Well, I took the advice of other membersand orderedan IssproEGT and boost guage from Geno's Garage. The instructions they sent with the guages says to drill a 7/16" hole in the manifold then tap with a 1/8" tap. This is obviously a type-o, so I was wondering, what size is the tap? It looks like a 1/2" NPT, but I wanted to make sure before drilling a giant hole in my exhaust. Can someone offer any advice?

 

Drill the hole somewhere else first, like a scrap piece of metal and see if it threads in

 

It is a 1/8 NPT tape (at least it was for my pyro,) I dont know what the 1/8 means, but I know it's not 1/8". The bit hasa tapered end. The drill bit size I used was R. I found a package deal at Menards (I live in MN, not sure where else they are) that had the tap and the drill bit.

I hope that helps, hopefully some one will be a long to give a more technical explination.

 

1/8 npt is 1/8 id. Use 1/8 pilot and then 21/64 for the main hole, then tap away.

 

It might be easier to find an 11/32 drill bit. That will work too, on an 1/8 NPT tap.

 

What kinds of stores carry NPT taps? Auto part stores do not.

 

NAPA has 1/8" NPT Taps. They are for some reason typically standard in a metric tap and die set. I got a Metricset from Sears and it had a 1/8" NPT tap in it.You can also check out plumbing supply places as plumbers use a lot of NPT items.

 

Sears has them. If you cannot find a 21/64" 5/16" works but it puts more of a load on the tap and the manifold.

 

I found the tap at Lowe's.