Shavarsh New Reader
10/6/20 11:09 a.m.

Hello Everyone,

A piece of my current project involves running a 28 spline thunderbird 8.8 in a miata rear subframe (in a pinto). After researching the high dollar swap axles available I have come to the conclusion that I can make the center bars and have them heat treated for a reasonable cost. I am particularly interested in the "direct fit" axles that use a miata outer cv and a ford inner. These axles are rated to 400hp. My question is this: does anyone have any experience with these axles behind a mild V8? My quick math for the splined end of the miata cv bar puts the torque capacity at an optimistic 325ish ftlb for case hardened steel. I'd love to know if the outers on these axles resemble the stock outers or if they are a different design. Really any information I can gain before ordering the chromoly shafts is much appreciated.




therieldeal Reader
10/6/20 12:04 p.m.

I’m fairly certain that CV failures on high power turbo miatas are not a common problem.  Broken transmissions and differentials, yes… but not axles.

Shavarsh New Reader
10/9/20 11:04 a.m.

Has anyone seen the direct fit conversion axles? I have found lots of questions about them across the internet but haven't found any first hand experience.


10/9/20 12:14 p.m.

What exactly is a direct fit conversion axle?


I got my axles from Monster Miata and it seems to be a ford inner stub to a ford CV to a custom middle shaft to a Ford outer CV with a cord outer stub going into a "broached" Miata hub. So really, just a standard Lincoln rear axle with a shorter mid-shaft.

ShawnG UltimaDork
10/9/20 12:47 p.m.

Can your tires stick 325ish lb/ft to the pavement?

If they can't the axles will be fine.

Shavarsh New Reader
10/11/20 7:04 p.m.


The axles I am referring to are sold by DSS and probably some other companies. They have an 8.8 stub to 930 CV to custom bar to a miata outer cv joint. I plan to make a 4340 center bar to connect a stock 8.8 inner plunge joint to the stock miata outer CV. This will allow me to keep everything outboard of the CV joint stock miata (hubs, brakes, wheel pilot, etc.) The only part I am unsure of is if the outer "miata" cv joint they are using for the conversion axles is in fact a stock style joint, or if it has been beefed up/heat treated/etc.



You make a good point. I'm only running a 225 but at the drag strip they hook pretty nicely. The 325lb/ft sounds like enough until transmission/ring gear multiplication is considered. I did use some very conservative values to take shock loading into account so hopefully with the added strength of the chromoly i won't have a problem.

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