What is the difference between having a dual diaphragm vs a single diaphragm advance mechanism for Duraspark distributors?
Which is better for a truck application, and why?
Thanks

 

From what I understand the dual diaphram model was used to be able to reduce hydrocarbon emissions. There are two diaphrams that work independently of one another. The front port goes to the "timed spark" port on your carburetor(like a conventional vacuum advance). The rear port goes directly to manifold vacuum to provide additional retardation of timing during closed throttle deceleration & idle to help with a reduction of hydrcarbons. Personally, if emissions weren't an issue, I'd replace it with a single diaphram unit & tune it to give you better power & mileage. Just remember anything that was designed to reduce emissions usually hurts performance. I hope this helps.

Todd
BB79RANCH