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by mjan22640 434 days ago
> Also how they use aluminum for the connecting rods instead of stronger and stiffer metals like titanium

The 7000 aluminium alloys are similar to titanium in strenght/weight

1 comments

Yes but they have lower Young's modulus[1] so compress more under the same force. Thus acting as a shock absorber to reduce peak loads on the rod bearings.

Again no expert but from what I can see, high-end aluminum rods can use 7075 aluminum[2], which has a Young's modulus of about 72 GPa, while titanium has a modulus of about 105 and up[3][4], depending on grade.

At least that's my understanding.

[1]: https://en.wikipedia.org/wiki/Young%27s_modulus

[2]: https://www.enginebuildermag.com/2017/03/racing-rods-builder...

[3]: https://titanium.com/alloys/titanium-and-titanium-alloys/gra...

[4]: https://titanium.com/alloys/titanium-and-titanium-alloys/ti-...

An aluminium part with 105/72 cross section of the titanium will have the same modulus and incidentally the same weight.

Aluminium is also significantly cheaper, and easier to machine.

Titanium (or high strength steel, which is the strongest both per area and per weight and also the most expensive and difficult to machine) would be used where the volume of the part would be a concern.

Perhaps I misremembered. Seems difficult to find some written sources on this.

In my quest I stumbled upon this[1] article where they discuss composite connecting rods for Fop Fuel dragsters:

Designed for Top Fuel engines, this connecting rod is half the weight of a conventional aluminum rod, yet is projected by company engineers to last an entire season instead of just 12 to 15 races.

Seems they're still at it, perhaps it'll be the next thing?

[1]: https://www.performanceracing.com/magazine/featured/08-01-20...