I have had similar experiences as Gerry, I had a bone stock 302 2 barrel Fairmont, with a C4 and factory 2.47 gears about 25 years ago. I started doing a few bolt ons, bone stock it ran a best of 17.2 ET at 78 MPH in the 1/4 mile, first modification was a set of 3.55 gears and Traction Lok 8.8, and a pair of 1 1/2" long tube Hedman headers with a factory dual exhaust system from a 5.0 Mustang. (No cats, straight pipe from the collectors to the Mustang mufflers). HUGE improvement, 2 full seconds, best of 15.2 and 84 MPH, with the stock 2 barrel engine. next step was a factory aluminum 4 barrel intake from a 84 Mustang 5.0, and a 600 Holley. Expecting big things, the ET was exactly the same, up a mere 1/2 MPH. Figured it needed a cam, I swapped in a popular .448/470", 204/214@ .050 hyd. cam. Imagine my disapointment when it only picked up another 1/2 MPH, but actually ran slower ET, and lost over a tenth in 60 feet. Only after I installed a higher (2400 ) stall speed converter, did it run much quicker, and then a pair of early 351W heads picked it up another 1/2 second, likely more from the over a full point of compression than the slightly larger ports and valves. It`s all about combination. Even the 428 CJ in my 59 liked less carb, When I ran it last weekend, it ran 14.07 with a Holley 600 vac, when I swapped to a 780 Holley, it lost ET, MPH, 60 foot, as well as part throttle drivability to the 600. I am shifting this 428 at 5400 RPM, (on the dyno, it actually made peak HP at 4600 RPM, peak torque at 3800), with a bigger cam and more RPM, the bigger carb may help, but not here.And as I said before, even my Fairmonts 454 FE ran quicker with a 780 than it did with 850DP, 1030 3 barrel, 950 HP, or a 1050 Dominator (with an adapter). More ain`t always better.