I ran a set of 660 center squirts on my 452 RB for years. They were done by Chuck Nuytten. I had them on a 3400 lb. Super Bee, a 2200 lb. 33 Ford 5 window coupe and a 1900 lb dragster. In all the years I ran those carbs I didnt change the jetting in them more than 3 or 4 times and after I changed it I came right back to where it had been when I started.