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3.90 or 4.11 ratio?


HaZmatt

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Hey guys, looking for some advice. I'm running a 3.0L stroker and a short ratio 5 speed putting down roughly 240hp/220tq to the wheels. I'm currently running my factory rear open diff with the 3.36 gears I believe. Time for a new diff. I want an LSD for sure but cant decide on the 3.90 or 4.11 ratios. Will there even be a noticeable difference between the two? Would the 4.11's be  too much for cruising speeds? I've searched and read other threads but looking specifically for info regarding the difference between the two. Thanks!

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Never run either of those diffs, but can tell you I'm running one car with a 3:54 diff in an L28 with a 240Z crank and rods and at 60 mph on the highway, I'm turning 3000 rpm's .......not good for long term cruising. I would err on the 3.90 side IMO.

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Haz, I put a 4:11 R 180 from a 200SX in mine. Loved the acceleration, especially in 3rd and 4th. Then I decided to replace it with a 3:54 for lower rpms at higher speeds. BIG mistake. Way too much shifting in the canyons and twisties. So, I will go back to the 4:11 when the garage floor warms up a bit more. Yes, the rpms are higher with the lower gearing, but I don't drive it at those high speeds over 90 much any more, and I do drive the canyons and twisties. My friend, Kenny, has a 3:90 R 180 from a Datsun pickup front axle and I can pull him just barely. Some on here have done the Subaru LSD 3:90 swap and are happy with it, but it possibly involves new half shafts and adapters...too much for me. Just sayin'

 

Cheers, Mike

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15 hours ago, Diseazd said:

Never run either of those diffs, but can tell you I'm running one car with a 3:54 diff in an L28 with a 240Z crank and rods and at 60 mph on the highway, I'm turning 3000 rpm's .......not good for long term cruising. I would err on the 3.90 side IMO.

Guy,

What transmission are you running?

 

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Patcon....I'm running a 1983 280ZX close ratio 5 speed. With the 3:54 rear, I'm turning 3,000 rpm at 60 mph. Believe me, if you are doing any long distance driving, it'll work on you:( . Can't say from experience what a 3:90 or 4:11 rear turns at 60 mph, but don't think I'd enjoy it. Just my humble opinion.

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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.

Something odd here though.  The calculator shows that 3000 RPM at 60 mph with a .745 gear and a 3.54 diff (Diseazd setup), would have an 18" tire.  Kind of small.

 At 60 my car should be at 2400 RPM.  25.3 tire, .773 5th, 3.9 diff.

tiny tires.PNG

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Sorry folks....Zed Head is right....it's the 72 (orange car) that runs right at 3000 rpm at 60 mph....it's running a 4 speed ( 1.0 ) final drive and 205 55 16 tires.....the 73 (silver car) is running a 3:54 also, but a 280 ZX 5 speed tranny....much more civil at speed....sorry for the mix up.:blink:

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I was running a 3.90 open diff when I first got the car. It definitely had some advantages as it was turning about 2500 at 60mph on my 5-speed (from an 1982/3 ZX). The problem for me, though, was that because of my 3" exhaust, the drone was unbearable just at that rpm, and it was a little pokey off the line and picking up speed as the powerband my my 3.1 stroker doesn't really kick in until 3500 or so.

When I upgraded to an LSD, I swapped to the 4.11, which pushed the rpms to about 2950 at 60mph. Gas mileage got worse by a hair, but it is quicker and more agile plus the drone went away, so I'm happy. I don't drive this car long distances, mostly to work and back (15 miles one way), so the mileage didn't make any real difference. I also understand that these engines don't mind running at a higher rpm, so I"m also not worried about wear and tear (I only put 3-4K miles on it a year anyway).

BTW, I had my car on the dyno last fall and before any real tuning my numbers were almost exactly the same as yours.

Good luck with your decision!

Edited by z boy mn
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