Engine secondary explosion strength is random between 1 and 25% of engine power.

Nice graph, were all the engines tested the same tech level? I Doubt it makes a difference because that seems to match up with what I would expect.

Yeah they were all interal fusion confinement drives (I don't remember if that's the exact name, but eh). Power modifiers varied a little, but it doesn't look (at a glance) like any of the points are significantly out of line. Don't feel like doing a hypothesis test, so just going by sight.

Okay so I did it, it's a bit sloppy (like this forum post is going to be, because I accidentally deleted the previous one), but the results seem consistent, so without further ado:

Engine size doesn't matter.
It's linear.
See the following graph (mean explosion damage vs. engine power):



The equation is:
mean explosion damage = 0.12 * EP + 0.81

And the standard deviation is likewise linear (I can pull up a graph if you guys want) and the equation is as follows:
stddev explosion damage = 0.07 * EP - 0.11

Also, as the previous post says, military and commercial engines might be different (I can test if people are curious), but I did all military engines.
I can also put the actual data up here if you guys want, but the means were all calculated from many explosions (between 30 and 336), most significantly more than 30.

Well, searching the forum I found another question about it where they showed a 1500 power top tech level engine had a secondary explosion strength of only 20 or 30... so... I dunno. Unless someone finds the details buried in an arcane mechanics post, or steve shows up we'll need to science this.

I can't find it, but have a suspicion that it's virtually linear with engine size, perhaps with a little randomness.