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Probably the best "upgrade' i did to the car, replaced the original 4:56 non LSD. I live in San Diego and spend 1/2 the time on freeway, and its so nice to be tooling at 70 at 3500 rpm. The motor has mild porting on intake and no real performance mods, running SPICA, at first I thought 4:10 might be too tall for 1750 but it is just right. No problem taking off in 1st and with everything in balance, the ride is awesome. Not a hole shot car by any means but an all-around fun driver.

If you are on the fence on 4:10 for 1750, again, depending on your driving style, location (Im at sea level and relatively flat), some stop-n-go with mixed freeway, this combo is really sweet.
 

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I have a spider with 4.56 gears and a sport sedan with 4.10s. I live at 5500 foot elevation. I much prefer the 4.10 gears.
 

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I have done it on my Super and Junior Z. Super has a 1750, Junior Z has a 2000, they can pull the gearing easily. If you drive freeways and whatnot a lot, definite improvement. If you're in town, country roads, stuff like that more, I'm not sure I find it better; the 4.56 to me puts the engine more in the sweet spot. I do find I'm always speeding in town, 10% too fast! To each his/her own though.
Andrew
 

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The U.S. spec 1971 1750 spiders did not have the limited slip of the '72 and later cars, either 4.56 or 4.10. So, if you change to a complete 4.10 axle, you get LSD in the process. Way back in the early 1970's I changed to a 4.56 with LSD for my '71 Spider and realized a significant improvement in autocross performance.
 

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I would say 4.10s may not have that much limited-slip left in them unless they're been set up. For a normal driver Bosch Spider, I bet they are worn in that department.
Andrew
 

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My '70 European GTV came stock with a 4.10, although I don't think it is a limited slip. It never felt like it, anyway. My impression is that it was the US bound cars that got the 4.56 gears. If you can't have a close-ratio box (which works exceptionally well with a 4.56), then a 4.10 or 4.30 will give you a much more usable gearbox and slightly lower highway rpms.
 
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