Ok I'm in third gear and am going downhill in a turn. I downshift into second. Seems there's no engine breaking. Eventually it feels like the engine breaking starts kicking in, after a good 2-3 seconds.

Anyone venture an explanation?

 

the car auto rev-matched those 2-3 seconds and then engine braking kicked in.

 

That was my initial impression but after entering the curve in 2nd and abruptly letting off the throttle it was the same. No gear change.

 

Hint: After excessive engine braking, check your oil and be prepared to replace a little. You'll blow a little bit out the back hole over time doing that.
No big deal but just be aware unless you spend a whole day in the mountains occasionally spinning the lump at 5500 RPM in 2nd gear for a mile or two down a 12% grade, then you'll need a quart or two.

 

Auto or manual?

I have a manual, and my experience is there is NO engine breaking on this car (2015 MC) other than in first gear.

The revs may be there, but there really is very no engine breaking to speak of going on.

Now, if you go hard into a turn, stability control does kick in. In fact, until you either get used to it, or turn it off, it's going to throw you off. I went fast into a curve with cruise control on, ready to turn the wheel hard and quickly. I found myself oversteering. Then looked at my HUD and saw my speed had dropped as the car accelerated coming out of the curve. With cruise control, I expected my speed to stay the same through the curve. Instead, it braked on it's own (which I wasn't expecting, hence my steering was off), and then accelerated back to the cruise setting after the curve.

The stability control was likely your delayed (what you thought was) engine braking.

I initially did my practice of downshifting to slow down, but all that happened was the engine reved to come up to my given speed in the new gear, but then let the clutch out and no engine breaking experience. Now I either don't downshift at all, or just go to neutral to let the revs drop to 1000 and use the brakes. Sure my brakes will be used up faster, but right now I'm on the free maintenance plan so why should I care if I need brakes sooner? Factor in less wear on the clutch, which is doubtful to ever be paid for on the free maintenance plan window, then go to neutral, save gas, and get on with it. And for normal back and forth to work, not needing to punch it to every next light, or being constantly on the brake after speeding up on a stop and go freeway, I'm easily averaging 7 to 9 MPG more in this 3 cyl F56 vs my 2009 R56 MCS.

And while I would say you need to keep an eye on oil consumption (which is more difficult by the lack of a dip stick), my experience at about 2800 miles is that at least the three cylinder MC vs my prior 2009 R56 MCS uses very little oil just based on the cleanliness of the exhaust tip vs what it would have been on the R56. As far as the electronic reading, it still shows full, vs my R56 was drinking the oil between changes (not to mention virtually impossible for me to read the oil level on that dipstick -- so while I miss not having a dipstick, as far as I'm concerned I might as well not had one on the R56 because I could never read the level whether the oil was freshly changed or dirty as hell).

 

Another hint few people without track time don't think about:
Higher RPM going in to a curve adds stability. You've got a pretty heavy gyro spinning up front and the faster it spins...
Those big lumbering SUVs would corner better if folks would down shift their automatics too. Just east it out of over drive down a click or two and you've got it.