late 260z diff ratio

dazzibazz

dazzibazz

Well-Known Forum User
Hi Im wanting to upgrade my 260z diff to a 280zx diff does anyone know what ratio the standard diff is I am told that the 280zx one is 3.7
 
I understand 280ZXs to be either 3.7(early) or 3.9(late) and harder to find. Think the 260Z was 3.5 or 3.7, if so what is yours?

What is the reason for a change?
 
If I recall the late 280ZX had

The "close" (more like closer) ratio 71B gearbox (overcomes the 2nd/3rd gear hole on the earlier units), the 3.9 R200 (with finned cover) and the CV shafts/joints.
 
Manual 260Zs and manual 280ZXs share the R200 diff.
Early 260Z had the 3.7 ratio. Late one the 3.5.
Early 280Zxs had 3.7 and late 280Zx the 3.9.
Remember we are talking MANUAL 280.
Auto 280Zx s had a R180 diff.
As already said the late 3.9 ratio R200 is had to find cos very few cars were sold originally in that spec hence units now command a premium price as it will "upgrade " any 240Z without altering the ratio. But you all knew that anyway didnt you????;)
Back plates and output shafts vary too ... but thats another story...........
 
What PMAC said is spot on, but always pull the rear cover find out. I broke what would have been an early manual 280zx, but that had a 3.9 ratio R200 in istead of what "should" have been a 3.7. It was an un-modified car.
 
can i join in,,, so iv got an early 260 2+2 and an early 280zx 2seater am i understanding this ??? that the diff should be the same in both cars?? also 3.5 3.7 3.9 what do the numbers mean to us which 1 gives better top end and which gives acceleration??????


thanks martin
 
Martin the higher the number eg 5.2 : 1 would give better off the mark performance but a lousy top end at red line revs, but at the other end of the scale eg 3.5 : 1 would give u low revs at high speed and not so good away from the lights, so what the numbers mean are 3.5 turns of the propshaft turns the wheel once if u have a 3.5:1 diff ratio and so on
 
which 1 gives better top end and which gives acceleration??????
Click to expand...

It all depends on engine/tyre/gearbox characturistics

Put a long 3.5 into a modest 150 hp car and it will stuggle to hit big top speeds because it lacks the torque to do so...like wise it will stuggle to pull a decent 0-60 as the diff ratio is just to long.....good thing is it will make a great motorway cruiser....but thats not what you bought it for is it, no you bought it because its a well sorted sports car.

The opposite also applies, put a 4.375 into Dave Porters turbo nutter missile and it will be just to lary to drive and you will be changing gears like a fiddler on speed, with no traction in either 1, 2, 3, 4 or probably 5th.

Its all about getting the right balance between car characturistics and driver ability and desire
 
see im sure i learnt all this at collage back in the day but it all seams so foggy now :lol: thanks for the help :bow:. i kind of thought it was like that but could not be sure:unsure: hence the Qs


cheers martin
 
Martin, in a 3.7 diff, 3.7 turns of the prop will give 1 turn of the driveshafts.

Think of it in push-bike terms, to start off (accelerating) you need to be peddling like crazy but when you get moving you need a lower ratio (numerically) but higher gear.

So a 3.9 diff would be easier to start off with a 3.5 diff would be better for cruising.
 
I changed my (upgrade) R200 3.9 diff for a 3.7 to reduce revs at crusing and more particulary at crusing speed, drop under the rev point where the camshaft began to open up everything and bring forth hell.

Much better fuel consumption, less noise and wear and tear. No noticeable acceleration loss and a higher top speed obtainable (not yet though).
 
well im going to use the 1 from my early 280zx so i guess it will be a 3.7 will use the zx engine and box too with mild mods to the engine to up the power a little and 15" wheels i think, will see how it turns out


thanks martin
 
Martin W said:
well im going to use the 1 from my early 280zx so i guess it will be a 3.7 will use the zx engine and box too with mild mods to the engine to up the power a little and 15" wheels i think, will see how it turns out


thanks martin
Click to expand...
Thats interesting Martin i should be getting my 240 on the road soon ,it to has a ZX engine with tripple 45s and manual g/box and at the moment running an early 260z diff, its probably the same ratio as the 240 one, i also have a 260 2+2 diff (R200} which i have no idea of the ratio of that will be having a lsd unit planted in it, (parts courtesy of pmac} i will let u know of any improvemeants if any, i realise i'm not in the league of the pro's on here but its all good fun, i'm sure there is a calculator somewhere that coud work out all this as i wil be running 17" 40 profile tyres ,although as Sean says he didn't notice any loss of acceleration but gained a better top speed at less revs i like that feel of torque rather than revs but still knowing that i have the revs if needed
 
SKiddell said:
It all depends on engine/tyre/gearbox characturistics

Put a long 3.5 into a modest 150 hp car and it will stuggle to hit big top speeds because it lacks the torque to do so...like wise it will stuggle to pull a decent 0-60 as the diff ratio is just to long.....good thing is it will make a great motorway cruiser....but thats not what you bought it for is it, no you bought it because its a well sorted sports car.

The opposite also applies, put a 4.375 into Dave Porters turbo nutter missile and it will be just to lary to drive and you will be changing gears like a fiddler on speed, with no traction in either 1, 2, 3, 4 or probably 5th.

Its all about getting the right balance between car characturistics and driver ability and desire
Click to expand...

Old post I know Steve but this is where i'm at
 
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