OMG, it sounds like you need help in the mechanical knowledge area too!
I said the same car d00d, my analogy is sound. Same car means same transmission and differential. Same RPM means same RPM. You can have the throttle open 15 degrees or 40 degrees or whatever, I said same RPM.
This is possible. Think about it a minute. If it still baffels your mind, think about it some more. The V8 would be under low-load, the 4-cylinder under moderate load.
OK, so let me put this in reverse: 1:1 used to be THE ratio for top gear in a manual transmission, before overdrive became the norm, yes I'm talking about the early 70's and before. Now, you have a Pinto, I have a Mustang, you have a 4-cylinder, I have a V8. We're crusing down the highway in top gear, we both have 7.80-14" Coopers on our cars (metric sizes aren't popular in the U.S. yet), we both have a 3.11 rear end. We're both going 60MPH too, and my car is at 2,000 RPM so guess what yours is? Sure, your throttle is open 1/3 and mine is open 1/8, that's beside the point.
I once had an audio amplifier with two transistors on each channel. Those two were in parallel. If you removed one, the other still worked and the music had the same frequencies, but at 3db less volume. And eventually overheated, but that's again beside the point.