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Can I use this port on a Q-Jet manifold for the brake vac line or PCV line?

handloader90

handloader90

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Cast iron Q-Jet intake.

Was gonna use the vac port on the back of the intake in front of the dizzy but my th350 vac line is hooked in there along with some vac lines for the A/C all on the same fitting.

My Holley only has one 3/8 vac line. No provisions for me to put in another fitting that I've found.

My brake vac line was connected to the vac port on the carb... never had one setup like that before. I've always ran my brake vac line from a fitting on the manifold.

I've always connected my PCV valve line to the fitting on the carb.

Can I use this big port on the drivers side of the intake just under the carb?

20170429_090623.jpg
 
My guess is you won't get that plug out...

The brakes usually come out of the intake (preferred) or the throttle plate of the carb
 
Not only that plug will be unlikely to unscrew,but even if you do get it out,the barb fitting and hose will probably interfere with the throttle lever and or cable...bad spot ..

I know a Q-jet had the power brake hose screwed right into the carb casting facing the distributor..

Why a Holley only has one manifold vacuum port is stupid,the only way out is to use a "T" fitting if there is room and run one side to the PVC valve and the other to the power brake booster--I would use the stock GM charcoal canister dewhickey in line to the power brake booster so the oil fumes wont rot the diaphram in the booster out sooner..

You may be able to drill and tap the carb spacer plate for a barb fitting if it is thick enough,or find one that has a port in it already..
 
diesel4me said:
Not only that plug will be unlikely to unscrew,but even if you do get it out,the barb fitting and hose will probably interfere with the throttle lever and or cable...bad spot ..

I know a Q-jet had the power brake hose screwed right into the carb casting facing the distributor..

Why a Holley only has one manifold vacuum port is stupid,the only way out is to use a "T" fitting if there is room and run one side to the PVC valve and the other to the power brake booster--I would use the stock GM charcoal canister dewhickey in line to the power brake booster so the oil fumes wont rot the diaphram in the booster out sooner..

You may be able to drill and tap the carb spacer plate for a barb fitting if it is thick enough,or find one that has a port in it already..
Click to expand...

Yea... idk why Holley would do that either.

I'm just gonna say F-it and not hook the pcv up.
 
handloader90 said:
Yea... idk why Holley would do that either.

I'm just gonna say F-it and not hook the pcv up.
Click to expand...
I like your attitude. Might find a push in breather to fit in there at the auto store. That's what is in mine whet the tube went back to the factory air cleaner.
 
bent72 said:
I like your attitude. Might find a push in breather to fit in there at the auto store. That's what is in mine whet the tube went back to the factory air cleaner.
Click to expand...

I bought an Eddy push in breather for the shit stock breather that was on the engine.

Didn't fit. Was gonna holesaw it but I would lose rhe baffling.

I'm just running open holes in both sides, gotta be good for at least 10 horsepower.
 
No PCV valve will not do your engine any good--pressure can build up in the crank case and seals and gaskets will leak,oil will sludge up quicker too..also most carbs are jetted to compensate for the "vacuum leak"a PCV valve creates, and will run rich without one..

You could drill & tap the intake for another 1/4" npt barb fitting for the PCV valve or brake booster...

I think a better solution is to ditch the Holley and put a Q-jet that belongs on a GM back on it...then everything fits & works and it'll handle off roading better too..
 
diesel4me said:
No PCV valve will not do your engine any good--pressure can build up in the crank case and seals and gaskets will leak,oil will sludge up quicker too..also most carbs are jetted to compensate for the "vacuum leak"a PCV valve creates, and will run rich without one..

You could drill & tap the intake for another 1/4" npt barb fitting for the PCV valve or brake booster...

I think a better solution is to ditch the Holley and put a Q-jet that belongs on a GM back on it...then everything fits & works and it'll handle off roading better too..
Click to expand...

Don't have the time or money right now to find a Q-Jet worthy or rebuilding and then trying to tune it.

I found a metal plate bolted on the intake on the passenger side near the rear of the carb.

If I pull this plate, drill a hole in it, tap it and put a barbed fitting in it will it be sufficient to run my brake booster vac line into?

20170501_152300.jpg
 
I drilled and tapped a early Qjet baseplate for powerbrakes once.
Otherwise use a T fitting.
 
blazer74 said:
I drilled and tapped a early Qjet baseplate for powerbrakes once.
Otherwise use a T fitting.
Click to expand...

The problem with using a t fitting in the hole behind the carb is that my th350 vac line runs there. I don't have anywhere else to run it at this time.
 
The issue with with the brakes is that they require a higher volume of vac generally dedicated.
The trans can be T'd off with the other large port in the rear of the manifold or vice versa.
Not a lot of options here with that set up.

If you don't run a pvc you need breathers to prevent internal pressure like was mentioned.
 
Well, I found another vac port on the base of the carb under the front metering block, comes out at an angle towards tge passenger side.

I'm thinking I can run the th350 vac modulator line to that port. Pcv to the 3/8" fitting in the carb then put in a 3/8 fitting in the hole in the manifold in front of the dizzy and run my brakes there.
 
Just make sure that port has manifold vacuum (has vacuum at idle ,that dies off when you open the throttle)--otherwise your transmission modulator will not react properly and could lead to slipping clutches or downshifting when its not supposed too..
 
If all else fails you can either buy a spacer with a PCV port,or drill a 3/8" hole in your existing one if there is enough meat,and install a hunk of 3/8" steel tubing with a little J-B weld to seal it in place for the power brakes or PCV valve..or put a piece of 3/16" tubing in it ,if there isn't enough meat for a 3/8" tube,and run the modulator off that instead..carb spacer with pcv valve port.jpg
 
diesel4me said:
If all else fails you can either buy a spacer with a PCV port,or drill a 3/8" hole in your existing one if there is enough meat,and install a hunk of 3/8" steel tubing with a little J-B weld to seal it in place for the power brakes or PCV valve..or put a piece of 3/16" tubing in it ,if there isn't enough meat for a 3/8" tube,and run the modulator off that instead..View attachment 229430
Click to expand...
That's nifty.
 
I've got a vac gauge somewhere in my garage. I'll hook it up and see what the vac gauge says.
 
What about your vacuum advance for the dizzy.
Your trans requires constant vac to up shift correctly.
Some egr vac ports will zero at idle and also reduced with the throttle open and tend to be larger.

Make sure you have manifold vac at idle and full vac with the throttle open

image.jpg
 
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