Topic: K&N filter for plenum

[Scott S]

 What's your thoughts on the K&N filter that bolts to the plenum? It keeps the stock boots/velocity stacks and plenum and runs this round style filter where the stock air filter box would go.

[LesterPiglet]

It doesn't go inside the airbox then?

[dave500]

do they make any claims about it?

[lucky]

What's your thoughts on the K&N filter that bolts to the plenum? It keeps the stock boots/velocity stacks and plenum and runs this round style filter where the stock air filter box would go.

THE AIR BOX is not a plenum!! Confusing the discussion.
A plenum is what is used in a fuel injection system for the cold start injector etc.,.

What readers want to know is does that filter connect to the air box?
Otherwise how to the stock rubber velocity stacks interface with that filter???

[LesterPiglet]

I've been led to believe that the chamber the airbox feeds to is called the plenum, if not what is it called?

[lucky]

I've been led to believe that the chamber the airbox feeds to is called the plenum, if not what is it called?

It is the air cleaner or air filter housing.
That word Plenum was not introduced until fuel injection was manufactured so to keep things clear they did not call it the air filter box or air cleaner because on fuel injection the plenum box looks like an air box and then it had a separate air box with filter off to the side. But the big plenum box was right over the top of the engine. To keep people from mistaking it as the "air filter housing they made that name plenum chamber.

The plenum chamber on fuel injection actually has a gas /air mixture inside it.
The Air filter or air filter housing box DOES NOT have a fuel mixture inside JUST fresh air coming in.

[LesterPiglet]

I wouldn't call it the air filter housing as it doesn't house the air filter.

CHAMBER,CLEANER : #17310323010B : HONDA

[Scott S]

 Ok, ok....whatever. It sure looks and acrs like a plenum to me!

 It fits where the box that holds the air filter would attach. The box is not used. This flter would hang out in the open behind the side covers. The air box/plenum/whatchamacalit that the carbs attach to and holds the stock rubber boots/velocity stacks stays.

 I haven't heard or read any claims about it.

[lucky]

Ok, ok....whatever. It sure looks and acrs like a plenum to me!

 It fits where the box that holds the air filter would attach. The box is not used. This flter would hang out in the open behind the side covers. The air box/plenum/whatchamacalit that the carbs attach to and holds the stock rubber boots/velocity stacks stays.

 I haven't heard or read any claims about it.

Like I said a plenum has a fuel mixture in it,

[Retro Rocket]

Ok, ok....whatever. It sure looks and acrs like a plenum to me!

 It fits where the box that holds the air filter would attach. The box is not used. This flter would hang out in the open behind the side covers. The air box/plenum/whatchamacalit that the carbs attach to and holds the stock rubber boots/velocity stacks stays.

 I haven't heard or read any claims about it.

Like I said a plenum has a fuel mixture in it,

Not necessarily, Plenum's are defined as a chamber with positive air flow for distribution to multiple ducts {velocity stacks} Plenum's or plenum chambers are commonly used in air conditioning ducted systems, no fuel in them.... Airboxes are quite commonly referred to as "plenum Chambers" .

[scottly]

Like I said a plenum has a fuel mixture in it,

Fuel injection systems do not have a fuel mixture in the plenum; the fuel is injected into the individual runners, downstream from the plenum.

[scottly]

Scott, how much does the reusable K&N filter cost, compared to stock paper filters?

[TwoTired]

I've been led to believe that the chamber the airbox feeds to is called the plenum, if not what is it called?

Honda calls it a chamber in the part list.   

I've called that part a plenum, as that is what it would be called in heating and air conditioning duct works.  But, the technical description of a plenum includes internal pressure higher than outside atmospheric, which is not really the case for the SOHC4.  The internal pressure in this case is less than outside atmospheric.  Sure looks like a plenum to me, though.

Anyway, if a stickler wants to do correction, he should get the term right before espousing opinionated bs, imo.

Also, I have one of those K&N filters I removed from a bike I rescued.  It won't change the carb inlet pressure as drastically as pod filters do, and it keeps the chamber and rubber vstack thingies.  ...Which makes it better than pods in my book.  The filter is still openly exposed to rain and road spray.  On the rescue bike, the dumb PO also removed the entire rear fender, so any water and grime the rear tire picked up from the road was flung directly onto the filter element, which is probably why it was dirt black in color.

Cheers,

[scottly]

Did you ever clean it up and try it, Lloyd? With  side-covers and a proper fender wouldn't it be somewhat shielded from the elements? 

[TwoTired]

Did you ever clean it up and try it, Lloyd? With  side-covers and a proper fender wouldn't it be somewhat shielded from the elements?

No. I didn't try it.  I can't think of a good reason to do so.  Anyway, I had spare air filter box and breather element parts, so I put it back to a known working configuration.  I wanted to use the bike for daily all weather commuting.  Bike is now sold.  And, I don't think a replacement element is available.  Anyone know for sure?  I did try to clean it in my parts washer.  It is now a lighter grey than before.       I'm not sure it will ever be clean again.

