Following a year of running with a very compact log style exhaust (as pictured) in 2014, Mercedes have now chosen to ditch the concept and go for a more conventional equal lenght exhaust manifold as seen on the 2014 Renault engine.
An obviously different noise coming from the Mercedes powered cars yesterday was followed by a further confirmation from Mercedes' Head of Engines at Brixworth, Andy Cowell that the new Mercedes 2015 power unit, named PU106B, features an 'entirely new exhaust concept'.
Having strolled around in the pitlane at Jerez, I can confirm that at least Lotus is not running with a log style exhaust, but instead a wrapped package of exhaust tubes very similar in size and location to the configuration of the Renault powered cars in 2014. Sadly a picture is missing, but I'm sure visual confirmation will follow.
In 2014, Mercedes already started testing with an equal length exhaust manifold before switching to a log type at the final pre-season test in Bahrain. While that proved to be a good solution, not in the least for packaging reasons, an equal length manifold can provide advantages for the effectiveness of the turbo. As exhaust tuning is a rather complex subject and designing the optimal exhaust layout depends highly on the power requirements for a certain rpm range, it may be that the change is influenced by the reportedly higher revolutions that the new Mercedes is capable of.