It seems like the 916 exhaust system is sized for a little more power than a stock 916 makes.(888s can make almost 100 HP with a much smaller pipe.

Testing with an Arrow 'intermediate' system, (it replaces the cross-over and pre-mufflers, as well as the mufflers) has shown a result more like what is commonly expected. (Improvements!)

First, testing a set of Termignoni slip-ons, before and after, and subsequent cam timing and chip changes.

The next chart shows a back-to-back test between a stock 851 head pipe and a 'Farne' pipe (50mm) from a Roche Replica/SP2/3

It appears from the preceding results that the 916 likes a little back pressure.

The results of a more recent test with an Arrow intermediate system, tell a different story.

The 'drop-on' test used a different chip for WOT fuel, but the same ignition curve.

With the huge variation in 'out-of-the-box' cam timing one can expect a large variation in results with a drop-on only.

The greatest improvement comes with arranging for both cylinders to be on the 'same page', or working together, (the red trace.)