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favorite rear diff with 5.7 LS1/t56?

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I've been collecting parts for 5 years now, and finally have everything sorted out for the most part. Car is getting caged at the moment, and before it's done i thought i'd look for a bit of feedback (since I'm apparently indecisive). I have the rear diff from a 92 300ZX n/a (4.08 i believe), and i was curious as to what people have found to be pros/cons to their setups. I have thought about going with the TT rear end, but since I'm staying NA and will be shooting for mild upgrades (looking for 375-400 whp) I'd like to know if anyone would like to share their experiences.

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i have a r-200 from a 280zxt with 3.54 gears and quaife internals, z31 turbo half shafts and custom stub axles. i wouldnt change a thing. its in a 280zx with a LS motor with 405whp. i have been beating on the rear end for 10yrs now with a LS motor and 6-speed. i dont know what car your doing but if its a s30 then it worries me about the 4.08 gears. im sure its not a s-130 cause there isnt too many of us odd balls out there. but with mine i dont have as many options but im completely happy. i think with the horsepower your planning you will be fine with most options, just make sure its limited slip. if your doing stick shift car then your first concern will be half shafts and stub axles. im not a pro like some people on here so there may be someone wiser than me out there. good luck  

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Depends on which T56 you have.  Mine has 2.66 first gear and with my 3.9 rear end and 24.85" tall tire and a shift point of 6800 rpm (my redline is 6900) first gear is 48.48 mph.  In 6th gear top speed is calculated at 257 mph.  Plugging in your 4.08 rear end I get 46.34 mph for 1st and 246 top speed for 6th.  Obviously we can't pull 6th to those speeds but I don't think you need to worry about running out of gear.  Trackspeed is right though...1st gear goes by in a second...no matter what rear end you use.  I like my 3.9.

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For an all around car, I think a good starting point would be to go with a gear ratio close to what the factory used with that transmission. A mainly  strip car, autox car, or a track car may need something much different.

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First question is what tire diameter and what you going to do with it.  Typically Z’s seem to run 23” tire on 15” rim or 25” tire on maybe 17” rim.  For 25” my experience says 3.7 for most road courses is perfect.  23” favors the 3.54.  3.9 is silly IME. 

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For most folks with a T56 it really doesn’t matter. I’ve run 3.90 and 3.54. With the 3.90, I used 6th gear a fair bit, but really didn’t need 1st gear. With the 3.54, I use 1st gear, but rarely get into 6th. With that low 1st gear and the super tall 6 th gear, and plenty of torque at any rpm, you will be fine with any ratio. 

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IMO you need to consider the usage to choose a ratio. If it's just a street car it probably doesn't matter that much, but for a car that does drag racing you're going to want to be winding out a gear as you cross the line. For my use, autocross, I figured I wanted to be able to do about 80 mph at the top of a gear. 23.5" tire I was using with 4.11 and T56 puts me at 81 mph in 3rd at redline. Just going to start in 2nd and not use first at all.

 

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