Would it really be plausible to install Klingon engines on the distinctly Romulan BoP design, though? Especially without changing a bit about the exterior appearance of the vessel?
When the Germans gave the Japanese modern inline engines, the Japanese had to design all-new aircraft for them... And never mind jet engine technology!
Sorry, I'm not following this. The question was about speed in "Balance of Terror" vs. "The Enterprise Incident". In TEI, they were using Klingon ships, presumably with Klingon engines, as GSchnitzer
said. I don't think anyone suggested retrofitting Klingon engines into the BoP... presumably the BoP would still have the same speed deficiencies vs. the Constitution
class in the TEI timeframe that they did during BoT.