I have been reading and searching a lot about Miatas in general and there seems to be a general rule regarding transmissions, or more exactly, the 5 speed transmission:
"After 230-250 hp, the tranny life expectancy is uncertain, some last some dont, with the average Joe breaking 5 speeds left and right"
Anyway, there seem 4 options:
1-Reinforcing the stock 5 speed (cryo, micropolishing, shot peening, Carbonizing the gears)
2-Upgrading to a Quaiffe gearbox or complete tranny.
3- Make a 6 speed swap and be safe at least until 400whp
4- Make a 5 speed RX7 transmission swap.
To do a 6 speed swap, and I quote from Solomiata:
"The 99+ Miata 6-speed is made by Aisin and is not related to the Type II 5-speed (it is listed below for reference ony). Will the 6-speed bolt in a 5-speed Miata? Yes, make sure to get the trans plate and shifter from the 6-speed donor since they are unique to it. You will have to use only two of the three 5-speed starter bolts but that shouldn't be an issue, otherwise it bolts in (same PPF mount, etc). Keep in mind the 6-speed is combined with a 3.909:1 rear in the USA (3.636:1 other markets) since the tranny gearing is much steeper so your '90-93 or 99+ 4.30:1 5-speed rear should also be changed to the 3.909 or at least the more common 4.10:1 otherwise you'll have a nice tree stump puller"
What about the RX7 tranny swap? What does it envolve?
Anything else needed for the 6 speed swap?
Any personal advice on transmissions for the Miata and BP platform?
My goal is 400 whp.
BTW We should make more stickies!!!