[Arizoni]

A few days ago I was in the local O'Reilly's Auto Supply store and noticed a air filter that looked almost like the paper filter used on the UCE Royal Enfields.
Rather than having orange rubber ends it had black ones and the paper was white.
A nice screen on the inside and outside connected the ends.

The filter is made to replace filters for KOHLER K181, Tecumseh HH80 & VH100, John Deere AM30800 and Tecumseh 31925, most of them being small single cylinder applications.

They only wanted $7 for it and I figured that was a good price if it worked so I bought it.

After getting home I did some measuring.
The OEM air filter measures 3 inches inside diameter, 4.7 inches outside diameter (the orange rubber ends) and it is 2.90 inches tall.
The outside screen is about 4.62 inches in diameter X 1.7 inches tall giving an open area of about 24.7 square inches of open area.

The newly found filter measures 3 inches inside diameter, 4.4 inches outside diameter (the black rubber ends) and it is 2.4 inches tall.
The outside screen is about 4.3  inches in diameter X 1.7 inches tall giving an open area of about 22.9 square inches of open area.  This is about 7.6 percent smaller than the OEM filter.

The shorter length of this filter was too short to work with the bikes stock metal end cover so I bought a roll of .61 inch wide masking tape to work as a spacer.  This masking tape has the same 3 inch inside diameter as the new filter and with it stacked on the end of the new filter, the metal cover clamped everything in place.
With the tape and new filter installed I took it for a ride.

In city traffic it seemed to work as well as the OEM filter but when I'm riding around cars I go with the flow so this really didn't test the overall performance.

The next day I rode over to get on a smaller freeway in my area to see how the bike would run at higher speeds.

This freeway is climbing a grade where I get onto it.
It climbs about 250 feet rise in elevation over a distance of 3/4 of a mile.  The speed limit is 65 mph.

Accelerating thru the gears with a wide open throttle, the bike was working hard to get up to 60 mph and 70 mph was the maximum I could get to before I turned off on an exit ramp about 3/4 of a mile from where I got on.  The overall feel of the bike was it was definitely running out of power.

After this ride I blew the dust out of my old OEM air filter that had over 1000 miles on it and replaced the new filter with it.

Returning to the freeway on ramp I again accelerated at WOT and the bike pulled smoothly to 77 mph and was still accelerating by the time I reached the exit.

The bottom line is if you want to buy this other filter to save a couple of dollars and you ride sedately on city streets it probably will work.

If you ride the freeways at all, the smaller filter will leave you wanting.

[JVS]

Thanks for the report, Jim. Even way after the 7500mi/12000km service (where the manual tells us to replace the filter), I am using the same (stock) one as it was never that bad. Just gave it a good clean with an air-compressor and put it back. The bike has always ran fine with it. I do have a spare filter lying here (OEM one), so if it needs to be replaced, I have it on hand.

But it is good to know regarding the smaller filter size and how it can affect performance etc. I don't think I will be changing to any aftermarket filter as the engine aspect of my Bullet is stock and will probably remain like it is.

[Ducati Scotty]

WIX 42371 and/or Napa 2371 are close to the stock dimensions, pretty cheap, and easy to get most places. Specs OD 4.4", ID 3", HT 3.4".

Oh, and there are two OEM filters.  An older one that was a bit wider and shorter, and a newer one that is taller and smaller around.  I think the new one is the only one you can get now, but you never know with RE

Scott

[gashousegorilla]

  Pretty interesting, how less then 2 sq in. made a 7 mph drop in top end.....   Did the screen on the filter seem restrictive ?

[ace.cafe]

It seems about normal for the smaller filter area being 7.6% less.
If you take  92.4% of your max speed of 77mph, you get 71.148 mph, which is close enough to 70mph to probably be within the margin of error of that speedo.

So, it is a pretty good correlation of reduction of size vs reduction of top speed.

