Bmw M3 is the last model with a naturally aspirated engine

My how times are changing. Not too long ago, I remember reading BMW literature that spotlighted BMW's superiority in using ONLY naturally aspirated engines because [insert marketing hyperbole here].

My understanding is that well-designed turbocharging systems do wonders for engines, in terms of increased peak power, increased torque that comes on a lot sooner, and even increased fuel efficiency, assuming you use a smaller engine to get the same HP and torque. I don't think it's a bad thing that BMW is going to turbos. Sort of like when we left carbs behind in favor of fuel injection.

Why did they do this? A smaller turbo engine will use just as much gas as a similarily powered larger naturally aspirated engine. My guess is to increase hp/liter numbers, as everyone knows that's a sure sign of excellent engine tuning! </sarcasm>

I so rarely agree w Joe, but I do here.

Huh? A smaller turbo engine can get much better fuel economy than a larger naturally aspirated engine with similar power. The new M5 will have roughly 80hp and 150lb-ft more than the last one and get 25% better fuel economy. The next M3 will have roughly 450hp and 400lb-ft from its twin turbo straight six, and again likely increase fuel economy around 25%. More power, better performance, better fuel economy. Are those good enough reasons?

"Compared to the fourth generation of the BMW M5’s power unit(NA V10), the newly developed engine(TT V8) has a significantly increased output level, whilst at the same time lowering previous fuel consumption and emission levels by at least 25 percent."

With the peddle to the floor, yes they will be about the same, but when you're not heavy on the throttle the smaller turbo engine does use less fuel.

@jrob, and larger engines can use cylinder deactivation. When it comes down to it, there is no fuel advantage.

My 2005 6.0 GTO averaged 23 mpg with intake and engine software. My 2006 Mazdaspeed 6 with it's 2.3 Turbo with intake and engine software gets 23. I dunno. I'd prefer a normally aspirated engine.

I can't speak for the GTO, but the MS6 isn't geared for fuel economy, it's geared for torque. If they had given it a taller final drive ratio then it could have easily gotten a lot better than does. That said, your 23 number seems a bit low. I was getting 25 with a short intake + inlet tube and AccessPORT tune (50/50-hwy/city), and saw as high as 29 when all ~60mph highway cruising miles.

Also, your comparison isn't showing quite what you think it is:

The MS6 runs at about 16psi maximum, plus about 14psi ambient air pressure at sea level, for a total of 30psi consumed at 2.3 liters. To convert the displacement to an equivalent non forced-induction engine, 30psi / 14psi * 2.3L = 4.9L

So your MS6 got 23mpg at an equivalent of 4.9L, vs. 23mpg at 6.0L for the GTO. Not as big of a difference as you were suggesting, and could easily come down to gearing, or the aggressiveness of the tune (Mazdas are also known to run on the rich side).

I thought a turbo engine is by its nature more efficient due to the recycling of lost engine power. For the same engine wouldn't the turbo version always provide more power relative to the fuel spent?

Turbo charging and any other forced induction basically increases cubic inches by compressing air and forcing it into the engine. so the more air you have, the more fuel you need to keep the ideal air fuel ratio. I.E. a 3.4l engine with 6psi of boost needs the same amount of fuel under full boost (6psi) as a naturally aspirated 4.5l engine, because at 6psi the 3.4l is using the same amount of air as a non turbo 4.5l engine. the only difference is that air is compressed and forced into the 3.4l because compressing the air and introducing it into the combustion chamber under pressure during the intake stroke is the only way you can increase the cubic inches of an engine. The only other way is to bore and stroke it. When the engine is not under full boost, like cruising down the highway, it will use less fuel because less cylinders are being fired and there is not enough of a load to make the turbo spool up and provide boost, which in turn would require more fuel.

On the other hand the reason cars like the Corvette get goo gas mileage is because they have enormous low tech push-rod V8 engines up to 7 liters, that produce alot of torque so they gear them much taller so the engine is barely above idle at 60mph. No 6 speed manual exotic is going to be turning 1400 or 1500 rpm at 70 mph like the Vette with the 6spd manual Since the engine is turning much slower, less fuel is being burned.

im currently getting 12.6 mpg on my e93 m3, a tad better than the 11.5 i was getting on my is-f... but only slightly worse than the 13.4 i was getting on my 335xi..
i dont mind turbo, but i didn't get so much better mpg's with it...
if there is a reason i prefer turbo its because with a $ 2000.00 chip you can add nearly 100hp and 100 torque.. when i called dinan asking what i could get for 2grand he said about 10 hp and 6lb torque, lol

to get an extra 100hp and torque dinan told me i would need to spend about 10 grand...

With the torque curves they are getting on turbos these days, I say good riddance NA.