thoughts on 5spd and diff combos

[GGRIII]

I believe have a non close ratio 5spd and know that I have 3.54 rear end in my car currently.  I don't cross it but it does see some highway cruising and 5th seems a bit short.  As part of an engine upgrade (see CO posts on F54/P90 build) I also acquired what should be a close ratio 5spd and 3.9 rear from an 83 non-turbo.  I was thinking that I may run the close ratio 5spd but keep the 3.54 rear end - effectively making all of the gears about 10% longer.  They way I see it the acceleration out of first would be a bit slower but everything else doesn't much matter as long as you wind it out 10% further.

Has anybody driven this combination or does anybody have thoughts on the close ratio 5spd - it seems that there is a larger gap between 2nd and 3rd but has a longer 5th which I would like for cruising at 80...

Edited September 23, 2019 by GGRIII

[Dave WM]

I run the CR 5speed and a 3.54 rear end. 5th is useless below 65, 70 if there is any hills nearby. Great for 80mph on flat roads (3k). Its pretty much a high speed cruise only, any hill and you end up down shifting. Since I live in Florida it works great, but on my recent cross country I noticed I was going in to 4th often on interstates that had some inclines. Starting out in 1st is not a big deal but again if you lived where you would find yourself stopped on a hill it may make it more of a challenge.

[Zed Head]

16 hours ago, GGRIII said:

I believe have a non close ratio 5spd and know that I have 3.54 rear end in my car currently.  I don't cross it but it does see some highway cruising and 5th seems a bit short. 

People use "short" and "tall" differently and many use them incorrectly.  Not sure what you mean by short.  A 3.54 will give you the "tallest" 5th you can get with any transmission, unless you find a 3.36 diff.  If you install a 3.9 5th will get shorter.  I'm using tall and short as I understand them  Tall is lower RPM, short is higher RPM, or faster acceleration.  With short you run out of RPM sooner.

There are only three 5th gear ratios available.  80-81 is in between the other two.  After 81 gives you the lowest cruising RPM.  "Tallest" 5th.

[GGRIII]

Agreed and i am talking about using an 83 5spd, tallest 5th, with the 3.54 diff, tallest diff.

[Terrapin Z]

I ran the 83 5 speed with 3:54 as well and liked it. Although 5th was a little sluggish, good for highway cruising.

I switched the rear end out with the 3:70 (Maxima) and gained a little more punch out of it. 

All the 5 speeds are still 1:1 in fourth so it is the same as 4th in the four speed. 

There was that one ZX transmission shown for 10 months in '79-'80 that had the in between ratio, but that is hard to find. 

The tallest diff would be the 3:36, standard on the 4 speed 240's and some 280's. The 3:54 came in the automatics. 240 280 and ZX.

[Zed Head]

Actually the early 5 speeds are the one with the gap between 2nd and 3rd.  The later "close ratio" boxes are well spaced.

I've used a 3.54 behind a close ratio with the tall first gear.  It just takes more attention to the clutch.  If you live on flat land it won't be a big deal.  If you live around some hills you'll put extra work in to your starts from a stop sometimes.

Don't overlook tire size in your calculations.  And, like Dave said, you might find that 5th never gets used.

Why do you think 5th is "short".  Does the engine get buzzy?  I found that once I got my engine squared away, cruising at high RPM was much nicer.  An unbalanced engine is annoying.  

[cgsheen1]

I ran my stock 3.36 R180 with a close ratio ZX 5-speed in my 260Z for years before swapping the diff to an 3.54 R200. I loved it, but it was also sitting behind an L28ET so, big torque difference. Like Dave, I now run 3000 RPM at 80 MPH. But, I've always believed that you use the lower 4 gears for spirited driving - 5th for cruising.

[GGRIII]

Great info,  thanks a bunch!.  My 260 will become a 280 with some minor head work so it should have a bit more to give than my 200K mi 260 motor has now.  I agree with cgsheen1 'I've always believed that you use the lower 4 gears for spirited driving - 5th for cruising'  I know that driving to Atlanta 2 years ago, I spent a fair amount of time above 3000 rpm, That is why I feel that 5th is too short right now - I want don't care if I need to down shift on a hilly highway, it may help to keep me awake!

[Jarvo2]

I run a 4.11 and a ‘77 wide ratio 5speed. It’s very spirited driving and I love it. On the highway it’s at about 3500rpm in 5th at 75mph. I don’t have my Z for efficiency, fun is more important to me.


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[gundee]

This Z car RPM calculator is really good.

https://docs.google.com/spreadsheets/d/1KOX4bwXzLoidUFdJKkwnIQwq1AMafdbv-LmCBuyJdcg/edit?authkey=CPTj89IN&hl=en&authkey=CPTj89IN&hl=en&authkey=CPTj89IN#gid=0

[LeonV]

I ran the close ratio box with a 3.54 and it really fit the GT feel of the car. I've since swapped to a 3.9 LSD and while it's turned into a more spirited drive, it's definitely buzzier on the freeway. I seem to settle into a natural cruising speed closer to 70 rather than 80mph with the 3.54. There are merits to both but if you're doing a lot of cruising, the 3.54 is the way to go. I run an L28/P90 combo with a decent cam and 10lb flywheel and have no issues with hill starts with the amount of torque the motor puts out.