the three pistons in the top row on the left with the discolored skirts are 312 standard pistons.

Due to a problem with cylinder wall on a 292” +.040” I had to enlarge it .010” for a 312 std piston. It was done with a Lisle hone in the car. The taper was kept to under .0005” top to bottom and the gap at the bottom at the skirt of the new piston was .0015”. I made lot special tooling to keep the crank from being touched and the cast iron/lube funnel straight down minimizing crank case contamination. Yes it was a pain. 

56 Vic, B'Ville 200 MPH Club Member, So Cal.

Yep. "Standard" pistons in a .050-over 292 block would be 312 pistons. The pin location/compression height are the same, but the 312 uses shorter rods to compensate for the longer stroke.

Silent Rick.  Pictures can be deceiving to the eye because of the angle of the view.  In looking at your pictures, it appears in my view that some of the piston skirts are different.  They appear to have a greater curvature at the bottom edge.

You will be able to tell best, Check to see IF the shape of the lower piston skirt is different on some from the others.

Remember that the skirt on an OEM Ford 292 piston is shaped different from that of a Ford OEM 312 piston skirt.  With the longer stroke, Ford had to modify the shape of the piston skirt to clear the crank.

IF some of your pistons are marked STD. it may be an indicator that those pistons were intended for a 312 application.  While they fit your engine bore, the piston weights may be different IF they were not adjusted in the balancing process.

Aftermarket piston manufacturers' understandably adhere to the OEM piston skirt configuration for the engine series that they were intended to replace.  In the case of the Ford y-block, they could have used the 312 piston skirt configuration for the 292 piston skirts to allow production of pistons from 3.750 inch diameter all the way up to the commonly available 312 engine's 3.860 available oversize.  The only variable they would have had to adjust for would be the piston weight as the size increased.  The piston pin heights would have been the same.

Idle speculation on a rainy Saturday. 


NoShortcuts
a.k.a. Charlie Brown
near Syracuse, New York

three of these pistons are marked "std" standard, the others have no markings on them. zero hours on them

.050 over 292 pistons and EBU rods. .050 over 292 is standard bore 312. the story goes my 292 short block was rebuilt in 1967 but never run. it sat on a shelf in a dry and heated shop. the only reason i'm not running them is i decided to go with a 4-71 blower and wanted better rods and forged low compression custom blower pistons. i want $100.00 plus shipping.