I have a 1972 Chevelle with a LQ9, patriot 226 cam, turbo 400. I'm planning to run a single plane of some sort, long tubes and a 3400-3500 stall, Gears are 4.10s. I have a 750 Holley vac secondary carb from the last engine, should I reuse this carb or should I step up to a bigger carb or another 750 with mechanical secondaries??? I plan on swapping the heads out later to a set of SDPC cnc'd 243s.
If your just making a cruiser that will work but if your wanting to make some power go with a mechanical.750 or 850.. I ran a 75010 vac sec. On mine and could only get 119mph out of it went to 850 and picked up to 124 with my old lq4.
I take it you are setting this up for the track? You will be moving a good bit of air with that cam and ported heads. I'm sure it could use the extra CFM up top so I would think at least an 850 would be a better choice. I would be tempted to run what I had for now and upgrade later.
Mechanical vs. vac secondary, I don't know what to tell you. Some guys on here say never run a vac secondary cause they cost HP up top. Holley only recommends them for light weight, low gear cars with manual transmissions.