47-59 Need Ideas for a Chevy 235 PCV and brake booster to coexist

[daveshilling]

Truck Geniuses, I have a challenge I'm trying to resolve without making it look like crap or buy too many expensive brass fittings.

I have a 3/8" steel line headed to the intake manifold to tap into the vacuum port that is commonly plugged.

I also have a vacuum hose coming from the brake booster that needs vacuum from that same location.

I have the ability to add an inverted flare fitting to the steel line. I'd really prefer not to drill another hole in the manifold....what approach would yall take to cleanly integrate both of these hoses into this one port?

The intake manifold vacuum port is 3/8" NPT. Any ideas?

So far I thought of an 3/8 NPT male to 3/8 npt female tee, then add a 3/8 NPT to 3/8 hose barb on one side, and a 3/8 NPT to 3/8 OD inverted flare adapter to the other... and thats a whole lotta fittings and crap.

[1project2many]

Could you use a fitting with multiple ports? GM often resolved these issues with specially made fittings. There are many versions.

https://www.google.com/search?q=gm+v...w=1024&bih=622

[daveshilling]

Originally Posted by 1project2many

Could you use a fitting with multiple ports? GM often resolved these issues with specially made fittings. There are many versions.

I could potentially use something like that if I were doing hose on both sides. Currently I have a hard line for the PCV, although I could switch to all rubber hose if I had to.

[Wrenchbender Ret]

you can't run the PCV hose off the vacuum outlet in the Intake manifold behind the carb. It feeds off the back cyls. & will cause a bad miss at idle & low speeds & cause a rough idle. The power brake unit only draws vacuum on desceleration so it won't cause this unless the booster dia. is leaking. There usually is an outlet at the bbase of the carb for the PCV system.
George

[Zenwren]

I can't comment on what Wrenchbender says, but I have mine set up exactly how you are describing, I used this fitting... https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
with 3/8" line threaded into each side, then ran the hard lines to the PVC and booster. So far I've only yard driven the truck but it seems to work fine. You will need a 1/4" to 3/8" reducer/adapter bushing to fit into your manifold.

[daveshilling]

Originally Posted by Zenwren

I can't comment on what Wrenchbender says, but I have mine set up exactly how you are describing, I used this fitting... https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
with 3/8" line threaded into each side, then ran the hard lines to the PVC and booster. So far I've only yard driven the truck but it seems to work fine. You will need a 1/4" to 3/8" reducer/adapter bushing to fit into your manifold.

Oh, I didn't think about running a hard line to the booster.. that would be pretty cool. I assume you were able to flare the line somehow and add rubber hose to meet up with the booster end of things. Good to know you have the configuration I'm thinking about and its working!

[_Ogre]

Originally Posted by Wrenchbender Ret

you can't run the PCV hose off the vacuum outlet in the Intake manifold behind the carb. It feeds off the back cyls. & will cause a bad miss at idle & low speeds & cause a rough idle. The power brake unit only draws vacuum on desceleration so it won't cause this unless the booster dia. is leaking. There usually is an outlet at the bbase of the carb for the PCV system.
George

this ogre agrees with wrenchbender. every pcv i've retrofitted went into the bottom of the air cleaner. the pcv valve is an engineered vacuum leak, it might be possible to adjust for it with a carb

[Zenwren]

Originally Posted by _Ogre

this ogre agrees with wrenchbender. every pcv i've retrofitted went into the bottom of the air cleaner. the pcv valve is an engineered vacuum leak, it might be possible to adjust for it with a carb

Are we both talking about a 235 and not an SBC? I know V8's draw vacuum off the rear cylinders but the vacuum port on a 235 is directly below the carb and an open log manifold? A PVC system will draw fresh air into the crankcase from the air cleaner housing but still needs a feed from the crankcase gasses into the intake (vacuum) stream going into the combustion chambers.

[Wrenchbender Ret]

Originally Posted by Zenwren

Are we both talking about a 235 and not an SBC? I know V8's draw vacuum off the rear cylinders but the vacuum port on a 235 is directly below the carb and an open log manifold? A PVC system will draw fresh air into the crankcase from the air cleaner housing but still needs a feed from the crankcase gasses into the intake (vacuum) stream going into the combustion chambers.

Yes, I had v-8 on my mind. Sorry.
George

[daveshilling]

Originally Posted by _Ogre

this ogre agrees with wrenchbender. every pcv i've retrofitted went into the bottom of the air cleaner. the pcv valve is an engineered vacuum leak, it might be possible to adjust for it with a carb

This is replacing the road draft tube in the 235, so by nature its not a valve cover=> air cleaner type. That being said, feeding it into the air cleaner could reduce the need to lean out the fuel potentially.

Another option might be to use a spacer under the carburetor and add as many fittings as necessary.

A spacer is actually GM standard on the 235's. I couldn't find one that had a vacuum port in it. That's a smart idea but a custom item that may be out of my budget for this particular truck.



Here is a link to the PCV conversion I'm doing that replaces the road draft tube.

[mr48chev]

What Zenwren suggested should work.

I'd suggest putting a check valve in the line to the booster and you may end up needing a vacuum booster tank for the brakes
They are sold by Summit, Jegs and other speed outfits for cammed up cars with vacuum boosters on the brakes to store up vacuum. That would let you have reserve vacuum for the brakes.
Example https://www.summitracing.com/parts/s...+5ba29eacb7da9

I think some of the big luxury sedans in the 70s and maybe 80's with all the miles of vacuum hose and vacuum controlled stuff had reserve tanks but have no idea and those barges are few and far between in wrecking yards now.

[mr48chev]

This is my crusty 292. 500 bucks worth of polished aluminum in boxes and it is still grimy.



PVC line runs from back of valve cover to the intake. Red arrow.

