Johnny Rad

Figured this was the best place to post my noob-tech question about how the factory turbos are programmed to function in my '12 E550 w/M278.

Question: At a steady state ~3K rpm (not accelerating), is my waste gate programmed to divert flow away from the intake side? The key to my question is steady state motoring; no acceleration.

Situation (only been in it a few times): Using the flappy paddles to hold a gear and keep the revs up while I wait for my opportunity to hit it ... feels like I'm getting turbo lag when I go WOT. I "thought" that I was holding the revs up to keep the turbos spinning so I'd get instantaneous acceleration, but I felt a bit of what I figured was turbo lag instead.

Thanks for the education.

Johnny Rad

Bump.

Anyone know a good educational site where I can learn more about turbos that may shed light on is potential phenomenon?

Thanks

Welwynnick

Question 1: The waste gate is programmed to stop the boost pressure exceeding the limit, so it only opens when the turbos are actually boosting. In your example, the engine will be under low load, so the waste gates will be closed.

Question 2: Yes, you still have turbo lag at high revs. The turbos don't speed up and slow down strictly in proportion to engine revs. It depends on the exhaust gas flow, which is a function of both speed and load. You need both to get the turbos fully up to speed.

Nick

Johnny Rad

Thanks, Nick.

Good stuff.