Eric Peters blogs about the auto industry, and provides an insider's perspective on many issues. His blog is worth following, if you aren't already doing so. This morning, he takes on the issue of changing vehicle engine technology for the sake of fuel economy.
It is becoming practice to put undersized engines in oversized vehicles ... Today you pay [for this] in other ways [than just fuel economy].
Power/performance is one way.
The [Mazda] CX-9’s no-longer-available 3.7 liter V6 was much stronger than the turbo 2.5 liter four which replaced it – 273 hp then vs. 225 hp now, a difference of almost 50 hp, which is a difference with a distinction.
Another is stress – and expense.
Undersized engines rely on turbo boost as the replacement for displacement. The theory is that you’ll use less gas when the engine isn’t being turbo-boosted. Which is fine – and true – when the engine is idling and the car isn’t moving.
The reality is that because the engines are too small (and not strong enough on their own) to adequately propel the vehicles they’re tasked with moving, they are on boost almost all the time once they’re not sitting still. The turbo boosts the power to adequate-engine levels, but also results in about the same amount of fuel being used by an engine that is working harder to make it and meanwhile, as a result, its internal parts are subjected to higher stress because of the higher pressure experienced inside a turbo engine.
An engine that isn’t turbocharged sucks air into its cylinder via the vacuum – negative pressure – created by the pistons as they travel downward, inhaling (so to speak) the air that will be mixed with fuel to create the explosion which makes the power to propel the vehicle. A turbocharged engine is force-fed air, which is crammed into its cylinders under positive pressure (boost) which is typically in the range of 18-22 pounds per square inch.
Turbocharged engines can be built with tougher internals, to withstand the additional pressure – but the fact remains they are subjected to higher pressure (and stress) than engines which are not force-fed air. And no matter how tough-built they are, they are built with additional parts – the turbocharger and all its related bits and pieces. This adds certain expense up front – when you buy the car so equipped – and at least possible expense down the road, in the event a problem develops with the turbo and/or any of its related bits and pieces.
There's more at the link.
Another factor that he doesn't mention in this article (but has covered elsewhere) is that the modern, high-efficiency engines are designed and constructed for ease of robotic factory assembly and installation. It's therefore almost impossible for a home mechanic to get at critical parts of them without almost disassembling the entire engine compartment, and/or removing the engine. Even after he does that, without access to a computer and the necessary software, he probably still won't be able to do much more than change the oil and filters. Maintaining your own vehicle has been almost purposely engineered out of them, forcing you to spend a great deal more money taking them to dealership workshops.
We're going to be buying a new (to us) vehicle within a year or so, as soon as our finances permit. I'm not looking forward to the prospect. I prefer to buy used, and pay cash; but nowadays it's hard to be sure just how good a used vehicle is, and how well it's been maintained. Even something so mundane as a cylinder pressure check is no longer nearly as simple as it once was; in fact, the electronic monitoring and control systems on some engines will not allow you to run a compression check, because the necessary fittings must be occupied by a compliant device before the engine will start! That's not a happy prospect.
I'm seriously considering whether to buy a ten- to fifteen-year-old large sedan (something like a Buick LeSabre or a Cadillac Deville) from somewhere like Florida, where they can be had for reasonable prices, and keep it running for another decade or more. I'll have to spend more on maintenance, and perhaps a new engine and/or gearbox at some point, but that'll still be a lot less than paying inflated prices for new or nearly-new vehicles - and it will be maintainable! On the other hand, Miss D. and I aren't getting any younger, and something with more comfort for older bones and less responsive backbones might be worthwhile, even at higher cost and/or more expensive maintenance. It's a dilemma.