Omniseed, on 12 October 2016 - 07:56 PM, said:
I notice in the Urbie that it almost seems possible to add engine size without gaining weight because of built-in heat sinks.
The main point is multiples of 25. Every 25 sizes, the engine will gain an internal heatsink.
Another point to keep in mind, which I highlight in My Mech Building Guide is that during the sizes in between the multiples of 25, is it worth it to get an extra heatsink, or an extra couple of Kph? Answering that question can help you make your mind up.