Cheers,

[scottly]

Anyway, I had spare air filter box and breather element parts, so I put it back to a known working configuration.  I wanted to use the bike for daily all weather commuting.  Bike is now sold. 

Cheers,

So the K&N filter did it's job protecting the motor, despite being subjected to such abuse?

[bwaller]

I use a single large K&N like this and it works well. At the time I only had the plenum and no airbox plus a set of these huge GSXR1100 pods. I won't get into any arguments about comparisons with stock. I did try to isolate it as much as possible from wet weather, but it obviously needs to be cleaned more often then a stock set-up, but is also easily removed. I also have three others left as spares!

The filter feeds stock PD carbs on a 592cc engine. The 2.25" inlet opening ultimately would be restrictive for anyone looking for big numbers, but this is a street bike in mild trim. At 51 RWHP though it is certainly doesn't show any ill effects!

[scottly]

The filter feeds stock PD carbs on a 592cc engine. The 2.25" inlet opening ultimately would be restrictive for anyone looking for big numbers, but this is a street bike in mild trim. At 51 RWHP though it is certainly doesn't show any ill effects!

That sounds like real data to me!

[78 k550]

What's your thoughts on the K&N filter that bolts to the plenum? It keeps the stock boots/velocity stacks and plenum and runs this round style filter where the stock air filter box would go.

I have used that setup and still have it.
It worked great. Not using it now.

Paul

[Scott S]

Scott, how much does the reusable K&N filter cost, compared to stock paper filters?

 I'm not sure. There's a complete kit on ebay for ~$48 plus shipping. I occasionally see them attached to air box parts on ebay as well. I've thought about grabbing one of the cheaper "parts" ones, but I'm unsure about a replacement element if, like TwoTired's, the filter is too dirty to get clean.

[becken]

Scott, I put one of those on my 76 550F back in the 70s and am still running the same filter. I have the entire rear fender and side covers in place and have never had it get wet or dirty from road spray or pouring rain. You shouldn't have to change jets by much if at all. Do a plug chop to be sure. I'm running stock main and idle jets and it runs fine. Make sure you oil the element but not too much. I would recommend getting on of these http://www.knfilters.com/clningacc.htm

[Doo Bee]

Hi everyone. I just joined this site and have owned my cb750 since 1977.
I still have K&N dual flange chrome air filters. I need new ones. I saw on ebay
the part number listed was RC-224/2. The guy was asking $100 bucks plus
shipping. Well, I went to K&N and found a RC-2240 that has the same dimensions.
It claims to have a 1.125 offset which is crucial---so the 2 filters don't clash in between
carbs 2&3. These filters work well---unlike pods. Flat spots were never an issue. I
have run 836---915 kits kerker headers and 3 different cams. Never had any issues
other than if you get a crosswind on the open highway it will lean out. What I need
to know if anyone has tried the RC-2240's and if they are the REAL MCCOY?
Thanks also I zip tied my carbs in the rear for support many years ago, just to let you
know.

[TwoTired]

Anyway, I had spare air filter box and breather element parts, so I put it back to a known working configuration.  I wanted to use the bike for daily all weather commuting.  Bike is now sold. 

Cheers,

So the K&N filter did it's job protecting the motor, despite being subjected to such abuse?

Quite possibly.  The bike did run well after restoring.  I never peeked inside the cylinders.  And, it had decent compression.  However, it was one of nine bikes in riding rotation, so I really only put about 3000 miles on it before selling.  With no fairing/windshield, it was just a summer bike.  I have no firm data that the K&N filter extended or diminished the engine's longevity.  I can only the filter mod didn't kill it outright.   

Cheers,

[TwoTired]

I use a single large K&N like this and it works well. At the time I only had the plenum and no airbox plus a set of these huge GSXR1100 pods. I won't get into any arguments about comparisons with stock.

Just from this picture, I wonder whether this filter has and more (possibly less) filter media area than a stock paper one.
Of course the membrane type you have there could also be more porous, making raw external size comparisons less interesting.

The stock paper filter presents about 95 sq inches of the filter media to the outside world.
The Uni NU-4055 has about 27.5 sq inches presented to the outside world.  Of course, it is more porous than the paper type, as it combines statistical collection as well as passage hole blockage for the membrane rather than an absolute particle size blocker like the paper type.

My K&N (below) has 43 pleat edges or 86 pleat faces of .375 x 3.25 dimension giving a presented area of about 105 sq inches.
I can easily see direct rays of light passing through the K&N membrane.  So, the pore size is most definitely larger than the stock paper type, and it is clearly not a statistical type using oil and momentum to trap particles, as the Uni foam filter does.

This is as clean as I could get my K&N, by the way. 

Cheers,

[lucky]

Like I said a plenum has a fuel mixture in it,

Fuel injection systems do not have a fuel mixture in the plenum; the fuel is injected into the individual runners, downstream from the plenum.

Many plenum chambers have the cold start injector spray right into the plenum.