Quote:
Originally Posted by serialk11r
http://www.asminternational.org/cont...81G_Sample.pdf
Interesting read on fatigue. 300M steel seems to have a fatigue limit >4 times higher than aluminum (with 10^8 cycles or so), so in theory 300M rods built to the same strength would be lighter. Damn.
I think for lower rpm street cars the stresses would be low enough and the compressive forces would be comparatively greater so aluminum rods could outlast most of the other engine parts. I think aluminum is probably cheaper than say 300M steel so we might see it in street cars someday.
BTW WoW, the red lettering is quite menacing 
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Serial, if you want to blow your mind on rods, there are currently some dirt-bikes that use an aluminum matrix composite rod. Also it's one-piece and has no bearings.
http://www.ret-monitor.com/articles/...omposite-rods/
Also keep in mind what fatigue is. Repeated loads, over and over again. Then think about how many cycles a con-rod goes through driving over only a half hour. If you look at rods for racing, they are exceptionally well surface-finished as well as fancy metals, and this has to do with fatigue. Any small stress risers will affect the fatigue limit, and then also think of aluminum's relative softness/how easily it will notch on even slight impacts.
And there is also stiffness, (which Old Greg has enlightened be about on numerous occasions) in which aluminum is again inferior to steel. Also why we see the 'H' rather than 'I' pattern cross-section in certain racing rods, more stiffness. In huge HP drag racing where aluminum is most common in rods, the lack of stiffness is actually desirable due to something about how quickly they build power, and the rods bending actually prevents crank failure.