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1972 GT 1300 Junior with 2L engine, 2001 916 GTV 2.0L Twin Spark
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18 Posts
Discussion Starter · #1 ·
Does anyone have some tables for the different 105 gearboxes where I can see for each gear what the rpm/velocity ratio is.
Want to know what kind of gearbox I have.
 

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Premium Member
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15,012 Posts
It will depend upon axle ratio and tire size as well as gear ratios.
 

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Premium Member
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1,631 Posts
So, you’re trying to figure out if you have a1300 gearbox or not?
i did a quick search and got a few numbers, search:
‘AlfaBB speed versus rpm’
there’s some info in there which might help.
The manual for my 1600, 4.56 diff says .79 5th gear.
This equates to 20mph/1000 rpm with stock tire sizes.
You might have to get your calculator out...what about trying to calc % drop in revs from the 1:1 4th gear with .79 and .86 and compare result with your observed rev drop? A proper mathematician could advise...
 

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Richard Jemison
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8,308 Posts
The only difference in gear ratios in all the split case factory production transmissions is 5th gear. All but the "Jr" labeled cars use .79 fifth and the "Jr" a .85 fifth.
Forget trying to match speed in gears to see if you have a "Jr" 5th gear.
Mark the flywheel or set the engine at TDC and in that position mark the flange on the Pinion shaft and make a pointer to that position. If you turn the engine 1 turn exactly, then it should be easy to see if the mark has gone past the pointer on the pinion flange. A .79 will show a distance of appx 20% of the diameter past the pointer and the .85 about 15% past the pointer.
 

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462 Posts
I thought the workshop and owners manuals also listed max speed per gear at redline, which is essentially a speed/rpm data point.
 
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