For those of you in Novi Michigan who pay attention to these things, you may have been hearing about the new direct injection engines and want to learn more about them. Some deliver the power of a V8 with the economy of a V6.

For example, in one family of engines the conventional V6 makes about 250 horsepower. The direct injection version of the same engine makes over 300 horsepower and gets essentially the same gas mileage. The turbocharged version makes over 350 horsepower.

So what are the differences from a conventional engine?

The core difference is in the fuel injection system. The system most vehicles use now is called a port injection system. The fuel injector squirts fuel into a port just outside the cylinder where it's then drawn into the engine with the air.

With a direct injection system, the injector squirts the fuel directly into the cylinder. The gain in power and economy come because fuel injected directly into the cylinder during the combustion cycle is burned much more efficiently.

First, the fuel is squirted in at hundreds of times more pressure, so it's atomized much better and burns cleaner and stronger. The other big advance is in electronics. Faster engine management computers can control the additional precision required to manage direct fuel injection.

Fuel injectors are precision instruments. They have to deliver a precise amount of fuel at exactly the right time. The design of the engine also dictates a particular spray pattern for the fuel. If a fuel injector is dirty or gummed up, it can't do its job as well. That means less power and worse fuel economy for your SUV and can lead to damaged fuel injectors.

Replacing fuel injectors isn't cheap. Direct injection injectors are even more expensive because of the extremely high-pressure they use. Same thing for diesel fuel injectors; we're talking mortgage payment-range to replace a set of diesel injectors.

A professional fuel system cleaning from Sovel's Auto Service gets out the gum and varnish in the whole system, including the fuel injectors. Keep those injectors clean and they'll last a long, long time.

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