TURBOCHARGERS: THEORY VS. REALITY

Garrett-turbo

ALL CHARGED UP

It seems that just about every car manufacturer is jumping on the turbocharging bandwagon these days. Even Honda — which has typically resisted turbocharging — is launching its first turbocharged Civic for the 2016 model year.

And why not? Turbocharged engines have been touted as being the Holy Grail of power and efficiency. We constantly hear car companies promising that their turbocharged 4-cylinder engines can provide the power of a V-6 — while still delivering the fuel efficiency of a 4-cylinder.

In other words, we’re being told we can finally have our cake and eat it too. 

But hold on, tiger. Turbocharging isn’t always everything it’s hyped up to be, and some manufacturers do it better than others. Let’s take a look at what turbocharging is and if it’s really automotive engine nirvana.

 

WHAT IS TURBOCHARGING? 

Turbocharging is simply a form of forced induction, which means that the turbo forces more air into the engine. This process allows the engine to also burn more fuel. And more air + more fuel = greater combustion.

Of course, in a car engine, greater combustion translates to more POWER. In case you didn’t know, your car’s engine is like a miniature Fourth of July celebration inside every time you start it up.

turbo-parts

 

HOW DOES TURBOCHARGING WORK?

In the simplest of terms, a turbocharger uses the exhaust gases coming out of the car’s engine to spin a turbine inside the turbo. This turbine is the mechanism that forces more fresh air into the engine.

Basically, think of yourself as the engine, and a leaf blower as the turbo. Now, imagine putting your mouth over the nozzle of the leaf blower as you turn it on, and think about how much more air you could take in on your next morning jog (obviously, do NOT try this).

The point is, the leaf blower would forcefully ram more air into your lungs in the same way a turbo would ram more air into a car engine. And as we’ve already mentioned, where we have more air, we can also create more power.

 

WHAT ARE THE PROS?

Power, first and foremost. You can get a much smaller engine to produce the power of a larger one. For example, the 2012 BMW 3-Series has a 2.0-liter turbocharged 4-cylinder engine, and puts out 240-hp and 255 lb ft of torque. Compare that to the previous generation 3-Series, which had a larger, naturally aspirated (non-turbo) 3.0-liter 6-cylinder engine which put out 230-hp and 200 lb ft of torque.

BMW’s 2.0-liter turbocharged engine also gets considerably better fuel economy than the V-6 (not surprising considering it uses two fewer cylinders). Oh yeah, did I mention that BMW’s turbo four is also faster from 0 – 60 mph as well? It’s obvious why manufacturers have fallen in love with turbos. Maybe you’re thinking, “Sounds great! I want to slap a turbocharger on my car right now!” and “Why aren’t all cars turbocharged?”

 

WHAT ARE THE CONS?

Well, I’ll tell you why. Like many things in life, what looks great on paper doesn’t always translate in the real world. Remember how we mentioned that a turbo is powered by the car’s exhaust gases? Well, think about how much exhaust is coming out of your car’s engine when you’re idling at a stoplight. Not very much, right?

Without much exhaust gas, there’s very little energy to power the turbo at lower speeds. This has the effect of producing something known as “turbo lag” — the delay between when you step on the pedal to when the car begins to accelerate.

This can be especially frustrating when you’re trying to pull out at an intersection and you floor it, only to have your car respond, “I’ll get going when I’m good and ready, dammit.” Meanwhile, you’re bracing as an oncoming car is trying to put its nose into the rear end of yours.

While manufacturers have come a long way in reducing turbo lag (and these types of sphincter-tightening situations) with variable-flow turbos, twin-scroll turbos, etc., current technology still has yet to completely remedy this problem.

Some of you are thinking, “But I’ve read reviews that said turbo lag didn’t exist on my car.” To which I can only say this: If anyone tells you a turbo doesn’t have turbo lag, they don’t know how a turbo works.

“But hold on,” you say, “my car says it produces peak torque as low as 1,500 rpm! Isn’t that much lower than most engines?” Yes, most turbocharged engines do produce peak torque at very low rpms. But most engines typically idle around 500 – 600 rpm. That means there’s still about 1,000 rpm to go before peak torque is achieved in many cases.

 

A CASE STUDY

Case in point, my parents used to own a 2000 Ford Expedition (they tow trailers, so…). It had a 5.4-liter V-8 engine that put out 260-hp and 350 lb ft of torque. It was a great engine — incredibly torquey and responsive, if a little coarse sounding.

2002_Ford_Expedition

I can’t count how many times I would peel out at stoplights (OK, most of the time it was intentional). It had enough low-end grunt that passengers would be pressed into their seats at the slightest prod of the throttle, which I must say, brought me a slight sadistic pleasure. This old Expo made most of the cars I drove afterwards feel pretty slow.

Well, the time came to replace the Expedition, so naturally my parents wanted something bigger. “What? They don’t make anything bigger? OK, we’ll get another Expedition.” Then we saw something interesting. The 2015 Expedition only had one engine option: Ford’s much-touted EcoBoost V-6.

800px-Frontendcutright

My dad was hesitant at first, but when we looked at the specs we were impressed to find this new engine put out over 365-hp and a whopping 420 lb ft of torque. That’s over 100 more horsepower and 70 lb ft more torque. On top of that, it was connected to a 6-speed automatic, versus the old 4-speed in our last Expedition.

