[slowbird]

Originally Posted by steve25

Yup! Due to the geometry of a roller and the stock block limit of a .842" lifter a solid lifter lobe as I posted can kick the valves open faster initially, but for the spring pressures needed to attain 7000 rpm or so the only advantage in running a roller in the 600 hp range is the start of the slight reduction in fiction.

Number 48 casting heads where never used on production 428 motors be they HO combo's or not, the number 46 casting on 360 hp 2 bbl 428s are often mistaken for number 48s!

If a 428 did slip out of the factory with number 48 heads it done as a one or two of situation so as to not tie up / stall the assembly line .

This has been seen many times as in the case of a late run motor that came stock with one 6X casting and one 5C casting.

Can you show dyno proof?
A flat tappet is limited by velocity (the edge of the lifter catches the lobe and kills everything) a roller isn't. For the same amount of duration you get more area with the roller vs a flat tappet.