Originally Posted by allansmith859
BOGIE are you saying that on swirl port heads they made the spark plug where it ignites on the exhaust side.
Moving in that direction but not quite there. The big thing is they move the plug well inboard toward the valves so it has a more centered position relative to the bore diameter. This results in less burn time as the flame front spreads out to the bore limits rather than starting on a distant side then having to travel the entire bore diameter. The Swirl Port head used on the trucks shares a lot of common design with the L98 Corvette head. The truck head gets messed up with the added swirl vane. There is a cast iron version of the L98 head or if you will the Swirl Port head without the vane which are casting numbers 14096217 and 14101083. Castings 14096217 and 14101083 make part number 10125377 for 1986 to 1995 intakes using the 72 degree center bolts. Casting 14096217 is also used to make part number 10159552 for 1955-1986 intakes using the 90 degree center bolts. If you're interested these can be had quite cheaply on the used and rebuilt market for a bolt on replacement to Swirl Port heads or other applications. These heads also show up on some crate motors.
The Vortec is another step forward it borrows pretty heavily from the combustion chambers and port designs of the mid 1990s LT1 and LT4 heads as does the aluminum GMPP Fast Burn head but both the Vortec and Fast Burn use conventional coolant routing and will fit any GEN I block that has enough bore diameter to clear the valves.