K&N filters for flatslides

[Gammaboy]

On 8/7/2018 at 9:23 AM, arnout said:

Bell mouths is a variable not yet well addressed in comparing K&N cotton-mesh and RamAir foam filters. Perhaps the absence of bell-mouths/stacks with running K&N filters contributes to the poor part throttle response behavior now attributed to the closed end cap ? 

 

I think I'm probably the one who's pointed the finger at the closed end cap.

Back story - I was running K&N style filters made by Vance and Hines - these had a quite good bellmouth moulded into them - I'm not sure if the same shape filters from K&N have the same, never having had a set. The bellmouth was however quite short, and a tighter radius than the ones Mikuni supply for RS series carbs. Carbs were set up as good as I could manage. Anyway, I swapped from the V&H K&N style filters to the shortest Mikuni bellmouths combined with these Ramair  filters:

Immediately upon starting the bike, i noticed less pulsing of the carbs/carb rubbers at idle, and the thing flat out seemed to carburette better all through the rev range and at all openings - more than could be attributed to the different filter flow, or the different bellmouth radius, so I suspected that what I was seeing was due to a reflected pulse off the flat plate not being there with the ramairs (With the V&H filters it had a real 2-stroke like kick in the rev range, was smoother with the later setup).

Some time later I moved to longer bellmouths (Mikuni's "55mm" units), and saw a slight loss of topend, and a large improvement in mid range (may not actually be a loss of topend, just felt less topendy because the midranges was so much better) - if I still had the V&Hs it would be interesting to back to back it across the 3 setups. Either way, it performs waaaaaaaaaaaaay better with the 55mm bellmouths and ram airs than it did with the V&H/K&N filters.

 

[vizman]

i run ape filters on our 36's (1216oilboiler+1135efe).....but i have a set of bellmouths that at a later date i might mix with foam filters and see if i can notice any change.

[Dorkburger]

This has been an interesting thread. As a free experiment, I had a go with pulling off my K&N oval pods and taking a ride with the old rubber airbox snorkels. (Open, no filter) Bike is stock internally,  Yoshimura 4-1 exhaust, original 36mm CV carbs with a K&N jet kit installed. 

I was surprised at the difference. Smoother all around, better acceleration from cruising speeds,  and less throttle opening needed at highway speed. It even seemed to idle better.  

Live and learn...

[Fjbj40]

I am playing with this idea, what you guys think?

 

KN pod with the Suzuki airbox rubber velocity stack.

gonna give it a run and see if it makes an improvement

 

Edited September 9, 2018 by Fjbj40

[coombehouse]

I have done similar but I used the rubbers with Ramair foam filter socks over them rather than k & n's. As has been said the solid end of the k & n seems to cause some sort resonance which messes with fueling. Will be interesting to see what happens if you compare this to how it runs with just the rubber trumpet & no k & n.

[nlovien]

I suspect part of the reason the short filters with back plates cause issues is because the back plate is too close to the carb - you might try fitting a venturi extension then the K&N's - i.e. there could be a bit of early mid range tuning benifit to keeping these type of filters but at a longer length from the carb

[Dorkburger]

I have no room for extensions on the 1150. The outer pods nearly touch the frame as is.

I like the idea of the socks over the trumpets,  but have some concerns about the issues noted earlier of the oiled filters causing problems in the rain.  

[coombehouse]

Oiled filters in the rain are pretty much the same whether they are foam or cotton. Neither are as good as an o.e. filter tucked away in an airbox but it's all about compromises.

[Blubber]

Plus...On the 1150 the side panels cover the pods 

[arnout]

20 hours ago, Fjbj40 said:

I am playing with this idea, what you guys think?

Very good. In fact, I had the same idea..

Sadly though -as Dorkburger also reported- there was not enough room on my Kat to fit these. Also the rubbers had shrunk which would've made it difficult to attach them to the flatslides anyway.. Using different rubbers (shorter and closer fitting into the pods) it might still work.

I tend to agree with Gammaboys revised take on the K&N pod filters stating that the closed back flange is of far less importance than the use of stacks/bellmouths. Which is why adding rubber  stacks to K&N pods seems like a good idea. Finding stacks that wil make everything fit is the difficult bit.

Edited September 10, 2018 by arnout
spelling correction

[Dorkburger]

Yea, makes sense about wet cotton / wet foam, and yes the 1150 hides then nicely. 

I can personally attest to the fact that pods are fine in the rain. I was recently caught in an absolute deluge on the highway with no safe spots to pull over.   About 45 minutes to an hour I rode in it. Other  then pools of water in my boots and the tell tale sign of a proper soaking - wet nuts - everything was fine and no bike issues.