Choosing a 5 Speed and Diff Combination

[Muzez]

Hi Guys, 

As far as I am concerned, gear ratios are black magic so I was hoping to lean on you guys for advice on how to pair a transmission with a diff.

I am replacing the 4 speed in my 280z next year. I find myself in the enviable position of having two rebuilt 5 speed transmissions (1977 280z and 1980 280ZX) and 2 R200s (3.545 & 3.9).

• Is there any advantage to mixing and matching transmission and diffs?
  (e.g. a 77 open ratio 5-speed with 3.9 or a 80 close ratio 5-speed with 3.54) 
• And are there different applications for the close ratio versus the open?
  (e.g. one is better for cruising and hills versus one is better for acceleration) 

I mostly drive the car to cruise or corner with a little SCCA next year. The car is mostly stock and the plan is to keep it that way (for now 🙂 ). I tried to look through some of the old posts on this topic, but some of it is contradictory and a lot of it was stored on GeoSites which is offline. Thanks in advance for the help!

     77-79    1980              

1    3.321     3.062            

2    2.077     1.858          

3    1.308     1.308            

4    1.000     1.000           

5    0.864     0.773       

 

[texasz]

@muze, I just went through this exercise earlier this year and have a TON of data in the post where we discussed it.  Let me look to see if I can find it for you.  You may also search this site for info.

[texasz]

Found it!

 

[siteunseen]

I have a 5 speed "wide B" swapped in my 240. Original in my '77. 

Easy to work with, shifter stays the same but I did change the speedo cog from the 4 speed to a 5 on the 240 upgrade. Not sure the color but with 15" wheels in pretty dead on with the MPH on my GPS as the speedometer gauge reads. 

About 2,000 to 2,500 RPM at 75 MPH through 80 MPH highway. That's my best info as far as constant speed, you see I have an aluminum flywheel so red light to red light and traffic driving is all over the place on my tachometer.

[Muzez]

3 hours ago, texasz said:

Found it!

 

This is just what I was looking for! Thanks so much! What did you end up going with?

[Muzez]

2 hours ago, siteunseen said:

I have a 5 speed "wide B" swapped in my 240. Original in my '77. 

Easy to work with, shifter stays the same but I did change the speedo cog from the 4 speed to a 5 on the 240 upgrade. Not sure the color but with 15" wheels in pretty dead on with the MPH on my GPS as the speedometer gauge reads. 

About 2,000 to 2,500 RPM at 75 MPH through 80 MPH highway. That's my best info as far as constant speed, you see I have an aluminum flywheel so red light to red light and traffic driving is all over the place on my tachometer.

You have the stock diff installed for your 240z? 
 

And do you like the lightened flywheel?

[siteunseen]

8 hours ago, Muzez said:

You have the stock diff installed for your 240z? 
 

And do you like the lightened flywheel?

Yes, 180 differential with the 5 speed. No problems ripping around town or 2 hour drive on the interstate.

Aluminum flywheel is my best modification so far. I'm a rev freak I guess, grew up riding dirt bikes with power bands. It's in my blood.

 

[texasz]

12 hours ago, Muzez said:

This is just what I was looking for! Thanks so much! What did you end up going with?

I decided on the 3.9 ration rear diff and the wide ration tranny ('77-'79).  I think I mentioned that in my last post in that thread, if not I intended to and completely forgot.

[Muzez]

2 hours ago, texasz said:

I decided on the 3.9 ration rear diff and the wide ration tranny ('77-'79).  I think I mentioned that in my last post in that thread, if not I intended to and completely forgot.

I think that is the direction I am heading as well.

I like the idea of a bit more top end because I drive the thing out to my parents house an hour+ away and usually dial in at 80mph. 4.5k rpm the whole way might get a little annoying after a while. 

Also one clarification because I was curious, you mention in your post “The sweet spot for 'stock' like acceleration” what did you mean by this? I assume your goal when you set off on this whole evaluation was some degree of performance improvement over your current setup but did I misunderstand?

[Dave WM]

the later zx  trans with the .75 od and a 3.54 stock r200 diff will get you 80mph right at 3k

[Muzez]

1 hour ago, Dave WM said:

the later zx  trans with the .75 od and a 3.54 stock r200 diff will get you 80mph right at 3k

Any idea what the performance is like compared to the wide ratio with 3.9? Also, I have an early ZX trans. How different is the .77 to the .75 od?

[Patcon]

.77 to .75, unnoticeable