Why Small Turbo Engines Are Not Efficient

Why Don't Small Turbo Engines Get Good Gas Mileage? (Real World)

In attempts to improve fuel economy, many companies are choosing to downsize and turbocharge engines. These small turbo engines tout the power of larger engines, but with much better fuel efficiency. You may notice however, your real world fuel economy may not always match up with the EPA numbers provided on the vehicle's monroney sticker.

Why is this? Well while downsized turbos do have many advantages, such as less moving parts, less weight, better packaging, lower frictional losses, and lower pumping losses, once the vehicles start to get into boost, that efficiency can be significantly lower. This video will discuss fuel enrichment and why it's necessary for high boost engines in order for them to run reliably.

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[SpaceCadetJesus]

There's only ONE reason why my turbocharged 4 cylinder gets bad gas mileage....

REASON: It's because my foot's in it so far that the fan is clipping my toenails..

[kosta]

People forget - your right foot is connected to a valve. That valve drains your wallet ;)

[sruijc]

you’re telling me....is that they *ARE efficient*, but idiots keep flooring it while expecting to get 40mpg.

[teop]

My Alfa Giulia has the 2.0 turbo, and if I don't push it, the mileage is amazing.
It really comes down to driver input.

[Kraigmire]

I always looked at turbo'd engines as having the smaller displacement when driven softly and a larger displacement when driven hard. Therefore, you will only get good fuel economy when you drive very easily, but you have the option of way more power when you want it. You just have to sacrifice that fuel economy when you want power. Kind of like cylinder deactivation, only more reliable.

[MartinA-xhck]

A turbo engine is great power when you kick it and eco when you don´t. Its that simple

[tokinGLX]

3:37 "as you floor it" well there is your problem right there. if you want fuel efficiency, why would you ever floor it, n/a or boosted?

[LegacyIvyTerascale]

in short : you're Jeremy Clarkson, or James May

[notmirelnam]

You mean to say that when my engine is making more power, it's also using more fuel? Say it ain't so!

[Explorerman]

All I heard was V8s are more efficient and I should drive my turbo car fast for better mileage. Don't correct me, this is the world I want to live in.

[humanperson]

"You dont want that many cylinders"
*laughs in Italian*

[beenusirimanne]

So short version: you get a small Turbocharged car to drive it sensibly for economy, and to have some power reserved for when you need it.



I own a 2006 Land Rover Discovery 3 with a 2.7 litre diesel V6. On the Motorway doing 70 it happily gets above 37 Mpg, whereas in the city, it drops to around 27. The key is just how much you put your foot down; that thing pulls away hard once the turbo spools up, but then the Mpg goes out the window. Its all down to driver input and how you drive it. A good example of this is the race that Top Gear did with a BMW M3 and a Toyota Prius.

[jaredhoats]

I'm a proud owner of a 2018 Civic Si with the 1.5 L turbo that's pushing 20.6 psi from the factory. I get well over 30mpg under normal circumstances because I don't rev the crap out of it like some people do. They complain the mileage is bad; yeah it's gonna be bad when you're hammering the throttle all the time. These cars were built for the instances where you need power, but most of the time you want to save fuel. They're not supposed to be efficient when you're hammering on them

[panther]

When my Firefly Turbo kicks in around 3000 rpm, it feels like an extra cylinder just started firing. My 3 cylinder, 1 litre suddenly becomes a fire breathing 1300. Hold onto your hats....!!!

[mattdagger]

I’m surprised you didn’t mention the option of higher octane fuels to help reduce knock. Typically the factory turbo cars use a specific type of programming or ecu tuning called “adaptive octane logic” so the computer can tell how high of octane the fuel it’s using is. Most of the factory turbo cars tend to “recommend 91/93 octane” for this reason. Basically it allows you to use 87 if you want but once the adaptive octane logic sees the fuel is crap it can set a lower cap on the engine timing. So let’s say you use 87 octane. The adaptive octane logic may set the limit of the timing to 12 degrees(advanced) well once you throw 93 in the tank and the sensors sample that fuel it will increase the limit of the timing from 12 degrees to lets say 20 degrees (advanced) resulting in more power out of the same calibration all while keeping the engine safe.

[benjaminturpin]

I used to have a modified jetta tdi diesel. That thing was awesome. No matter how hard a drive it. I never really got under 35-40mpg in town. On the highway 50-55 all day long.

[johnferguson]

Not everyone drives at sea level. Turbocharging makes a huge difference when driving at higher altitudes.
For the vast majority of the time, the engine is operating at only a limited throttle opening. Sure, if you smash down on the gas pedal all the time, your fuel mileage will decrease. The advantage of the turbo is that the extra power is there when you need it; entering onto a freeway or climbing steep grades or over-taking slower vehicles.
You must factor in the effect of the intercooler in any discussion on engine efficiency.

[Kristian-ojqy]

Stay out of boost and your gas mileage will be good 🤷🏻‍♂️ (really hard to do sometimes)

[TLS]

Two things:

1) This is not only linked to "small" displacement engines with turbo. It is the same for any *gas* powered engine using a turbo.
2) This is only relevant for gas powered engine. Diesel-turbos is another discussion.

[FlatPlaneCranky]

This makes perfect sense. My 2017 GT Mustang gets 26 mpg on road trips. My Kia Optima gets 28 mpg on the same trip. You can guess which vehicle I prefer when I go!🏎