Starfleet Jedi

What's the size of the Executor power generator, from both purist and EU databases?

We'll assume the Executor to be 17.6 km long.

Edited for "correct" lenght.

You know, that's a very good question, and there is almost nothing I know of in any of the EU or other so-called "offical" sources out there. In fact, I know of no offical cutaway drawings or blueprints, ala ICS or the Shane Johnson technical material.
-Mike

For example, here's what the ICS shows about the Venator class.

Yes, but again, there is nothing like this for the SSDs in any of the ICS or other technical SW material. With the inclusion of all kinds of starfighters and other ships and vehicles in the ICS compilation, you would think that the SSD would have been added in there. However, that is not the case as far as I know.
-Mike

Indeed. A pity.
Here's an ICS shot of an ISD.

There's one main reactor, and apparently two subsidiary reactors, one on each side, plus two backup engines reactors as well.

Fiddling with the ICS shot, I found that the lenght of the main reactor is about 207 meters long.
The width of a subsidiary reactor is 74 meters.

These are respectively 12.93 % and 4.62 % of an ISD's lenght (1.6 km).

Applied to an Executor, if we can scale it up, this would give us a main reactor roughly 2,276 meters long.

The most interesting part is when you compare these figures to my estimation of the DSII's core, which is said to power everything.

This core had its upside down hemisphere core being something like 510-520 meters wide, while the whole chamber is approximatively 6 to 7 times wider, ergo an average width of 3,347.5 meters.

This is quite interesting in terms of reactor volumetrics, and power generation.