I thought to myself, “This thing should be able to pull a tree trunk out of the ground on the first try!” Or at least rip a stilt out from under a house like Mel Gibson did in Lethal Weapon.

So I called up our local Ford dealer and set up a test drive. I was pretty excited — the last review I read in Motor Trend had this behemoth doing 0 – 60 mph in only 6.5 seconds! That’s comparable to a lot of sport sedans and pocket rockets. I inserted the key (still no keyless access, Ford?) and drove the car around until the engine had a chance to warm up. Then, I did what the juvenile in all of us like to do: I found a deserted road, came to a complete stop and floored it.

But that thrust that I was expecting — that feeling of being pressed into the seat — never happened. Compared to the old Expo, the new one felt like we had small car in tow under acceleration.

Did we unknowingly back into a Focus at the dealership and now its bludgeoned body was somehow being dragged from the Expo’s tow hitch?

But after a second or two, that thought went away as the Expo woke up, almost as if to say, “Oh, so you did mean to floor it after all.” Once we were up past 20 mph or so, the new Expo picked up speed quite nicely. In fact, it’s almost two seconds faster to 60 mph than the old Expo (at least on paper). Its passing power on the highway was also enthusiastic.

But I have to say, I still came away disappointed. Where did that 420 lb ft of torque go? How is it that a 15-year-old SUV — with 100 less horsepower, 70 lb ft less torque and 2 fewer gears — could be so much faster off the line? Well, I already knew the answer: turbo lag.

OK, so it’s off-the-line performance was a let down. At least the fuel economy should be noticeably better, right? After all, there must be a reason why they put the “eco” in the EcoBoost name. Since the engine and transmission were so different in my parents’ old Expo compared to the new one, I looked up the specs on a 2007 Ford Expedition equipped virtually the same way (minus the engine, of course).

'15_Ford_Expedition_EL_--_Front

According to the EPA, the 2007 Ford Expedition 4×4 with a 5.4-liter V8 had a rating of 12 city/18 highway. The new Expedition comparably equipped with the EcoBoost V-6 has a rating of 14 city/20 highway, which is only two mpg better in city/highway driving. But in real-world testing by Consumer Reports, the 2015 Expedition with the EcoBoost V-6 only delivered 1 mpg better overall compared to the 2007 V-8 model and fell short of its highway rating — an area where most cars tend to do better.

So while I don’t doubt that the new EcoBoost engine in my parents’ new Expo produces the power it claims, I can’t say it delivers a better driving experience. Even though it’s faster from 0 – 60 mph, it’s noticeably slower off the line, lacking the old V-8’s grunt, and it doesn’t get much better fuel economy.

 

SO WHAT’S YOUR POINT?

My point is this. Turbochargers are here to stay. They’re a fantastic way to get more power out of a smaller engine. But like most things in life, turbos have limitations, and it’s good to know what those are upfront. That power boost you’re expecting may not be delivered the way you expect it to be (which can take some getting used to at lower speeds). And while many turbocharged engines do indeed help reduce fuel usage compared to some larger engines, not all manufacturers follow through on this promise.

There are also other complexities you may have to face with turbos, such as additional maintenance on some cars, including the tendency for some turbocharged engines to use more oil.

Back to our previous comparison, despite the performance advantages of BMW’s 2.0-liter turbocharged 4-cylinder engine on paper, given the choice, I’d still take the old 3.0-liter inline 6-cylinder. Not because the 2.0-liter is a bad engine, because overall it’s pretty great.

But if you’ve driven a BMW with the old 3.0-liter 6-cylinder, you’ll know why I feel the way I do. Even though the old inline 6-cylinder produces less power and is a tad slower, it’s much more rewarding to drive. Its responses are more immediate; its power delivery is more linear; its operation is smoother and it just sounds better. It’s why I’m still a huge fan of naturally aspirated engines.

As of the writing of this post, I have a supercharged S4 (we’ll go into supercharging in another post). And while I LOVE this engine — it’s one of the best engines out there, in my humble opinion — I can’t help but lust after an RS5 for some of the reasons we just covered. Not to mention the RS5 has a V-8 with an intoxicating 8,250 rpm redline.

RS5 e-turbo

Of course, I eagerly await the electric turbo that Audi debuted in the RS5 TDI. That could totally change my mind on turbos. But until then, I’ll enjoy driving my supercharged S4, and continue to get giddy when I get the chance to ride in my friend’s RS5. Maybe she’ll even let me drive it.

 

UPDATE: Only helping further drive the point home, the fantastic Csaba Csere from Car and Driver posted this in a September 2015 article on Porsche’s new turbocharged engines, stating that:

“What we still don’t know is how strong the throttle response will be at low revs. The dirty little secret of turbocharged engines is that, while they develop lots of low-rpm torque, they don’t necessarily produce it as soon as you squeeze the accelerator.

Under intense questioning, one of the Porsche engineers admitted that at 1800 rpm, the engine needs three full seconds to produce full torque from a closed throttle, though he was quick to add that the turbo lag dropped to two seconds at 2000 rpm and only one second at 2300.”

http://blog.caranddriver.com/tech-dive-in-depth-with-the-new-porsche-911-carreras-twin-turbo-flat-six/

I rest my case.

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