X15 down on fuel economy recently?

[Rawze]

(opinion based on what I have seen). As far as performance goes, I wold think the intake impeller differences themselves would be about the same. One is likely a bit more quiet than the other is all.

Otherwise, the only way to tell what 400-series turbo you have, is to measure accurately, the intake housing inlet to see if it is 34mm or 36mm. The 34mm housing is the fuel efficient one, and the 36mm is the heavy haul one with the heavier duty exhaust turbine. This is assuming that they are original and no one has swapped parts around in them at a turbo repair shop or something.