i have an edelbrock performer 1406 that i was planning on rebuilding cause im starting to get some idle problems and a huge wot bog that almost kills the car.
i was playing with the idea of getting a demon and looking on there site it said you should use vac secondarys on any auto but mechanical on manuals and autos with over a 3000stall

i have a mild h/c engine 503/510 224/230 112lsa p&p vortecs performer rpm airgap intake and hedman longtubes with true dual and an h pipe.
built 700r4 with a 3500stall fuddle converter.

would i see any performance gain going with a mechanical secondary?

forgive the dumb questions this is the first carb motor i have ever had. im pretty good with tuning the edelbrock and im ordering an lc1 on friday so i can wideband tune anything i get. need advice as to what kind and how big of a carb to get.

I'd wait until you have the LC-1, then try to tune the edelbrock a bit. You might be able to get satisfactory performance out of it. You will see some performance upgrade going to a mechanical secondary, but is it worth $400 or so? Not for me

The 3500 stall in your converter will get you up in the RPMs real quick when you nail it. A DP will work well and hit harder than a VS with that combo. It's when you try to put a DP on with a tight converter that problems can arise with low RPM softness/bogs. With the loose converter you'll never be "lugging it" at a low RPM range.