Does incorporating a turbocharger in an otherwise standard internal combustion automobile engine improve, reduce or have no impact on gas mileage?
I think it should improve overall performance, which I interpret to mean more power, but there’s no such thing as a free lunch, so I assume that mileage suffers as a result.
And does having a gas versus diesel engine make any difference?
Turbochargers work by forcing more air into the system. Since a specific fuel/air ratio is needed, more air means more fuel.
Depends on how you look at it. A turbocharged 4-cylinder will have poorer mileage than a normally-aspirated 4-cylinder of the same displacement, but better mileage than a larger displacement engine offering similar performance. It’s a way to improve CAFE numbers without alienating gearheads/enthusiasts, especially since they’re easy to tune for more power.
Let’s say that you have a turbocharged 4 cylinder and a naturally aspirated V-8. The both put out the same horsepower. The 4 cylinder will weigh less and therefore the chassis, brakes, and other parts of the car can weigh less. The 4-cylinder will have fewer moving parts and therefore have less friction. So the turbo 4 cylinder should get better mileage.
In Theory. But reality has a way of slapping theory up the side of the head.
I think the biggest problem still comes down to the “Foot - Brain” interface. I seemed to have my foot to the floor quite a bit when driving a turbocharged car!
One of the problems with small-turbo/big naturally-aspirated comparisons is that smaller engines produce less torque, which is the real measure of performance in any style of driving that depends on acceleration. What’s called road horsepower or sustained horsepower - the amount of power needed to keep a vehicle moving at some steady speed - can be surprisingly low. You could put a 20HP engine in almost any car and drive at 80-100 MPH all day… but it would take you damned near all day to get to that speed.
So if you have a blown 4-banger that puts out 150HP and 140 foot-pounds of torque, and a small V8 that puts out 150HP and 200fpt, the V8 is going to blow the doors off the 4-banger in any kind of acceleration comparison. Both will have about the same top-end speed, but the 4 will have an edge on mileage.
Since most people spend a lot of time accelerating and gauge car performance by that seat-of-the-pants feel, the trend has been towards bigger engines with copious torque. Which is not always bad for mileage: look at the current Corvette, which has world-class 0-60, quarter-mile and top-speed capabilities, but gets 18-20 mpg in normal driving.
All that said, I think the trend will be to smaller and smaller engines, using all the technology that’s been developed in the last 20 years to squeeze enormous power-to-displacement ratios out of bigger engines. Instead of 5-6 liter 400+ HP engines, we’ll start seeing 1-2 liter, 150HP mills in smaller vehicles.
A turbocharger reclaims some of the exhaust gas energy that is otherwise lost in NA cars, and uses it to push more air into the engine.
In theory that could offset some of the intake pumping losses and increase overall engine efficiency.
Turbos are widely, and mostly correctly, seen as a “free ride” - capturing wasted energy and using it to improve engine operation. (Not so superchargers, which use crank horsepower to generate greater efficiency.) The question is what you use that improved efficiency for - to boost horsepower, which means mileage will be reduced, or to reduce engine size for a given application, which means mileage will be increased.
A turbocharger means an engine has higher performance. Any layman can learn that from simple arithmetic using numbers found in every April issue of Consumer Reports. Horsepower divided by liters. A minimal fuel injected engine should do at least 70 Hp/liter. A turbo charged engine should do at least 85 Hp/liter.
Turbocharge so that an engine can be so much smaller. A car only needs maybe 4 Hp most of the time to maintain a constant speed. Today’s engines are so grossly oversized to provide maybe 80+ Hp during rare events (ie accelerating, climbing hills). Trick is to make an engine that outputs less Hp more efficiently most of the time. And can output much more Hp during those rarer events. IOW it adapts better to changing loads.
A turbocharger is one solution. That engine will have sufficient Hp for those rare events. And can be much smaller for times when cruising only needs few Hp. Then gas mileage also increases.
So yes, if properly implemented, a turbocharge can result in higher gas mileage. Unfortunately, too many want a turbocharger on the same oversized engine. Then no useful advantage exist.
Turbos can and usually do get better MPG. The reason is that you are not always “boosting” and you have no need to “boost” at a constant speed, like 60 MPH. So, in theory, you could have a smaller engine that will boost when you need it and then not while on the highway. Giving you an engine which has a higher power capability and better MPG.
