What diff ratio to use?

[GTR-240Z]

Can anyone help me, I need to start looking for an R200 diff for my zed soon and i dont know what ratio to go for. The engine is from a 280, and the gearbox is a 5-speed from a 73-74 240z. If i use a 3.9 what kind of acceleration could i expect and would it rev really high when travelling on the motorway at say 95mph.

Thanks
Darren.

 

[zman240uk]

Darren

If you want to work out max speeds using different gear and diff ratios try the link below.

http://www.csgnetwork.com/speedcalc.html

I believe the 3.9 ratio diff was the one fitted as standard to Uk 240z's.  If you want a bit of extra acceleration go for a 4.11, top end speed wont suffer too much.  Lowest I would consider for the road is a 4.375.  This will be very quick but you will have to work the engine harder and your top speed will be limited to about 115mph.

You may find that you are limited in choice by availability of different ratios.

Ken...

 

[Mr.F]

You have a 3.9 now, so the R200 from the late 280ZX manual would be the obvious choice to keep everything the same. If you want a more relaxed car, with a little less acceleration use the 3.7 diff from an early 280ZX manual. With 280ZX diffs, you will need the back plate and output shafts from a 260Z also. Most 260Zs come with the 3.7 diff, some with 3.5.

 

[Zed2k]

Is there any way of telling diff ratios from outside the diff other than turning and counting wheel turns and prop turns I also need to uprate my standard R180 diff as wanting 300+ hp?

Nick <img src="http://www.zclub.net/iB_html/non-cgi/emoticons/biggrin.gif" border="0" valign="absmiddle" alt=''>

 

[zedhead260]

Not from the outside. You need to remove the back cover, on the large cog (I'm sure there's a more technical term for it) you'll find 2 numbers stamped into it seperated by a :
Divide the numbers and that will tell you the ratio.

 

[Mr.F]

Large cog is the crown wheel. The little cog driving it is the pinion gear. The numbers on the crown wheel represent the number of teeth on that item compared to the number of teeth on the pinion, e.g. 37 crown wheel teeth and 10 pinion teeth = 37/10 or 3.7:1 ratio.

 

[zedhead260]

<img src="http://www.zclub.net/iB_html/non-cgi/emoticons/tounge.gif" border="0" valign="absmiddle" alt=''> &nbsp;Crown wheel.......of course.

I really should have known that

 

[Tony 260Z]

Soooo... on my 260 I presumably have a 3.7 or 3.5. Would sticking a 280's 3.9 give me a bit more zip, or should I try to locate a 4.11? Would this be easy to find, and would I need to swap anything else too?

Tony

 

[zedhead260]

Early 2 seater 3.7:1
Late 2 seater 3.5:1
Think all 2+2's are 3.5

A 3.9 from a 280ZX will give you better acceleration, but will mean higher cruising rpm, less fuel economy and less top speed.

The only thing you need to change is the speedo cable to gearbox cog (these technical terms are evading me of late). Anyway, they are colour coded for each ratio. You'll need a black one for a 3.9.

 

[Mr.F]

Speedo drive sleeve and pinion gear....

These are coded to the final drive ratio and again, the differences are in the number of teeth in the gear. Somewhere in the magazine archives is an article on all the combinations which would probably merit transfer to the the FAQ section (anyone?).

 

[Tony 260Z]

I'd be prepared to swap a bit of top end for some 0-60. Realistically, my Z doesn't darken a motorway all that often and a little nippiness is more often required. I think I might go for that at some time. Thanks!

 

[GTR-240Z]

I finally got a 3.7 R200 LSD from an 88 300ZX (not a viscous one either) and some 280ZX Turbo cv shafts for america i don't think shifting from a 3.9 to 3.7 will ruin the acceleration much as once i've got an engine in my zed it should be good for 225bhp so it should still shift.
But will i have to change the back cover on the diff for one from a 260z like you do on diffs from 280zx's.

 

[zedhead260]

stilesie : got a 3.7 R200 LSD from an 88 300ZX and some 280ZX Turbo cv shafts

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How do the CV shafts attach to the wheel hub ?

 

[GTR-240Z]

You have to use an adapter, I'm going to buy some pre-made from a company in america called modern-motorsport, if anyone else is interested take a look at there site they also sell rear disk brake kits etc for zeds.

Modern-Motorsport website

 

[zedhead260]

$205.....plus import duty plus VAT, Ouch.

But I suppose it is a cheaper way to getting an LSD.