Modifications

[JEZ 280ZX]

Originally posted by SeanDezart
Well, I lit up the tyres all the way in 1st at the weekend so Mike sIS right and Autocar IS wrong, shame as I'd liked them to be right !

So Mike, with standard turbo wheels and 225/5016 tyres, if I change the diff to a 3.7 and assuming 5600 revs, what mph readings will I have and at how many revs, ie at 80 mph, how many revs in fifth ? Please !

This is assuming tha the N/A 3.7 diff will fit into the Turbo and is strong enough ?

Over here, top speed is becoming less interesting but short-term sprints are !

Hi,
Why don't you just fit smaller 15" NA wheels with low profile rubber?....That will give sharper acceleration too...some of the Z31Turbo drag racers in the US do this!
Before you start reving the life out of your 300ZX, best to check if the cambelt has been changed...if not it's worth doing, as they are fairly cheap to replace!
Cheerz,
JEZ

 

[SeanDezart]

Thanks, all belts changed 6000 miles ago ! I like the tinted, standard rims, especially with the colour of car !

 

[SeanDezart]

Great site this US Z31 one !!! Where's my chequebook ?

 

[JEZ 280ZX]

Hi,
I too like the grey Turbo wheels and when I had mine refurbished, I kept the standard colour....They just look a bit different to the usual shiny silver norm!
Cheerz,
JEZ

 

[SeanDezart]

Now were talking, an US 88 non-turbo rear diff at 3.9:1 !

 

[Mr.F]

standard turbo wheels and 225/5016 tyres, if I change the diff to a 3.7 and assuming 5600 revs, what mph readings will I have and at how many revs, ie at 80 mph, how many revs in fifth

Theoretical top speed 145 mph

80mph would be 3080 rpm in 5th.

 

[SeanDezart]

I don't get it - the top speed for this car is listed (with a diff ratio of 3.5) at 142 mph, if I change to a 3.7 or even 3.9, surely this will decrease the top speed ???

 

[JEZ 280ZX]

Hi,
The Autocar road test recorded a best of 144mph at 5125rpm....the 'theoretical' top speed at Mike's 5600rpm would be 157mph!...or if you were able to attain the in gear max revs of 6100 rpm that they recorded, then the theoretical top speed would be 171mph!
According to Brian Long, the earlier US Turbo cars were governed to a maximum of 137mph(220kph)...funnily enough the mk1 Autocar UK test car achieved a max of 137mph!....was there a speed limiter on the facelift cars too?
Cheerz,
JEZ

 

[SeanDezart]

Seems with Nissan that for each car, the story is never too clear !

Anyway, are our Z31s series 1,2 or 3 Z31s ???

 

[Mr.F]

It is rare for most production cars to be able to attain maximum rpm in an OD gear. Also, aerodynamics will begin to have an effect at elevated speeds. You could have a really high gear set machined to give you a theoretical top speed in excess of 200 mph, but I doubt that even a highly tuned Z31 would make it there!

 

[SeanDezart]

So is a 3.7 or 3.9 diff 'fittable' and strong enough and are there acceleration from rest and 'in the gears' advantages to be had, albeit with the later addition of all the goodies you quoted me ? I don't care for top speed, fuel consumption when cruising is of no small interest however, hence my earlier question of engine revs at 80 mph !
It's going to drink when I boot it, sure and when I boot it I want it to go ! When I don't and I'm off turbo, I like the idea of not dropping below 25 mpg as I've already been able to achieve !
Thanks for the time on this one !

 

[SeanDezart]

This is what the US Z31 site has to say about diffs:

84-87 NA: 3.7 open
88-89 NA: 3.9 open
84-86 turbo: 3.54 open
87-89 turbo: 3.7 (post 4/87 clutch LSD, pre 4-87 open)
SE: 3.7 viscous coupling LSD

Z31 models after 4/87 are the only cars to have r200 clutch LSDs from the factory.

The clutch LSDs are a direct bolt in replacement to any 300ZX that came with an open differential, but you may have to swap your stock driveshaft flange onto your new differential depending on what year/model you are putting the LSD into. To fit the viscous LSD to a car that didn't come with one you only need the half-shafts for the viscous differential on turbos, and on non-turbos you also need the turbo companion flanges. If you're putting a LSD on an early car you'll also need to swap the early pinion flange onto the differential from your stock differential. These differentials are indestructable, change the oil every year or two and you'll never have a problem. Nissan Motorsports sells complete ready to install R200 clutch LSDs for approximately $700-$1100 with your choice of standard R200 ratios.

 

[JEZ 280ZX]

Originally posted by SeanDezart
Seems with Nissan that for each car, the story is never too clear !

Anyway, are our Z31s series 1,2 or 3 Z31s ???

Hi,
In the US they had the mk1, an in-between 1986 version, with modified bodywork and the later, fully facelifted cars...whereas we didn't get the updated '1986' model.

Cheerz,
JEZ

 

[SeanDezart]

Surely a Mk1 was the 1983-5 model ? This a Mk 2, and ours the Mk3 ??? The Z32 would therefore be a Mk4 ?

 

[JEZ 280ZX]

Hi,
That's right...our facelift cars are mk3's...although they're the second version in the UK market!...A z32 is a completely different car, starting at series 1 again!
Cheerz,
JEZ

 

[SeanDezart]

Now I thoght that the Z31 started off as a Mk1, then had a small facelift (1986 ?) , ie chrome trim around the windows etc, then ours !

 

[JEZ 280ZX]

NA's have chrome round the windows!

 

[SeanDezart]

Well, you learn something every day - never did like the chrome trim anyway !

Anyone want to help out with the diff change question (s) ?