Broken exhaust manifold studs

[fireguyfire]

I'm helping a buddy refresh his 383 out of his 68 charger and he has 2 exhaust manifold studs on the drivers side that are broken off flush with the head.
I'm guessing the only option is to drill them out and tap them.
Can anyone give me any tips or tricks to do this the best way?
What size of drill bit do I need to build up to before I can go to the 3/8" course tap?

[Chryco Psycho]

Brad is the expert , heating it & using parafin wax helps , I would drill a smaller hole on center & use a spiral remover & try to get the stud out rather than try to retap the holes

[JS29]

I have had limited success using left hand drill bits, If the bit grabs, sometimes the broken bolt will spin out. try to get it as centered as possible. 

[Dakota]

There are several videos on YouTube that involve welding a nut onto the end of the stud.  I've never done it.  The combination of the heat and having something to wrench does the trick.  Using a mig welder seems to be pretty risky given the spatter.  I saw an episode of Wheeler Dealer where a TIG was used that looked to be a saner approach. 

I have had success a couple of times removing stuck bolts and brake bleeders by heating them up and then melting candle wax into the threads.  I've always had something to put a wrench in though.

Brad is one of several wizards here on all thing mechanical, so as CP stated I'd follow any advice he provides. 

[EV2RTSE]

I would drill a smaller hole on center & use a spiral remover & try to get the stud out rather than try to retap the holes

Agree, have done this successfully on my 340.

https://www.youtube.com/watch?v=SMrDYJvY0Ts

[RUNCHARGER]

Exhaust studs are tricky because of continuous heating and cooling. I would try welding a nut to it first and then drill and ez-out if that doesn't work. Helicoiling can be done but sealing the water can be difficult afterwards.
I had a particularly difficult one on my 71 Road Runner and I didn't want to pull the head, I ended up building the stud up with a weld nub and then welding a stud to the nub after nothing else worked.

[Daveh]

I've had similar issues as well and I've welded on a bolt in a few instances and it works great if you have the welder.  Good luck.