280zx 5 speed swap question

[Tonellius_620]

Before anyone starts giving me crap, YES, I’ve done my research here on ratsun before making this post. I am new to all this and I’m still not sure if I made the right choice.

 

I picked up a 5 speed off a 280zx, which is a close gear ratio. I have the stock diff, which Is 4.375. 
 

I want to haul stuff sometimes but mainly want to keep my rpms low on the highway.

 

not sure if I made an oopsies by getting this transmission because I don’t want the truck to feel sluggish.  

Thanks everyone 

[datzenmike]

There was only one close ratio transmission and it was in the '80-'83 280zx. It's rather popular and commands a premium price and it's only natural that someone might sell you something else. Lets make sure first. Place it in first gear, mark the input and output splines, turn the input 20 turns while counting the output turns.

 

6 turns....... close ratio

5.5 turns.... mid ratio

5 turns....... wide ratio

 

Now you're absolutely sure what you have. It would mostly affect starting from a stop. Here are the first gear ratios or the number of engine turns for one driveshaft turn...

 

3.062 close

3.321 mid. This is what would be in the 620 4 or 5 speed.

3.592 wide  

 

Get a good nights sleep you're fine. Fourth is the same in all wide, mid or close transmission gear sets. The close ratio might be most noticeable with a close to maximum load on the truck. With 4.375 differential, this helps. 

 

Overdrive 5th.

Stock overdrive is 13.6% and the close ratio is 25.5% or basically double if an '81-'83 and 22.7% if an '80 transmission. Either way a big drop in highway RPMs. Assuming about 3,000 RPMs in 4th then fifth would drop to 2,592 on the stock transmission and 2,235 on the close ratio. This can drop the engine to a point where it has reduced power and trouble holding speeds into the wind or climbing up hills. Never use 5th for passing, hill climbing, carrying a load or driving into the wind. It is strictly for part throttle cruise.

[Tonellius_620]

Thanks Mike, you saved me once again!

19 minutes ago, datzenmike said:

There was only one close ratio transmission and it was in the '80-'83 280zx. It's rather popular and commands a premium price and it's only natural that someone might sell you something else. Lets make sure first. Place it in first gear, mark the input and output splines, turn the input 20 turns while counting the output turns.

 

6 turns....... close ratio

5.5 turns.... mid ratio

5 turns....... wide ratio

 

Now you're absolutely sure what you have. It would mostly affect starting from a stop. Here are the first gear ratios or the number of engine turns for one driveshaft turn...

 

3.062 close

3.321 mid. This is what would be in the 620 4 or 5 speed.

3.592 wide  

 

Get a good nights sleep you're fine. Fourth is the same in all wide, mid or close transmission gear sets. The close ratio might be most noticeable with a close to maximum load on the truck. With 4.375 differential, this helps. 

 

Overdrive 5th.

Stock overdrive is 13.6% and the close ratio is 25.5% or basically double if an '81-'83 and 22.7% if an '80 transmission. Either way a big drop in highway RPMs. Assuming about 3,000 RPMs in 4th then fifth would drop to 2,592 on the stock transmission and 2,235 on the close ratio. This can drop the engine to a point where it has reduced power and trouble holding speeds into the wind or climbing up hills. Never use 5th for passing, hill climbing, carrying a load or driving into the wind. It is strictly for part throttle cruise.

 

[datzenmike]

Did you spin and count the output turns? Good to know what you have as your speedometer pinion is going to need changing

 

 

[Stoffregen Motorsports]

Close ratio - wide ratio. Splitting hairs. Day to day driving you would never notice the difference between the various ratios.

 

In a nutshell, if you bought a trans already, use it.

[datzenmike]

I wouldn't go that far. It's just noticeable but has no real downside unless heavily loaded or starting up hill. I noticed my wide ratio in my 620 would be ready to shift before the far crosswalk which was mostly annoying for the guy behind me.