Looking for 3"ID pod filters with no step or flange inside.

[arcticXS]

I want to use a pair of nice alloy velocity stacks on my RS/TM 34 carbs. The bellmouth on these stacks is 3", but so far I haven't found any pod filters that will not to some degree mess with the airflow improvement that I hope these stacks will provide. I even bought a pair of UNI UP-4300, only to find that they have a quite abrupt ridge inside the neck, that maybe has an ID of 65-70 mm. Which made sense, once I realized the filter OD is only 3 3/4".

For anyone interested, it is the longest version of the stacks found here: https://www.mikuni-topham.de/DEUTSCHSITE/Deutsch/FRAMEDEUTSCH.html
I have already made a smaller battery box from 2mm alloy sheet, creating space for stacks and filters.

So what I need help finding, is a pod filter with 3" neck ID, no internal ridge or stop smaller than 3", max 4" long and max 4 3/4" OD.

 

[jay760]

I've just been looking for air filters with velocity stacks built in but can't find any

 

[arcticXS]

I've just been looking for air filters with velocity stacks built in but can't find any

Depending on what you want, some K&N filters have a molded radius inside, so can be used with a straight piece of tubing, to create a sort of velocity stack. Unfortunately, the radius of that molded "horn" is very small, so in no way ideal for best flow.
As to my setup, I may end up using an open ended K&N replacement filter for H-D Sportster, and making my own plates for it. It seems to be the closest match for my 76x196 mm opening requirement, having internal dimensions of 108x213 mm. Just need to check if it will fit inside my side covers......Alternatively use 2 round, open KN filters with suitable dimensions, and make end plates from alloy sheet, HDPE sheet, or fiberglass

 

[Signal]

Ram air in the UK might have what you are looking for. I was looking for some filters to fit with velocity stacks on a bank of 3 RS 36's.
https://www.ramair-filters.co.uk/pr...etor-itbs-automotive/sock-filters-automotive/

 

[stinky78]

A couple of years ago a guy on the SR500 forum used a large oval k&n and cut a hole in the plastic end piece and inserted the stack from the back, the stack was still attached to the carb and the filter clamped over the top of it, he then came up with a way of fitting some filter sheet to the end to close it up, I’m not sure if it was k&n or unifilter sheet, the stack was tested on a flow bench with and without filter and it didn’t affect the flow adversely, shame the old forum is no longer accessible or I’d provide a link, the final result was great, it just looked like any other k&n from the outside.

 

[jay760]

I

Ram air in the UK might have what you are looking for. I was looking for some filters to fit with velocity stacks on a bank of 3 RS 36's.
https://www.ramair-filters.co.uk/pr...etor-itbs-automotive/sock-filters-automotive/

⁸

I just found these on Ebay, searched velocity stack sock filter, will be getting some for next year, try and save some of the ware to my engine.

 

[stinky78]

I’ve not seen those ramair ones before, pretty neat solution, the advantage of using a k&n fitted over it is youcan have clearance all around, with a properly designed stack you don’t want anything close to the mouth, even things slightly forward of it will cause turbulence and upset the flow.

I just found the guy’s bike on another site, has a few pics of the stack and filter, on the forum he had heaps more detail about the build , it went for pages and spanned several years, all gone now unfortunately.

https://grassrootsmotorsports.com/forum/sprockets/my-sr500/53899/page2/

 

[arcticXS]

I’ve not seen those ramair ones before, pretty neat solution, the advantage of using a k&n fitted over it is youcan have clearance all around, with a properly designed stack you don’t want anything close to the mouth, even things slightly forward of it will cause turbulence and upset the flow.

I just found the guy’s bike on another site, has a few pics of the stack and filter, on the forum he had heaps more detail about the build , it went for pages and spanned several years, all gone now unfortunately.

https://grassrootsmotorsports.com/forum/sprockets/my-sr500/53899/page2/

That is great stuff! Very helpful for my XS, project as well as the XT250 and SRX600 awaiting my time and attention.

 

[arcticXS]

Ram air in the UK might have what you are looking for. I was looking for some filters to fit with velocity stacks on a bank of 3 RS 36's.
https://www.ramair-filters.co.uk/pr...etor-itbs-automotive/sock-filters-automotive/

Yes, it looks like some of their 80-100 mm neck pod filters may be the ticket. Thanks for the tip!

 

[arcticXS]

I ended up with these, K&N RB-0900:
https://www.knfilters.com/rb-0900-universal-clamp-on-air-filter