Stage 8 hardware with Inconel studs

Our exclusive Inconel 718 studs combined with slip-proof Stage 8 fasteners. The studs will deal with the heat produced by hard turbo use, and the fasteners will ensure it’s impossible for the nuts to back off.

Under extreme use, the stainless steel studs that we used to use in our turbo kits can expand enough to loosen off and eventually break. So we did the same thing NASA did for the X15 rocket plane, and went to Inconel. Space-age! Keith promised not to write anything else about the X15, which is good for you because he starts babbling about it every time you mention Inconel. Inconel 718 is an extremely strong material (with nearly double the tensile and yield strengths as 316 stainless steel), but it’s also a much closer match for the thermal expansion of our (and most other) cast iron manifolds. Meaning that not only is the stud much stronger than stainless, but it will also be much less stressed, as the differing thermal expansion rates won’t be trying to tear things apart, like with stainless steel studs. 

These M8x1.25 studs are made exclusively for FM by ARP and are a straight replacement for the originals. No drilling or retapping required. They’re made of the Inconel 718 alloy and given a full 16 hours of heat treating. The threads are rolled for maximum strength.

You might notice they look a bit different than most studs. There’s a reason for that – they’re not a generic stud, but one that was made specifically for this application. The shoulder (the unthreaded portion in the middle) is an exact match to the depth of the flange on a turbo, so the turbo is not riding on a threaded portion. We also made both threaded portions 12mm long for more thread engagement in the manifold. Yes, they look a little weird. But they’re a perfect fit.

The Stage 8 locking nuts are a brilliant design. Tighten up the nut as usual, then slip the locking tab over top and use the C-clip to hold it. Voila, a nut that cannot possibly loosen. If you need to remove it, pop the clip off and remove the tab. Simple and effective. We recommend this hardware on the turbo-to-manifold studs for any Miata that sees track use. Available as an option on our turbo kits.