So, the discussion was bout the engine running at low RPM to recharge. What I meant to say is that all else being equal, RPM and displacement are related to the power output by similar magnitude. (more of either, more power)So if a similar displacement engine with similar technology goes 200hp at 5,000 RPM, you are not going to get the same power at from similar design engine going 1800 RPM. You would need way more displacement to get the same power.
I attached a 200hp engine chart from a Saab. (random engine chart I found) If you want more power at the same RPM, you are going to need more displacement. Notice how power and RPM have a common slope... That's what I meant. Apologies because the statement was not true as presented, but this was the idea I meant to convey. Just because there are engines that are 200hp at 2000ccs, they won't make much power at low RPMs. That HP rating is for 5800+ RPM. Got to rev it up to get the power.
You guys are talking past each other.
While you are in general correct, a motor will make more HP as it reva up higher, he is also correct that it's all but guaranteed by the way HP is calculated. For HP to not rise with rpm, you need a significant torque drop over that same rise, and at the end of the day, the engine really produces torque, HP is a measurement of the amount of torque created over time in essence.
This all goes out the window with modern vehicles. Turbochargers allow you to make a boatload of torque down low, and more importantly, vary that power output via a wastegate. So while previously you could really only vary output via throttle position and rpm, now I could peg a motor at 2000rpm and vary my boost pressure via an electronic wastegate if I need more or less power. Not only that, but the size of the turbocharger can be specified such that it makes more power at low rpm and cannot keep boost pressures up at higher rpm, resulting in less power.
In reality, I don't know that a turbocharged 4 cylinder is more suited to use in a generator than an NA v6. It's possible that the required torque to spin a generator of the required output is easily matched by a normally aspirated v6. It's been a long time since I took classes of electromagnetic fields, but as I recall the field resistance doesn't go up with speed, so if I'm remembering that right, that means that you could generate more power out of a generator by spinning the generator faster, and as long as you're able to keep the required torque up at that rpm, you're fine.
Obviously, Ramcharger is a first of it's kind, and is certain to have not nailed the efficiencies thing by sheer luck the first go around. I suspect the 3.6 was chosen due to its low cost, plentiful availability, and the fact that it's existing and fairly.compact in the ram engine bay. The next gen Ramcharger will likely have a better motor for this purpose.