My understanding is that the tuning is the same. That it's a difference in the exhaust and intake. The stock E55 tubes are constricted really bad. It bottle necks to like 1" x 1" at on point on the drivers side. The exhaust has 4 cats, a resonator, and 2 mufflers. So I think if I took SL55 tubes and exhaust and threw it in place it would be the exact same power as an SL55.