This is the finished chamber for our 425 Windsor with the valve "ghosted" in at .500-inch lift. In stock form, there are two main fuel streams. The smaller one (arrow "A") tends to wash the chamber wall area directly in line with the direction of the arrow. This, combined with a stronger fuel stream (arrow "B"), causes a large washout at area "C." After port and guide mods, the fuel stream is spread out more, as indicated by the solid yellow arrows. Also, by making the ridge (red arrow) more pronounced, fuel from the cylinder center side of the intake port is sheared into a finer state off the edge of this ridge.
The rockers were also from Crane. These nominally 1.6:1 rockers have a high off-the-seat ratio (about 1.72:1), which gets the valves open quicker-and that's important for success when a lot of cubes are involved. For pushrods and springs, we used COMP parts. The most important item in the valvetrain is the beehive spring. This allows us to moderate spring loads to counter lifter collapse without paying an rpm penalty.
Ignition! For an ignition system, we elected to use a Chevy HEI-style distributor made specifically for a Ford 351 Windsor by Performance Distributors. This has several advantages like low cost, high performance, and total simplicity. We told the guys there what the engine spec was in detail, and they built a unit with the appropriate mechanical curve built right in. Normally, we would also use a vacuum advance as well (for best mileage), and that too would be appropriately tailored for the job; however, our 425 was for all practical purposes a dyno mule, so we elected to use a Performance Distributors micro timing adjuster in place of the vacuum advance. This allows precise adjustment in small increments to get the very best from the engine in terms of WOT.
Intake & Carb If we were building a hopped-up 351 for the street, the carb size most recommended would probably be a 750. This would almost certainly be paired up with an air-gap-style two-plane or maybe a Victor Jr. single-plane, but we have 425 inches here. This engine is more like a big-block in terms of displacement, so some serious reevaluation of the carb cfm was needed. If we step up carburetion in proportion to the cubes, then this engine is going to need something along the lines of 920 cfm. Also, for any motor that can potentially pass the 550-570hp mark, a Super Victor intake is probably the best bet. The reality here is that if this 425-inch Windsor did not make at least 570 hp, our engine building skills would be seriously called into question.
 Apart from subtle port "bending,"...  Apart from subtle port "bending," the large guide boss of the final port was, with subtle reshaping, instrumental in aiding wet flow, dry flow, and swirl. |  Did our wet flow efforts pay...  Did our wet flow efforts pay off? Judge for yourself from this chamber shot taken after our dyno testing. Note that the fuel wash (shown by the small patch of still-shiny chamber wall just by the plug) is minimal. Normally, this area is 4-5 times larger. |  Not only did our port work...  Not only did our port work improve wet flow characteristics, but it also improved the swirl, dry flow, and port velocity. Note how the flow curve substantially levels out at a little over .600-inch lift (about where our valvetrain will lift, too). If flow had continued to climb, it would indicate that the port could be too big for the job. |