Doing a rebuild of my 350 and just bought the "Sealed power Performance Piston Ring Set" (part#SLP-E-251K) to go onto my stock pistons (1975 4 bolt). just wondering on where about my end gap should be because I don't have a piston manufacture spec to go off of

 

.0045" per bore inch on the top ring, .005" on the 2nd, "enough" on the oil ring that it doesn't butt up against itself when it gets hot.

So, for a 350 (4.000" bore), that's around .018" on the top, .020" on the 2nd, maybe .025" on the oil ring rails. Err on the side of a bit more gap (say, a .001" or 2) rather than ANY less. Too much ring gap is a minor annoyance, even ALOT too much; too little, even .0005" too little, is CATASTROPHE and DISASTER.

The pistons are ABSOLUTE GARBAGE. Sorry to hear that you're going to actually spend money to re-use such ... ,,, ... , ... words have failed me.

 

Good info on the ring gaps but the piston comments might be a little harsh. Those run about forever without problems, were on the engine as balanced (as much as the factory balanced back then), and if buying new pistons might as well rebore, and have to replace on rods. Machine work is crazy expensive these days. Unless really adding some power I'd not worry about reusing those slugs.

 

Stock pistons are detonation prone garbage. GM could have gotten away with a full point more compression using a D-shaped area rather than the horrible chili bowl dish they used. The stock pistons offer nothing in the way of quench. They are also not well balanced to the rotating assembly as I found on the L31 I pulled apart. I put that engine together with LT1 Mahle flat tops and appropriately balanced crankshaft and they were much closer in weight and lighter weight as well. The lightweight mahle LT1 pistons are identical in weight to 305 pistons. I highly doubt a 1975 block does not need a bore and hone anyway, they are extremely prone to taper and out of round wear living their life carbureted with substandard oil. Personally I would find the most cherry 350 Vortec in a wrecking yard I could find and build it over any 70s flat tappet smog garbage. Factory roller cam, better block all around, less cylinder wall wear and the 1-piece rear main seal are all worth the price to find one. A stock, untouched good running vortec will put almost every other earlier small block to shame minus maybe a 1970-1972 LT-1. Add a small cam around 218/224 @ 0.050 and the LT-1 is lame in comparison.

 

its by no means a high performance engine. just something to get the car up and running with a simple cam, carb, and headers.