I put the FBO plate in my Hemi, but with the vac advance hooked up, when you got off the gas after a banzai charge, it sounded like a machine gun as the 2-fours slammed shut, vac shot straight up and over-advanced. The guy at FBO told me that limiting the vac advance to add only 10-12* was the answer. I hooked my timing light up and, at idle, used the allen wrench to set it to 10* additional advance and noted the idle vac reading, this is using non-ported vac, as recommended by FBO. I shut the engine off, removed the cap and used my mity-vac to duplicate the idle vac on the advance can, used a sharpie to mark the arm where it goes out through the slot milled in the dist housing, drilled a 1/16 hole through the mark and put in a spring type roll pin, Problem solved! The pin physically limits the arm from moving further while allowing an additional 10* advance when driving normally. Backyard engineering, but it has worked fine for several years now.
THIS!
This is the one of the best ways I've read about to modify or limit the amount of canister vacuum advance. The small wrap of wire also sounds good. I have been contemplating adding vacuum advance too, and have been planning on welding and filling the vacuum advance canister arm to adjust the amount of vacuum advance to my engine's needs, but have not gone there yet. I don't know how to tailor the vacuum advance to my engine at cruise speed. Can anyone please describe the theory on that?
I am thinking of buying a quality vacuum advance equipt distributor, locking out the mechanical( or buying the MSD Programable box) Deciding which distributor to buy is a dilemma. I like the HEI style terminals, and would like to have a bigger cap that's high enough to clear my valve covers. No one makes one like that.
I really need to put a vacuum gauge on my motor to see how much vacuum I pull at cruise on the freeway. I know it idles in the single digits at 900 rpm, but don't know how much it pulls at steady state cruise out on the highway. I have always read it wants more that the 35* while cruising on the highway. I speculate probably 12* to 18* more, but how does one know what is optimal at steady state cruise and how does one test for that???.
I have tried all the bigger bushings from Four Seconds Flat, and the motor liked 22* initial with 35 total, but my timing was still bouncing around between 22* and 35* at idle. I tried using the stiffer springs which did help stabilize it , but the advance was coming in too late. I finally locked the Pro billet dizy out, and of course my timing is rock solid now.
On top of all this, my MSD Pro-Billet has a significant phasing problem. I have to use their pricey adjustable rotor at nearly maximum adjustment just to get the rotor lined up with the terminal. Taking care of the phasing problem dramatically reduced the wear on my cap and rotor for obvious reasons.
