If you make the rest of the rotating assembly & block out of titanium, it might work. But I would think that if only the pistons were titanium, then the pistons will wear out much faster because the wrist pins & cylinder sleeves are an iron-based composition (iron is more dense than titanium).
Just for example, if you take a sapphire and rub it against a diamond, even though the corundum family is pretty tough, the diamonds' crystal structure is much more dense, and will result in a scratched sapphire. They actually take diamond dust, and use it to make cutting wheels for cutting stones.
So, if you take a much denser element and rub it against a less dense element, the likely end result will be the less dense element wearing out much faster than normal.
This is just my opinion. Don't take it as the final word. Some of the more serious engine builders might be able to comment from past experience.
Also, I don't know the thermal properties of titanium. It may not be able to take the constant heat cycles that an engine component is subject to on a daily basis. I do know they use titanium to make the shells on the newer stealth bombers (F-117 specifically); and if a panel breaks, they just can't weld a new piece in like you would with steel. It's a much more complicated process.
Scott
