I’d love to jump on here, but there was some really good info posted on page 1 of this thread that covered most anything you could ask about this topic. I would add that because rod length does affect the “time” that the piston rests at TDC, the choice of rod length gives you choices on valve events when building a camshaft for a given combo. We always considered rod length choice when building a camshaft for R&D stuff. It’s a viable factor that could help one find a few HP, and at the CUP level, a few HP was big. We evaluated in testing, rod lengths from 5.5” up to 6.5” and found that there’s not a lot to gain from a power perspective, but longevity via friction (heat) came into play in big ways. We often selected the longer rod end of the spectrum because friction and heat mattered in a 500 mile endurance package. We also adjusted the primary lengths of our headers according to rod length, and found a couple HP. We were the first to use inconel tubing in headers and found power there also vs. stainless steel.
Now…in my own circle track stuff that I ran on short tracks where the main event was usually 50 laps, we found power (torque) with a shorter rod due to piston speed in our limited engine package. Again playing with valve events to go along with the short rod was key. Friction and heat wasn’t a prevalent issue for a 50 lap race to me.