4.11. It is a easy bolt it process. Just pop/pry out the axles and pop yours in. You may need to swap the pinion flange with the one from your existing unit. Your speedo will be off (in error) Maybe 200sx speedo gears swap too? Why not use a 3.90 unit from a 81-83 280zx. There are about a zillion more of them. Ed G.

[ComicArtist]

I do have the 5 speed transmission. I'll start looking around at junkyards for turbo 200sx's.

 

I could do the 3:90, but I was looking for the most I could get. I don't really care about top speed as much as I do acceleration. Is there that big of a difference between the 4:11 and the 3:90?

 

How far off would the speedometer be? I did some searching but couldn't find anything definite.

 

Thank you!

[Pharaohabq]

Yeah I was going to say you don't much care for speed do you? 4.11's are what I have on my rockcrawler, it's got power, but over 50MPH in 5th gear is rough. (on 35's even) Are you making a drift car? That's really the only thing I could be thinking you'd need it for. 3.90's are going to be plenty for acceleration. You might be better off putting a lower 1st and 2nd gears in your tranny and keeping the higher top end, that way you'll be fun on both ends.

 

Phar

 

P.S: oh and your speedo will be off about 9.6% (3.9/3.56)

Edited June 1, 2010 by Pharaohabq

[FlatBlack]

I've got 3.54 in my 78 with the stock 5 Speed, at interstate speeds I'm around 3200 RPM. I couldn't imagine what a 4.11 diff would do.

 

If it's a track only car I suppose it wouldn't matter.

 

 

Subaru 4.11 R160 on the right, Datsun 3.54 R200 on the left. Those Subaru diffs are SUBSTANTIALLY weaker than the Datsun units.

 

Power adders are going to do you much better than messing with the gearing.

[JMortensen]

Comicartist, I suggest you disregard all the advice you've been given up to this point, and next time search before you post as I know this topic has been covered before.

 

Let's disprove what has been said already. 4.11's are bad for anything but drifting? Think again. With a 225/50/15, a ZX 5 speed, and 4.11's the car tops out at 155 mph at 7000 rpm. With 3.90's that the ZX came with the theoretical top speed is 165 mph. 70 mph with the 3.90 is 3000 rpm, with the 4.11 is 3133 rpm. The difference in top speed or rpms on the highway is minimal. Consider that you'll need something close to 300 hp to hit 150 mph in a Z car and suddenly 4.11's with a ZX transmission looks like a pretty good choice for MOST Z cars on the road. Might not be the best for mileage, but if you want acceleration, they're certainly going to multiply the torque better than a 3.54. 16% more torque from the 4.11 is a good thing for most Z's out there.

 

Similarly Mat, your 78 has a 5 speed geared for a 3.54. If you put a ZX 5 speed in it, you'd wonder why the car was so slow off the line. The trans and rear gears have to work together. When they do, the 4.11 is a great choice, and the 3.54 is a great choice. Mix a close ratio 5 speed with a tall rear gear and you'll be unhappy, mix a wide ratio trans with a short rear gear and you'll be unhappy too.

 

Comicartist, here is a tool that will help you to figure out what gearing is best:

http://webspace.webring.com/people/cz/z_design_studio/

[Tony D]

I will have to chime in in the same vein of JM here. A 4.11 will NOT alter the top speed of a Z Car in stock, or relatively modified form.

 

The car in stock form is drag-limited to 125-130mph. With a 5 speed, you will not be over-revving the engine to reach this speed.

 

An early five speed is a great option, as everywhere in the world it was mated with at LEAST a 3.90 rear gear. In Japan on the 2L cars, it was with a 4.11, and in ZL (Heavy Cars) it came with a 4.38 from the factory.

 

In practical terms of cruising, the car will spin roughly 500 more rpms per gear ratio. Meaning if you are cruising at speed in top gear with a 3.54 (whatever that cruising speed may be), you will turn about 1000-1500 rpms more with a 4.11.

