Quadrajet adapter plate

[Mertz]

I am going to convert my 350 from an Edelbrock carb to a Quadrajet. I have a performer manifold that is only for a square bore. How much performance will I loose by using an adapter plate? I understand it is best to use a 4 hole plate rather than an open plate.

I am looking for better normal driving gas mileage while having some more power to pull my 5000lb trailer up a 7% grade. It really bogs down now and has to down shift frequently. I am hoping the bigger secondaries and the way they work on the Qjet will make it easier to climb the long hill.

I have a stock cam, MSD ignition, roller tip rockers and ceramic coated headers. I have the time set as far advanced as I can. It did ping a little with the trailer but not under other conditions. I switched to higher octane and the ping went away. It also got better mileage without the trailer going from fishing hole to fishing hole.