After playing with the engine power numbers myself for a bit, I think that the proposed C# changes are pretty good. In fact, the original numbers are much cleverer than I had realized. The engine power goes up by a steady 26% every time, with a little rounding and the 6.4 and 10 levels skipped. (The fact that the plasma-core tech had engine power 60 instead of 64 was probably just an ancient typo, considering that the 8, 16, and 32 engine power techs existed and were spaced every fourth level just as you'd expect.) Even the research cost is not as arbitrary as it first looked; if the the nuclear thermal level started at 600 research instead of 2500, then doubling at every tech would reproduce the costs of 10 of the 12 levels with just a little rounding. The cost of the first two levels is too high, but if they include the costs of the skipped levels then they're pretty close. (I will note that 6.25 or 6.3 would be better choices than 6.4, because you picked 12.5 later on.)
Desdinova's suggestion to add a couple of extra levels at the low end sounds like it would be a positive change for the conventional start. Putting them at 3.15 and 4 engine power respectively would continue the trend. (Putting the first one at 3.2 requires you to later round 51.2 down to 50!) The question then is how you do the costs; you could just put them at a quarter and a half of the nuclear thermal, or you could shift some of the points down from the first four levels, keeping the cumulative research costs the same. The former probably makes the first level too cheap; there'd probably be no reason to build a ship with a conventional engine when the first engine tech only costs 150 points.
However, the changes Steve proposed already do that too. They bring the cost of the first engine tech down from 2.5k to 1k research, which means that it's 40% of the cost. If you build a conventional ship at the start of a conventional game then it can do useful work while you spend a couple of years researching the first engine tech. That might not actually be the case if that first tech is 40% cheaper. It's almost as if that first tech should have a much higher cost, even though that makes the second and third techs super cheap by comparison and then everyone will skip over them for sure. If the first four techs all cost 2k and got you 3, 4, 5 and 6.3 engine power, then I would expect a multi-faction conventional-start game to have a shorter period where only the largest power was in space, a decent period where everyone was in space with useful engines, but with the some factions having moved up a level, followed by the gap narrowing considerably as everyone was able to build more labs and the smaller factions start to catch up. It essentially slows down progress through the early levels without making the first level extremely cheap. (You could also make tech cheaper for factions colocated with other factions that already have the tech. Or at least do so if the other faction's civilian ships have the tech, since that implies that anyone can just buy an engine and reverse engineer it.)
Whatever happens I'll be happy to get my hands on the game.
