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> I am thinking to change my 4-speed to
> 5-speed transmision, Do I need
> drive shift and differental ? Will my
> differental match ?

You have two options. Either one of them will work without changing out your driveshaft. Your stock one will work fine.

Option 1:
Install a 5-spd. from a '77z-79zx. These cars have 5-spds with the exact same gear ratios in 1st thru 4th that you have now and have a .864:1 OD. You won't need to change the differential with this model and they are easier to find.

Non-Option: Do not use the 5-spd out of an '80zx. It has the same 1st-4th as the 81-83 so you will need to change the differential and its OD is a .777:1 so it doesn't give you any cruising advatage over the earlier 5-spds. More cost for not much gain.

Option 2: Install a 5-spd from an 81-83zx. Do NOT use one from an 83zx turbo. It won't fit.
These transmissions have different gearing ratios in 1st & 2nd than your current 4-spd. They are lower numerically so that means that you will come off the line like a slug unless you install a 3.90 differential in place of your stock 3.545. The really good news here is that the OD is a .745:1 which, combined with the 3.90 differential still gives a better final drive ratio than the older 5-spds. It also has closer ratios between 2nd and 3rd and gives you better 3rd & 4th gear accelleration.
I went for option 2 with my '77. I got a 5-spd and 3.90 differential out of a NA 83zx and have loved the results. Cost me $550 for parts & labor.

Option 3: If you want best accelleration and OK cruising put in the older model 5-spd and a 3.90 differential gearing. It will get you off the line quicker than your current 4-spd and the 5th gear will give you OK highway cruising. Just slightly better than your 4-spd does now.

Merry Christmas,
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