Vacuum line questions?

[Phoenyx]

OK looks like I finally have a nice enough day to start working on the Malibu. First thing I'm gonna do is replace the valve covers, I am keeping my fingers crossed that I have no damage there.

Then I have to work on my vacuum lines. Need to hook up the one for the transmission, and the one for the distributor. So here are my questions:

1: What size vacuum line do I need?

2: What port do I hook the distributor line to? I have been reading up on it. Seems like finding an answer to that is pretty tough. Seems to be a debate on full or timed vacuum. Here's my set up if it helps:

MSD Streetfire distributor, Edelbrock carb. 10.5:1 355, and here are the cam specs:
Cam Style Hydraulic flat tappet
Basic Operating RPM Range 2,200-5,200
Intake Duration at 050 inch Lift 218
Exhaust Duration at 050 inch Lift 218
Duration at 050 inch Lift 218 int./218 exh.
Advertised Intake Duration 274
Advertised Exhaust Duration 274
Advertised Duration 274 int./274 exh.
Intake Valve Lift with Factory Rocker Arm Ratio 0.450 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio 0.450 in.
Valve Lift with Factory Rocker Arm Ratio 0.450 int./0.450 exh.

So what do you all thing, full or timed vacuum?

 

[DRIVEN]

1/8" should be fine. The transmission goes to manifold vacuum and the distributor goes to ported (timed) vacuum.

 

[Phoenyx]

Ok thanks.

 

[DoubleV]

the distributor goes to ported (timed) vacuum.

Says who? You can't just flat out say it goes to ported. How do you know manifold would'nt be better? Some setups prefer one over the other and I know many ( like mine for one ) loves manifold vacuum for the much better idle it provides. I know others have claimed their engines run better on ported ( and I won't dispute that ) but I guess I'll just never understand why as I personally don't see much advantage it offers over full manifold.

Phoenyx, just try both ported and manifold vacuum yourself and just use the one you prefer. Getting the proper size vac line is as easy as bringing in a vacuum T to the autopart store and getting the line that fits it best ( which from memory I've always thought was 5/32 ).

 

[Phoenyx]

Yeah once I get it timed I will try both to see what is better.

I just find it weird. The two different ports do the opposite (I think), but it's a big debate on what one to use.

Where do they get hooked up from factory on our cars?

 

[DoubleV]

Yeah once I get it timed I will try both to see what is better.

Sounds good.

I just find it weird. The two different ports do the opposite (I think), but it's a big debate on what one to use.

They're not opposite really. The only real difference is is that ported has no vacuum at low throttle positions ( like idle and cruising ). At higher throttle settings, it's exactly the same as manifold vacuum. So since more timing usually provides you with better idle and milage, manifold vacuum is usually prefered. The only advantage ported has over manifold is is that when you stab the throttle, it will give you an instant 'vacuum spike' ( which very quickly goes away ) and therefore gives you a little timing advance boost for an instant before the vacuum becomes exactly equal to manifold vacuum. This is why some claim better throttle response using ported.

Manifold vs ported could also depend on the advance curve/base timing of your distributor to some extent too.

Where do they get hooked up from factory on our cars?

Nowhere since most were CCC cars! Most smogger engines used ported because not having the extra advance at idle/low throttle meant higher engine temps. Higher engine temps meant better emmissions. Extra advance wasn't needed for a smooth idle either because the cams were so tiny they didn't require it. Now muscle cars of old use manifold vacuum to give you better idle ( lots of big cams back then ) and emissions weren't a concern. This is the way I know it to be.

 

[Phoenyx]

Ok so I changed the valve covers, and that went pretty good. Put on some cheapo chrome ones with FEL-PRO rubber gaskets (black ones). Can't see any leaks and there is no more noise coming from the valve covers. Bought the wrong size vacuum line so that will have to wait until tomorrow. But I was also able to hook up the vacuum line to the transmission, and now it shifts!

I removed the vacuum line from that heater core valve, because it was hooked up wrong and causing a vacuum leak. How does this valve work again? With no vacuum is it open or closed?

Now for tomorrow I gotta get a better distributor hold down, and some more vacuum line and hopefully I can tune it. Then all I need to do is figure out the kickdown, figure out why the choke isn't working, and then some cleaning. Also need to replace the power steering pump, but that can wait for now.

 

[bigalturk1]

Non-ported lets you run the car at less initial timing so it will crank over and start easier.
I find that the distributor mechanical advance has a lot to do with it. Smog distributors come in at a different time and advance quicker. I use old (Pre 71') distributors and convert them to Pertronix Ign. Install the distributor and rev it up (Use timing tape or balancer cover) and set total timing to 34 degrees w/vacuum line disconnected (Then connect after).
Of course this is on a smallblock Chevy, no nitrous or blower.