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Tapping Exhaust Manifold

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I found my thread tap, but what size drill bit. For pircol gauges.

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Should be 1/8" NPT which uses a R drill bit or 11/32 would be closest.

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I may have found the wrong tap then. I found a 12mm x 1.75 This is for my pyro.

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I guess I will just put the old exhaust man. on the other eng. The reason I was going to tap it was I tap the old man. in the wrong place, it's on the 123 cylinder side:doh:Cant be to far off, you think?

Some taps are within just a few thousandths between metric and standard so if you matched them up they will be basically the same. I am not sure if 1/8" NPT would be the same as 12x1.75, guessing not because 12mm is nearly 1/2" which is considerably larger than the 0.343" drill you use for 1/8" NPT. Either way it still wouldn't work because NPT is tapered so that the threads on the probe will tighten down once it gets far enough on the taper, otherwise it would just bottom out. If you still think it will work, the drill for your metric tap is 13/32". I was wrong on the Q drill bit, there is a lot of blown around info on the net. Here's the right guide. http://www.physics.ncsu.edu/pearl/Tap_Drill_Chart.html

I was reading a bit about drilling the manifold... saw an idea which I thought was very smart... to put a couple of strong magnets next to the drill... to suck shavings away from the hole.I tend to get carried away with tapping... I read to only tap 2-3 threads so threads would be tight without protruding into the manifold. {Something (dumb) I could see myself doing!}

You read right, you dont want to go to far down with the tap. Where did you get Di pricol gauges at? I have been trying to finish my set out and have only been able to come up with a trans temp gauge. I need boost and egt in black face if anyone has them.

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