Like TS1955 said, but there are a number of 23* heads that do take an offset lifter and also a an offset rocker. EX: i have a set of Brodix 10's 23* that takes a .180 offset lifter and .250 offsst rocker. As TS1955, it's because the ports are so big the pushrod won't clear the intake port. There's probably more, but i only have the Brodix 10's as as example. As i understand it most of the higher flowing 23* heads do have to use the offset lifters and the offset rockers. the Brodix 10's that i have flow close to 320 CFM at .700 lift int.
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