Looking to get a rear LSD Diff, what ratio/config?

Engine, Transmission and related drivetrain.
B^2
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Looking to get a rear LSD Diff, what ratio/config?

Post by B^2 »

I'm in the market for a new rear differential for my 1970 510. Currently running an L20B with dual mikuni 40's. No immediate plans to upgrade the engine. Current diff is clunking so I'm in the market for a lsd diff and thinking 4.11 gears. I know lsd 4.11 diffs are rare so I'm wondering if I'm better off getting a 3.7 LSD and swapping the core into a 4.11 diff?

Also I see a lot of diffs on ebay but it's not quite clear what it would take to fit it up to my 510: https://www.ebay.com/itm/234135521644?e ... _1PAcpiW9c


Should I be looking at a ratio other then 4.11?
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icehouse
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Re: Looking to get a rear LSD Diff, what ratio/config?

Post by icehouse »

Needs to match your trans, tire size and driving style.
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B^2
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Re: Looking to get a rear LSD Diff, what ratio/config?

Post by B^2 »

Running a dog leg 5-speed right now. I've got 195 width tires on 15's. Driving style is just cruising around the hills having fun.
iceman510
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Re: Looking to get a rear LSD Diff, what ratio/config?

Post by iceman510 »

If you buy one of those Subaru diffs, I have an extra set of the axle stubs you need to make it work. They connect to your stock rear halfshafts. Made by Datsun Restomods (he's not making anymore of them). PM me if interested.

I am using a set of them to put a Suby 4:11 in my 73.
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icehouse
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Re: Looking to get a rear LSD Diff, what ratio/config?

Post by icehouse »

4.11's is going to suck on the freeway with the dog leg trans. The 5th isn't much of an overdrive.
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datzenmike
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Re: Looking to get a rear LSD Diff, what ratio/config?

Post by datzenmike »

If you are used to 3,200 at 60 MPH in 4th (stock tire and 3.70 differential) then in 5th it would be 14.5% reduced or 2,736.

A 4.11 is 11% increase over the 3.7 so 4th will now be 3,552 an increase of 350 rpm and 5th 3,036 an increase of only 300 rpms.

Another way to look at it is the differential gearing multiplies torque. This is an 11% increase in torque at all rpms.

I put a 4.11 in my 710 and love how fast it races through all the gears. Really woke it up!. Didn't notice any change in mileage on trips as it's wind resistance that must be overcome and not really the rpms the engine is going. Around town is basically the same as I can run in a higher gear. No problem going a steady 50k in 5th or around a corner in 3rd. I have the wide ratio CA18ET 200sx 5 speed with the 18.7% OD
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icehouse
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Re: Looking to get a rear LSD Diff, what ratio/config?

Post by icehouse »

Makes sense if your top speed is 60. Down here where we have highways you hit 80mph all the time just hanging with the fast lane guys which is what I do.

With my 4.44's and a .85 firth gear I was always at 4500 RPM's plus. So annoying. Now I have 3.7's and a 6 speed but want to find 3.5's.
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datzenmike
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Re: Looking to get a rear LSD Diff, what ratio/config?

Post by datzenmike »

You have to balance the power needed to push through the wind at the speed you want to go and the engine RPMs. If it requires 30 hp to go 50 MPH you'll need 4 times this or 120 to double the speed. It's easy to over drive too much and lower the RPMs to where you can't go over a certain speed.
"Nissan 'shit the bed' when they made these, plain and simple." McShagger510 on flattop SUs
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funwithmonkeys
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Re: Looking to get a rear LSD Diff, what ratio/config?

Post by funwithmonkeys »

I love my 4.6 gears with the zx 5 speed. .74 OD makes it just right. Sure you don't have much acceleration in 5th but 3100 rpm at 100kph is pretty nice on the long drives. Need power? Drop to 4th and I'm at 4200 where my car just starts to make power.
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B^2
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Re: Looking to get a rear LSD Diff, what ratio/config?

Post by B^2 »

funwithmonkeys wrote: 31 Aug 2021 17:25 I love my 4.6 gears with the zx 5 speed. .74 OD makes it just right. Sure you don't have much acceleration in 5th but 3100 rpm at 100kph is pretty nice on the long drives. Need power? Drop to 4th and I'm at 4200 where my car just starts to make power.

What gears were you running before you had your engine built? I have a feeling the gears I want for my L20B are different then the gears I'd want for a 2.3 stroker or other engine build.
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funwithmonkeys
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Re: Looking to get a rear LSD Diff, what ratio/config?

Post by funwithmonkeys »

I have run 3.9 and 4.44 with the stock motor and 4.11, 4.44 and now 4.6 with the fully built motor. For me now that I have run a bunch of different ones I would stick with the shortest gears you can handle. I ran the .87 overdrive with the 4.44 gears and it was over 4k on the highway. It was a bit buzzy but what it gave me in acceleration was worth it. I would never go back to longer gears unless I had huge power. Even then knowing that it could accelerate faster and not doing it would drive me nuts.
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icehouse
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Re: Looking to get a rear LSD Diff, what ratio/config?

Post by icehouse »

datzenmike wrote: 30 Aug 2021 17:04 You have to balance the power needed to push through the wind at the speed you want to go and the engine RPMs. If it requires 30 hp to go 50 MPH you'll need 4 times this or 120 to double the speed. It's easy to over drive too much and lower the RPMs to where you can't go over a certain speed.
I put a super tall trans in my VW bus with 36HP and it will do 80MPH since I sit in the crumple zone I try and not go that fast. Yep hills I have to go to 3rd but that's always been the case, now at least 3rd is somewhat close to traffic speed! haha. I just know unless you are racing it's super annoying to be super buzzy on the freeway. gear your car for what you enjoy doing most.

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icehouse
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Re: Looking to get a rear LSD Diff, what ratio/config?

Post by icehouse »

funwithmonkeys wrote: 01 Sep 2021 08:18 I have run 3.9 and 4.44 with the stock motor and 4.11, 4.44 and now 4.6 with the fully built motor. For me now that I have run a bunch of different ones I would stick with the shortest gears you can handle. I ran the .87 overdrive with the 4.44 gears and it was over 4k on the highway. It was a bit buzzy but what it gave me in acceleration was worth it. I would never go back to longer gears unless I had huge power. Even then knowing that it could accelerate faster and not doing it would drive me nuts.
That's why I went with the SR 6 speed. The 1st-5th is the same with 3.5 gears as it was with the 5 speed and 4.44 gears. For fun I ran the 6 speed and the 4.44's it was like a dirt bike. Way to much shifting. The 6 speed weights the same as the 5 speed to! Maybe you should make an adapter for your L series.
"People don't like it when shit doesn't match their rule of thumb." Sam
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funwithmonkeys
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Re: Looking to get a rear LSD Diff, what ratio/config?

Post by funwithmonkeys »

I would love a 6 speed. I've got a pretty wide Rev range so it would probably work out well.
If no one from the future comes back to stop you from doing it then how bad of a decision can it really be?
B^2
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Re: Looking to get a rear LSD Diff, what ratio/config?

Post by B^2 »

Can anyone tell me if this diff will work: https://www.ebay.com/itm/234177237749?h ... SwcEdhN-xg

I know the datsunrestomod cv kit works with clip in style diffs but it's unclear to me whether that diff is a bolt in stub axle or clip in.
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