"...Now that I have decided against the Silvolite pistons and have to purchase new pistons anyway, could I achieve my goals with a dished piston? I would love to use this head and keep the engine "pump" friendly to at least premium fuel. I found that the dished pistons are available at +17cc here:
Can buy custom dish pistons, with a big enuff dish to lower your CR for pump gas. But DON"T buy those "hypercast" pistons !!! You need forged pistons, NOT cast. There have been a lot of problems with those pistons. And the top ring gap must be bigger than the 2nd ring gap, by quite a bit. I would not consider those pistons for any build. If you wanna use those heads, you'll just have to bite the bullet an buy expensive forged custom pistons with the dish you need.
I'd shoot for 9:1 CR, but definitely no more than 9.25. Some say 9.5 is OK. But why take a chance on possible engine damage, for just a small amount of power.increase ? There is an Icon piston with a 15cc dish. But that's not near enuff to get the 670 heads down to 9.5 CR or less, unless the chambers are enlarged to around 90cc or so
"...I am open to additional expense for valves, thicker head gaskets, machining, or other hardware to use these heads..."
DON"T use thicker head gaskets !!! You need to keep your quench distance down to as close to .040 as possible. If you were to use, say the Butler .045 thick gaskets, and had a deck height of .010, that would make your quench distance .055. Some say that as the quench distance approaches .050 & beyond, detonation becomes more likely.
Fel-Pro 1016 gaskets are .039 thick. So, if you can get the deck height down to between zero & .005, the quench distance will be OK. When using stock length rods, there are 2 ways to reduce deck height. (1) Cut the block decks down by machine. (2) Order pistons with a larger pin height(compression distance) . Custom pistons can be ordered with a larger pin height(distance from the center of the pin, to the top of the flat part of piston).
The cheapest custom pistons I know of are the Auto Tec/Race Tec brand. They'll be $500 + shipped. Some of the other brands, such as Ross, can be on up into the $700-$800 range, with pins & shipping. Butler is probably the best place to order, if you decide on Ross pistons, since they can help you order exactly what you need. But, they are $700 + pins + shipping.
There are other Pontiac engine builders who can order the Auto Tec pistons, and help you build correctly using the 670 heads. I'm not positive, but I think Paul Knippen can order the pistons. And he probably can supply most all the other info & parts you need.
The chambers in the 670 heads can also be opened up to decrease compression & become more pump gas friendly. You can get all the 670 head info you need on the PY site. There are several well known Pontiac engine builders who post there. One of 'em has also started his own Facebook page. He works at a machine shop in AZ, and has a LOT of Pontiac engine building experience. He goes by the name gtofreek--real name Paul Carter. He can probably provide all the correct info you need.
