Originally Posted by Sporting Wood
From lots of dyno time, the snorkle restricts airflow into the box. Simply taking it off makes a huge difference in top end, this after upsizing mains. In stock condition, the first thing to run out are the mains. Factory mains are still lean even with the snorkle on. I assume the 990R makes its higher top hp numbers from either/ or both more fuel flow through the injectors or higher rev limit, greater displacement...dunno. I have a 950. Simply put, an airbox equipped 950 benefits from a bigger main, its smaller fueling ability being the top end restriction in stock form, a 950 without an airbox benefits far more, as the next restriction caused by the snorkle is eliminated.
In regards to using h2w's kit intended for the prefilter, this would be a total donkey show. That system relies on greater vacuum and less atomization. The airjets will be way off, really way off, and the mains beyond dangerously small and lean. I'd not be at all surprised to see a seized motor as a result! I'm certain Ken has warned against this, repeatedly. Shifting to a tune with greater airflow, less vacuum and better atomization is totally, completely different, and require totally different settings.
Also, the stock needle has to go!
Well, I will report first hand tomorrow when I get to ride my previously H2W jetted SE, with 160/165 mains and obviously the snorkel in place of the prefilter. But various people have reported that the bottom H2W jetting works fine both with CPR as well as pod filters, as long as the mains are correct. Which sounds logical to me since at small throttle openings , the restriction of the filters combined should not make a difference compared to the stock setup.
I still cannot understand why a snorkel that has larger inlet area than the carb inlet can restrict the flow (as far as top power is concerned) it makes no sense to me. I don't dispute anybody's experience, but it is a mystery to me nevertheless.