jhumbo

iTrader: (1)

I went from driving a 3.2L V6 Acura TL (2004) to driving a 2.0L Turbo I4 Kia Optima (2012). Both cars are similar weight and similar power. (The Kia is actually slightly quicker, but doesn't have the low-end torque. The turbo does a nice job of having very little lag, but there's no lag in the V6 of course.) I've been in the Kia for over a year and a half now and while I am very happy with the car overall, I would have preferred if it had a V6 vs. a Turbo-I4. When purchasing I thought to myself, since they don't offer a V6 at least I'll get better gas mileage and still have similar power.

And therein lies the sham. In my Kia I typically get MPGs in the low 30s on long highway trips. Usually somewhere around 31 mpg. Around town it varies a lot but is usually somewhere in the low 20s. The MPG numbers I am getting are almost identical to what I used to get in my TL, if not slightly worse around town.

While it is possible that Kia/Hyundai's 2.0T isn't as efficient as it should be, I now believe that the whole idea that a Turbo4 will give better MPG than an equivalent V6 is just not true.

This article seems to confirm my thoughts:
Do Small Turbo Engine's Really Give Better Gas Mileage

So my question is, since surely carmakers know this, wouldn't they prefer to produce simpler V6 engines than turbos? Or is a turbo less expensive? Why are all the carmakers abandoning bigger engines and jumping onto smaller turbos?

Costco

The answer was in the quote you posted. The EPA ratings are higher with turbocharged 4-cylinders. If multiple models have improved MPGs, the make's overall EPA score goes up.

Packaging is another.

Ken1997TL

Remember, some countries tax engine displacement. So there's that factor...

Which is why a Mustang 2.3 turbo will sell in Europe far better than a 5.0

YeuEmMaiMai

basic rules of thumb

a certain level of HP produced requires X amount of fuel.

Moving A amount of weight requires X amount of fuel

so if you have a turbo 4 that makes 225HP and a 3.2L V6 that makes the same amount of HP when you are going to use similar amounts of fuel to achieve that power. More air requires more fuel

my Subaru makes 165HP and the CL-S makes 290 (headers added) and both cars return similar fuel economy numbers when driving the same route to work
the CL-S weighs in at 200 more lbs and makes 125 MORE hp

My best educated guess is that it takes MORE effort for that 2.5L to move that 3300lbs than it does for that 3.2L to move 3500lbs. I find that I have to keep the Subaru around 2.6K on the tach to get acceptable acceleration vs 2K for the CL-S and getting better acceleration. I really wish that Subaru had a 5th gear because at 75mph that little boxer is turning just under 3K while the CL-S at the same speed is turning 2

I recently drove a NEW (as in less than 6K on the odometer) Subaru Forrester and on the same route to work it returned an average fuel consumption of 28.3mpg vs 24 for the Legacy and 25 for the CL-S

if you want good economy from that small turbo, you got to keep out of the boost as much as possible

YeuEmMaiMai

forgot to add

Marketing also plays a factor "get the power of a V6 with the fuel economy of a I4"

charliemike

I believe that turbos are much more sensitive to aggressive driving than NA motors for some reason. When i am moderate worth the throttle, I get good results. When I'm not, I don't.

Also, city driving seems to be bad for turbos too. Which is why turbo hybrid or stop/start is really helpful.

That said, everyone knows I am a FI whore. I would take that 2.0t over the V6 every time.

I'm not sure about Hyundai/Kia but my guess is that they haven't programmed the powertrain to be as efficient as they could. And your driving habits are not suited for a turbocharged car. They can't be driven identically.

All my $.02 of course.

Saintor

It is just a stupid fashion.

Gimme a larger displacement NA engine anytime.

jhumbo

iTrader: (1)

Interesting point and it makes sense.

Yes, I agree and this seems to be the case with my car. If I really try hard around town I can get better MPG numbers in the high 20s. But it really has to get to the point where you wouldn't know the difference between being in a NA vs Turbo car because you never accelerated hard enough to know which engine was in the car. In which case, why get a Turbo.

My bigger surprise in with highway driving. I do lots of long road trips for work. Cruise control set at 70mph for hundreds of miles. MPG is no different than a V6. But I think this goes back to your first point above.

