I am installing the Edge Juice w/ Attitude and was wondering which size drill bit to use for the 1/8" NPT tap for the pyrometer. Thanks for the help in advance.

That would be an R drill

TAPER PIPE SIZES - NPT

----------------------------
TAP DRILL
SIZE SIZE
----------------------------
1/8-27 R
1/4-18 7/16
3/8-18 37/64
1/2-14 23/32
3/4-14 59/64
1"-11-1/2 1-5/32
1-1/4-11-1/2 1-1/2
1-1/2-11-1/2 1-47/64
2"-11-1/2 2-7/32
2-1/2-8 2-5/8
3"-8 3-1/4
3-1/2-8 3-3/4
4"-8 4-1/4
----------------------------

What size drill bit is an "R"? My drills bits are either a fraction or metric size. Thanks for responding.

8.5mm .3346" M10x1.5 coarse
8.6106mm .339" R 1/8"-27 NPT
8.7313mm .34375" 11/32"

If you use metric, 8.5mm is the closest and will be a bit small.
11/32 is very close and will be a bit large.

For purposes of tapping the thin cast iron of the manifold, why not go to Home Depot or your local hardware store and just purchase an R bit? It'll cost around $10 and is a lot cheaper than a replacement manifold. That being said, you shouldn't have any problems using an 11/32 if you're careful not to oval out the hole and don't overtap the threads (which could happen with any size hole).

You know, if you go to Google.com and enter "tap drill size" you will get the table I posted in the first reply. Same goes for "drill size" which I've entered above.

Did a search as you recommended & I found this chart which varies from yours. It calls for a "Q" drill bit size. Thanks for the info.

NPT Size Tap Drill Size (in.) (Decimal) (in.)
1/16 - 27 "C" (0.242)
1/8 - 27 "Q" (0.332)
1/4 - 18 7/16 (0.438)
3/8 - 18 9/16 (0.562)
1/2 - 14 45/64 (0.703)
3/4 - 14 29/32 (0.906)
1.0 - 11•1/2 1•9/64 (1.141)
1•1/4 - 11•1/2 1•31/64 (1.484)
1•1/2 - 11•1/2 1•23/32 (1.719)
2.0 - 11•1/2 2•3/16 (2.188)
2•1/2 - 8 2•39/64 (2.609)
3.0 - 8 3•15/64 (3.234)

You will see 1/8 NPT tap drill size listed either "Q" or "R".
Q=.332 R=.339
The important thing is do not to tap too deep. This is a tapered
thread.

Completed the install last year.
I recommnd the R size drill, but what ever you use , do not rely on the size Edge has/had in their instructions. My Edge instructions say to use a 5/16" drill hole in the manifold for the EGT probe. DO NOT use this size. I nearly broke a Tap off, before I decided something is wrong. After hours struggling with this, I did little research on this site and discovered I needed a larger hole. I called Edge to let them know of the error in printing.

With engine running, start with a small drill and work your way up to the proper whole size. Then go slow with the Tap, working it back and forth until you break through.
Hoot, a member here, has a good article in the archives on the subject that many have followed.