The plug on the outside of the intake would be for the brake booster. I see no reason to not run them of one Tee though .

A breather with an actual filter in it will work fine at the filler hole of the cover. The line to the air cleaner on top of the carb just insures clean air going into the engine from the factory stand point.

[G&R's57GMC]

Dave don’t forget to install a vapor separator in the booster line high on the firewall.

If you don’t in time the oil/fuel vapors we do a number on the p/b booster diaphragm and you’ll have to replace it .

[daveshilling]

Originally Posted by G&R's57GMC

Dave don’t forget to install a vapor separator in the booster line high on the firewall.

If you don’t in time the oil/fuel vapors we do a number on the p/b booster diaphragm and you’ll have to replace it .

Yep, I'll be doing that one again for sure.

[1project2many]

The line to the air cleaner on top of the carb just insures clean air going into the engine from the factory stand point.

It also helps ensure the crankcase air is warm which reduces tendency for heavy hydrocarbons to settle and build deposits in the crankcase.

Another option might be to use a spacer under the carburetor and add as many fittings as necessary. A phenolic spacer would insulate the carb slightly and could help prevent or reduce unwanted fuel vaporization. Today's fuel definitely does not perform like gasoline in the '40s and '50s.

[mr48chev]

Originally Posted by 1project2many

It also helps ensure the crankcase air is warm which reduces tendency for heavy hydrocarbons to settle and build deposits in the crankcase.


Another option might be to use a spacer under the carburetor and add as many fittings as necessary. A phenolic spacer would insulate the carb slightly and could help prevent or reduce unwanted fuel vaporization. Today's fuel definitely does not perform like gasoline in the '40s and '50s.

I never heard that one in all the time I have worked on cars including all the years I did it for a living. The only time there is warm air at the air cleaner is when the heat tube valve is letting heat in thought the tube that goes to the exhaust manifold but as soon as the temp is up to normal that closes so only cool air goes though the air cleaner.

Ford did that for years on their V8 engines using an aluminum plate with passages for what ever setup they were needing vacuum for.

[1project2many]

I never heard that one in all the time I have worked on cars including all the years I did it for a living.

I know. We never used to think about stuff like that. Hell, in the '70s if the engine made 200k miles we figured it was a miracle. These days 200k miles is about the time a vehicle goes to the third owner.

Most of the thermac systems try to maintain a minimum of 90 degrees for emissions. But getting warm air into the crankcase sooner helps get the engine to temp quicker and helps keep water and blowby from condensing on the engine walls. And most folks are installing the PCV to "clean up" the inside of the engine, so why not go the extra step? It isn't going to make an engine run a million miles. IMO it's more like taking time to make sure the electrical connections are all clean if you're already replacing wires.

[geezer#99]

I’m a bunch confused here.
Thermac controls inlet air temperature into the intake and cylinders.
Not into the crankcase.

[1project2many]

I’m a bunch confused here.
Thermac controls inlet air temperature into the intake and cylinders.
Not into the crankcase.

Well, it does both on systems from maybe '79 and up. Closed PCV system connects to the manifold or carb base at one end and the air cleaner at the other. Under most conditions the carb end makes vacuum and draws air from the air cleaner into the valve cover, through the engine, then into the carb base. In this system air temp in the air cleaner is warmed through thermac so air going into the PCV is thermac air.

It's up to the builder of course and ultimately it likely makes only a small difference. My '36 Plymouth hasn't gotten a PCV even though Mopar offered a "Vacuumatic Crankcase Ventilator" modification for those engines. I keep thinking about it and it's likely I'm going to do it eventually. The garbage the builds up in that block is incredible, even running detergent oils.


For closed type PCV look at the bottom half of this drawing...

[geezer#99]

I see what you’re getting at but likely that warm air won’t make any difference in the crankcase temperature. Minuscule amount of warmish air mixing with a huge volume of air in the crankcase likely doesn’t amount to much.
Likely better heating for the crankcase could be had from an oil pan heater or water jacket block heater which helps on initial start up and run.

[1project2many]

Originally Posted by geezer#99

I see what you’re getting at but likely that warm air won’t make any difference in the crankcase temperature. Minuscule amount of warmish air mixing with a huge volume of air in the crankcase likely doesn’t amount to much.
Likely better heating for the crankcase could be had from an oil pan heater or water jacket block heater which helps on initial start up and run.

Agreed it's not much. But if you're going through the effort to install one, why not set it up for max benefit. The flip side is that if you happen to go on the highway with oem gears any blowby will go into the air cleaner instead of out the valve cover breather.

I just wanted point out something that most folks don't think about...

[daveshilling]

Well I had the bright idea of contacting the guy who created this how-to and he affirmed what ZenWren said, that compiling together the brass fittings is the most straightforward option, so I'll likely take that approach and I'll post photos on this thread when I'm done for search purposes.

[Divine 59]

This is a good way to eliminate the road draft tube.

http://devestechnet.com/Home/PCVInstall

Many good tech articles and options for the Chevy and GMC sixes.

[mr48chev]

Now that my brain kicked into gear, I have changed a couple of stock valve cover 235's to PCV by cutting off the road draft tube an inch or so from the tube it runs off and putting a rubber plug for a PCV valve in the cut off end and sticking the PCV valve in it.

I think that we did it on one we built in the school shop that one of my students who did a lot of work on it now owns.

[daveshilling]

Originally Posted by mr48chev

Now that my brain kicked into gear, I have changed a couple of stock valve cover 235's to PCV by cutting off the road draft tube an inch or so from the tube it runs off and putting a rubber plug for a PCV valve in the cut off end and sticking the PCV valve in it.

I think that we did it on one we built in the school shop that one of my students who did a lot of work on it now owns.

I went all the way and put the PCV directly in its place