Originally Posted by Red Bread
Yeah, I just used the difference in 89 and 91/93 octane, since 87 will almost certainly ding performance and mileage more than the potential savings.
Interesting that this conversation hasn't led to the inevitable discussion of carbon buildup on these engines. Our 2008 N54 was getting to where it needed to be cleaned at 43k miles when we sold it and it was always run on top tier fuels, either 91 in CA or 93 in TX. The N55 and N20 will suffer from the same thing, and since direct injection bypasses the intake valves, no amount of Techron or other fuel additive will help. SeaFoam into the intake or physical cleaning is the only option. We leased this car, in the hope that BMW will follow Toyota/Subaru and others approach with adding a set of supplemental port injectors back into DI designs.
I was under the assumption that most manufacturers were already doing this. I mean this problem has been around for at least 5 years. And with so many CPO vehicles being sold and a sure fire way to defeat the problem, how can BMW ignore this issue and afford to allow it to continue.
I find it disturbing that BMW would choose to "follow" when they've always been a leader...or so most any German Engineer would have one believe.
FWIW, Audiworld has had few if any reports of CBU with their 2.0T. Most reports of CBU have been with the 3.2 V6 and V8 engines.
I'd like to see a BMW engine schematic to see if any kind of intake port injection has been engineered into our cars.