Recently purchased 1971 442 with 455 engine doing some light engine bay cleaning I took off the air cleaner and noticed a vacuum line on the back of the plastic housing that was not connected to anything I tried looking through the threads to find info but no luck. Does anyone have a break down of how the vacuum lines on these air cleaners routed. Also after putting the air cleaner back on and starting the car my idle went up to 1000 RPM to where I had to adjust the idle screw to bring it down pretty sure i messed something up. Any help would be apreciated.

 

Hello,

Ok, that is not a vacuum line. That is a drain line and it goes back over the back of the right side head. It ducts water that gets in the snoots from rain overboard.

Now, vacuum. The air cleaner is controlled via a vacuum line from the rear of the intake manifold. A normal air cleaner has it going to the thermac air door on the chimney of the air cleaner. An OAI air cleaner also has that.

However, with an OAI car, that line has a T fitting for another line, and that is where your air flapper door plugs in.

So, summary: big hose is drain, one vacuum line from intake manifold back center goes around to passenger side of air cleaner, tees, and supplies the thermac and the flapper.

 

@Koda Thank you that makes sense now as there was nothing to connect the drain tube too. My air flapper door is connect to a T fitting that goes to the carb and distributor is that correct? Also at idle the air flapper door is open, and closes on acceleration is this also right? I apologize in advance I'm still trying to figure out how this engine and air intake all work as they are all new to me, I am waiting on a Chilton repair manual to help me out but it hasn't come yet. I do appreciate the help.

 

Look for an 1971 Oldsmobile Chassis Service Manual (CSM) on Ebay. You DON'T want a reprint, you want an original.

 

This is incorrect. You need a CSM, not a Chiltons. In short, the hose for the air cleaner is off a port in the back of the manifold, the hose for the vacuum advance is off a tree in the front of the intake manifold, and it is supplied from various places on the front of the intake and carb.

The air flapper should be open when the car is off, and close upon starting. It will be closed at periods of manifold vacuum which is idle and cruise, and open at periods of low vacuum, which is stomping on it.

 

@Koda I appreciate your help. I ordered a CSM, in the mean time I took some pictures of my current set up which I'm sure is wrong. In the first pic the vacuum line goes from what im not sure is, inside the air cleaner base to the thermac. Then the flapper door vac line goes to a T fitting that goes too the Dist Adv and one to the carb. In the front of the intake manifold there is a tree with three open ports and in the back behind the carb there is a plugged port. So do i supply the thermac door in the chimney, and air flapper from the intake port behind the carb and if so what controls the thing on the base of the cleaner, not sure what it is. And for the unplugged tree in the front of the intake manifold what does that supply (Dist Adv)? Thanks again for your help. I did try to search the forum but couldnt find the answers I was looking for.










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That is the temperature switch that controls the Thermac on the snorkel of the air cleaner. The open port on that switch needs to go to manifold vacuum (directly or via a "T" with the OAI flapper).

 

Good pics. Like JohnnyB said, that is the temp switch for the Thermac.

Ok, the lines go as follows.

Back of intake, the capped off fitting you pointed it. Vacuum line from it to the T fitting, one side leg of the tee. Center leg of tee, goes up to OAI flapper. Other side leg of tee, goes up and back to the clip on the underside of the air cleaner, and into the switch on the air cleaner base, and that other port should already go to thermac. So: capped fitting > tee > OAI on one leg and temp switch then thermac on the other.

Front of intake. Use the timing tree. Three lines go to it. Ported vacuum from your carb (use the line currently going to distributor advance), manifold vacuum from the intake manifold fitting that is directly under that ported line (figure out where it goes currently) and both those plug into the tree, and the distributor vacuum is the other one. I believe it is Ported on top, distributor in middle, manifold on bottom, but please confirm.

The theory on this is as follows. Ported vacuum and manifold vacuum differ in that ported is not there at idle and manifold is. Cars with less timing idle hotter and cleaner for emissions. You still have vacuum advance while driving but not while idling. Unless your car overheats, and the bottom of that tree is a temp sending unit which should get you manifold vacuum at idle to help the car cool down. Modern day solution is to direct plumb the advance to either a ported source or a manifold source depending on which your car likes better, but that's how to use the T. Be happy you don't have the 72 version that has the TCS switch in there, which is a subject for another thread.

