I'm unsure if this is a bug or if it is intended, but Infernal Engines is not giving my base burn 7 ship +2 burn at max rank. The Infernal Engines upgrade at level 10 increases burn by 30%. 130% of 7 is 9.1. However, in-game lists the bonus at +1, giving a total of 8 burn instead of 9.
Okay, while I was typing this, I did some more testing. Is the actual burn bonus of the Infernal Engine 2% per level instead of the displayed 3%? On an 8 burn ship, upgrading it to level 4 Infernal Engines has the fleet window show the burn speed as 9, but it has no parentheses bonus displayed (no bonus makes sense, as at level 4, the burn speed should be 8.96). Upon exiting all menus and going back to the main screen, checking the fleet viewer shows the burn speed has returned to 8. However, at level 5, when the bonus should push the burn speed to 9.2, the same issue occurs. It isn't until level 7 (9.44) that the ship gains the (+1) display and the 9 burn speed becomes active. All other stats related to the positive and negative bonuses for Infernal Engines appear to be working correctly, at least according to the stats page. So it's either some weird bug that doesn't seem to be an issue for the other stats, or it's only a 2% increase per level. this makes sense as the 7 speed ship would not reach 9 speed at level 10, and the 8 speed ship would hit 8.96 at level 6 and 9.12 at level 7 going by 2% per level.