1StGenCL

While I see both sides here, my company gave me a ecoboost escape, which averages around 25 mpg. I was surprised at how low that was, considering how small the car is mixed with the small engine. Other half has a v6 ford edge and gets similar mileage but MUCH better power and larger car.

wackjum

Conceptually, a turbo engine tries to combine the best of both worlds. Street cars use only a fraction of their engine's power most of the times, like cruising on a highway or coasting. That huge engine is wasteful since it requires a certain amount of fuel for upkeep even when running at such low loads.

On the other hand, everybody likes power for acceleration and passing and that requires high output engines.

In a perfect world, we would have two engines we swap out as needed. But that's not practical. So a turbo engine tries to give you a small engine for that 90% of motoring, and then power when you need it.

A turbo engine will consume fuel faster, and in some cases, much faster than its size might suggest. The trick with a turbo car is to stay off the boost and only keep that turbo around when you need the power. If you are constantly on the boost, you will suffer really bad mileage.

Also, that was the problem with the 1st gen RDX. The car was too heavy for the engine and it required boost all the time just to move at a reasonable speed so mileage was horrible.

charliemike

Once cars go to 48v systems, electric surpercharging is going to change the game and make this all moot IMO.

SamDoe1

Stay off the boost with a small (or even big) turbo engine. If you have a small turbo engine that's a quarter of the size of a larger V8 but still throw 4x as much air into the cylinder, it'll still burn just as much fuel as the larger V8. If you're off the boost, it'll burn much less fuel which is the point.

As was said, the point of a small turbo engine is to gain the fuel efficiency of a small engine while off the boost while gaining the power of a larger engine while on the boost. Trick is to right size the engine such that the car doesn't need to keep the turbo spooled all the way up to run at highway speeds but only provide the assist when needed. This is why the BMW N20 is such a good engine. Big enough to stay off the boost while cruising and in traffic but the turbo is there to provide big engine power when needed.

oonowindoo

Modern Turbo cars when driven incorrectly: will provide better MPG

When driven correctly: you are lucky if you can get low 20s.

if MPG is people's #1 concern, then they should get Chevy Volt, Prius or other traffic blockers.

oonowindoo

i don't know how accurate this is. But i have seen a lot of ppl use this.

http://www.fuelly.com/car/bmw/328i

As you can see there is definitely improvement in MPG with the F30 328 over the previous Gens, whether that is because of the Turbo I4 or 8AT or combination of both, we will never know.

I don't like the idea of I4 turbo to replace V6, because no matter how good the turbo is, it still feels like a 4 banger.

However, if you want to compare I4 vs I4 turbo (TLX 2.4 vs 328) and NA V6 vs. I6/V6 Turbo, i would take the added help from turbo over NA anyday for DD.

RPhilMan1

It all depends on the driver. To each their own.

I get great gas mileage on my 2.0 EcoBoost.

b52bgz

It is very simple math. It takes "X" (energy) to move "Y" (mass) at "Z" (rate). If the powertrain efficiencies are the same and the mass is unchanged, the amount of energy (fuel) required will be the same for a given rate (speed) regardless of engine type.

So the variables are efficiency and mass if you assume the same rate. A vehicle with a 4cyl turbo should have less mass and, therefore, should yield better fuel economy than an NA V6. But additionally, turbocharging generally makes an engine operate more efficiently. So, again, less fuel required for the same rate.

DAYTA

IMO, the engine is only half of the equation. Gearing and the transmission itself has alot to do with fuel economy as well.

These days, car makers are producing 8-speed transmissions regularly. For city driving, this will help a turbo I-4 transfer it's power to the wheels more efficiently and at a lower RPM than a comparable V6. For highway driving, like others have said as long as you stay out of boost, an I-4 should be more efficient than a V6. In both scenarios, you should theoretically save fuel.

I say "theoretically" because I have a EA888 turbo I-4 in my VW Tiguan and I get terrible gas mileage because I often drive like an a-hole .

cjTL

iTrader: (2)

I've wondered the same since I got my Fusion.

Didn't buy it for fuel economy though so whatever.

charliemike

Volvo has an eight speed auto for their 240hp T5 turbo-4. Gets about 37 mpg on the highway.l

Rockstar21

iTrader: (1)

gimme the turbo, I can up the boost and forget what mpg is.

if I want mpg, i'll get an 95 civic hatch with the 1.5 and roll up windows getting 40+ mpg.

SamDoe1

Yes, because the 8 speed is capable of keeping the engine off boost unless needed. Transmissions with less gears need to rev higher to keep moving. more gears, less revs, better mpg.