anyone know the lengths of speedmaster drives from input to output shaft. i know a 5 is shorter than a 3. but was wondering what a 3, 3A, 4,and 5 length difference is

thanks in advance!

I'm about 99% sure---
A 3/3A are the same length and 4/5 are the same length
A #4 is a short #3 and a #5 is a short 3A.
The 3A and 5 just use bigger shafts than the 3 and 4.

I don't know the lengths, but I think the 4 and 5 are about 3-4" shorter

3 and 3a are 24.311"
4 and 5 are 6" shorter 18.3

legnth is not the only factor,,each drive has differant cavatation plate locations,,like the plate covers part of the prop on a 3 drive and plate is shorter on 4 and 5 drive..

Thats correct ,and on a v bottem ,there is a change you will not get the boat on plane due too excessive prop slippage ,you can space a 4 and 5 down ,and /or add trim tabs to help the boat coming in plane .
I,ve seen some custom fabs that uses a 1/2 inch thick ali plate cut and formed like a cav plate that can be clamped between the upper and lower unit (4and 5 ) it bent up a few inches just behind the actual cav plate to make room for 17 1/2 inch props.
O ring grooves need to be milled in around the studs just like a mercruiser spacer has.

What you doing now Tim?

So then is a 3 or 3A a better option for a heavy flat bottom V hull than a 4 or 5 due to cavitation?

a 3A is a stronger drive rated for more power than a 3. from what ive been told over the years to run a 4 or 5 on a T/G you benefit from having extension boxes. if not they do big burnouts since notched transom boats are tough to get the x dimension low enough to get the props to bite the water

The #6 gets on plane because of the huge cav plate and the huge amount of negative trim it has.

The boxes don`t help all that much, the right prop and cupping does. Also Ive heard of guys modifying the rear trim pin to get more negative trim like the #6 .. but in the end its all in the prop.
My #4 1 1/2 below bottom planes in 8 seconds