The SPX pistons are 20 grams lighter over the stock pistons and provide serious performance gains! The SPX rings also seal the motor better than stock rings and provide approx 2HP gain over the stock setup because the ceramic coated piston domes reflect some of the internal engine heat back into the head so that all of the heat does not have to be transferred through the rings. SPX have 3% more silicon over the stock pistons and this helps stop the growth of the piston which then in turn helps stop the skirt wear. This makes the pistons and rings last longer and allows for more ride time. PISTON FITS- Futura 444 1978-79, Futura 464 1980-82, Sonic L/C 1984