Kawasaki has showed a supercharged 4-cylinder engine earlier this year, while the Suzuki Recursion concept is also said to be one of the final steps before the introduction of turbo-charged models. The reason for the turbo’s comeback are the increasingly aggressive CO2 emission regulations in Europe, which are said to soon impose a special carbon tax on bikes.The EU Commission has already envisaged a new legislation which would require motorcycle manufacturers to align to the rest of the automotive industry in providing the CO2 emission figures for their products, thus laying the foundation of the aforementioned carbon tax.With the displacement of bikes being one of the key factors in the CO2 emissions, finding ways to raise or maintain the power output of the engines while lowering the cc figures seems like one solution Honda and possibly more manufacturers will have to consider very seriously in the upcoming years.One of the new Honda turbo engines is said to be derived from the successful architecture of the V4 mill powering the current VFR1200 machine. It will retain the front cylinders, while the turbo charger will occupy the space freed up by removing the rear ones, rumor has it. The new turbo lump would be capable to produce about the same power as the V4, but with only half the displacement.The second engine is rumored to have an 4 in-line architecture, with the cylinders tilted backwards, front intake and the exhaust ports in the rear, and with a compact supercharge mounted close to the crankshaft position. Should we hope to see these prototypes introduced this fall at the 100th EICMA edition? We kind of doubt, but we’re positive it will not be long until they surface, either.Via CMG