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Diff Ratio Choices


Marty Rogan

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I have a '71 240Z that I use for High Speed AX at the track, and for lapping days, along with street driving. It has the stock engine at the moment. In the near future, I will be installing a 5spd from a '78.

I have been looking into diff choices. Was thinking of using a 4.11 out of a '84-85 Nissan 4x4. I might have a shot at an R190 with a 4.44 ratio. My question is, how much difference would there be between a 4.11 and a 4.44?? Also, what would the differences be?

TIA,

Marty

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The difference between the 4.11 & 4.44 is roughly 6 1/2 %. In my 240...I have the late model 5 spd with 4.11 LSD and 24" diameter tires. At 3000 rpm in 5th gear, I'm traveling at roughly 70 mph. On some of the tires shop sites, they provide the equations to calculate your speed, based on your set-up. But for an approximation....with 4.44 in my set-up at 3000 rpm, I would be going approximately 65 mph, instead of 70 mph with the 4.11s.

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Here's a cool website that will show you the differences between all of the different tranny/diff combos. You can even manually enter any ratios that are not listed.

http://www.geocities.com/z_design_studio/

Since my car is a dedicated autocross-only car, I know I will seldom be going over about 70 mph, so I chose the tranny to give me a top speed of about 65 mph in 2nd. That way I only have to shift up on the fastest courses (but then again, my motor has LOTS of torque). If you know about how fast you will be going on the tracks you run, you can figure out the gears that will minimize shifts and/or optimize acceleration.

Tom

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Thanks for the calculator website.

So it looks like the the 4.44 will drive up the RPM's slightly. Does that mean it would accelerate quicker than the 4.11?

I'll have to play around with the calculator. On the track that I normally compete at I can get up to 80-90MPH. I will be doing an event or two at Road America, where I can get upwards of 110+. I wouldn't want to drive the revs up too much for that.

Marty

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I'd suggest a ZX 5 speed. Look at the 2nd to 3rd gear gap on the two 5 speeds to figure out why. I had figured with my 23.5" tires and 4.11 my top speed would be limited to 145 mph or so, so I think you should be OK to hit 110 with the 5 speed unless you put 13" rims with 20" tall tires on...

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