Carb guys....vacuum vs. mechanical advance

[85_SS_302_Coupe]

Just wanting to hear everyones experience and preferences. I've got the option to run either one now and i'm torn between the two. Right now i'm running a GM HEI ignition conversion (just the module, not an HEI distributor) with a Duraspark II distributor that hasn't been modified yet, and i swear it pulls harder than the Mallory with mechanical advance.

Two things i can think of that might cause this...is the Duraspark is set up with more initial advance than i can run with the Mallory, because i don't have the advance kit for it so i have to tune the Mallory for total timing and sacrifice initial. The Duraspark right now is set up for 13-14 degrees initial, but i've been reading that it's hit or miss what the total timing could be in a rebuilt distributor because there were so many weights/springs/canister arms used over the years and it doesn't even matter if you order one for a certain year, you could a number of combos.

Right now i'm concerned about what my total timing is and being vacuum advance it's really a PITA to figure out, and i haven't taken the distributor apart to see what weights are in it yet. I've tried to unplug the advance vacuum and read the timing that way, but when you rev it up the timing pointer just maxes out (past 40 degrees). If i try to back the initial timing down to where that doesn't go up so high, there's so little initial timing that it won't run. However, with the initial set to 13-14, the car runs awesome and i haven't noticed any pinging.

So...opinions would be greeeat. :lol:

[IEATLT1]

I have an msd dist (mech adv) in my car not sure how mallory are setup but mine shipped with the firm springs installed and I had to buy the light spring kit so it would allow it to advance more just changing the springs to allow the correct advance netted me 31hp at the wheels so double check those springs and make sure you don't have the heavy ones installed

[85_SS_302_Coupe]

I believe the way the Mallory works is there's some kind of key sort of thing that goes into the side that unlocks it, and you push it in or let it come out and tighten it back up and that changes the advance rate. Of course, i don't have this yet..lol.

I'm gonna be getting springs and weights for the Duraspark II distributor and seeing what i can do with that also. From what i've been reading, mechanical advance is preferred for racing because at WOT the distributor is working off full mechanical advance anyways, and for street you're better off with vacuum where you're not going to be running at WOT all the time. What i'm curious about is, can i find a sweet spot between the two? Can't i set up the vacuum advance to work great a low RPM but have it set up so that the mechanical advance comes on extremely easy so when i mash the gas it basically switches to full mechanical? Or should i just set it up for full mechanical advance and lock it out and not run the vacuum part? (if that's the case, why wouldn't i just run the Mallory?)