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Which differential to use?


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I don't think I've got the perfect combination, but that's ok.  I'll work with what I've got.

L28 & 5 speed wide ratio with one of the following:

R180 /w 3.36 gearing (existing diff)

R200 /w 3.54 gearing (have all components to install in car)

Some highway driving and some city driving, but no track or racing.  Is there a preferred combination here?

 

From what I understand, 3.36 might be a bit sluggish in lower gears but better on the highway while the 3.54 would be a bit better for light to light but higher rpms on the highway.  Correct me if I'm wrong.

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The 3.54 and the wide ratio is the factory combination for the 75 to 78 280Z coupes.

Here's one of many calculators out there if you want to see where you might end up.  Tire size matters too.  5th gear would be 0.864 for the wide ratio.

https://www.crawlpedia.com/rpm_gear_calculator.htm

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On my ‘77 260z I have the ratios quoted and a 3.54. It’s an absolute hoot for traffic light races as 2nd can take me to around 70mph so no loosing ground on gear changes. The drone zone on these cars is around 1.8k to 2.4k rpm give or take depending on your exhaust etc. I find at 50mph I’m square in the middle of that in 5th and often change down to 4th. Although with Sean’s Zstory Race/Sport set up the drone is 95% gone (compared with my straight 2.5” from header to rear muffler) but even then I just prefer to be closer to 2.5k.

At 70 she is doing about 3kish rpm - I don’t fully trust my taco as I think it’s about 10% optimistic.

Of course size of wheels has a bearing on this - I’m on stock 195 / 70 / 14 all round.

I find 3.54 and that ‘box are a great compromise between cruise and spirited driving especially if changing up around 5.8-6.2k rpm which lands me exactly back to where the engine “comes on cam”.

My diff is pretty worn so I’m about to go to a 3.9 especially as it would suit the characteristics of my modified engine better.

Give that a 3.9 is 10.2% more turns of the engine for the same speed, all things being equal, you will dial 10% more revs and 10% less speed at the top of the gear change.

The 3.36 by the same calculation is 5.4% more revvy so you will do 153 rpm less than a 3.54 at the same speed. You will nearly notice that on the highway.

Now if you went 3.9 then you have a 16% uplift in revs which equates to 61.7% more fun!

If you are city and highway driving but enjoy putting your foot down on the odd occasion, then your available 3.54 gets my vote. The L28 with a decent header should have a lovely wide torque spread but you get a bit more sports car for the money with the 3.54.

The other bonus of the 3.54 is that it will make your gearbox “feel” closer ratio. Remember that gearing has a torque multiplier effect so it’s going to “feel” more like a sports car.

Then sell your 3.36 to the drag racers who covet tall gearing!








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