[Ducati Scotty]

That settles it!  I'm stacking two together tomorrow and I'm going out to break the ton!

[gashousegorilla]

  Interesting stuff....  What is the effective filtering area of that K&N replacement filter for example ? ....  That you hear conflicting opinions on.  Are they the same size ?......  Are they being oiled ?.... not oiled ?.... over oiled ?  Is it restricted in the box ?

[Craig McClure]

MY Orielly Air filter is actually a little larger than the original, & pleated white paper(no metal)& black rubber. Mine works better than stock on my G5, in all circumstances.
I like white pleated paper filters, & have used them for years.
I can't remember the part # of mine, but sounds like yours is to small.

[hortoncode3]

I bought a K and N for my B5, and on top of being expensive, fit like crap. I don't think performance was enhanced one bit either. I'll buy a stock filter the next time. Now...has anyone managed to find a decent and locally available oil filter?

[tooseevee]

I bought a K and N for my B5, and on top of being expensive, fit like crap. I don't think performance was enhanced one bit either. I'll buy a stock filter the next time. Now...has anyone managed to find a decent and locally available oil filter?

               Help me understand this: It was the FILter's fault that it "fit like crap"?

[High On Octane]

Why do people have this false believe that K&N filters magically give you horsepower?  I hear it all the time "K&Ns give you like 10-15 hp".  No.  No they do NOT give you hp.  If you actually read the package it says it "can produce 10-15 PERCENT HP increase over stock".  These filters do not increase HP, they increase the efficiency of how the motor operates.  The UCE has about 29 block HP, even if the motor was able to actually scavenge a full 10% increase, that's only 2.9 HP increase.  If you have a full stock set up, regardless of the vehicle, you're not going to see any gains because your heads and TB are still flowing the same amounts they always have, and that's where the real increases come from.

Scottie

[gashousegorilla]

  More like 18 or 19 at the rear wheel..... And even at that. IF , and thats a BIG IF ! Without fuel corrections of course..You could pick up a cheap 10-15 % increase in HP.... You're doin' alright. HP ain't easy to come by on these bikes...   I think K & N actually claims UP TO 4 %... I could be wrong on that though.

[GreenMachine]

Isn't marketing great...Can you imagine the amount of air filters and filter oil they sell over the years...I'm just as guilty as the next guy , with one retrofitted inside the enfield filter box and as part of a stage 1 kit on the yamaha...Both bikes start up great and I think they go faster...

[High On Octane]

Don't get me wrong they are good filters and I have used them on several different cars, trucks and bikes I've owned.  It made a big difference on my'83 Suzuki.

Scottie

[ace.cafe]

Okay, a couple of basics.

The filter element should be rated for the same (or greater) flow in cfm as the engine inlet system can pass. This helps prevent a low pressure zone from being created inside the filter element. The engine ingests air by the difference in pressure outside the throttle body(preferably full atmospheric pressure) and the partial vacuum in the cylinder during intake. If the air outside the throttle body is pulled lower than atmospheric pressure by a restrictive element, then that reduces the available outside pressure to feed the engine.

Also, the internal air volume space inside the filter mesh barrier should be as large as is feasible, and should be at the very least the same as the engine displacement. This allows the engine to take a full "gulp" of air without having to pull air thru the filter mesh. It gets almost an unrestricted gulp from this internal volume, and then the internal volume can re-fill with air during the next 3 engine cycles, and be ready for the next intake gulp.

And, the mesh should be fine enough to filter the particles out of the air at the desired filtration spec, and have enough area to ensure the flow rate even after it has gotten a bit dirty.

A suitably sized pleated paper filter element housed in a properly sized air box is probably the best overall solution. This is why we use this formula in the construction of our Ace Air Canister. It's simple, but it follows the proper design criteria. The factory design has some of the right concepts, but it could be improved. I think it has also been established that the small pod filters like K&N have not given good results in this application due to insufficient internal volume.