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Discussion Starter #1
Dear all, my 1300GT Junior already has a LSD with the higher gearing but I am still at about 4000rpm at 80mph. Also the first three gears are just silly short, I'm in 3rd by 30-40mph. Is there a way of swapping out a final drive to lift the all of the gears? Cheers.

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Dear all, my 1300GT Junior already has a LSD with the higher gearing ..... Is there a way of swapping out a final drive to lift the all of the gears?
Without knowing the numerical ratio of that "LSD with the higher gearing" it's hard to comment. Replacing a 4.56 with a 4.11 is a pretty common swap here in the US. 4.11 differentials are fairly common, as the Bosch injected spiders came with them. A more exotic swap is a differential from an automatic, late-model, 115 spider. Those are pretty rare, however, and probably wouldn't be well-suited to a 1300cc engine.
 

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Without knowing what the numerical ratio is of that "LSD with the higher gearing" it's hard to comment. Replacing the a 4.56 with 4.11 is a pretty common swap here in the US. 4.11 differentials are fairly common, as the Bosch injected spiders had them. A more exotic swap is a differential from an automatic, late-model, 115 spider. Those are pretty rare, however, and probably wouldn't be suited to a 1300cc engine.
The car is a 1300GTJ but it has a 75 Twinspark engine, it also has 15" wheels with normal profile tyres. I will speak to the mechanic about the auto box diff, thanks.
 

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According to this site (https://www.automobile-catalog.com/auta_details1.php) late model Alfa Spiders were available automatic and had a 3.6 final drive ratio. Surely these late model Spiders in automatic form would not be that rare, as by the time they were making these they were for cruising and looking good in ...
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Your 1300 transmission has a .86 fifth gear. Std Alfa transmissions in 1750-2000 cc versions all have a .79 fifth. I suspect that will bring your top gear RPMs nicely.
Differentials out of Automatic spiders are rare, and sell for $1500-$2000.
Did you change out the speedometer gears in the transmission to match the Diff ratio?
 

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Did you change out the speedometer gears in the transmission to match the Diff ratio?
I don't read off the original speedo, there is a GPS speedo and another sensor on the propshaft. The ecu logged speeds in the initial posts are correct. My problem isn't just 5th or the distance between the gears, its the fact that they are all to low, hence looking for a option to swap the final drive. Its quite an expensive proposition, cheaper to buy a clapped out car!?!
 

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but I am still at about 4000rpm at 80mph.
That is 120 mph at 6000 rpm or 130 at 6500 which is where the power peak is likely to be with a well tuned 2L motor. It seems that you are used to having 4 real gears plus an overdrive which was typical for some classic British cars.
 

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Discussion Starter #8
That is 120 mph at 6000 rpm or 130 at 6500 which is where the power peak is likely to be with a well tuned 2L motor. It seems that you are used to having 4 real gears plus an overdrive which was typical for some classic British cars.
All the gears are too low, for a normal TS engine in such a light car its all a bit too frantic in my opinion. Even on more energetic drives, the gearchange is too slow to compensate for speed at which you need to change gears with this box. Torque curve is like a table top, first is a waste of time on the road unless you want to kill your prop, second lasts for a couple of second and then third becomes useful. Anyway, it's just a personal taste thing, 99.9% of the community seems to be happy!
 

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Start at about 40 seconds in the video of a Spider with a 4.55 axle. The time in gears is 10% longer with a 4.1.
 

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Discussion Starter #10
Start at about 40 seconds in the video of a Spider with a 4.55 axle. The time in gears is 10% longer with a 4.1.
Lovely car on a lovely road! I'll try and post the logs which will show times, rpm, etc etc. I believe I have the 4.11 final.

Cheers.
 

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If its any consolation I have the same issue. Fitted 160hp Nord, first gear is all but redundant and she runs out of gears too quickly. Can't help feeling I'd be quicker overall with longer gearing. I'm on a 4.55 diff with standard 1600GT gearbox. On the upside, although it's a 10% lower ratio than the longest diff, the engine is built for at least a 10% higher rev limit so top speed is still sort of OK.

Changing diff is more difficult because I invested in a gripper LSD which is great. I don't want to lose that, which I guess I would if I fitted a 4.1

At a steady (true) 70-80 the car is overall much harder work than my old 1750 Berlina with a 4.3 diff. Much more engine noise and wind noise. Honestly, that 1750 would run smooth & quiet as you like at 90mph all day if you could. If you want a car for an actual Grand Tour then ironically the Saloons are often better than the GT's

If you've already got a 4.1 in there then fitting an auto diff which is 4.3 won't help. But actually from the rev vs speeds you quote you may well have the same 4.55 as me which would make sense. A 4.10 diff would give you around 22mph true / 1000RPM, your figures are closer to 4.55 diff at just under 20mph/1000rpm.

The 4.3 diffs are rare as hens teeth though and you'd be better anyway with 4.10 so if you're going to change I'd focus on that.
 

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If you've already got a 4.1 in there then fitting an auto diff which is 4.3 won't help.
As PSk notes in post #4, the automatic diffs were 3.6, not 4.3, so would represent a lower numerical ratio compared with whatever is in AJSG's car.

Not to get too off-track, but does anyone know why automatic spiders needed such tall gearing?
 

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My diff is a higher ratio (LSD in a 68 1750). "22mph true / 1000RPM/4.1" sounds about right as at 60mph I have about 2800-2850 rpm. Cable drive speedo has been re-calibrated by GPS. First gear on most cars is just to get things moving. UK sports cars, of which I have had many, had ridiculously low first gear ratios and most were straight cut and whined loudly.
 
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