Quote:
Originally Posted by davids2toys
Patrick, what are your thoughts for mechanicals vs. your vacuum in this situation?
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The goal of secondaries, be they mechanically operated or vacuum operated, is to provide just the right amount of increased air/fuel at just the right time when the engine is calling for that increase. If you have your mechanicals, or your vacuum, adjusted
perfectly, then it doesn't really matter which one you have. Your car will run as perfectly as possible for the condition that you adjusted them for. It's very easy to mis-adjust mechanicals and very easy to mis-adjust vacuum secondaries. If your secondaries don't open when they're needed, you're robbing your engine of performance. If they open too soon, then you get a bog. If they open "unsmoothly," then you get unsmooth performance. In a light weight, powerful car, like a Cobra, the last thing you want is an unexpected blast of power, maybe after a subtle bog. It makes the car more dangerous to drive.
The physical act of adjusting mechanical secondaries is easier than adjusting vacuum secondaries, because you don't have to take the canister apart and pull the spring out. With mechanicals, you can do your adjusting by the side of the road, as you're testing your acceleration and, most importantly, testing the smoothness. I know Holley has a "quick change" kit for their vacuum secondary spring, but I've never used it, and I have my doubts that it's that "quick." Personally, I always drop little springs, and I always rip holes in diaphragms. That's why I bought the Quick Fuel adjustable vacuum canister for my Holley:
It makes adjusting the opening of the vacuum secondaries as simple as turning a screw. If you can just avoid dropping the screwdriver, you'll be fine.
My personal opinion is that a "perfectly adjusted" vacuum secondary will be preferable to a mechanical secondary, especially in a light car like the Cobra. It will give the engine all the fuel/air it can handle, and it will do it nice and smoothly, so you don't get any unexpected surprises. Here, all I do is turn the screw, circled in yellow, and I can control how quickly (too much creates a bog) the secondaries open, or how slowly (too little and I'm leaving power on the table) they open. It does not take long to find the spot that is "just right." Anyone can do it, even RodKnock.
