Originally Posted by sparky (Post 10006891)

I can understand that the OP would be squeamish about metal chips running through his turbo. I didn't realize that the turbo was on the car. I just did not see a need to remove the manifold. But that being said I wouldn't hesitate to tap that hole with the turbo on my car. As a matter of fact, I have done it a bunch of times myself. Never had a problem.

Look, on my Evo, I have drilled and tapped my exhaust manifold at the number two runner with the manifold and turbo both still on the car and lived to tell about it. If you are just cleaning up an existing hole and tapping the threads you are not going to produce much in the way of metal chips. I did it the same thing on my Buick Turbo Regal.

Pre measure the thickness of the manifold wall at the location of the hole. Place a band of masking tape around the drill bit to act as a depth guide. This way you will know when you reach the proper depth.

Put vaseline or grease on the drill bit. Set the drill at a slow speed. Drill part way down and then remove the bit from the hole and clean the vaseline and chips off of the drill bit. Reapply vaseline and go down further again. This way with the vaseline there should be no chips falling into the manifold's interior.

Once you are done drilling then take one off those pencil thin extension magnets and pick up any micro chips that may have fall inside the manifold.

I come from a turbo diesel truck background and all the guys with modified diesels on the Cummins forum run an EGT probe in their exhaust manifold. All of these guys drilled and tapped the thermocouple holes while the turbo and manifold were still on the car. They just fired them up and blew the chips out through their turbine housings. No one ever lost a Holsett this way. Just be careful and you'll be OK. believe me.