Manly and JE are names of companies that make forged internals. for instance, i have forged Manley rods and forged JE pistons.
detonation is when the gas in the cylinder explodes earlier than it's supposed to. that's not good. it can damage the engine. with forged internals, there is a far less chance of detonation hurting the engine. forged internals do not prevent detonation, they just help protect against the damage it can cause.