How much vacuum should my engine make at idle and where should I measure from? Measuring from the vacuum port on the weber 38, the one that drives the distributor advance I get about 6" at idle and 25 or so at 2000rpm. That seems incredibly low for an engine that runs well and strong. should I be measuring from elsewhere?
how much vacuum at idle?
- Thread starter falcon fanatic
- Start date
8) depending on where you pull the vacuum from you are ok as it sounds like you are using ported vacuum not manifold vacuum. ported vacuum means you are pulling from a source that has little of no vacuum while the throttle plate are closed but full vacuum as the throttle opens.
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Anonymous
Guest
Hi falcon fanatic,
Engine vac is measured at the manifold, i.e., under the carb. If you have an automatic you can pull the manifold vac line to the trans from the manifold and check engine vac at that source. Normally speaking, you should see 15" - 18" at idle (Approx 600 rpm - in gear if automatic). This value will vary with altitude and temp (air density). Having said that, I find your current reading unusual. The numbers don't seem to conform to what I would expect for either a manifold or ported source. Manifold should be relatively constant, increasing some with rpm. Port vac should deteriorate as rpm increase. Your values 5" - 25" do not conform to either norm. Are you running long duration cam? What type ignition are you using? You say the car runs strong. What is your initial advance setting?
Very curious - Steve
Engine vac is measured at the manifold, i.e., under the carb. If you have an automatic you can pull the manifold vac line to the trans from the manifold and check engine vac at that source. Normally speaking, you should see 15" - 18" at idle (Approx 600 rpm - in gear if automatic). This value will vary with altitude and temp (air density). Having said that, I find your current reading unusual. The numbers don't seem to conform to what I would expect for either a manifold or ported source. Manifold should be relatively constant, increasing some with rpm. Port vac should deteriorate as rpm increase. Your values 5" - 25" do not conform to either norm. Are you running long duration cam? What type ignition are you using? You say the car runs strong. What is your initial advance setting?
Very curious - Steve
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Anonymous
Guest
A stocker should be pulling 15-20lbs at idle, measured from the manifold. Mine does about 18-19.
Bill
Bill
