I recently bought a 280zx engine and 5 speed transmission (81) to transplant into my 78 z 2+2 with a locked up engine and a 4-speed tranny. I've read it's a straight swap, but I'm no mechanic (my dad is helping me rebuild the car for those interested). Do I use the driveshaft that is already in my z or is the driveshaft going to have to be lengthened?

As long as I'm making a post, I've read on Z spec sites that my tranny has 3.54 differential, whereas the 81 5speed I'm swapping in is normally paired with a 3.9 diff. I understand that I'm going to be slower off the line with the 3.54, but how much difference is this going to make in real life driving situations? I'm rebuilding the car because I like it, not for a 12 sec quarter, but I don't want it to be slower than it should be, if you catch my drift. Just wondering.

 

The swap will go right in. Use the 280Z 2+2 driveshaft that is already in the car.

The car will not change acceleration very much. Your 4-speed did have slightly lower 1st and 2nd gears but those gears offer good torque anyway, so the 280ZX transmission will hardly be noticed. You'll cruise the same in 4th gear as you always did, but then you'll have this nice tall 5th gear for highways.

You will want to swap out the speedometer cog. Where the speedo cable plugs into your transmission, undo the one little bolt that holds this plate around the speedo cog. Pull the cog out of the 4-speed and put it into the side of your new 5-speed. This will keep your speedometer reading the same as it always has.