I managed to break all 4 studs on the turbo to downpipe connection during my last track day.

Two of the studs would not come out at all and in the attempt to drill them the bit wandered forcing me to open up a hole that removed the M8x1.25 threads from the casting.

In opening up the holes I tried to stay with in the diameter that would let me add a M8x1.25 Helicoil insert. One of the holes is slightly ovalized over the 21/64th drill bit dimension (0.34” instead of 0.328” on one side)

How will Helicoil threads hold up in such a high temp environment?

I could go oversized to M10 but I’m concerned about alignment and if I can get a M10 nut to fit in the space under the elbow of the dp.

Last option is to drill all the way through and try to find studs long enough to put nuts at both ends.

I bought some Inconel 280zx turbo bolts that I was hoping to use but I don’t think they are long enough to go through the flange and the casting and still have threads sticking out to put a nut onto.

If anyone knows of a source for extra long M8 Inconel studs, please let me know.

 

I think helicoil will be fine, stronger than it was before.

 

It does look like your throttle cable housing may be getting a little molten from the heat / DP leak proximity.

 

Add speedo cable, remote for boost controller, stock O2 sensor cable, and the spot welds in my FM heat shield.

 

Helicoil should work fine! Just make sure you drill and tap as clean as possible