R180 3.90 Differential

Mr Tenno

Digital Officer
Staff member
Site Administrator
Really appreciate all the information guys - it's really useful (and I'm sure future readers will think so too). Is there more than one type of Nissan R180 3.90 or are they all the same?
 

SeanDezart

Well-Known Forum User
Is there more than one type of Nissan R180 3.90 or are they all the same?

'Nissan' didn't make them....Fuji Heavy Industries who also made the Subaru R180 and R160 diffs.

The R192 diff is found in which export cars/trucks Alan ?
 

Albrecht

Well-Known Forum User
Really appreciate all the information guys - it's really useful (and I'm sure future readers will think so too). Is there more than one type of Nissan R180 3.90 or are they all the same?

You have to watch out for spline counts as they were fitted to several different models over the years (including as the front diff on 4x4s), but if you source one that you know came from a UK market 240Z you should be OK to plug-and-play after popping the rear cover and checking the ratio.
 

johnymd

Club Member
IMO the best diff ratio for a general road car with a 5 speed box is a 3.9.

All the US 240's I've had and driven had/have 4 speed boxes and I really like the laid back manner these have. None of these cars are especially fast but for general cruising around, this setup is perfect. I have a late 5 speed 280 box and a 3.9 R180 diff that I had planned to put in the silver car but I like it just the way it is. I can put it in 4th at 20mph and it pulls all the way to 100mph with no issues at all. Cruises at 80 and the revs are below 4k. I guess it all depends what you want from the car but for a general cruiser, you either still with what you have or go 5 speed and 3.9 IMO.
 

Woody928

Events Officer
Staff member
Club Member
I'm following this with great interest as it will be an upgrade I'm looking to do in the near future, however I'd love some further clarification.

Can someone explain the difference between a 3.364:1, 3.7, 3.9, 4.1 etc? I know there seems to be a lot conversation about the 3.9 being the best choice with a five speed however how does that compare to the diff in a stock US car? Does the higher the number mean the lower the gearing?

To provide some context I have a USDM 240Z with an L26 using a standard 4 speed. I've already acquired a 5 speed gearbox from a UK 260Z+2 that we're planning on rebuilding and installing however I'd also like to install an LSD and would ultimately like the car to cruise at a lower rpm on the motorway (revs sit too high at the moment). For me more limited knowledge we will need to swap the diff to achieve this however I have no idea what would be best, I've heard both a 3.7 or 3.9 diff thrown around as very conceivable options however I don't fully understand why. Car is intended for mainly fast road and long journey's primarily.

Would I notice much difference if I swapped from the 4 speed to the 5 without a diff swap?
 

uk66fastback

Club Member
Using my limited knowledge if you kept the US diff and put the five speed in it'd be much lower revs but as sluggish as hell! (I am partly guessing)

The higher the no. (3.x, 4.x) the higher the revs in fifth (put simply) ...
 

toopy

Club Member
Using my limited knowledge if you kept the US diff and put the five speed in it'd be much lower revs but as sluggish as hell! (I am partly guessing)

The higher the no. (3.x, 4.x) the higher the revs in fifth (put simply) ...

As above, as i understand it, given the same gearbox, the higher the number, the better the acceleration, but higher cruising revs

I have a 5 speed box from a 280ZX and i believe the 2+2 has a 3.7 diff as standard, which equates to 70mph being approx 3000rpm
 

Rob Gaskin

Treasurer
Staff member
Site Administrator
Using my limited knowledge if you kept the US diff and put the five speed in it'd be much lower revs but as sluggish as hell! (I am partly guessing)

The higher the no. (3.x, 4.x) the higher the revs in fifth (put simply) ...

I'm sure you're right.

A 3.9 diff requires 3.9 turns of the propshaft to turn the wheels once.

I don't think an LSD is a priority for road use. I didn't have one in my trackcar and got away with it.
 

johnymd

Club Member
A US 4 speed has a 1-1 4th gear. Exactly the same as 4th on a 5 speed. So the first 4 years would feel exactly the same and 5th would be an overdrive and lower the revs. In order for 5th to be of use you would need to move to a 3.9 or 3.7.

My blue car has a 3.7 diff and the Toyota gearbox ratios are pretty close to a zed box. When I did a speed test on the autobahn at 160mph the revs were only around 6k so at 7k I would be in the 180's. If you do pair this to a lower powered non turbo zed, you would sacrifice acceleration too much for top end you will never achieve. IMO this is why 3.9 is the best ballence between comfortable cruising and reasonable acceleration.
 

SeanDezart

Well-Known Forum User
This should help !

The Excel sheet lists a common rev limit of 6500 and same wheel/tyre sizes for both the 3.54 and 3.9 diff ratios.

Play around with it with YOUR rev limit wheel and tyre sizes AND and in the different diff rations to see what adds up to what and THEN choose the 'best' for YOUR own use and application.

Second Excel sheet is a compilation of diffs and gearbox ratios that I knocked up with info from here and there for our members here wanting to convert from US import specifications*.

*there may be errors and I'd be grateful if you'd point any out so as to be corrected.

Enjoy, discuss but don't let anyone tell YOU what is 'best' for YOU......remember, "you're all individuals - you've all got to work it out for yourselves"..;):rolleyes:
 

Attachments

  • gearspeeds v2 (3.54 and 3.9).xls
    75 KB · Views: 27
  • Ratios.xls
    28 KB · Views: 24

SeanDezart

Well-Known Forum User
I don't think an LSD is a priority for road use. I didn't have one in my trackcar and got away with it.

