Gearbox
 

I'm slowly gathering parts for my tinkering and I'm reading more and more about people running 6spd gearboxes. As I understand it people running 200lbft and above for heavy racing (drag, auto and track) have or would like to run 6spd boxs. Logic dictates this is because they are stronger but what I would like to know is where.
Where does the 6spd gearbox differ in terms of durability?
Is it because the gears are of a better material of better grind? Is it the casing material (thickness or quality)?

Gears. It's the gears that go in the 5 spds.

Interesting. The only breakdown where they have said what went I have known of was the casing shattering under 320lbft

2/3rds Cobra/Quaife did some research and decided that the pitch of the gear was too steep, among other things.

2 months ago the question was covered pretty well here...


https://www.miataturbo.net/forum/t37888/

Pitch= too small or too big

helix angle= too steep or too straight

FYI.