this is kind of strage , do you mean your ship's speed gets effected although you have installed the "Engine Booster" on a different ship ?
I'd be very surprised if it's a problem of the script
To be more precise, a ship that has no Engine Booster installed in it cannot fly faster that its speed limit, that is, it has no speed boost. However, while flying at the maximum speed, such a speed gets reduced to one fourth when I do some quick turns. In particular, it happened to me in the Xenon K when turning up and down, but not when turning left and right. Other ships, like the Perseus, also had the same problem. I did not try with every ship I own.
Right now, I fixed the problem by restarting the game, loading the only save game I had from a time before installing the script, and later loading the last save game. I did not use the engine booster again, just in case the problem arises once again. But I can try to reproduce the problem if you are interested on it.
Thanks
Jose