LOL Cheat :rotfl:
No... its not really a cheat, because... well, at least in the Grey Wolves eXpansion... the power of the upgrades has been toned down to keep in line with more realisitc performances.
sooo.... that said... if you upgrade the engines on your IID to a man... then, you're pretty much wasting your renown because..... it won't go any quicker than 13 knots. Though it may accelerate just a tad quicker.
In stock game you could consider them a cheat though. Because no way do U-boats go as fast as they did. It wholly depends what mod you are using.