Best Air Filter set up for Split FCRs? Velocity Stacks?

[Kiwihame]

I've just bought some K&N Air filters from Ca-Cycleworks for my split FCRs. I asked them if I needed velocity stacks and the answer was no. (I have the short machined adapters.) However they were kinda vague.

The K&N filters they have sent me are RU-1750s which have a 62mm ID opening. The adapter has a 55mm OD. (See Pic) As you can see this is quite a difference, though within K&N's specification. Tightening up banjo clip it fits but with the flange ballooning out in a cone shape. Re air-flow this could be desirable? I dunno. Though maybe not with an angled flange.

I see other people here have used other K&N filters e.g. RU-1759s (Ron D). This model is no longer listed. And ian996 posted a pic of his setup. (See 2nd pic. Note the much narrower flange width)

Some of you have used the K&N nylon adapter/stacks K&N Velocity Stack Air Filter Adapter - Keihin CR Flat Side Carbs and some of you have used other velocity stacks with filters, though I'm only aware of the TPO Beast stacks, which are very expensive. st2lemans says "you must use stacks as well, pods on the end of the carbs do not work well at all!"

Is that the case? Do I need/should I get velocity stacks? What are the options? Or is my set-up with the RU-1750s the right one?

I'm interested in your experiences with your setup?

Thanks in advance.

[rond944]

I run the RU-1750 setup like your picture on my 750 track bike and it seems OK , but that bike spends it's life between 5K and 8.8K RPM . I'll have to measure the carb opening OD but I don't recall them bulging as you show . I do think Sudco has a different size carb/filter adapter as I had to acquire some when I tried to use some Pipercross filters once. I should still have them around here somewhere . Will look and see if I can find out the size difference for you . I got some of the plastic filter adapters recently and put them on the racked , long manifold FCR's on my street 900 SS and can tell you they work a treat . I can tell no difference between that setup and the old , open top airbox with panel K & N.

My friend /tuner/engine builder has given lectures on intake tuning at the Massachusetts Institute of Technology , and he assures me you need some type of velocity stack arrangement . I intend to try the plastic velocity stack/filter adapters on the split FCR track bike when I get a chance . That might necessitate a change to a shorter filter , but you can slide the RU-1750's down over the opening farther if need be .

[greenmonster]

If your current adadpters look like these below inside you don`t need other adapters/stacks.
Seems like you`ve got the wrong inner diameter on the KN`s.

[jman900]

Originally Posted by greenmonster

If your current adadpters look like these below inside you don`t need other adapters/stacks.
Seems like you`ve got the wrong inner diameter on the KN`s.
I have similar KN pods w on my M900.

Agreed, looks like the I.D. on the K&N's may be too big.

[Kiwihame]

Originally Posted by jman900

Agreed, looks like the I.D. on the K&N's may be too big.

You're (we're) right. Ca-Cycleworks have sent me the wrong filters. I told them I had 54mm adapters theyve sent me ones for 62mm adapters.

Well, lets see what they do now...

[TassieDave]

I have the same RU-1750 K&N filters for my split singles but (it seems) different adapters again. My adapters are similar to those in greenmonster's post but are oval - about 60mm X 65mm. Haven't taken much out of the boxes yet but I've just test fitted the filters to the adapters and the fit well enough. Tight with a very slightly swell as the rubber goes over a lip (0.5mm) on these adapters but nothing like in the OP photos.

All bought from Ca-Cycleworks but at slightly different times. FCR41s were one purchase and the filters and adapters all together in another. All were ordered as they are not on the website.

[Desmospeed]

Greetings:

Although not split, I have 41 FCR's on my bike. I used the velocity stacks since they are more effective at speeding up the air going into the carbs. I took my old K&N panel filter and cut it up to make screens. I doubled up on the screen, laid them at 45 degrees from each other and safety wired them in place. I could have used the cotton cloth sandwiched between the two layers of mesh but it was an afterthought. Hope this helps.

Cheers,
Ricky

[DME3]

Seems like this guy made a carbon airbox for the split FCR's.

[smadden]

Originally Posted by DME3

Seems like this guy made a carbon airbox for the split FCR's.

That's a serious engine. Double row oil coolers are dealing with some heat me phinks....and heat comes from comp and timing and all those good things that hang in there.

[DME3]

With smadden's issues with the split carbs, I was wondering if it would be hard work to use a 900 I.E. airbox on the carby SS with the split FCR's?