They definitely are restrictors and it definitely is restricted to 78 kW. Horrible! Gets weaker over 7k rpm instead of stronger and struggles as redline approaches.
Now that is very intresting thanks for the info as that is good to know and puts a diffrent perspective on things. What you have to remember is that you can't gain on top without loosing somewhere else. Everything is a compromise so you may just find out that you loose a little on the botton end and it may or may not
have an effect on intake reversion depending on if my theory is right or wrong. Saying that I quite fancy going the other way and installing them as I have never had them
I can always do with more bottom end
See the following link for more info on reversion and note that
Reversion refers to the movement of exhaust gases in the reverse direction, backing up through the intake flow path
Which is basically describing what we call a carb fart. So hopfully you can understand how I came to the previous conclusion.
Reversion redirection device for an internal combustion engine
Now this I'm not entirly convinced by but is a theory I have. A lot of folk suffer from carb farts as well as the bike suddenly stalling and often it is said to increase the idle speed. Not the aproach I would take as I see that as masking over the issue but it gets those less mechanically minded out of trouble. If you think about the inlet throat and plates (restrictors), having the half moon shape makes it smaller so in theory this should increase the velocity of the mix which is kind of like the same effect as increasing the idle speed. One can turn up the idle which shoves more mix in or do you give the mix a higher velocity shoving the mix in faster which in turn is pushing against the exhaust gases trying to escape out the wrong valve during overlap.
A reason why I think the restrictors may have been Honda's way to try to eliminate / minimise reversion (carb farts) and possibley the stalling as things spit back.
Another theory but I maybe wrong and it's related to above. It maybe that velocity is not increased and they do act as a restrictor but pausing the flow and the plate being there acts as a barrier to help prevent / minimise any spit back getting past that point and back up through the carbs and airbox. It's all very complex when you start to dig into things like porting. Some folk are happy to smooth off the inlet track and remove the textured surface but that is there to create a Golf Ball affect. The same reason a Golf Ball is pitted. It would be great if somone with an engine flow meter could measure things with and without the restrictor. I wonder if there is anyone on the forum with access to such tools. It would be good to get a true reading of the differances with and without.
The question has to be asked why would Honda restrict later bikes. Yes they are restrictors of sort but for what purpose and how much real world effect does this have. If they wanted a true restrictor they could have done as they did with the Jap bikes and IIRC do it on the ECU side of things which is another reason why I think they serve a purrpose. They may even have changed the mapping slightly to compensate for these restrictors, a slight advancement has said to have been added in later models so no point in a Factory Pro +4 advancer. One things for sure it's cause and affect and when you change one thing it has an affect on another. The question is where.
Let us know your findings. Intresting indeed but if you want more top end oomph then change your cam profiles at the sacrifice of loosing it somewhere else.
That PS measurment is a new one on me.
Though it’s still commonly used by carmakers, PS or Pferdestärke (horse-strength in German) was actually replaced by kW as the EU's ‘legal’ measurement of engine power in 1992.
One PS is about 98.6% of a brake horsepower – the two are virtually interchangeable, and PS is sometimes referred to as 'metric horsepower'.
https://www.which.co.uk/reviews/new-and ... -ps-and-kw