Alumunum Rods In A Street Engine ?

[olddog]

specific gravity listed in engineering toolbox is
aluminum 2.7
steel ----- 7.8
titanium 4.5

Tensile Modulus - Young's Modulus or Modulus of Elasticity - is a measure of stiffness of an elastic material. It is used to describe the elastic properties of objects like wires, rods or columns when they are stretched or compressed.

Yield strength (you have bent it past the point it will spring back to it original shape).
aluminum 95
steel ----- 345
titanium 730

So we have been loose with terms. Aluminum is not stronger than steel. Steel is stronger, but much heavier. When both materials are made to the same strength level, aluminum is lighter but must be bigger to achieve that. So pound for pound aluminum is stronger than steel. Now fuzzily, I remember, something about, even though two beams , one aluminum the other steel, is at the same yield strength, the aluminum beam will flex more at a given load than the steel beam. I believe the engineer told me that if deflection is the critical factor steel is better.

Titanium is stronger than steel (about twice) and half the weight. It is twice as heavy as aluminum, but 7 times stronger. Lb for lb, titanium is stronger than steel and totally blows aluminum out of the water. The US government didn't spend millions of dollars building aircraft out of titanium in stead of the much cheaper aluminum because they wanted to waste money. It has its advantages.

There are many other factors that must be considered. The experts are saying that because aluminum is more flexible than steel, it can act like a shock absorber in certain critical extreme condition for engine rods, which allow it to not fail where steel rods would fail. I expect kind of like a building too strong to flex will not withstand an earth quake where a less strong, more flexible, building will stand.