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Discussion Starter · #1 ·
I'm getting ready to install some gauges in my truck and was wondering what size drill bit to use to drill in the exhaust manifold. I know you use the 1/8npt to thread just not what size drill bit. Any help would be great. Thanks.
 

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i just did mine ... i used the r bit but i found it too small so i went to the 11/32 ng so 21/64 worked great ...nice tip on the install plug up youe exhaust 90% and start the engine let idle and start your drilling wear goggles cuz the metal flies up at u dont let the exhaust get hot so shut it down between the drilling and tapping ..but run it when u tap it also ....works great
 

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I used an R bit and a 1/8-27 NPT tap with great success. When drilling I went slow to make sure I was at a right angle with the manifold. Once you get going, the manifold seems real soft. I used a big magnet then after the hole was drilled I put a screwdriver in the hole and picked up the shavings. It was one of them screwdrivers with a light magnetic force, and it picked up a ton of stuff. When tapping, go a little ways, then back out. Then back in a little more, then back out. I ended up doing about two revolutions of the tap at a time. I got cocky at the end and went more than I should have and busted part of the tap. Luckily the probe adapter threaded nearly all the way in so it was all good. Good luck.

-J
 

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thats why i went with the bigger bit cuz when i was tapping it it felt too tight for comfort and even with the bigger bit the threads came out perfect...next time u do one try running the motor with the tail pipe blocked 90% ...its a good deal to go
 

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should make this a sticky...theres some good tips here
 

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should make this a sticky...theres some good tips here
i think there might be something on this site already..not too sure i know i read it somewhere..and it works sweet:thumbsup:
 

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this site has so much info that Im still trying to read it all
 

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Should I drill before the turbo or after?
 

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pre turbo is most accurate post turbo is a few hundred degress cooler..
 

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I just tapped mine I also used the 1/8 th 27 but I went with the 5/16 bit worked great. Please be aware when drilling in the manifold to stay towards the cab side of the middle as in the very center is a webbing hope this helps !
 

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Discussion Starter · #14 ·
How much of a difference would there be if it was placed in the front half of the manifold?
 

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The rear is the best since the rear can be just a hair higher than front. You want to monitor the absolute worst temps to prevent damage to engine.
 
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