But, that engine system is obviously more complex and you have more parts and more electronics associated with it. So, to make a reliable daily-driver that can last years might cost more than the benefit it provides.
I’m not sure I can call you wrong since you did throw in “mostly” but they aren’t quite a free ride since they increase back pressure in the exhaust and increase intake air temperatures even though an intercooler can help with that. I will agree though that there’s less drag than from a supercharger and since it doesn’t do much at cruise, is more efficient than a larger engine with the same peak power. Keep in mind also that street cars with superchargers have a bypass so they cause little drag when cruising as well.
Another example of a point made previously. A typical low performance engine is poor at adapting to changing loads. To solve that problem, make it bigger; add more pistons. Since gasoline even at $8 per gallon is so cheap.
A supercharger upgrades a tiny engine that generate little power most of the time. And more power only when needed. Most of the time, engines don’t need all that power. But a typical low performance engine is made two or three times larger. To burn much more energy constantly when so little is needed. In part, because gasoline is so cheap.
Some will turbo charge a 5 liter engine to be more of a man. A supercharged 4 cylinder engine can generate almost as much horsepower - and also have gas mileage similar to other 4 cylinder engines.
Why do that when gasoline is so cheap? Supercharging increases the auto’s cost. Many consumers do not grasp advantages. Only know what their peers have told them to believe. For example, many think supercharging is only for Indy race cars. Well maybe. But even Indy cars no longer use obsolete technology V-8 engines.
I hardly think so. As they say, there’s no replacement for displacement. Last I checked, Mustang Cobras with their 5.4 liter supercharged engines were putting out around 500 hp. You’d have to do a hell of a lot of modding to get that from a 2 liter I-4, modding that you could just do to the 5.4 and get 900 hp.
I’m guessing Indycars, like Formula One cars, have strict guidelines on the engines in them. Less strict are top fuel dragsters with their V-8 engines putting out 8,000 hp. I’d like to see an I-4 throw down that kind of power.
If you want a car that gets good fuel economy, handles well, and is quick when it needs to be, a blown I-4 is a good choice. If power is absolute priority and you couldn’t care less about fuel economy, you’d be a fool not to go with the big block.
Back when I was twisting wrenches for a living, I would see one of two complaints on cars brought in for their first service:
Non turbo cars the complaint was car was too slow
Turbo cars the complaint was poor gas mileage.
That was the difference between 112 naturally aspirated horse power and 162 turbo horse power.
Turbo have the ability to get great gas mileage, but as JerrySTL said the problem is the Foot-brain interface.
From EDN (an engineer’s magazine) of 11 May 2012 entitled “Indy engines still pack a 700-HP punch”:
Better racing circuits pioneer technologies that can appear a few decades later in consumer vehicles. The 70 Hp/liter engine was a 1948 technology in Indy. Would it have been standard in American vehicles after 1975 if bean counters did not stifle innovation in the name of cost controls. Back then, a standard American engine did a paltry 35 Hp/liter.
Today’s race cars demonstrate crude and early versions of what all should expect decades from now. Same Hp from a many times smaller engines. Superior engines (ie Indy engines) mean less displacement. Innovators love that concept. Naysayers or bean counters fear it.
Innovators know same horsepower with higher gas mileage means smaller engines every decade. Companies that, instead, resorted to and created myths about more displacement deserve the bankruptcy created by stifling of innovators (car guys).
A supercharged engine had to do at least 100 Hp/liter. So GM sold supercharged Pontiacs and Buicks in 2003 that had less performance than all Toyota cars with only fuel injected vehicles. And, of course, inferior gas mileage. An engine designed by bean counters.
Meanwhile, Ford replaced bean counter (MBA) designers with car guys (engineers) in 2000. Superior Ford designs started appearing in the market around 2008. A Ford employee carried the block for their newest engine in his checked luggage. Because Ford knows the better engines do same horsepower with much less displacement (and weight). The block could have been lighter. But it was cast iron - obsolete technology. Once refined, that engine will be even lighter - aluminum.
Read it in the NY Times of 8 Mar 2013 in Packing 123 Horsepower Into 3 Cylinders.
Every decade, every engine must do higher gas mileage, smaller displacement, less pollution, and longer life expectancy. That is contrary to what many believe only because GM, Chrysler, and the old Ford management preached myths such as ‘more displacement’.
