What does your combined turn rate show in space (listed on the movement tab on your ship props). The engine is a modification to the base stat, not a reflection of the total bonus.
The mouse-over tooltip stat shows you the Base Turn rate with that engine, it's not modified by skills or other factors except for the [Turn] bonus available on some engines. A base engine (a common one with no bonus stats) indicates what the base turn rate is on the mouse over tooltip.
The base stat for the Orion Patrol Cruiser is set to 6 on the ship, however, the documentation (the starship console) says it should be 7. On engines without a [Turn] bonus, it's showing 6. It's also turning slower than the Kar'Fi, which also has a base turn rate of 7.
My guess is that a last minute design change was made and someone didn't update it. Either they didn't update the documentation for it (the info you get from the Ship info Consoles), or didn't update the actual turn speed for the Patrol Cruiser. I'm hoping of course that it is indeed supposed to be set to 7, but at least fixing the documentation if it was supposed to be set at 6 and a confirmation that the documentation is wrong and not the turn speed would be something.
It was set to 6 on the Tribble server the same time they changed the bonus power (support fighters) to a clickable. I remember testing it and it didn't feel as nimble and fun to fly as it used to after the patch.
When in space though, with at least 25% throttle, my turn rate was 11.2 at 57 Engine Power. However, in the Kar'Fi, which has a base turn rate of 7, I get 13.4 with Engine Power at 52.
If they were both correctly set to the same value of 7, I should actually be at or slightly above the Kar'Fi due to the higher engine power.