Any oil ingestion into the intake air charge increases detonation so the PCM will pull timing to protect the engine from damage and thus less power and less MPG. Also, oil does not burn well at all so if it is in the combustion chamber contaminating the air/fuel mixture less power is produced per explosive event (the combustion process).
That and the carbon deposits, but the V8 still is port injection so the intake valves stay clean if a top tier fuel is used.....but the rest of the issues from oil contamination are enough to want to prevent it.
2014 and up the V8's will be DI and have the same issues the 4 cyl & V6's do today.
