Ive heard that you can do this with the manifold on and the engine running. Is this safe for the turbo? I know 2 people that have done it this way. I have a post-turbo probe, but I want to install a pre-turbo probe. thanks

also, where is the best place to drill the hole?

 

No problems at all doing it the way your talking about. I started with a small 1/16" hole through the manifold engine not running. Then I started the truck to drill the 5/16" hole with a well greased bit to catch the shavings. Shut off the truck and used a magnetic pen to catch any shaving that fell into the manifold. I didn't find any.

As for placement there is a good diagram but I put it 5/8" back from center on the rear portion of the manifold. I'm sure someone will post the image or just search, it's on here 100's of times.