Should vacuum advance be hooked to ported or manifold vacuum?
Most experts suggest a stock engine run a ported connection. A hotter street driven engine should try a manifold connection. In all cases experts agree that a street driven engine should run vacuum advance.
What is a ported vacuum line?
Ported vacuum is zero at hot idle and rises in response to throttle butterfly opening to a maximum value and decreases with increased opening and thereby reduced intake manifold vacuum. So, it advances the spark first at tip in throttle and then lets it retard back to base under heavy load.
Where does the th350 vacuum line connect?
In case you are still uncertain on where to hook up vacuum line: There is usually a port directly behind the carb. on one of the intake runners. If not there is the port on the bottom backside of carb. (usually for power brakes), or on the front of the carb.
What happens if vacuum advance doesn’t work?
Eventually the deterioration will reach the point that the vacuum advance no longer adjusts the timing, causing the vehicle to hesitate when the engine attempts to move the vehicle’s weight. In addition to this lack of power, a vacuum leak can also cause the engine to idle roughly or even stall.
Should there be vacuum advance at idle?
Plugging your vacuum advance into a direct source will allow it to engage at idle, which is good for a number of reasons. Much like cruise conditions, engines run leaner at idle than they do under load. Again, this means the mixture burns slower and needs an earlier spark to optimize the burn.
Where do I hook up my vacuum advance?
You want to plug the line to the vacuum advance when setting the timing. After setting the timing, hook the vacuum line back up and adjust your idle speed if necessary. When checking you mechanical (centrifugal) advance, the vacuum line must be plugged as well.
How do you test a ported vacuum switch?
You test it by heating it up and measuring when the vacuum port switches. You do not need one, provided you defeat the retard port on the distributor. The cons are that you will generate unnecessary harmful emissions during deceleration.
What is a ported vacuum switch used for?
When the DVCV senses an overheat condition, defined by Ford as 220°F, the shuttle valve switches vacuum advance from ported vacuum to manifold vacuum. This advances engine timing, which increases idle speed, which runs the radiator fan and water pump faster, cooling the engine.
Do automatic transmissions have vacuum lines?
A lot of people take gear shifts in their vehicle for granted. But every time your automatic transmission needs to shift into a different gear, there is a vacuum modulator inside which ensures that the gear shift can be successfully completed.
Does a Turbo 350 need vacuum?
You need vacuum from the manifold to the modulator on the tranny to shift properly. It won’t shift or it will shift at really high RPMs if you don’t hook it up. Gilbert Morin Jr.
How do you connect a vacuum line to an engine?
To determine which is what when you cannot see the switch. Connect a chunk of vacuum line to any port and blow into it. Move the line until you find the port you cannot blow through. This is the port that goes to the engine vacuum. Connect it up. Start the engine and shift the case into four wheel drive.
What happens to timing on a ported vacuum?
Ported vacuum: With that thought in mind consider if the distributor hooked to Ported Vac, as air speed increases the ported vac activates and starts to pull more and more timing in the motor as velocity increases.
Where does the ported distributor vacuum advance come from?
Ported distributor vacuum advance was a result of early 70’s emission equipment. It comes off the venturi above the throttle plates and is effectively isolated by the throttle plates from manifold vacuum, more specifically the throttle shaft as the defining point much like an expansion valve in a refrigeration circuit.
How does a ported vacuum source work in a car?
Generally, emissions equipped vehicles use Ported and they are connected to a computer, OBD1 or 2 to retard the timing based on information gather from a multitude of sensors in the vehicle. Non-Emissions Hot Rods and Street Muscle Cars Pre-emissions use Constant.
To determine which is what when you cannot see the switch. Connect a chunk of vacuum line to any port and blow into it. Move the line until you find the port you cannot blow through. This is the port that goes to the engine vacuum. Connect it up. Start the engine and shift the case into four wheel drive.
Ported distributor vacuum advance was a result of early 70’s emission equipment. It comes off the venturi above the throttle plates and is effectively isolated by the throttle plates from manifold vacuum, more specifically the throttle shaft as the defining point much like an expansion valve in a refrigeration circuit.
Ported vacuum: With that thought in mind consider if the distributor hooked to Ported Vac, as air speed increases the ported vac activates and starts to pull more and more timing in the motor as velocity increases.
Where does the HEI hook up to the VAC port?
Hook your HEI up to the ported (part-time) vac port on the pass side front metering block port. No vac at idle, so you can set your initial timing and idle speed without any vac intterference. On this port, you only get vac advance when you hit the gas.
