The new biturbo M54 engine BMW is offering in the 335i e92 coupe looks very promising, i understand it will be making its way into the new e60 by 07.
I am very interested in this engine but very reluctant to go for the turbo design.


I must drive standard transmisison, my habit is to downshift enabling engine braking (foot off the gas). reducing speed by not touching the brakes.
I have the fear that once I downshift and the rev goes up (past 4K), the turbo will 'kick in'. Thus instead of slowing the car, I am picking up speed.

Can anyone here please advice me on the subject?
Has the 'new turbos' in general overcome this engine braking driving method?

Anyone here planning a test drive on the new M54 on the 335i (e92)?
Or any our our european friends here, can you please take a 6 speed manuel and see how this works?

I am also very concerned with turbo lag, although BMW specifically says its been reduced and refined. How true is it? Not even a tinest of the tinest turbo lag feel? Smooth as silk, glides like butter all the way?
I highly doubt, but will be so glad to be told otherwise.

comments / advice appreciated.

 

If your foot is off the 'gas' then the engine runs in over-run mode (until revs drop back down to just over idle) where no fuel is entering the engine... No fuel = no exhaust = no boost...

This is how most modern engines work so the turbo's should make no difference...

In regards to lag this engine produces peak torque lower down than diesel engines, so my guess lag will not be an issue, just a constant stream of power/torque from 1,300rpm to 5,000rpm! (Incredible!)

 

First of all, brake pads and rotor replacement are much cheaper than transmission and engine replacement.
Turbo "kicks in" at low RPM ~2000rpm, not somewhere near that 4K rpm. I'm sure BMW engineers know manual transmission drive WILL do engine-braking, so they MUST take this into account.
Regarding "turbo lag", I think it'll be negligible because of the two small turbos. This means that the turbo fan is very light. Think about this a 2.0L would crank out 280hp, roughly with turbo, and BMW I6 w/ turbo cranks out only 300hp. All and all, test drive is a must to figure out if there is any sign of turbo lag at round 2000 rpm. This you don't feel any turbo lag or engine braking issue, this engine will be a gem. I'd rather go for I6 300hp than 360hp V8 which is 150+lbs heavier.

 

Foot off accelerator, no fuel injected, no acceleration possible, even a turbo is no miracle worker.

 

A turbocharged car will drive essentially the same way as a normally aspirated or surpercharged car under normal driving conditions. I am not sure what the BMW turbo set up will be like, but if the company says that there won't be any, or only a small amount of, turbo lag, then I would believe them. Bad turbo lag need not be present. There are several ways of overcoming this problem. For example, once can use a smallish turbo since a smaller turbo will spool up more quickly than a larger one--and, thus, produce much less lag than the second. On the other side of the coin, the smaller one will produce less HP. But, all things considered, BMW should be able to produce an engine that provides the HP it wants without significant turbo lag. Another way to deal with the lag issue is to use multiple turbos, for example, in a sequential set up--where a smallish turbo gets things started and then hands off to a larger one.

 

I thought with most turbos that when at light loads, at idle, or under high vacuum, the wastegate is open for exhaust gasses to bypass the turbocharger equating to no boost.

 

Right.

 

? I thought everyone used downshifting to reduce speed quickly and eventually come to a stop in a manual.

Does downshifting really damage the transmission and engine?

 

The engine and tranmission was not made to slow you down - that is what brakes are for and The turbo will not slow the car down at any greater rate than a normal motor.

 

It's always the drivers choice which he or she allows to wear the most--unless one has no choice for one reason or one way is easier than another for some reason. Using a combination of the two possibilities is not a bad idea.