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Old 04-13-2010, 05:56 PM
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750 Holley mod for PCV hook-up

Hey you guys,
I am considering removing the pressed in tube for the pcv hose on the base of the carb, and trying to tap the port for what I believe to be a 1/4"NPT elbow. I can't find out what size drill I need for a 1/4" pipe tap, or if the existing hole is already too large? I know its a 3/8" tube now. Can I just run the tap into the existing hole? Or should I say "hole to be"? Can I even get the tube out? Or will the elbow be too restrictive? The elbow has .220" ID where the tube has a .292"ID.
I want to run the pcv hose to the rear of the passenger side valve cover. Its going to get a little crowded in the general area because of all the vac. fittings and dizzy, but I'm trying to make the rest of the engine look better by keeping as much of the hoses and wiring in the rear of the engine.
I know other people have much more important issues that need attention,
but if anyone knows what size drill I need, or where to get a rubber 3/8" hose with a molded in 90 degree elbow, or any suggestions, I would be grateful.
ssmonty
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Old 04-13-2010, 06:07 PM
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It would appear the pipe is already too large for the street el you are showing. there is also a compression fitting that slips over a straight tube that accepts an AN fitting and looks real clean. Measure the tube OD and see if you can find a supplier, I have used them before with ease
Bill
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Old 04-13-2010, 10:25 PM
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1/8" X 27 NPT (aka "1/8 inch pipe thread") = 11/32 drill.
1/4" X 18 NPT (aka "1/4 inch pipe thread") = 7/16 drill.

Removing the port can be a chore. It WILL come out, but usually not very easily. I'd suggest you use a bolt or length of round stock that's a tight or at least close fit, inserted inside of the port. This will allow you to really get a grip on it (vice grips or channel locks) to twist it to free it up. If you find you have to use heat, I'd recommend you remove the base plate from the carb, lightly clamp it in a vice using padded soft jaws, and use the heat sparingly.

If the hole in the carb base is too small and you use the tap, because the tap is tapered, it can- and will- split the aluminum base plate unless the hole is drilled to the correct size to begin with.

As you tap the hole, check your work often so the threads don't become too "wide" to allow the new fitting to seal properly (remember the tap is tapered). Use a bit of thread compound when assembling to lube and seal the joint.

For molded hose, go to the parts house and ask to see their "wall"- usually hoses and such are hung up rather than piled into boxes or drawers. From their selection, there will many bends and lengths to choose from, should you want to go w/a molded rubber hose.
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Old 04-14-2010, 05:57 PM
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Thanks for the replies!!!!
I gotta admit that I'd rather use a 90deg. rubber hose. I don't know why I didn't think of that hose wall! I just knew some auto company makes a hose that would be just right, but I couldn't come up with a part number.
Cobalt, your the man!
ssmonty
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Old 04-14-2010, 06:07 PM
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The hose needs to be stiff enough to resist the low pressure of manifold vacuum it will be exposed to, MB used to have hose for the brake booster that had a wire wrap imbedded in the hose wall.
Bill
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Old 04-15-2010, 07:10 PM
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You can get preformed 90deg 3/8" hose pcv hose from any chevelle, camaro, etc parts house. I did for my pcv valve hose. I hear ya on the carb connection. I also wanted a nice clean connection there. Ended up using a 3/8" PEX elbow, as in plumbing. They're nice and small, with a full 3/8" i.d. Filed the barbs a bit, because the hose is a TIGHT fit.
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Old 04-19-2010, 06:17 PM
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Just to follow-up.
Thanks again for the replies!
I went to the local NAPA to browse their hoses, but the local store didn't have very much to choose from in the size I needed(3/8").
I went to another parts place, and found a Gates hose PN 18031 that looked like it would do just fine with a little trimming.
Thanks again!
ssmonty
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