which distributor

[kirkallen143]

8)

for those of you that are building turboed engines by the way, use the dual diaphram unit, and plug the vacuum line in after the turbo outlet. that way you get a boost retard function automatically. it really works nice to eliminate detonation under boost.

THIS IS ONLY FOR A DRAW-THRU TYPE TURBO SYSTEM. Do not use this for a blow-thru turbo system. When under boost, the vacuum changes to boost and will actually advance timing through the retard port, pushing instead of pulling. Ask me and a headgasket how we know.

Kirk

 

[Bort62]

8)

for those of you that are building turboed engines by the way, use the dual diaphram unit, and plug the vacuum line in after the turbo outlet. that way you get a boost retard function automatically. it really works nice to eliminate detonation under boost.

THIS IS ONLY FOR A DRAW-THRU TYPE TURBO SYSTEM. Do not use this for a blow-thru turbo system. When under boost, the vacuum changes to boost and will actually advance timing through the retard port, pushing instead of pulling. Ask me and a headgasket how we know.

Kirk

Yup. That's my point...

The boost applied to the normal vac advance port should actually retard. I haven't tried it yet but I plan to.

 

[66 Fastback]

Regarding the dual vaccuum cannister. It was used in conjunction with the vacuum switch tee as an emission control device. While the engine was warming up, it sent full manifold vacuum to the retard side of the distributor canister. This retarded the spark advance resulting in higher combustion temperatures which had the effect of warming up the engine faster and burning some of the otherwise unburned hydrocarbons during the warm-up period. Once the engine coolant was warm, the thermo-vacuum switch closed off the manifold vacuum port signal at the tee, and very little or no vacuum was sent to the retard side of the vacuum canister. Simon posted a nice drawing of the vacuum tee hookup on this thread.
I don't believe dual vac cannister were used to improve fuel economy. Higher vacuum advance helps promote smoother idling and cooler temps. You can idle the car with the throttle plates openned less if the timing is advanced compared to retarded timing.
Doug