If you're talking about the 05/06 model, a lot of folks who still have a lot of warranty left on their trucks! What year is the 4Runner your buddy is swapping engines on? I would suspect you'd find more information on this topic in about three years when these trucks are no longer under warranty and people are more willing to experiment! Of course you could bravely pave new ground and drop a 304 HP 5.6L Titan engine in your Frontier! I'm betting it would give your buddy's 4Runner a run for your money!whats out there?