A smaller engine producing better gas mileage and same horsepower: one old technology solution was a 20% smaller and turbocharged engine.
The car that won the F1 world championship in 1950 (Alfa Romeo 159 Alfetta) was a 1.5 litre with over 400 horsepower.
And how much do these engines cost? Probably more than a top-fuel dragster engine. As I said, four-bangers can be made to make big power but it costs a lot of money and that same money would reap more power from a larger engine. If you have however many hundreds of thousands of dollars to spend on an Indycar engine, go for it. Those who are on a more limited budget and simply want massive power are better off with a large engine. You just can’t spend the same amount of money to make a Honda Civic run 10’s as a fox-body Mustang.
Personally, I’d probably opt for a car with a smaller engine like a Lotus Elise or an RX-8 because I’d rather have a car that accelerates and handles well than one that accelerates very well and handles poorly. But that’s just me; different people want different things out of a car.
Turbochargers have been used for decades on diesel engines to compensate for their negative attributes compared to gasoline engines. Diesel engines without turbocharging are less powerful and less refined than gas engines of similar size. They have more low-speed torque, but lack power in the mid-upper speed range. The addition of a turbocharger results in similar performance to gasoline, but with the benefit of diesel efficiency, durability and low-speed torque.
In the last few years, several automakers have started using smaller gasoline engines with turbochargers in place of larger displacement engines with additional cylinders. Ford is one of the companies relying most heavily on turbo technology.
Ford’s 2.0L EcoBoost (turbocharged) 4-cylinder makes 240hp and 270 lb-ft of torque. It is offered in place of the standard 3.5L V6 as a more fuel-efficient option on the 2013 Ford Taurus, Edge and Explorer (among others). The full-size Taurus with the 2.0L does 0-60mph in 7.0 seconds flat and the Edge 2.0L does the same in 7.6 seconds. Those numbers are only 0.3 slower than the 290hp 3.5L V6. Despite a 50hp drop compared to the 3.5L, the 2.0L makes 17 lb-ft more torque. Peak horsepower and torque ratings are also achieved at 1000rpm lower than the V6. The 2.0L EcoBoost also increases city and highway fuel economy ratings by 3mpg.
I recently had a 2013 Ford Taurus Limited with the 2.0L EcoBoost as a rental car for a week. The power delivery was very smooth and linear, with no turbo lag or flat spots in acceleration. It actually felt just like a good V6 and, after a little while, I forgot that I was driving a 4-cylinder turbo.
I’ll make “mostly” very small there, as turbos are the closest thing to a free ride as you can get. Yes, they have some loading on the overall engine cycle, but at the benefit of boosting engine efficiency enormously.
For one thing, exhaust back pressure is not a completely bad thing; most engines will run like crap if you simply put open pipes on them. A degree of backpressure is assumed, calculated and required for proper F/A flow. If the engine (mostly the cylinder head) is designed for the backpressure curve of a turbo, it’s a nonexistent problem.
I’ve never heard of turbos heating up intake temperatures, other than that they can make underhood temps somewhat higher. Intercoolers are used to reduce intake air temp as much as possible because it’s a simple linear relationship between cooler air and a denser intake charge. If you can knock ten degrees out of the intake air, you have a denser air charge to go with your added fuel charge, and thus more power.
(Yes, the air downstream of a turbo is hotter from compression, but that’s an unavoidable matter; intercoolers simply work to make the best of the way the system works. There are even active, refrigerated intercoolers on some engines that use some small amount of engine HP to drive the cooling system, but at the gain of a great deal more F/A density and thus more HP net.)
ETA: This all assumes a *designed *turbo engine, not simply hanging a twister on an existing NA engine. Everything has to be redesigned to take maximum advantage of the compressed intake charge. You won’t get nearly as much from simply compressing an engine’s intake, as was done in the earliest era of modern turbos (1980-90 or so).
F1 is still limited to 1.5L, if my understanding is correct, and the cars produce insane horsepower for a reason no one has noted here, nor which could realistically be used on street vehicles: RPM. F1 engines turn at 15,000 to 20,000 or more RPM to produce so much power from so little. Indy cars used bigger engines with almost as much RPM to produce their superior power; now that they’re limited in size, the RPMs will go much higher to compensate.
You can’t do that in street engines because of the machining tolerances (expensive), the low durability and the noise.