3.90 or 4.11 ratio?

[Chickenman]

On 2/27/2016 at 0:14 PM, Zed Head said:

I have the 1980 5 speed, with 3.9.  And my 5th is .773, not .745, like 1983.  My car cruises easily at 60 mph for distance.  25.3 inch tires though.  The 1983 .745 5th with a 3.54 seems like it would be best  for highway cruising.  When I had the 3.54 diff, 1st gear felt sluggish, so I went to the 3.9.  Basically, the stock 1980 280ZX setup, except for a slightly larger tire.  At 60 my car should be at 2400 RPM.

 

That's a nice calculator. Thanks for sharing.

[gnosez]

With the same tranny, 23 inch tires and a 4:38 diff at 3000 rpm I'm at 61 mph in 5th gear. Not something I would ever do in the race car. While my street size with the same 1980 tranny, a 3:90 diff and 23-inch tires at 3000 I'm doing 68.

At 6800 on the dyno in 5th, the Centerforce pressure plate came apart after the harmonic dampener had an issue. That tranny has a 1.5-inch hole in the upper left side. Speed would have been 154mph

Edited March 17, 2016 by gnosez

[gundee]

With mine, I am running a 4:11 diff ratio with the 78 - 5 speed. I am using 205/60-15 to give me the oem tire diameter.

While it is fun around town, on the highway in 5th it just feels like it wants another gear shift.

With my set up I may look for a 3.70 diff. 

[John Coffey]

Quote

The problem for me, though, was that because of my 3" exhaust, the drone was unbearable 

Don't change gearing to fix an exhaust problem.  Add  an 18" resonator in the tunnel.

[z boy mn]

Sorry I fell asleep on this one, John, especially as you're so knowledgeable. I added a resonator first (not sure the size now), but the drone was still pretty bad. It did seem an odd way to make the car more comfortable, but for a strange work-around, it did the trick plus added some zip.

[RyanT67]

On 22/03/2016 at 11:22 AM, John Coffey said:

Don't change gearing to fix an exhaust problem.  Add  an 18" resonator in the tunnel.

Did that when I had drone issues and it helped quite a bit, then I ditched the chambered flowmaster muffler for a perforated core magnaflow.  Problem is all but gone now, although the car really screams at WOT, haha.

FWIW I run 4.11 and with my 5 speed and 23.9" tires I turn about 3700rpm @ 70mph.  Makes for loud highway cruising, but I still get around 25mpg so out isn't so bad.  These engines seem pretty content to sit around 3500rpm all day long.  

[Galaxybj]

On 3/22/2016 at 8:42 PM, Lumens said:

With mine, I am running a 4:11 diff ratio with the 78 - 5 speed. I am using 205/60-15 to give me the oem tire diameter.

While it is fun around town, on the highway in 5th it just feels like it wants another gear shift.

With my set up I may look for a 3.70 diff. 

I have the 280Z 5 speed with the 3.90 diff in one of my Z's.  It works really good.  The overall gear ratio in 5th is 3.369 which is basically the same as a stock 4 speed 240Z. (tire diameter not in the calculation, just the tranny and diff gear ratios).  The 3.70 will give you 3.20 overall in 5th.

If you want to keep the 4.11, I recommend switching to the 280ZX 5 speed, which has the higher 5th gear.  The overall gear ratio in 5th with the 4.11 is 3.061.  This is what I have in my other Z with a 4.11 diff ( turns 3300 rpm at 70 mph).  (NOTE: I normally run a 4.44 lsd diff, but it is out for repairs.)

 

[Travel'n Man]

I have a STi LSD 3.9 (use to have a regular 3.9) paired with a 81-83 5 speed.  Works great for me.  Get up and go is great and crusing RPM's are great as well.  You would not be disappointed at all.

 

[Zedyone_kenobi]

Travel'n man, that is my desired setup for my Z. I have LSD STI 3.90:1 diff in my car now, and the 4 speed eats it up, car pulls hard all the time, but I would kill for the 5th gear. Thought about taking the transmission out of the roadster and putting it in the Z but chicikened out.

 

You would not know where I can find a 5 speed do ya Guy old buddy.

[Travel'n Man]

Bought mine on ebay - buyer said it was rebuilt - yea, right.  Had to pull it out after the first year and have it rebuilt.  My buddy did the rebuild (Cert Master Mech) and only charged me $200.   If I were to do it again, I would buy one and have it rebuilt from the get go - that way you know once it is in - it is in correctly.  The 81-83 ZX 5 speed is pairing great for me.  I do not have a 3" exhaust either - thinking of going to a 2.5" for next winters project.  This year bought a set of Watanabe's for this past winters project- still waiting for delivery from Japan.