Any noticeable benefit of VHB velocity stack? -- CONCLUSION REACHED

[moto]

    All I have to add is be careful of how far the air cleaner element goes on the stub, if the K&N is on too far it will restrict airflow, kind of a piss poor set up as the filters have to be pushed on quite a bit to clear each other, the single element likely works better than 2 singles.  DonG

This ^^^^ .  according to  ‘The scientific and design and tuning of intake and exhaust systems “ the distance between the opening of the carb and the closed end of the filter should be at least 2.5 times the diameter of the opening . I proved this to myself by putting thin foam over the ends of open stacks. It would run better at less than WOT than at wide open throttle

For a set of VHBs with velocity stacks (either the Loop style of Tonti style) benefit from UNI filters. I used to get a single 8" long sock filter (U08?) and cut open the closed end. With a tube of UNI filter material, you simply slip it over both v-stacks simultaneously. A zip tie or hose clamp can seal it.

You all make good points. "The scientific and design and tuning of intake and exhaust systems" must refer to the book by Phillip H. Smith, which I do not have. I made some measurements from my installation:





The filter's flange sits right at the bottom edge of the 44mm diameter turning of the stack -- any further and there is no proper support to tighten it. Measuring from that edge to the interior of the end of the filter gives 80.6mm. Measuring from the same edge to the end of the stack is 46.5mm. The stack opening is 35.4mm (not the advertised 36mm).

Calculating from those measurements shows the end of the stack is (80.6 - 46.5) = 34.1mm from the end of the filter, a ratio of only 0.96, compared to the 2.5 cited. I don't know the research the value 2.5 was based on, nor whether a simple cylindrical filter was used, nor whether the large offset to one side of this K&N filter would change the conclusions based on a cylindrical filter.

Of course I don't exactly know what result is obtained with the two-inlet K&N or the joined UNI sock filter, but I trust you all know what you found.

All I can say at this point, to rationalize my expenditure of about $130 on the two filters, is that I don't have much use for the very top of the power band where and how I ride. I value power lower down more, so I'll tell myself I'm OK. Maybe at some point I'll stuff a sock on 'em just for fun, if I can figure out a good way to measure power at the top end.

If I lived in Kansas ....   

Moto

P.S. Mike, was it one of these sock filters?




picture uploader

[jhem68]

My 850T has the same set up as your pictured T3 has now and I went to that after having had the K&N's mounted on the carb outlet when I purchased the T some years ago. The original filters were in rough shape and clamped up poorly, so I added the velocity stacks and new K&N filters. Seemed to perform as well as before the change and have never had a problem with having them work loose. I wouldn't know about the changes to top end power even though I live 25 miles closer to Kansas. I was not looking for the performance difference just a better securely fitting filter, and hence lived with the end of the filter being as far from the carb inlet throat as space would allow.

For comparison, my SP has the two velocity stacks into the single K&N and I have no preference for one type over the other.

I have a uni U-801 sock filter that I would have tried, and still might someday, if I was dissatisfied with either K&N set up.
Your well thought out impressions add food for thought for those who may be seeking a similar option. 

[John A]

Space considerations make getting a 2.5x the diameter a difficulty sometimes, I’ve come to the conclusion that theory and practice have to be less ridged so I’d make the distance as long as possible and try it. There are so many variables and I’m going from memory. One of the nice things about the book is he uses a 500cc single cylinder for most of his testing. Another thing he found was that the exhaust box or muffler should be 10X the swept volume of the cylinders. That’s not even done on a lot of stationary engines

[mtiberio]

> P.S. Mike, was it one of these sock filters?

YES, all green, no rubber flange