Fazer 600 has a detuned R6 engine

[darrsi]

Think it is more accurate to describe the FZS 600 motor as a RETUNED Thundercat unit & similarly the FZ6 as RETUNED R6 motor.
It made sense for Yamaha to adapt existing engine designs for alternative use (general all-round road rather than pure "sports") since the development costs had already been paid.( Thereby increasing profitability making use of existing jigs/machine tools rather than starting from scratch)
Its not so much differences in clearances between parts inside the motor rather a case of changing things like cam profiles since altering  these has a marked effect on valve timing/duration in turn changing the way in which engines develop their power.
For all round everyday use its more important for the engine to develop its power(torque) lower down the revs scale than in similar sized sports & race bikes where the power can come in at higher rpm.

I'm presuming that's why plenty of people have opted for the one down on the front, and one up on the rear sprockets for a bit more grunt for daily road riding?
I might give that a go next time.