Mac,
The 460 in our Mustang has a cam with similar specs 280/280 duration,.587" lift and 108 degree lobe separation. Ours runs fine below 3000 rpm but does not have the Q-jet. It's the lobe separation that is causing you the problems. I suspect that the power valve is opening way too soon because the carb "thinks" your engine is running faster than it really is because of the lower vacuum signal. I had the same problem with my 4-4-2, and oddly enough, cured it by switching to a Q-jet. So I know it can be done. I bought mine already modified so I cannot tell you how it was done. I do that there are some parts still avaialable from GM and there is a pretty good book available about modifying Q-jets (similar to those for Holleys). The guy who modified mine claimed to be a factory trained Q-jet carb tech, he may be able to get you started in the right direction. He specializes in 4-4-2 stuff which by the way uses Q-jets exclusively. Let me know if you're interested and I can get you his e-mail address.
Jim Gates
72 Mach 1
Posted on Jul 30, 1999, 9:27 AM from IP address 144.15.249.33