Vacuum teeing question

[mchyphy]

I want to run my vacuum advance with manifold vacuum, but my carb (old Edelbrock 1408, discontinued smog compliant carb from what I've heard) only has ported vacuum on the front driver's side, instead of the usual manifold vacuum. I'm wondering if I can tee it in with my power brakes, which runs to the back of the intake manifold to a tee with an unused port. Would this cause any interference with the advance signal or would I be good? Also I'm wondering whether the modulator for the trans should be on manifold as well, as it's also connected to ported.

[James the III]

Why do you want the advance on non ported vacuum?

[mchyphy]

From what I've read there's benefits to running manifold vacuum for advancing, like running cooler at idle, slightly better fuel economy at idle, and better off the line throttle response.

[El Dorado Jim]

I have always been told to run ported vacuum

[geezer#99]

Originally Posted by mchyphy

I want to run my vacuum advance with manifold vacuum, but my carb (old Edelbrock 1408, discontinued smog compliant carb from what I've heard) only has ported vacuum on the front driver's side, instead of the usual manifold vacuum. I'm wondering if I can tee it in with my power brakes, which runs to the back of the intake manifold to a tee with an unused port. Would this cause any interference with the advance signal or would I be good? Also I'm wondering whether the modulator for the trans should be on manifold as well, as it's also connected to ported.

Post a pic of your carb and intake behind the carb.
I'm sure there's other sources for manifold vac to do everything you need.
And there are other vacuum trees available too.

[davepl]

Only spark should be ported. I'm a big fan of keeping things as GM intended, but some of the reasons for ported spark were emissions based (less advance at idle keeping a hotter EGT netted less NOX or something like that). And in some of those cases they'll run better on manifold.

I'd hook it up like your truck was from the factory unless and until you have a compelling reason not to.

Trans should be manifold.

[Myoldtruck]

Im running a edelbrock carb also. I connected my Hei dist to the tree fitting behind the carb, which is manifold vacume. I have no pinging while driving.

Ive been considering connecting it to the carb to see if there is any performance gains off the line and while im towing.

[HO455]

Ported vacuum is the better way to go. For several reasons. One is that your idle speed won't be affected by your vacuum. Timing at idle is unaffected by vacuum whether in gear and out. Two, coasting with the throttle closed is the time of highest manifold vacuum, by having the vacuum shut off you prevent the engine from running on the idle circuit with a lot of timing advance, possibly causing detonation. (Pull the vacuum advance to full when your idling to see how well the engine runs, assuming that it works properly to start) Not to mention the extra wear on the advance diaphragm from being exposed to the high vacuum level every time you let off the throttle. Virtually every car manufacturer used ported vacuum on carbureted four stroke engines.