Good afternoon,

I had been searching the forums for answer to this question but didn't come up with one. I sent JohnZ an email shortly ago asking his opinion on manifold vacuum placement. Then I thought I'd pose this questions to the members, so in the event someone else searches for the same info, they can find it.

I have a 69 Camaro, 350 smallblock, 700R4 transmission, Edelbrock Performer intake, Holley 650 Spreadbore (Holley's version of the Quadrajet), RV cam, power brakes. Currently I am using ported vacuum for the vacuum advance, but after reading John's article, I am converting to manifold vacuum.

My question is this, where do you get your manifold vacuum from? I have two choices.

1. I can use a "TEE" on the manifold and run the power brakes and the vacuum advance.

2. I can remove the plug at the base of the carb, replace it with a fitting that I can run either the power brakes or the vacuum advance, and have the a single port fitting on the manifold to do one or the other.

Is there any advantage to one over the other?

Thanks,

Rick

duskblue69

Either ...I run my vac off the rear T then the line has a T for va and to internal vac gauge

Look at this shot of JohnZ's and you can see where he has his hooked up. Also note the capped off port right next to the vacuum can, you can use it for the VA if you want.

http://img.villagephotos.com/p/2002-2/13522/2002228131959-3-Znoaclcarb.JPG

Thanks guys,

I picked up a "tee" today at YearOne and put it on. The car idles much smoother, throttle response picked up. I didn't drive it long so I don't know how well it does at idle and temp. But it's a start.

Rick

II Look at this shot of JohnZ's and you can see where he has his hooked up. Also note the capped off port right next to the vacuum can, you can use it for the VA if you want.

http://img.villagephotos.com/p/2002-2/13522/2002228131959-3-Znoaclcarb.JPG
I just read JohnZs article on distributor advance mechanisms and I'm impressed. I will be moving my distributor can advance to manifold vacuum. I'm confused by the picture above. I understand the T is being used to provide a tap for mainfold vacuum from the full vacuum port on the front of the carburetor. However where is the vacuum hose laying across the valve cover going. Is this temporarily connected to a gauge? Also it appears that the distributor can is still connected to ported vacuum on the side of the carburetor. One more thing - the capped off manifold port next to the can is typically used for brake booster vacuum. How is vacuum connected to the brake booster for this vechicle?
ColoradoZ28

My Carb has no Ported vacuum and I run Breakerless Mechanical advance distributor.The only Vacuum Source I have is just off the plenum into #7 intake runner from which I hose my Power Brake Diaphram. I do have a "+" spliced into the Power Brake Hose to take Manifold Vacuum readings and run the PCV. If I have to I can also run a Points Distributor with a Vacuum Pod from the "+" with absolutely no problems.

II
I just read JohnZs article on distributor advance mechanisms and I'm impressed. I will be moving my distributor can advance to manifold vacuum. I'm confused by the picture above. I understand the T is being used to provide a tap for mainfold vacuum from the full vacuum port on the front of the carburetor. However where is the vacuum hose laying across the valve cover going. Is this temporarily connected to a gauge? Also it appears that the distributor can is still connected to ported vacuum on the side of the carburetor. One more thing - the capped off manifold port next to the can is typically used for brake booster vacuum. How is vacuum connected to the brake booster for this vechicle?
ColoradoZ28

I think the hose your are referring to goes to the A.I.R. valve on the passenger side of the engine.

alan

John's VA is hooked into the base plate of the carb making it manifold vacuum. It would have to be above the base plate to be ported...

That larger spare hose on the valve cover I think goes to his air cleaner base where there is a spark arrestor type fitting on the side of the air cleaner base that plugs into that hose.

II
I just read JohnZs article on distributor advance mechanisms and I'm impressed. I will be moving my distributor can advance to manifold vacuum. I'm confused by the picture above. I understand the T is being used to provide a tap for mainfold vacuum from the full vacuum port on the front of the carburetor. However where is the vacuum hose laying across the valve cover going. Is this temporarily connected to a gauge? Also it appears that the distributor can is still connected to ported vacuum on the side of the carburetor. One more thing - the capped off manifold port next to the can is typically used for brake booster vacuum. How is vacuum connected to the brake booster for this vechicle?
ColoradoZ28
He isn't talking about the big hose that goes to the air cleaner, he is talking about the hose coming from the "T" off of the carb and it is draped over the valve cover.
Read original post again.

I believe Alan got it, it goes to the smog equipments diverter valve.

hmm I have the same hose and it goes into the bottom of my air cleaner and it ends up as an open tube inside the air cleaner base, Im told in case of excess pressure in the engine, it pulls those gases back into the carb to be burned again. ??

http://www.carsbyjim.com/storage/UnderHood/Air%20Cleaner%20Vac%20hose%20001a.JPG
http://www.carsbyjim.com/storage/UnderHood/Air%20Cleaner%20Vac%20hose%20002a.JPG

I think Chevy did have an aircleaner that had a vacuum tap like that but for the Z28, it was just the bigger rubber pipe into the valve cover. The diverter valve on the A.I.R. (if still installed on the car) has a vacuum tap like the picture of JohnZ's car(which has the factory A.I.R. if memory serves me) so everyone is right!!!!!

alan

http://www.carsbyjim.com/storage/UnderHood/Air%20Cleaner%20Vac%20hose%20002a.JPGThis is the inlet to crankcase ventilation, a filtered input. However, if enough blow-by gases are developed, this is where the gas would escape since the PVC is already removing its rated volume.

Throttle plate is manifold vacuum.
Tee'd hose goes to AIR divertor valve.

Those photos of my Z show the stock factory setup, which is ported vacuum (the "show" setup). The photo below shows my "drive" setup, with full manifold vacuum to the distributor. I just cap off the back end of the stock vacuum advance pipe, and add a length of hose from the distributor to the tee in the choke pull-off that normally feeds the diverter valve (which is the full manifold vacuum source from the front of the carb baseplate), and let the diverter valve hose just dangle - the A.I.R. pump is gutted anyway. :) I keep the hose and cap in the glove box - takes about ten seconds to swap it either way. :thumbsup:

Thank you JohnZ for posting the follow-up picture since it clears up my confusion. I have a DZ302 where the AIR has been removed due to having headers. I want to try your manifold vacuum direct to the distributor can modification since I do have a stumble from idle. I was also curious about your vacuum connection to the brake booster. It appears from the second picture there is the standard hose connection to the manifold nipple. There also appears to be a second, capped off connector on the same nipple. Is this your modification? I'm currently vacationing in Ontario, Canada and will try the vacuum hose modification after I return to Colorado next week.
Thanks, ColoradoZ28

There also appears to be a second, capped off connector on the same nipple. Is this your modification?

Yes, it is - I add that capped vacuum fitting to all my cars so I have a handy connection for a vacuum gauge for setting the idle mixture screws without having to disconnect other things or adding tees or loose hoses. :)

John,

That's a good idea to have the extra port for setting the idle mixture. Could you not connect your vaccum cannister direct to that capped off "T" port? A short loop of hose would keep that longer one from draping across the engine.

John,

That's a good idea to have the extra port for setting the idle mixture. Could you not connect your vaccum cannister direct to that capped off "T" port? A short loop of hose would keep that longer one from draping across the engine.

Yes, that would accomplish the same thing, but my capped vacuum fitting has a larger nipple to match the larger diameter hose on my vacuum gauge. With the setup I have I don't have to use any adapters to match the smaller-diameter distributor vacuum hoses. :)