Very interesting. I tried looking at BMW 535i vs several V8 competitors. The M45 is really the only V8 in that class that falls short (21 mpg hwy), but the Lexus GS, Audi A6, M-B E-class, and Caddy STS are all just about the same fuel economy as the 6-cylinder BMW (and about the same price!).

I also suspect that in general, a non-turbo V8 will likely be more reliable in the long run than a turbo 6.

Hey Josh in the Mini's case could low curb weight have a significant impact on fuel economy do you think?

As much as I like turboed cars, I have to say that I agree with Josh. Another great example of a NA engine with better-than-expected fuel economy is the Chevy small block. I can't remember the exact numbers, but I recall that it does quite well in the Corvette.

Josh, shouldn't you be comparing how a turbo version and a non-turbo version of the same engine compare?

You start with using the Ford 3.5 V6 as an example, and the NA and turbo make the same power, but then you compare different engines from different manufacturers?

Using Edmunds.com for information, and extending the use of the Mini as an example, the 1.6L for the base car returns 32 MPG while the turbo version returns 29MOG (combined figures used).

Same thing with the Mazda3/Mazdaspeed3. 2.3L engine..25MPG for NA, 21MPG for turbo.

I realize I'm just verifying what you're saying in the article, I'm just saying, apples to apples.

Josh, I see your point, but I suspect your article isn't telling the whole story. I know for a fact that BMW is gradually phasing out its NA engines in favor or turbos because of the fuel efficiency thing. I suspect that, when done right, a turbocharged smaller engine will get better economy than a larger NA engine of the same size.

The new Audi A5 is an example. The 3.0T gets better economy than the V8 but produce about the same power/torque.

The Ecoboost is also true: The Ford Flex SEL with 3.5L NA gets the same fuel economy as the Ecoboost model, but the Ecoboost is considerably more powerful.

Also don't forget that EPA ratings are about what a typical driver would get and not what an enthusiast who always maxes out the engine would get.

Turbos require a love compression ratio that hurts efficiency and mileage. The benefits come when you've good an engine with enough power to run the vast majority of the time without the turbo engaged. The Mini comparison is moot because all that torque makes the car a torque-steering monster(unless you like that sort of thrill) compared to a Civic Si.

@altimadude and blackadder,

Ford's 3.5-liter V6 isn't particularly efficient in the first place, so I'm not sure it's a good N/A benchmark. Having said that, yes, it's true that the EcoBoost 3.5 provides the same fuel economy as the N/A 3.5 while making much more power.

However, the EcoBoost 3.5 doesn't compete against Ford's own N/A 3.5; it competes against naturally aspirated V8s and sixes from Hyundai, Infiniti, etc. And measured against its competition, the fuel economy is not impressive, even though that's supposed to be the point of turbocharging -- comparable performance, better fuel economy.

Similarly, altimadude, the Mini Cooper S's engine doesn't compete against the base Mini's engine; it competes against engines like the Civic Si's, as noted in the post. And that's the one clear case where the "comparable performance, better fuel economy" mantra has serious traction.

Now, Audi's 3.0T is very interesting. Fuel economy's great, and so's performance. However, that engine is *supercharged* (the "T" is pointlessly misleading), and therein lies a mystery, as supercharging is understood to be *less* fuel-efficient than turbocharging, all else being equal. But I was talking about turbocharging in this column, so we'll have to save the 3.0T for another day.

Finally, @blackadder:

"don't forget that EPA ratings are about what a typical driver would get and not what an enthusiast who always maxes out the engine would get."

I didn't. Check item (3) on the list.

-JS

Sorry, guys, I should have said ".....when done right, a turbocharged smaller engine will get better economy than a larger NA engine of the same power/torque output".

Point taken about 3.0T and Item 3 on the list, JS! :-)

@charlesb,

"Turbos require a love compression ratio that hurts efficiency and mileage."

That was true before the advent of direct injection, which enables turbos to run higher compression ratios. The Mini Cooper S, for example, has a 10.5:1 compression ratio. The Acura Integra GS-R, with its high-strung VTEC four and 8,100-rpm redline, actually had a *lower* compression ratio of 10.0:1.

Indeed, even the EcoBoost V6 has a compression ratio of 10.0:1.

All of which adds to the mystery of why these turbo mills aren't doing a better job on the fuel economy front.

-JS

I find it ironic that the one company that has been putting turbos in cars for more than 30 years, appears to be off everyone's list here. The 2.0T 2003 I had got 35 miles to the gallon and plenty of torque. Its bigger brother (2006 sportcombi) has another 50 bhp and gets 26-30 miles to the gallon.

I will admit that the V6 turbo (298 bhp) wasn't as fuel efficient as I thought they could make it.

Anyway, Saab's track record with the turbo shows it can be done.

Why is the FSI or TSI not brought up? It's way more muscular than the N/A engine found in the TSX and nets better fuel economy. It's better than their V6 too and it's nicely efficient in the piggishly heavy 2.0T Quattro Automatic Avant. I think the Fronttrak gets 23/30mpg for 2010.

These comparisons aren't accurate. The Genesis that's 10% smaller, 10% lighter and doesn't have AWD. Take a look at the Lexus LS 460. It's got a little more HP at 380 but its fuel economy is at 16/23/18 or about 10% worse than the MKS. Similarly a Cadillac STS with AWD gets 320 HP and 15/22/17. If you actually compare cars with similar size, the MKS comes out on top versus V8s.

Updated list for my last post:

Audi A8 345 HP 18 MPG Comb
Chrysler 300C 340 HP 18 MPG Comb
Cadillac STS 320 HP 17 MPG Comb
BMW 550i 360 HP 18 MPG Comb (also no AWD)
Lexus 460 380 HP 18 MPG Comb
Pontiac G8 GT 361 HP 18 MPG Comb (also no AWD)

@comp386,

Good points about the Genesis. However, that car is clearly an MKS EcoBoost competitor, and the fact is, it gets about the same fuel economy despite rocking a V8. If Ford wants to impress people with turbocharged fuel economy, perhaps it should put the EcoBoost V6 into something that doesn't weigh 4,400 pounds. That weight kills any significant advantage the turbo motor might otherwise have.

Also, your list is well-taken, but I would question whether buyers at those price points give a hoot about a 10-percent improvement in combined fuel economy (20 for MKS EcoBoost vs. 18 for the others). A debate for another day, I suppose.

Finally, I'd note that the other three comparisons I mentioned are pretty much apples-to-apples in terms of drivetrains and curb weights. So even if you don't like the EcoBoost example, the others stand.

-JS

I had an '03 Saab 9-3 that would get 34mpg on highway trips, yet had tremendous passing power that felt effortless.

Comparable sized regular 4 cylinder cars could maybe match that fuel economy, but not the power by a long shot.