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DIY Oil Restrictor

Here is a simple walk through of how to make your own oil restrictor fitting for your turbocharger oil feed line. The size 0.065" (1/16") listed will work for most journal bearing CHRA's when used with a 1/4" I.D. (-4 AN) feed line. But always check to see what the manufacturer of your turbocharger lists as the ideal size for your application.

Items you will need:


(1) Drill press or small hand drill
(1) A small vise to hold your work firmly
(1) -4 AN to ¼ “ NPT adapter
(1) ¼” -20 UNC set screw, ¼” length
(1) ¼” -20 UNC bottoming tap
(1) 1/16” (0.065”) drill bit-may need to be substituted
(1) #7 drill bit ( a 13/64” will work also) For -AN fitting
(1) ¼” -20 UNC Acorn nut
(1) Tube or bottle of Med. (Blue) loc-tite or equivalent

Snug set screw into Acorn nut then clamp Nut in a vise

Drill out the center of the set-screw with the 1/16” (0.065”) diameter drill bit. Drill all the way though set screw.


Drill into the bottom of the AN adapter fitting, but only until the wrench flats, do not go all the way through. This is best done by clamping it in a vise that is bolted to a drill-press so you can set the depth stop. If you go all the way through the AN portion will be destroyed and the fitting will be junk. Also drill slowly and with light pressure, the bit will want to grab the fitting and that will also destroy it.


While the fitting is still in the vise carefully run the tap into the portion you drilled out, start slowly and only advance it in ¼ turn increments then backing off ½ turn. This clears out any chips that build up inside and could cause the tap to break. Now use some solvent, carb n choke or brake cleaner works best, to flush out the inside of the fitting. Also clean the inside and outside of the set screw you drilled.


Grab your loc-tite…

Place a small dab on the outside of the set-screw –not much is needed as it will disperse itself once you screw it in.

Now turn the set screw into the bottom of the AN fitting, bottom it out in the threads and snug it securely. Don’t over tighten it or you strip the fitting, but it needs to stay put. Now walk away from the project for 30 min or so to let the loc-tite cure out. It’s anaerobic so it will take a little while to reach full strength.

Check to make sure none of the thread locker has spilled inside and blocked the hole. You can turn the 1/16” drill bit through with you fingers if you need to clean it out. Now let the restrictor you just made sit on your work bench over night to totally cure the thread locking compound. We want to make sure that the set screw does not move once it’s put into use.

The restrictor can be fed oil from both sides without any worries. I’ve used it both ways with no problems. If you have a ball-bearing turbo, or something that has different oil requirements then you can substitute the 1/16” (0.065”) drill bit for whatever size you need.


If you ever need to change restrictor sizes, for whatever reason, you can clean off the fitting and heat it up a little bit -don't over heat- and the loc-tite will loosen right up. Just drill out your set screw to the size you need and reinstall as stated above.

Cars Modifications Power Turbo DIY Oil Restrictor

Document statistics: Last modified on 2008-12-16 22:11:40 by quicksilver99

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