A rebuilt Q-jet is only as good as the rebuilder. I can sucessfully rebuild just about anything except automatic transmissions and Quadrajets. It is an excellent carburetor if done right. You must use all emissions that it was set up for or it will not run right. If you want no emissions, use a late 60s/early 70s one. I have bought some of the Holley rebuilt from Autozone with good success, but I prefer them rebuilt by the Carburetor Shop in Ontario California. They come out of the box ready to run, and usually require minimum adjustment. Many people just try to put a kit in one and don't pay attention to the throttle shaft bushings or seals. They will not run well if you don't do it right. A Holley is more forgiving, but a Q-jet will give better full-range performance/economy.

What nobody has mentioned yet is the carb has to be tuned properly to the engine. Changing one carb for another without experimenting with jets and rods is a crap-shoot. You might get better performance because most aftermarket carbs come jetted rich for most engines, and may give a seat of the pants improvement over an emissions tuned (lean) stock carb. But the same performance increase can come from properly tuning the stock carb. There's this guy Lars on corvetteforum.com that put together a Q-Jet tuning paper. You should go there and ask him for a copy. He's very very helpful. Joe

Hey, sounds like my 78 L-82 is set up almost identical to yours and my stock Q-jet atop the stock aluminum manifold runs just fine. I find it hard to believe that changing to Edelbrock carb and manifold or Holley carb and mainfold would do very much without going for a cam or more. I had an 85 El Camino SS that I went from stock Q-jet to 600cfm Edelbrock with edelbrock Performer RPM Manifold, it was smoother at all rpm ranges and gave a bit more in the mid but I doubt I found 10 true horsepower via this addition, on the Vette I think you'd yeild even less overall hp.