NC 5 speed into an NB/NA
 

Does someone out here know a fair amount about the internals of the various years of the Miata 5 Speed? I am wondering about the value of using NC internals within an NA/NB case. I was reading the Walter website (walter-motorsports.com) about Miata transmissions, and noticed they said the NC 5 speed was an upgraded version of the NA/NB 5 speed.

The parts catalogues agree with that. The same bearings from 1990 – 2013, the same main shaft, the same synchro springs, the same 5/Rev set up from 1999-2013. The same shift forks and fingers from 99-13, with one exception. So swapping the front case and tail housing (and shifter fork fingers for 97 and earlier) would seem to allow the NC trans parts to go into an NB and NA. (Unless the length of the input shaft differs.)

The 1-4 gears and the synchros, selector clutch hubs and selector sleeves differ for the NC compared to the NB, based on the parts catalogues.

But what sort of an upgrade is it? Mazda changed the gears and synchros, and the 2 L engine made as much as 170 hp, a fair amount more than the 1.6 L NA. So it must be intended to be a bit stronger than the earlier versions, or maybe a bit more durable? Or was it primarily a ratio change? I see the NC has a slightly less close ratio for 2 to3 to 4.

I understand this upgrade might not be good enough for a turbo car, but could it be an advantage in durability on the race track for a normally aspirated NB or NA version?

There is a huge mutli page thread on this topic, would suggest looking that up. From what I recall it isn't worth the trouble.

Also involved people talking about custom gearsets so you might try searching that.

I suppose my search skills are poor, but my search did not find that huge topic.
I have found many debating 5 vs 6 speed. But I did not find this issue on NC vs NB 5 speed durability.
Can you help with a link?

Probably this thread but I don't have time to read the whole thing right now.

Somewhere around post 180 people begin talking about OEM parts bin swapping gearsets/cases etc.

https://www.miataturbo.net/race-prep...-73618/page11/

Thanks for that, my search did not find it. I read through it all, and through some of the links it refers to, including this mega thread https://www.miataturbo.net/suspensio...t-75506/page2/
But there is only the briefest mention of the NC, and that is in relation to the 6 speed in the NC. The general perspective is on a strong gear box for an FI engine above 250 hp, and mostly around 350 or more. That is not really what I am asking about.
A normally aspirated, tuned, 1.8 L tuned could use more a bit more gearbox durability than the 5 speed NA/NB gearbox, but not the sort of upgrade magnitude discussed in those threads.
So my question remains does the 5-speed NC upgrade offer any durabiity benefit over the NA and NB 5-speeds?