4.56 diff vs 4.10

2919 Views 12 Replies 10 Participants Last post by Bill S, Oct 25, 2007

Vivace

Discussion Starter · Oct 23, 2007

I need to find a LS 4.56 axle assembly ('72-'79) to finish my switch over to Ate brakes. The RezDoc guy has a 1986 rear end on ebay, which is a 4.10. (I'm cautious about buying from him after reading a few stories)

Is that going the wrong direction for a low-torque 1600? What would using a 4.10 do?

How many decent condition, low-mileage pre-'79 rear ends can there be out there?

Thanks -

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Gordon Raymond

· #2 · Oct 24, 2007

1600's and rear axle raito's

A lot depends on how your engine is set up. Where, in the RPM range, is max torque? I used a 5:12 with a GTA CR 5 spd and a 1600 with all the torque & Hp at high RPM. Milder cams let me go to a 4:56 and still launch the car relatively easily. I don't think with my seriously lightened flywheel I could get nice 1st gear launch with a 4:10. Again it all depends on how the engine is put together. If I used a 22 Lb flywheel, I might still be able to get off the line with a 4:10, but then it would chug and pop along until I got up on the cams at 3500 RPM or so. For rear axle expertise, contact Richard Jemison on this BB, (Alfar7) or Jack Beck @ Orion Motorsports in St. Louis. Both can, and have, built anything you might want.

Gordon Raymond

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Vivace

Discussion Starter · #3 · Oct 24, 2007

It's a stock, original 1600.

Sounds like 4.10 is going the wrong direction then. I'll stick with looking for a 4.56.

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dghii

· #4 · Oct 24, 2007

For what it's worth, In the last year I've purchase two items from rezdoc without any problems. Item condition was as described and the items were shipped promptly.

Not a plug, just a bit of information.

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ddouglas77

· #5 · Oct 24, 2007 (Edited)

Vivace said:
It's a stock, original 1600.

Sounds like 4.10 is going the wrong direction then. I'll stick with looking for a 4.56.

Stock engines love the numerically higher ratios, but again, should you ever build up your stock engine, the 4.10 may perform better for you (higher top speeds, better fuel economy and less engine wear). I don't know about you, but 1rst gear for me under full throttle only takes 4 seconds to wind out the motor, another 3 seconds to double clutch and get into 2nd, 6 seconds to wind out the motor in 2nd and again, 2 seconds to get into 3rd. Half the time I start in 2nd gear, if I actually start in 1rst, I'll shift into 3rd and then into 5th. I'd love a 3.73:1 rear end. Maybe that way it would actually feel like I have a 5 speed transmission...

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Alfajay

· #6 · Oct 24, 2007

Vivace had asked: "I need to find a LS 4.56 axle assembly...How many decent condition, low-mileage pre-'79 rear ends can there be out there?"

Only about a million! 4.56's are the common variety - it's the 4.10's that are more of a rarity.

OK, if you absolutely insist on low mileage, then sure, the newer spiders used the 4.10's, so perhaps in that universe, the 4.10's will be more abundant. But, Alfa was selling fewer cars in the 4.10 era, while in the mid-1970's, every Spider, GTV, and Berlina came with a 4.56.

Unless differential has been allowed to run dry, they tend to last forever, so I wouldn't worry too much about finding one with low mileage. Also, these are expensive things to ship - why not just look for one locally? Tell the BB where you live, and I'll bet you will find a 4.56 diff around the corner.

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Tifosi

· #7 · Oct 24, 2007

Alfajay said:
while in the mid-1970's, every Spider, GTV, and Berlina came with a 4.56

Except for the ones that came with the 4.3x (more common to the Berlina and Euro spec cars than the US spec GTV and spider if I remember what I was told correctly)

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Andrew

· #8 · Oct 24, 2007

As far as I know, all US 1750 and 2000 cars up through the Bosch Spider (4.10) came with 4.56; I believe 4.3 was standard in non-US cars.

The 4.10 might be a bit of a steep pull for a stock 1600. It's nice for freeway cruising, but I found in my 89 Spider I seemed always to be in the wrong gear compared to how I drive in all my other (4.56) Alfas. The 10% change makes more difference than you'd think.

I'd say unless the car's going to spend its life at high speed on the freeway, 4.56 is a better compromise. Go for 165-15 tires to lengthen (numerically lower) the gearing as much as possible if that's important.

Andrew

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msiert

· #9 · Oct 25, 2007

Couple of questions,
How long of a run did the 5.12 rear axle have and did all 4.56's have LS?

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rogerspeed

· #10 · Oct 25, 2007

generally 5:12 in Giulia 1600 single carb, 4:56 open duetto/GTV/Super,

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Bill S

· #11 · Oct 25, 2007

msiert said:
Couple of questions,
How long of a run did the 5.12 rear axle have and did all 4.56's have LS?

In the U.S., stock 4.56's got LS in '72, I believe. My '67 and '69 don't have LS.

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Andrew

· #12 · Oct 25, 2007

Yes, as far as I know, the only 105/115 in the US that got 5.12 was the 1600 TI, through ~1966. The Super, and all subsequent cars until the Bosch Spider, had 4.56.

Andrew

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Bill S

· #13 · Oct 25, 2007

Mike,

Aren't you out in Montana or something? I've got a couple 4.56 axles w/LS and set up for ATEs if you're interested but as Jay said, you should be able to find one a lot closer.

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