Not an absolute necessity but does give an advantage depending upon the type chosen and if one is changing diffs, why not change for another ratio with and LSD?:driving:
 

Rob Gaskin

Treasurer
Staff member
Site Administrator
I would imagine an advantage of the 4 speed gbox is that it's nice and quiet in top gear (direct drive). Some 5 speeds can whine.
 
I'm following this with great interest as it will be an upgrade I'm looking to do in the near future, however I'd love some further clarification.

Can someone explain the difference between a 3.364:1, 3.7, 3.9, 4.1 etc? I know there seems to be a lot conversation about the 3.9 being the best choice with a five speed however how does that compare to the diff in a stock US car? Does the higher the number mean the lower the gearing?

To provide some context I have a USDM 240Z with an L26 using a standard 4 speed. I've already acquired a 5 speed gearbox from a UK 260Z+2 that we're planning on rebuilding and installing however I'd also like to install an LSD and would ultimately like the car to cruise at a lower rpm on the motorway (revs sit too high at the moment). For me more limited knowledge we will need to swap the diff to achieve this however I have no idea what would be best, I've heard both a 3.7 or 3.9 diff thrown around as very conceivable options however I don't fully understand why. Car is intended for mainly fast road and long journey's primarily.

Would I notice much difference if I swapped from the 4 speed to the 5 without a diff swap?

I think fast road and long journey's are two ends of the spectrum? ish
 

uk66fastback

Club Member
I don't think an LSD is a priority for road use. I didn't have one in my trackcar and got away with it.

They certainly didn't come with them so I too, don't see why people would spend the money to get one in a road car.

I spent a small fortune having a Tru-Trac put in my old Ford and I can't think of one time where it would ever have been needed. Should have stayed with an open one.
 

SeanDezart

Well-Known Forum User
Just as I post up some real facts.....the thread dies off.....as if people revel in myths like :

an R200 diff is best

fit a close-ratio later (280ZX) box

only the N42 head is best...oh no, fit a P90, they're better

Disc brakes all round

etc....etc
 

Woody928

Events Officer
Staff member
Club Member
Thank you all for clarifying, this is making far more sense now!

I don't think an LSD is a priority for road use. I didn't have one in my trackcar and got away with it.

As mentioned earlier in the thread I'm sure I could get away without having one, however there are real benefits to be seen in certain scenarios from having one fitted. If I'm already making the effort to swap out the diff then why not upgrade and improve even further at the same time. I don't plan on going back to change again at a later date... (just my opinion)

This should help !

The Excel sheet lists a common rev limit of 6500 and same wheel/tyre sizes for both the 3.54 and 3.9 diff ratios.

Play around with it with YOUR rev limit wheel and tyre sizes AND and in the different diff rations to see what adds up to what and THEN choose the 'best' for YOUR own use and application.

Second Excel sheet is a compilation of diffs and gearbox ratios that I knocked up with info from here and there for our members here wanting to convert from US import specifications*.

*there may be errors and I'd be grateful if you'd point any out so as to be corrected.

Enjoy, discuss but don't let anyone tell YOU what is 'best' for YOU......remember, "you're all individuals - you've all got to work it out for yourselves"..;):rolleyes:

Wow this is brilliant! Thank you very much. I had to wait to get onto my windows PC today to get the spreadsheets to work however this certainly gives food for thought. Particularly given the potential for changing wheels and tyres long term altering the rolling radius. On that basis I think I’d be more tempted by a 3.7 than a 3.9 as it looks to cruise at 70mph at 3k rpm which seems pretty reasonable vs the nearly 4k I’m sitting at with the current 4 speed! (mods is this worth putting in a sticky somewhere?) Would a 3.7 really be sluggish with a stock ish engine?

I’ve just picked up a 5 speed out of a 1976 UK 260Z 2+2 so I’m assuming the below ratios will be correct.

260Z 1974-6
Euro
FS5C71B
2.906
1.902
1.308
1
0.864

I would imagine an advantage of the 4 speed gbox is that it's nice and quiet in top gear (direct drive). Some 5 speeds can whine.

Unless there’s something wrong with my 4 speed I can’t imagine how it would be better than a 5 speed! There’s a lot of noise cruising at just shy of 4k rpm. I don’t know why they didn’t just fit 5 speeds across the board, I’m sure they’ll make the car more refined. The 4 speed is great up to about 60mph on national speed limit B roads however anything quicker and I’d want a 5 speed personally.

I think fast road and long journey's are two ends of the spectrum? ish

I perhaps should have better clarified, it’s probably somewhere in between the two that I’m looking for. I’m not looking for stupidly short gears for quick acceleration with no cruising capability, however I don’t want to get a cruise able car and loose its driveability…. I’m sure there’s a balance to be found between the two!
 

Albrecht

Well-Known Forum User
...which seems pretty reasonable vs the nearly 4k I’m sitting at with the current 4 speed!

I think you might want to check on what diff ratio you actually have fitted in the car, as - reading between the lines somewhat - it seems to me that it doesn't sound like the original 3.3 ratio...

Also bear in mind that numbers on paper are all very well, but it's what you feel in the car (the old 'seat-of-the-pants dyno') that's most important to you. Gearing will always be a compromise in many respects.

Also bear in mind that R180 ratios ranged from 3.3:1 right up to 5.1:1, so - all things considered - the recommendation of 3.9:1 is a fairly conservative, intermediate one.
 

uk66fastback

Club Member
When mine eventually gets a few things done and MOT'd, I'm looking forward to driving a 45-year-old US spec 240z on British roads. With a four speed and skinny tyres and everything else that entails.

Bang stock. It's the future.

Back in the day - everything came with a four-speed! Not Zs, I'm talking Cortinas, Maxis etc.
 
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