Ported vacuum source? .... as air speed increases through the Primary venturi it creates high pressure in the center to fracture the fuel into small particles, the opposite and equal reaction is Negative wall pressure. If you look at the primary venturi you'll see a small hole in the venturi wall...That is the vacuum source for Ported Vacuum. So as you accelerate the vacuum increases with air velocity and draws more timing into the distributor via the vacuum can. It will pull the amount of timing into the motor based on the numbers stamped on the vacuum arm x 2 ie: 6.5 Arm X2 will give you 13* at the crankshaft.
So if you have the initial timing set at say 6* and the distributor has 28* of mechanical timing in it then as you build rpm you will hit the 34* based on the spring tension (6* initial + Mechanical of 28* = 34*)and THEN it will advance another 13* of ported vacuum timing for a total under load of 47* PING PING BOOM!
Ported Vacuum is for emissions controlled engines with a OBD1 computer that will retard the timing based on the data it receives from multiple sensors such as TPS, O2, knock sensor, engine temp sender, MAP and others as they became more sophisticated.
Think about the fuel formulation your trying to burn in these cars, it's designed for extremely lean burn, sophisticated combustion chamber, high combustion chamber temperature engines, this new fuel is formulated to run in a Injected aluminum V-Tech designed for MILEAGE not your old cold iron push rod motor.
Yes some of the old factory stuff was hooked to ported but look at the timing numbers some as low as 5* BTDC with total at maybe 25* and then the ported vacuum would pull it up another 10-12* to make it run.... very inefficient and always a 5-10MPG gas hog but gas was 28 cents a gallon who cared?
GM perfected the Vacuum advance distributor hooked to Constant Manifold Vacuum and all GM cars were always connected to constant, they also made over 300 different combinations of distributors by using different vacuum cans, vac arms, pin positions on the advance plate and limits on mechanical advance cans to accommodate everything from their 6 cylinder trucks to a 427 corvette.
In today's real world we need to have all the initial timing the motor will take without kicking back or dragging the starter down, that number depends on the compression ratio and the cam duration or valve overlap, the bigger the cam the more initial timing you can run. The Vacuum canister needs to be adjusted to read the manifold vacuum level at idle and then it needs to be set to the correct amount of timing (usually in the 28-32* range)at idle and at part throttle cruise (42-46* range). Where the mechanical curve is set is whole set of different perimeters but it needs to work together with the vacuum timing to maximize engine performance at all loads and RPM levels.
If you have a performance engine the distributor needs to be curved to be compatible with modern fuel and still achieve reasonable fuel economy and still squeeze all the power you can get out of it. Although our 6 position disc really helps in tuning your distributor it's not a $25.00 tune up in a plastic bag. Even after you get the distributor all dialed in you still need a good ECU that won't drop output when hot, retard the timing under load or skip cylinders because of an inadequate coil. Just because someone says this is a "The Best Coil" you have no way to test it to see if it's marketing or engineering data? We do, we tested over 30 coils and then programmed our Microprocessor to optimize it's efficiency even further without compromising longevity or reliability.
ANY ECU utilizing slow old 1960's transistors will NOT do the job in today's world I don't care what color it is or what ridiculous claims they're making there is NO Substitution for Modern Level 5 Electronics using Intel Technology microprocessors and Good Ole American Manufacturing Skills and Quality Controls.
Our .0053% failure rate over nearly 6 years and well over 5000 units says that loud and clear.
