No, he said they were 12.9 heat treated steel.

Oh yeah, forgot that part.
Nissan looks like my choice. Thanks for the part #'s guys.

Obviously we're all aware of the issues with the manifold to turbine studs. Concerning the turbine to downpipe studs however, I'm not aware that anyone has issues with the standard A2 / 304 stainless studs we've always used. We sell a ton of kits & if it was a problem I likely would have heard about it long ago. Does anyone have pragmatic feedback on this, most likely with the track cars?

Heat load at turbine to downpipe is MUCH less. Heck, I've even gotten away with mild steel for several thousand miles at that connection. Turbine does a heck of a job extracting the heat and turning it into mechanical energy.

I had a few fail before going to a better arrangement (v-band).

Edit-wrong thread lol

We've done a little research into thermal expansion rates. Here's what we've found so far. It seems that our Inconel studs actually match the expansion rate of the cast iron best. If anyone wants to do their own research I'd be interested to hear what you find- here's a great resource.

The Garrett & ATP turbo housings we use are described as “High silicone ductile cast iron” which is a little vague, but none of the different versions on matweb.com have a thermal expansion ratio. We did find a spec elsewhere for D-5 (which is typically used for gas turbines) that gives a spec of 7.8 at 1400°F.

Material Thermal expansion (microinch/(inch°F)) at temp Tensile strength, ultimate
Cast iron, A536, 100-70-03 (our manifolds) 7.56 69.8°F - 1650°F 110 ksi
Cast Iron, A536, 120-90-02 7.61 69.8 - 1650°F >= 120 ksi
Stainless Steel A2 / 304 (standard studs) 10.4 32 - 1200°F 73.2 ksi
Inconel 718 7.2 68 - 212°F 220 ksi
Inconel 718 alternate temp 8.9 1400°F 220 ksi
AK Steel type 410 6.5 32 - 1200°F 221.2 ksi
AISI 660 / A-286 10.8 69.8 - 1650°F 174 ksi
Turbine (assuming high silicone ductile, type D-5) 7.8 1400°F