The CSM will give pictures to make the line routing look right.

 

Thank you!!! I will reroute the vacuum lines tonight and see how that works out, on that temp switch in the base is there an open and a closed port? Does it matter what side goes to manifold vac and wat side goes to the thermac? Also the metal fuel line going to the carb from the pump is directly in front of that tree, is that correct and do I just need to rotate the tree and point it a different direction to hook on to it? Thanks again!

 

I don't think the side matters on thermal switch.

The fuel line may be routed wrong, or the tee can get moved. But, make sure you want to use it first. Read up on what you want the vacuum advance to be powered by.

 

Okay so I got the air cleaner plumbing down. The manifold vacuum line behind the carb that wasnt capped is going to the transmission modular. So if i want to run the distributor off manifold vacuum i will have to T off either that line or the one I ran for the air cleaner (can too many things be on one vac port?). That leaves the ported vacuum switch(tree) and the ported carb line. Can those be plugged off? Or should I just run the vacuum switch off the manifold, carb, and distributor like you mentioned. I did read manifold vacuum is better for the ditributor vs ported. Thanks again!

on second thought can I run the carb line to the vacuum advance and eliminate the thermal vacuum switch all together?

 

None of those.

If you want to run the distributor off manifold, figure out what the vacuum line in front of the carb is doing. It's right under the ported line in this picture of yours.

Ported vacuum has limited use. It is pretty much just for vacuum advances.

Manifold vacuum can also do distributor advances, it can do, power brakes, vacuum motors like flappers, thermacs, headlight doors, and it also runs HVAC controls and sometimes vacuum accessories. You don't have headlamp doors, or vacuum trunk, so the only things we need to supply are: power brakes through the big line, distributor advance (maybe), transmission modulator, air cleaner devices, and HVAC.

Please read the CSM for the vacuum line layout, this will all be illuminated. I used a 72 CSM. Page 6k-10. Do this:

1. On the back of the intake, one manifold port is for HVAC.
2. On the back of the intake, one manifold port is for OAI and Thermac Air Cleaner as discussed.
3. On the front of the intake, the manifold port in your picture goes by the the vacuum switch tree and Tees. One leg goes to the transmission, and the other goes to the bottom port on the three. The ported line on the carb goes to the top port on the tree. The line to the distributor goes to the middle line of the tree.

Modifications: If you want the distributor just on ported, use the ported line from the carb, and leave the front manifold line to the transmission as just going to it. If you want the distributor on just manifold, cap the ported port on the carb, and tee into the transmission line for pure manifold vacuum. You will need to figure out what your engine likes. In this case, you do not need to cap the tree, as it has nothing in, nothing out. You could, to keep it not dusty, or remove it and put a pipe plug in (but keep it somewhere, like the glove box).

 

Thanks for the info and helping me understand how this all works. My CSM doesn’t come in till Monday. One last thing is it okay to not hook up the thermac and air cleaner flapper? Would it just stay open at all times, and alleviate the worry of another thing that can fail. Also my rear manifold vacuum is going to AT module and my front manifold vacuum below the ported carb is going to what I believe is the vacuum tank for HVAC controls on the firewall. Does it mater where these get vacuum from off the manifold assuming vacuum is vacuum?

 

The simplest answer to your vacuum routing of the A/C vacuum tank canister vs. the AT Modulator Valve is to say - it makes no difference since they are both full manifold vacuum and they'll operate from either intake manifold port.

 

What Norm said. Does it matter? No. Was it routed that way for a reason (to use the tree)? Yes. If you're not going to use the tree, that is fine either way.

If you don't hook up the thermac, the car will take longer to warm up. Not an issue except in winter. If you don't hook up the OAI, it will be "on" all the time. Not a problem except in winter and a torrential thunderstorm.

 

It's only that way to use the tree, if you want. Not running vacuum to thermac means car takes longer to warm up. Not running vacuum to OAI means always on. Both are not an issue except in winter or thunderstorm.

 

Thank you all for the help. I deleted the TVS, capped the ported vac off the carb. and ran the distributor advance off the rear manifold vacuum that would supply the thermac and flapper door. Car runs alot better now with the air cleaner door open while in the throttle vs closing on acceleration. I think I should be ok on cold starts as I live in California and dont have super cold winters.