vacume advance
Racer
Joined: Nov 2006
Posts: 495
Likes: 1
From: Lubbock TX
To see if its advancing your timing, use a timing light and note the degree your running. Then block off the vacuum adv and check your timing. The difference is the amount of advance it is supplying.
To just see if the actual canister is working just hook it up to a vacuum line and see if it moves. But if it works here then it should work in your dizzy, unless something is wrong.
Im definitely no expert, but im pretty sure this is correct. If this didnt answer your question, explain some more and someone oughta help you out.
Sean
To just see if the actual canister is working just hook it up to a vacuum line and see if it moves. But if it works here then it should work in your dizzy, unless something is wrong.
Im definitely no expert, but im pretty sure this is correct. If this didnt answer your question, explain some more and someone oughta help you out.
Sean
Drifting
Joined: Jun 2005
Posts: 1,950
Likes: 498
From: Chino Hills CA
You can easily check if your vacuum advance is working, by sucking on the vacuum line going to your diaphram on the dist. Your sucking should cause the base plate to rotate. Your stock Delco distributor has 2 types of advance, vacuum through the diaphram and centrifugal through the weights just below your rotor. You will see both through your timing light. Centrifugal is a function of rpm. Vacuum advance depends on what you use for a vacuum source. If you used manifold vacuum, you will get full advance at Idle and light loads, none at wide open throttle, great for getting the best fuel economy. If you use ported vacuum (ie. a source on the carb above the throttle plate), you will get no vacuum at idle, and higher vacuum with more throttle, best for performance. Some guys limit or disconnect their vacuum advance and dial in more initial advance and use centrifugal advance at higher rpm. This isn't everything you need to know, but usually enough.
Le Mans Master
Joined: Jun 2008
Posts: 5,284
Likes: 235
From: Rockledge FL
If you used manifold vacuum, you will get full advance at Idle and light loads, none at wide open throttle, great for getting the best fuel economy. If you use ported vacuum (ie. a source on the carb above the throttle plate), you will get no vacuum at idle, and higher vacuum with more throttle, best for performance.
the paper lars put out says that ported vacuum is solely for emissions purposes.
before this thread goes any further someone smarter than me please clarify the two different vacuum uses.
Drifting
Joined: Feb 2005
Posts: 1,879
Likes: 38
From: Los Gatos CA
There are lots of opinions on ported vs manifold vacuum source for your distributer. Some say not to use vacuum advance at all, which I totally disagree with on a street car. My opinion: ported vacuum started with smog equipment. It was used to increase temps at idle. Thermostats also went from 180* to 195*, as I recall. After the throttle plate opens, they operate the same. I only use manifold vacuum on my 68 L36 and 65 442. I have tried both on my Vette, and prefer using full manifold vacuum source.
Instructor
Joined: Apr 2005
Posts: 200
Likes: 0
From: Finksburg Maryland
Ported or manifold, you get the same vacuum advance at WOT. The difference is, with manifold vacuum, you get advance at idle (which you want), and with ported, you have no advance at idle. For best performance, you want manifold vacuum, either from the manifold, or from a carb source below the throttle plates.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
Ported vacuum prevents any vacuum from getting to the distributor when the engine is idling with NO throttle applied. Once throttle is opened slightly, the vacuum is passed...just like with manifold vacuum. This was a design modification to limit hydrocarbon emissions when the engine is idling ONLY. You can use ported manifold...but probably only because you are choosing to be "green".
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