Doesn't matter what shims you use if you factor it in when checking your lift with a dial indicator. They had to give a spec so they picked one. Other cam manufacturers use different lift specs to get you off the ramp and using zero lash, some are metric lift some are imperial, depends on what they feel like. And after taking a completely anal approach once the engine warms up the timing has changed not to mention the belt stretches. And if lash varies from valve to valve then the cam timing is different on each cylinder and does anyone check that all 48 lobes are dead on spec? We're only checking timing on 2 of 12 cylinders and assuming the rest are right. Intake closing time to trap the amount of charge the engineer has in his calculations for dynamic compression ratio and exhaust opening time to start getting the charge out when intended.