Cliff's Quadrajet Parts and Rebuild Kits

Quadrajet Problem Solving => Dialing in your rebuilt Quadrajet carburetor => Topic started by: F250 Restorer on November 25, 2021, 10:33:46 PM

Title: turbo to non turbo considerations?
Post by: F250 Restorer on November 25, 2021, 10:33:46 PM

17059547

I'm wondering, if I use a QJ set up for turbo in a non turbo application, are there special considerations I need to deal with?

Thanks

Title: Re: turbo to non turbo considerations?
Post by: Cliff Ruggles on November 26, 2021, 07:58:29 AM

Yes, the turbo carburetors used external vacuum/boost reference.  They were also calibrated differently than the non-turbo engines.

They will have a vacuum port coming in thru the front of the baseplate to supply vacuum signal to the Power Piston and the baseplate is not drilled for it like other N/A applications.

Pretty simple to block off the external port and drill like the N/A baseplates, would take about as long as it took me to type this.......Cliff

Title: Re: turbo to non turbo considerations?
Post by: F250 Restorer on November 29, 2021, 04:39:45 PM

Thanks, Cliff. I can see that the p/piston has direct vacuum below the throttle blades, so I assume that no drilling is needed, right?

(https://i.imgur.com/6IFE7z4.jpg)

Title: Re: turbo to non turbo considerations?
Post by: Cliff Ruggles on November 30, 2021, 02:34:14 AM

Correct,  if the hole is drilled to supply vacuum directly from the intake to the PP good to go.....

Title: Re: turbo to non turbo considerations?
Post by: F250 Restorer on November 30, 2021, 09:41:46 AM

I'm going to need a kit for a 17059247, and idle tubes.

Regarding the baseplate above, for a 17059547, with a 280*adv cam and .480 lift, I believe I'll need a bit of bypass air. I don't have a drill press nor the know-how. Is drilling the throttle plates not an option?

Title: Re: turbo to non turbo considerations?
Post by: Cliff Ruggles on December 02, 2021, 01:47:58 PM

A drill press is NOT wanted, needed or a good idea for drilling anything on a Q-jet. 

The bypass air slots are in place, just not drilled.  "Free" drill them with the baseplate on a wooden block with a small hand drill, it's not fussy.

I do NOT recommend drilling the throttle plates on Q-jets that have the idle bypass air system in place.  It is a very precise controlled vacuum leak, use it if/when you need idle bypass air.......Cliff

Title: Re: turbo to non turbo considerations?
Post by: F250 Restorer on December 06, 2021, 11:52:40 AM

Thanks, cliff. I started with 70 thousandths. You're right. Easy.

Hey, I tried to test the pwr piston spring by taking the main body section and applying vacuum with a hand pump to the hole on the bottom, with only spring and piston in place. I could not get vacuum. Am I doing something wrong?

Title: Re: turbo to non turbo considerations?
Post by: quadrajam on December 06, 2021, 03:19:25 PM

I dont think a hand vacuum pump could keep up with the leakage around the power piston.
Maybe use vacuum sourced from a running car engine.
Or get fancy and try using a junk main casting, drill through the bottom with the right bit
and drive in a vacuum nipple. use a tee and install a gage very close to the casting. Then
run a longer piece of tubing to the car. use another tee and a needle valve to control some
bleed in air to vary vacuum at the casting . Never got around to trying this.Let us know how
it works.