Ported vs manifold vacum
Thread Starter
Safety Car
Joined: Mar 1999
Posts: 3,715
Likes: 1
From: VASS, NC, USA
Ported vs manifold vacum
I ALWAYs screw this one up:
How can I tell if a vacum hook up point on the carb is manifold or ported source just by looking?
Which source is used for vacum advance?
How can I tell if a vacum hook up point on the carb is manifold or ported source just by looking?
Which source is used for vacum advance?
Burning Brakes
Joined: Aug 2005
Posts: 1,126
Likes: 0
From: Hudson Falls, N.Y. 76 Vette Modified L-48
Don't know if ya can, just by looking....My Edlebrocks, looking at front, drivers side manifold, pass side ported..I only know that by experimenting, finger over ports, constant is always on,, manifold, ported when RPM's come up...
The concensus is advance should be on manifold vacuum...from a previous thread I posted with the same question...
Check this thread:
http://forums.corvetteforum.com/show....php?t=1240902
The concensus is advance should be on manifold vacuum...from a previous thread I posted with the same question...
Check this thread:
http://forums.corvetteforum.com/show....php?t=1240902
Last edited by kb2fzq; Dec 19, 2005 at 09:01 AM.
Le Mans Master
Joined: Jul 1999
Posts: 9,206
Likes: 17
From: Sewell NJ
The easiest way to see if a port is manifold or ported is to take the vacuum hose coming from the vacuum advance cannister and hook it briefly to each port. If there is no change in idle you have ported vacuum. If you touch it to a port and the idle increases you have manifold vacuum. This assumes that your vacuum cannister is working properly.
Drifting
Joined: Jun 2005
Posts: 1,950
Likes: 498
From: Chino Hills CA
You can't tell by looking but you can by blowing. Manifold vacuum is below the throttle butterfly, ie. high vacuum at idle. Ported vacuum is above the throttle butterfly, ie. no vacuum at idle. Blow into a line hooked up to the port in question and stick your finger down the primaries or just below the butterfly and you can feel where it's going.
Race Director
Joined: Sep 2004
Posts: 11,874
Likes: 263
From: Arlington Va Current ride 04 vert, previous vettes: 69 vert, 77 resto mod
just feel the end of the vacuum tube when the car is running.....if it is "sucking" on your finger its manifold vacuum...if not its ported vacuum
Drifting
Joined: Sep 2004
Posts: 1,532
Likes: 4
From: Fairview Heights Illinois, near Saint Louis MO, STL C3 Shark
GENERALLY speaking - not bible, a manifold vacuum port will be lower - ie closer to the baseplate of the carb. The ported vacuum is located closer to the top plate. But the aforementioned tests will tell you with no doubt.
