FYI: engine oil and gear box oil is without a doubt different and is not shared on all 4RT's and 300RR's.

1 hour ago, jonnyc21 said:

FYI: engine oil and gear box oil is without a doubt different and is not shared on all 4RT's and 300RR's.

Very true .

Still waiting to be convinced the lack of engine braking is not just smoke and mirrors rather than a clever valve on the crankcase but there is a difference in the 260's

Mine is crankcase is vented to atmosphere as are most 4ts. I have also run alternative ptb and maps so  maybe the electronic solution must be embedded somewhere other than ptb but not sure where or how.

as they used to say on x files - the answer is out there??

2 hours ago, jimmyl said:

... Mine is crankcase is vented to atmosphere as are most 4ts. ...

The pre-2014 4RT crankcase is not directly vented. The only gas path out of the crankcase is through the reed valve into the stator / timing chain case. Once there, gas travels to the head via the timing chain opening and out the breather tube on the valve cover.

So on the piston downstroke the crankcase vents. But on the piston upstroke, the reed valve closes and there is no venting. So as the piston moves up, it starts pulling a vacuum that resists the upstroke.

The 2014 and later 4rt crankcase has a small orifice between the left crankcase half and stator / timing chain case in addition to the reed valve. I haven't had one apart yet, so I haven't seen if the orifice includes a ball check valve or if it's just a simple orifice that flows either way. It's on the 2014 and later parts diagram for the crankcase, Reference # 18, P.N. 90901-NN4-D00 with description ORIFICE #190. If it flows both ways, I'm sure it could be sized such that the downstroke would still build up enough pressure to open the reed valve.

With this configuration, the downstroke is still vented through the reed valve and out the breather tube as above. Some venting may also go through the orifice and combine with the flow to the breather tube. But on the upstroke as the piston starts pulling vacuum, gas can be pulled back on the breather path, through the orifice, and relieve some of the vacuum and resistance on the piston upstroke.

The cam and ECU changes are probably also contributing. How much effect each one has... I have no idea. I'm just bringing up the crankcase difference between the earlier and later engines and how I think that change could affect engine braking.