This is a cut and past from an article I'm preparing for the G&D. Terry is a local machinist that has done a lot of work for me.
Terry mentioned in the old days guys used to hop up Chevy sixes and race them along side **** V8’s. That was an interesting comment, so I decided to dig into that a little deeper. As Terry told me, it really isn’t difficult to turn a 216 into (almost) a 235 by boring the cylinders .063 and installing larger 235 intake valves with a little porting work to the cylinder head. Terry has a sonic tester that he maps the cylinder wall thickness and said it is possible to bore a 216 .100 inches with plenty of cylinder wall thickness remaining! Now the thing to remember is a 216 has a 3.5” bore, and a 235 has a 3.563” bore. The stroke of a 216 is 3/16 shorter than a 235, but by boring the 216 block to fit standard 235 pistons your 216 is now a 224 with plenty of cylinder wall thickness.
I’ve since gotten my engine back together it runs great without any engine noise and loads of power. As a matter of fact, when I shift gears from second to third and step on the gas, the truck has noticeably more power … I was truly amazed! So, before you decide to junk your 216 in favor of a 235, why not keep the correct engine with a couple of speed tricks from an expert [Terry not me]? Most engine overhauls require the cylinders to be bored, and hardened seats installed to run unleaded gas (I know this point is argued). So instead of using 216 pistons and intake valves, why not use standard 235 pistons and larger 235 intake valves with hardened seats. The only thing left is to run a ball cutter inside the intake runner to “port” the head for a smooth intake runner transition to the larger intake valves. The bottom line is the only cost beyond the normal expense of a complete overhaul is about 2 hours labor with a ball cutter.
