Topic: Info 4 U from K&N regarding CB550 filter with airbox mod shown

[eworth]

Hey All,

Providing the following as reference only, not for debate.  Take what you will from the info given.

I've been involved in multiple emails with Vincent at K&N concerning the appropriate sized filter sufficient for my 77 CB550F.
This is not to debate the effectiveness of the modification that I am making.  Merely the appropriately sized filter for my application.  I am removing the housing for the air filter and attaching a conical K&N filter directly to the airbox that feeds directly to my four 069A carbs.   I opted to do this install as opposed to individual air pods.  (Preferring to stay somewhere in the middle of stock and the all-out mod of 4 individual air pods and many hours of effort to dial them in correctly)  And maybe limit my efforts to get my CB performing well for daily riding, not heart-skipping performance.

I 'm attaching a photo below that I found here on the SOHC site and is NOT the same filter that was recommended by K&N.  Just shows the type of modification I will be making  Believe or not, the one K&N states is sufficient is even smaller.   I'll get to that in a minute.

Vincent computed my correct filter using my 550cc engine, with maximum  RPM of 8000 (you guys may rev higher but I'm a bit conservative in my riding)

Will include exerpts from Vincents emails so you hear it right from the source.  And  you need to read from the bottom up to follow it in chronological order.
Hello Mark,
I have calculated the airflow needed for the entire engine and it is not that high. I also worked to compensate for the extra restriction that will be found at the flange and in the “airbox” you will be making to have all four carbs draw from the one filter. This filter should provide you with everything you need.
Thank you,
Vincent Pistonetti
-Product Specialist- ext. 4085
VincentP@KNFilters.com

.
Here is a summary of the info you are asking for :
Engine: 550cc
4-stroke
Max RPM: 8000 (this would not be constant, only quick acceleration /shifting)
NO boost
---------------------------------------------------------------------
K&N filter preferences:
Shape of filter: CONICAL
Clamp-on style (assuming all conicals are but just making sure)
Also prefer a filter in a shorter length as opposed to long and skinny to avoid potential interference with other installed parts.
Can you give me a few different filters with part numbers so I can select which one I will purchase with the information you provide?
Inlet size: Not sure Vincent. I will have to alter my airbox to accept whatever diameter is necessary to mate to the filter.


Dear Mark
I understand what you are looking to accomplish. In order to know which filter you will require I will need to confirm the engine is a 2 or 4 stroke, the max RPM, the amount (if any) of boost that is on the bike. With this information I will be able to find a single filter that will be able to flow enough air for your engine. Also, did you have an inlet size that you would like to use?
Thank you,
VPart RU-2580 Product Specifications
  Product Style: Round Tapered Universal Air Filter
Base Outside Diameter: 3.125 in (79 mm)
Flange Inside Diameter: 2 in (51 mm)
Flange Length: 0.625 in (16 mm)
Flange Type: Centered
Height: 3 in (76 mm)
Top Outside Diameter: 2 in (51 mm)
Top Style: Rubber
Top Material/Finish: None
Filter Material: Cotton Gauze
Filter Re-Oiling Amount: 0.22 oz (6 ml)
Flanges: 1
Inner Wire: No
Weight: 0.4 lb (0.18 kg)
Product Box Length: 4.63 in (117 mm)
Product Box Width: 4.63 in (117 mm)
Product Box Height: 4.25 in (108 mm)

K&N RU-2580 Inventory Status
USA: In stock
United Kingdom:  In stock


 Vincent recommends the RU-2580 or RC-2580.   Same size and profile. .


 

[eworth]

The correct filter and info per K&N is at the link below:

http://www.knfilters.com/search/product.aspx?Prod=RU-2580

[bwaller]

The picture you show is from my 550. That K&N filter is intended for one GSXR1100 carb... unreal. It was available and by my calculation definitely offered more surface area then the stock filter. That can't be a bad thing considering the engine is 592cc.

It seems small, but I won't argue with the K&N rep. The good thing is you maintain the stock velocity stacks in the air plenum

[BLUE71TURBO]

The correct filter and info per K&N is at the link below:

http://www.knfilters.com/search/product.aspx?Prod=RU-2580

    This 1 filter to flow for 4 carbs !!!?   NO FRICKEN WAY !!!   

[eworth]

Bwaller,

I really like the idea that you implemented.   Ya, I agree and I questioned the K&N rep but it's correct info.   I wanted to keep the new filter to flow about the same as the original.  Hoping not to have to do much for rejetting, etc.  But this mod would also clean up all the clutter.

How did yours run after you made the airbox mod?   Carb tuning problems, etc?

[DavePhipps]

All I can say is YAY!!!!! Something I don't have to research. I was thinking of doing this with my 550/600 project.
Bwaller, do you have a pic of the adapter to make one fit?

[bwaller]

First of all I did this mod figuring it would be a bit of an improvement over stock considering the larger bore, but high performance replacement...no way. This is my wifes bike for Petes sakes. Just in case there is confusion elsewhere on the forum.

eworth, this bike was a basket case, no baseline to measure. It needed re-jetting from stock settings because of engine work, not sure what effect the larger K&N alone would have, if any.

Dave, no picture. If you're building a race engine though, this won't be a good solution because of the single small opening into the plenum. 

[DavePhipps]

OK... sigh. Back to researching velocity stacks 

[DaveBarbier]

Bwaller,

I really like the idea that you implemented.   Ya, I agree and I questioned the K&N rep but it's correct info.   I wanted to keep the new filter to flow about the same as the original.  Hoping not to have to do much for rejetting, etc.  But this mod would also clean up all the clutter.

How did yours run after you made the airbox mod?   Carb tuning problems, etc?

Hey Eworth, ever get this mod going? I'm thinking of doing the exact same thing and wanted to see what kind of work this entailed.

I plan on getting a K&N filter (maybe the one you linked to) and then a reverse cone muffler. I'm hoping my re-jetting time won't be too crazy.


---
1978 Honda CB550K

[brewsky]

I just got the correct k&n for the stock box and removed the top of the airbox....just another option to accomplish the same thing (I think)

[DaveBarbier]

I just got the correct k&n for the stock box and removed the top of the airbox....just another option to accomplish the same thing (I think)

Right now I have the stock box with a Uni filter. What would removing the top of the box do? Let more air flow in?

I just really like how this looks. I've been looking at this bike. It's a bike of a member of this forum. I actually like this BETTER than individual pod filters.




---
1978 Honda CB550K

[brewsky]

"Right now I have the stock box with a Uni filter. What would removing the top of the box do? Let more air flow in?"

It would allow more in if needed.......
I didn't get you were going the cafe route, and if so your option would probably be better than 4 individual pods without velocity stacks

[Don R]

I use a larger version of that filter on my 567CI 7,600 rpm dragster. It's making around a thousand HP with a 1250cfm quick fuel carb. I can see where it would flow enough. The surface area is huge compared to the size, and only one cyl is pulling at a time anyway. right?
 The question is, is the work involved worth the benefit? Sometimes the challenge of trying makes it worthwhile. Keep us informed how it works and what it takes to make it work, if anything.