 

My car has a 3.7 and late ZX tranny, I cruise at elevated speeds on the highway, and the little L26 in there is right at home at 3200+ rpms. Many times I find myself in fourth cruising at 4000rpms if I am having to shoot and scoot for lane changes around slow movers. This is what the engine is DESIGNED to do, people thinking 3500 rpms on a highway cruise speed is 'too high' don't understand the design of the engine or how it's supposed to operate. Lugging the engine at 2800rpms for cruising in fifth gear makes for a DOG of a car, and doesn't net any real-world appreciable gains in mileage.

 

My L26 with SU's and 3.7 nets nearly the same mileage as my 2+2 with an Early five speed and a 3.9 in it, running comparable speeds. On both cars I have to work HARD to break below 20mpg on the highway. Hard as in averaging triple digit speeds in steady-state driving. If I drop the speeds to 65mph consistently (besides having to downshift to fourth in my L26 powered 3.70 geared car to keep the engine from lugging) I get near 27mpg with both of them...

 

All the lower gears will do is make you reach terminal speed faster. The operational speed of the engine at highway cruise will be well within design parameters. I know people with L24 powered FairladyZ's with Automatics and 4.38's who twist at 4000 through the Arizona Summer Heat and don't have an issue. They are 300,000 mile engines in stock form, wear 'from "excessively-elevated" rpms' is not an issue. They are not a SBC in a short bed pickup that will wear out in 75K miles due to poor block metallurgy...

 

<EDIT> Oh, I will also add that I have driven CROSS-COUNTRY in BOTH of these vehicles. Meaning 14-16 hours straight of highway cruising at 3500+rpms. In the case of the 2+2 with two passengers and TOWING an 800# trailer. Nothing is as satisfying as passing some slowpoke on a twisty-turny TOWING A TRAILER and shifting into third to punctuate the point they are going too slow as you pass them! (and then into fourth as you pull away in the distance...) The 3.7 gears will take you to highway speeds in second (say 100kph) with that early tranny. 4.11 will be in third, you will be slower 0-60 because of the rowing of the shifter, but once in 3rd, you are good to any legal speed and will be pulling harder than any other gear mentioned. My cars when at highway speed will accelerate in top gear unlike the majority of overgeared US Spec Models. Everywhere in the world, the STANDARD four speed offering was a 3.7, and five speed was 3.9. Minimum. A 4.11 is really only a 500 rpm increase over that base. If I can put 18,000 miles on within 3 weeks give or take, in the heat of the summer, driving across the desert southwest I'm thinking a 4.11 will be fine running the toll road from Spavinau to Altus...

Edited June 1, 2010 by Tony D

[FlatBlack]

Because my exhaust is so loud, cruising on the interstate is a pain at higher RPMs. Yes, this IS a personal problem. I'm also used to hearing my friends with T56s brag about cruising at around 1500 RPM.

 

Sorry for the poor advice, I've never messed with gearing, so I shouldn't have opened my fat mouth

 

I do stick to my Subaru diff advice, it seems like more money and trouble than it's worth. However, it sounds like people with the Subaru Impreza STi R180 CLSD are doing well with them.

[Tony D]

I find that the car goes miraculously silent at 140kph.

Perhaps you simply aren't going fast enough to get the benefit of proper resonation within the exhaust system.

 

It's nowhwere near the speed of sound, so throw that argument out the window!

[ComicArtist]

Hmmm. I think there's some good information in this thread.

 

Although, do you think the '78 transmission with the 4:11 diff would make a good combination for acceleration speeds? That's mostly what I'm worried about, even though this isn't a track car. I'm just building an extremely quick street car.

[JMortensen]

Although, do you think the '78 transmission with the 4:11 diff would make a good combination for acceleration speeds? That's mostly what I'm worried about, even though this isn't a track car. I'm just building an extremely quick street car.

