I haven't measured a stock 425 piston. Both my stock 401 and replacement Zollner pistons were a bit over 46 cc. A forged TRW was 45.3 and a Ross 425 piston was 44.4 cc. I made a simple fixture to measure piston cc..... 1" thick plexiglass, used a router to make a cavity, 1/2" deep. The round opening fits around the dome and seals on that machined outside edge. Used a flat plate on it to measure volume of cavity (100cc). Then replace flat plate with piston and refill.
I took a 425 piston to work, purged out a patty of hot plastic from one of our machines then stuck the piston in it and left it there until it cooled to mold the form of the dome. Once cooled I injected water from a syringe until the dome part was full. There is probably some error due to the convex meniscus effect but I tried to compensate for that. I came up with 45cc and would say its within +/- 1cc and if anything probably towards the lower side. Walts method is more accurate but this is what I had available.
Yes, stock type REPLACEMENT cast pistons. Not the same. I since have been doing the same type of various things & ALSO come up with 45-46 CC's on an original, stock bore 425 piston. So that should be good enough for what I'm looking for. Thank's to ALL for your replies. Tom T.
