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What blew me away was that the high-end engines[1] turn just a few hundred RPM during a race, which to me seemed ridiculous when you see wall of flames from the

What blew me away was that the high-end engines[1] turn just a few hundred RPM during a race, which to me seemed ridiculous when you see wall of flames from the headers when they release the car at the line. Also how they use aluminum for the connecting rods instead of stronger and stiffer metals like titanium, as they can then act as shock absorbers protecting the crankshaft bearings. Lots of interesting tech to eek out performance and lifetime. I've been enjoying watching Steve Morris's YouTube channel[2], he shares a lot of such information. He's mainly making drag and drive engines, which has the additional constraint of having to survive thousands of miles of regular roads between races. I've also enjoyed Brian Lohnes channel[3] for interesting historical accounts from the early days. [1]: https://en.wikipedia.org/wiki/Top_Fuel#Performance https://en.wikipedia.org/wiki/Top_Fuel#Performance [2]: https://www.youtube.com/@stevemorrisracing/videos https://www.youtube.com/@stevemorrisracing/videos [3]: https://www.youtube.com/@brianlohnes3079/videos https://www.youtube.com/@brianlohnes3079/videos

mjan22640 2y 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
- magicalhippo 2y ago
  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 https://en.wikipedia.org/wiki/Young%27s_modulus [2]: https://www.enginebuildermag.com/2017/03/racing-rods-builders-many-options-choose/ https://www.enginebuildermag.com/2017/03/racing-rods-builder... [3]: https://titanium.com/alloys/titanium-and-titanium-alloys/grade-1-cp-4/ https://titanium.com/alloys/titanium-and-titanium-alloys/gra... [4]: https://titanium.com/alloys/titanium-and-titanium-alloys/ti-grade-5-6al-4v/ https://titanium.com/alloys/titanium-and-titanium-alloys/ti-...
  - mjan22640 2y ago
    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.
    - magicalhippo 2y ago
      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/08-01-2020/balancing-priorities https://www.performanceracing.com/magazine/featured/08-01-20...
hnuser123456 2y ago
From your first link, they turn at around 3800 RPM, but the race only lasts a few seconds so they only complete a few hundred revolutions: "This calculation assumes an average racing engine speed of roughly 3,800 revolutions per minute over a period of 3.8 seconds."
- magicalhippo 2y ago
  Yeah, obviously they don't use a CVT so the RPMs are anything but the same throughout the race. I don't know the details of Top Fuel and such, but Steve with his SMX[1] wagon[2] keeps his car at 2000 RPM at the lights, so seems reasonable to assume Top Fuel is around there too. On the top end the Top Fuel cars are limited to just over 8000 RPM[3], with the red line at 8500 RPM. So an average of 3800 RPM seems reasonable. As a cross check, given that Top Fuel cars are single-speed[4], I guess one could calculate the same using the diameter of the wheels, keeping in mind that the tire expands a lot compared to its size at rest. [1]: https://www.enginebuildermag.com/2024/12/4000-hp-twin-turbo-572-cid-smx-engine/ https://www.enginebuildermag.com/2024/12/4000-hp-twin-turbo-... [2]: https://www.youtube.com/watch?v=LnrZdrp77Cs https://www.youtube.com/watch?v=LnrZdrp77Cs [3]: https://www.enginebuildermag.com/2023/03/top-fuel-and-funny-car-engines/ https://www.enginebuildermag.com/2023/03/top-fuel-and-funny-...

mjan22640 2y 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

magicalhippo 2y ago
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 https://en.wikipedia.org/wiki/Young%27s_modulus [2]: https://www.enginebuildermag.com/2017/03/racing-rods-builders-many-options-choose/ https://www.enginebuildermag.com/2017/03/racing-rods-builder... [3]: https://titanium.com/alloys/titanium-and-titanium-alloys/grade-1-cp-4/ https://titanium.com/alloys/titanium-and-titanium-alloys/gra... [4]: https://titanium.com/alloys/titanium-and-titanium-alloys/ti-grade-5-6al-4v/ https://titanium.com/alloys/titanium-and-titanium-alloys/ti-...
- mjan22640 2y ago
  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.
  - magicalhippo 2y ago
    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/08-01-2020/balancing-priorities https://www.performanceracing.com/magazine/featured/08-01-20...

hnuser123456 2y ago

From your first link, they turn at around 3800 RPM, but the race only lasts a few seconds so they only complete a few hundred revolutions: "This calculation assumes an average racing engine speed of roughly 3,800 revolutions per minute over a period of 3.8 seconds."

magicalhippo 2y ago
Yeah, obviously they don't use a CVT so the RPMs are anything but the same throughout the race. I don't know the details of Top Fuel and such, but Steve with his SMX[1] wagon[2] keeps his car at 2000 RPM at the lights, so seems reasonable to assume Top Fuel is around there too. On the top end the Top Fuel cars are limited to just over 8000 RPM[3], with the red line at 8500 RPM. So an average of 3800 RPM seems reasonable. As a cross check, given that Top Fuel cars are single-speed[4], I guess one could calculate the same using the diameter of the wheels, keeping in mind that the tire expands a lot compared to its size at rest. [1]: https://www.enginebuildermag.com/2024/12/4000-hp-twin-turbo-572-cid-smx-engine/ https://www.enginebuildermag.com/2024/12/4000-hp-twin-turbo-... [2]: https://www.youtube.com/watch?v=LnrZdrp77Cs https://www.youtube.com/watch?v=LnrZdrp77Cs [3]: https://www.enginebuildermag.com/2023/03/top-fuel-and-funny-car-engines/ https://www.enginebuildermag.com/2023/03/top-fuel-and-funny-...