Flex engines aren't wildly different from gasoline engines, nor are they space-age technology. The Ford Model T car, for instance, was a flex engine that burned either gas or ethanol.
FFVs don't cost more to build, and they aren't more expensive in terms of sticker price, either. If you really want to, you can even buy a conversion kit that lets you turn your gasoline motor into one that will happily drink E85.
From a chemical perspective, ethanol is different from gas in two major ways. It's more corrosive and conductive. It also burns hotter, so it has a higher octane rating. A flex engine must be built to handle those technical challenges.
For starters, your car has to know what kind of fuel you're pumping. An onboard computer analyzes fuel composition to optimize engine ignition, adhere to emissions standards and regulate combustion. No matter how much the ethanol-to-gas ratio fluctuates, your flex-fuel car can adjust on the fly.
In flexible-fuel vehicles, the fuel tank and in-tank components are built to withstand ethanol's corrosiveness. Similarly, the fuel lines, gaskets, seals and rubber fuel hoses all must be corrosion-resistant, too, as must the fuel injectors.
The same goes for internal engine components. Valve seats, piston rings, valves and other parts are all made from materials that won't easily corrode. These parts are also built to diminish the possibility that damage will result due to ethanol's tendency to break down and clean away engine lubricants.
Conductivity is another concern. All electrical parts of the fuel system, including wiring, must be insulated against ethanol's higher conductivity. In addition, the fuel filler parts have anti-spark features that reduce the chance of stray sparks or static electricity causing a dangerous flare-up.
Electrical worries aside, ethanol has a lower energy density than gasoline, so the engine needs more fuel to achieve high performance. Thus, fuel injectors are created to achieve higher fuel flow rates --otherwise, your engine would see a drastic reduction in overall power.
In terms of engine construction, those are the most notable distinctions in FFV motors. On the next page, you'll read more about flex engine performance and whether making the switch is logical for you.