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Which differential ratio is recommended


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Welcome Pounds, how do you like to drive and what's your intended uses for the car? You'll be using 1st very little if at all...my father doesn't use 1st in his 240ZLt1T56. He's using a 3.7 LSD. You WILL notice far greater corner control with an LSD IMO and I think some searches on this forum would yield similar feedback.

 

I usually look at a gear ratio spreadsheet I have to see what the mph ranges of the gears are and if the top 'power' gear suits my anticipated top 'power/ie. track or other' speed. 3.9's or 4.11's will have you shifting more often than 3.7's or 3.54's but you'll be shifting either way and traction will already be a large function of driver skill/control so see what suits you intended uses. I can flip you my gear excel sheet if you like. I recall someone has some similar sheets online as well (Bryan's Garage?).

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IT will depend on your priorities

do a search and read these posts

 

Ideal rpms at highway speeds?

 

why you should stay under 7000rpm

 

YOUR engines RED LINE

 

but if I was building the car Id use this calc to match the rpms of the engine to about 2650rpm to 75mph in top gear ( overdrive #2,or .62 ratio), and 7000rpm in the lights at the 1/4 mile in 1:1 ratio) thats about

a 4.56 rear gearing BTW and will give you about a 160mph top speed

 

http://www.sallee-chevrolet.com/ChevyTransmissions/gmt56.html

 

http://users.erols.com/srweiss/calcrgr.htm

 

http://users.erols.com/srweiss/calcrpm.htm

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T56 is .5 OD in 6th, unless you have a 93 which is .62

 

Go for alot less gear than 4+ IMO, even with my little engine I'm going with a 3.90 LSD, which for most road courses is actually just about perfect for me. Graph it out, and that should tell you much better than taking wild guesses.

 

www.f-body.org/gears

 

Dont forget to input your corrected tire sizes of course.

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I've got a 420hp(ish) 350 sbc and a T56 lined up for transplant this summer. Which rear-end ratio would you guys recommend for the R200? 4:11 or 3:9. I was hell bent on a lsd setup also but after reading my jtr manual i dunno if I'd even notice the difference. Those are the two options that I've been mulling over. Any input would be appreciated. Thanks in advance....

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Hey guys, thanks a lot for the links they were really helpful. My main goal with the car is to have a nice weekend cruiser for car shows etc...... but also want to kill some ricers and mustangs (long standing grudge) in a little light to light action, no really hard cornering though. From the calculaters view it looks as though I'll go with 3.9, does that sound about right for what I'm wanting to do? I never really was a math with. Thanks again.

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What a timely post! I've been wondering the same thing. So can anyone with 4.11's chime in as to how they like that gear? my tires a 225/50/15 ~23" tall. It looks like that you really wind up with a 5 speed. Either 1-5 or 2-6 gears being used. What has/had a 3.9 in it? I have a 3.7 and a 4.11. may as well collect the whole set!

All you T-56 owners speak up!

luigi

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your totally correct about that higher ratio gear =quicker car, lower ratio gear= faster car but!!!!! use the calc. below (even with a 4.56 rear gear your only spinning the engine 6200rpm at 160mph with that .62 overdrive top gearing, a 3.73 drops it to 5100rpm at 160mph

 

http://users.erols.com/srweiss/calcrgr.htm

 

http://users.erols.com/srweiss/calcrpm.htm

 

since the cars far more likely to spend most of its time in the 40mph-110mph range the lower gearing makes more sence in a performance car with that overdrive top gearing trans.

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Guest Anonymous

Pound... with over 400 HP and a 6 speed...a 3.54 diff will shame about every car opposite you at the stoplight on the way to the cruise in. And 3.54 is about what comes in every 280 Z R200 rear differntial and that first gear of the 6 speed tranny will not see much commuter use and neither will that second gear stay engaged long.That high horsepower motor in that light of car will hit 6000 RPM in about 3 blinks of the eye.

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