I don't like that combo. 1st gear would go to less than 40 mph and 2nd ends just before 60 mph. 1st is in my opinion unreasonably low, and even at an open autox you're hitting 3rd, which is not good. The earlier transmissions have a pretty big gap between 2nd and 3rd gear, so especially if you have a higher strung NA motor, that gap can be a real killer.

 

It's not like it won't drive though, and you'd still have a top speed of 140 with the aforementioned 225/50/15. That's probably plenty of top speed for the street and if you have taller tires the effect might be quite a bit less severe, but I wouldn't run it on my track/autox car. I think the ZX 5 speed would make the 4.11 a lot more user friendly. Again, this would be especially true if you have a cammed or triple carbed NA motor.

[ComicArtist]

By the ZX 5 speed, you mean the NA transmission, not the Borg-Warner, right?

[JMortensen]

Correct. The BW has even wider ratios than the early 5 speed if I recall.

[ComicArtist]

Sweet. I'm sure I can source a transmission at a JY somewhere. Differential might be harder to find, but I'll keep my eyes open.

[Datsun#1]

the BW tranz has awesome gears for a 3:90.It came out of the Turbo cars and had 3:54 gears to help the turbo build boost.So getting the BW tranz and putting some 4;11s in that puppy, It would make an awesome light to light car. Also, Are you keeping the engine stock? Or do you plan to run a bigger cam? the 4;11s will be great to keep you in the powerband if going with a larger cam.If you do decide to get the 4:11 gears, get your self a lighter flywheel and a rev limiter.also get your tack accurate.last thing you want to do is pull 1st gear to high with cast pistons and a dizzy thats only "good" until 6500rpms...cheers

[s30kid]

I have a 3.9 r200 in my turbo 280z with a 5 speed and i'm doing about 4k+ on the freeway. But the acceleration through 1st and 2nd is great, 3rd-5th is kinda of a dog but I blame my tune for that. However I do not regret the swap. Daily driving I fill up about once a week. Just my Input.

 

-Edit- Under 60 mph my speedometer is 10mph fast. So it says 50 but i'm actually going about 40. But over 60mph my readings are way off. If i'm going 90 it says 140 or so..  But I believe that's a problem with my speedo cable. 

Edited December 17, 2014 by s30kid

[JMortensen]

Don't know why Datsun#1 bumped a 4 year old thread, but my understanding is that even for a turbo you'll get better spool up earlier with a taller gearset than the T5 has coupled with a taller diff ratio. Clifton used to be a member here and he ran his turbo racecar with a NA ZX 5 speed for that reason, he discussed it in several threads if I recall. I seem to remember him saying that the NA ZX 5 speed was at least as strong as the T5 also. He had problems with both.

 

Even with a short rear gear on a NA car, the T5's gap between 1-2 and 2-3 is too big. I remember going to the track with my buddy who was racing a 510 with an L16, 44 Mikunis, and a 280Z 5 speed. Coming onto the front straight he would shift to 3rd and I would absolutely drive away in my Z with the close ratio box. Otherwise the cars were always a couple tenths off at autocrosses. Very closely matched. Too big an rpm drop in the 280Z 5 speed left him "off the cam" and he had to wait for all the hamsters to get him back up to 5000 rpm or wherever the power came back on. By that time I had 10 car lengths on him. 

 

Again, this wide ratio thing is much more pronounced with NA/cammed/sidedrafted motors, but if you gave me a T5, I'd sell it and buy a couple spare closer ratio 5 speeds. YMMV.

[aongch]

Since this thread is open, what recommendations can I get per my power and torque curve below? Still sorting out my build RB26 (stockish 8.7 lbs boost), stock Z32 5-spd and I believe 3.7 gearing. Start tracking it in 2015 and putting in a Quaife. So, what theoretical gearing will take me to 140+ (4th or 5th) typical at Auto Club Speedway front straight speeds, which I regularly reach in my tuned M3 and previous Stage 2 STi? Thanks guys.

 

Edited December 18, 2014 by aongch

[Tony D]

Quaife makes a nice sequential box.