I have to agree with David on this one, although i've never ran a Merlin manifold, but i also recommend a 454R and any B/BLK chevy i build or have ever ran. Last example 468" 1050 Dom. with a 200 shot Zex plate. Engine runs 9.77@138 and change in a 3700 lb Biscyne less driver on a 10.25 CR pump gas motor, also very streetable. We fill up the tow vehicle and the Biscyne at shell, go racing then come home and bolt up the mufflers and drive to Sonic.
But then i also wish you would have given the Toilet bowl a chance, i really think you would have liked it and the performance, even on the 540 motor. Not questioning the APD because they have excellent carbs.
Zip.
