The secret has been out for years now that MINI and BMW will be introducing a new family if 1.5L three cylinder engines destined for small front wheel drive cars. But would MINI be replacing all four cylinders with equivalent 3 bangers? Our sources are now telling us that looks unlikely for at least the first iteration of the next generation MINI family. Instead we now believe that MINI will likely continue to use an updated version of the four cylinder “Prince” engine for Cooper S and JCW models through at least 2015.

So one new car and two radically different engines. In fact one source has told us that spotting the differences is quite easy – even under the yellow and black swirled camouflage. If you see a MINI prototype with one exhaust pipe it has a three cylinder engine. If it has two in the center, it’s a MCS or JCW with a four.

So what about the 3 cylinders, what should we expect? Read on for the details.

MINI intends on spreading the three cylinders across the MINI One and Cooper models initially. Sources are telling us that power ratings should be slightly higher than the current range on both the three and four cylinder models. But it’s the efficiency gains and the weight losses that are the big story. We’ve been told to not be surprised to see US Spec Cooper achieve upper 40 mpg figures on the highway. Additionally the engines should be measurably lighter and allow for better weight distribution front to rear.

Ultimately we believe that the three cylinder engines will not only make their way to the MCS but also other models as well. For instance don’t be surprised to see the base Cooper Countryman eventually get the ultra efficient power plant in a late cycle update.

Look for the engine to debut in the front wheel drive BMW shown at Paris this September. While it’ll be officially labeled as a concept, it should be very close to production in technology and drivetrain – the very two things the new MINI hatch will be sharing with it when it hits the market in late 2013.