Thoughts on air cleaners...
 

I wrote this email to a friend of mine who asked for my opinion (big mistake). I thought I'd share it here and get all y'all's opinions.

My thoughts on air cleaners:

An engine is made up of finite dimensions (bore, stroke, etc.) and as such there is a mathematical limit on how much air the engine actually needs at a particular operating range. We all know that the stock intake is severely restricted, but how much? You can calculate the CFM required by an engine using the equation cu. in. X rpm x VE / 3456 = CFM. So, for our engines:

103 x 6300 (MAX RPM) x 1 (assumed VE of 100%) / 3456 = 188 CFM

So, our engines need 188 CFM at WOT. Now how much do the aftermarket air filters flow? I found these flow bench numbers a while ago, and while the models may be outdated it’s still useful to demonstrate my point.

HD stock - 171CFM
Stage 1 Big Sucker - 200CFM
Stage 2 Big Sucker - 250CFM
Kuryakyn Twin Velocity - 270CFM
E-3014 = 248 CFM RK-3009 kit
E-3037 = 301 CFM RK-3910 kit
HD-0800 = 231 CFM SE replacement
Doherty Powerpacc - 287CFM
SE Air Cleaner - 287 CFM
Zippers - 321 CFM
Woods Carbs - 4 models 235CFM upto 340CFM
BC Overflow - 800+CFM

So the stock filter element almost has enough to cover the 103 running at 100% efficiency, and the regular old SE air cleaner flows 68% more than stock. The BC Overflow at 800+ CFM is just overkill. Even at the maximum 127% VE you’ll only require 238 CFM at wide open throttle. Now the stock airbox, which effectively seals the element is where most of the restriction comes from. I couldn’t find any numbers on that. Exhaust is another factor, but that’s a whole ‘nother tirade.

Bottom line is that any air cleaner you can find will flow way more air than our 103 engines will ever require.

Regarding open vs covered, my feelings are that an element covered by the football can only suck air that has been heated by the engine because the football has all other routes blocked. The air has to come from behind the football, and has already been heated by the cylinder fins. We all know that cooler air makes better power, so I think on a dyno an open element will make better numbers. However, in real world situations, that may not always be true. An open element has to deal with wind sheer (created by the movement of the bike). The air being rammed in through the exposed element has to make a sudden right turn to enter the throttle body. Air does not take kindly to bending, so it’s possible with enough sheer the air will continue out the other side of the element, thus actually creating a small amount of vacuum in the throttle body. I say small because the movement of the pistons and opening of the valves will be enough to suck some air in allowing the engine to continue running. This may not be as big a problem on our fully-faired bikes as it would on say, a softail. And of course, you have the rain and the bug problems to deal with. So, how much power do you lose by covering up? I don’t know, and I doubt a dyno can recreate an 80 mile an hour ride across west Texas on a 95 degree day. Who cares, anyway? 6 months out of the year you’ll have 1 or 2 more HP and 3 lbs more torque, and 6 months you won’t. I don’t know about you, but I doubt I’ll feel that.

So, bottom line of all this? Buy whatever you like the looks of. My bike made decent numbers with the SE paper filter element, so I’ll stick with that until I see something that looks really cool. On my Dyna I run the Kuryakyn Hypercharger, and it seems really happy with that, although it has been dogged by so-called experts because of it’s flow qualities. I just like the flapping butterfly on the front of the scoop.

That’s my story and I’m sticking to it.

Great post, thanks.

I opened up the stock back plate on my Fat Boy football with a K&N element, reasoning that I had at least doubled the flow "potential".

My oldest son runs a Hypercharger on his Deuce, and likes it for the same reason.

Interesting reading. I couldn't stand the football. First thing I removed from my bike. Running with an open larger K&N for 4 years now.

That jibes with what I've heard. Until you get into a really big motor, the air cleaner is a non-factor once you upgrade from stock.

:Poke:DAN.... nevermind:roflback:

IMO, pure numbers don't tell the whole story. I think Zippers is the smallest I'd run. My $.02.

how far does any body ride at 6000 rpm at any given time? a k&n will give you all you will ever need on the street with the foot ball.

A couple hundred miles in ES last June.....:whistling:

That was my point. The calculations were at WOT with no restrictions, representing the maximum amount an engine could need. Actual requirements will be less based on the size of your valves, the size of your throttle body, cam choice, etc. People get hung up on which one flows more, but almost all use a K&N element.

Nice Post,
I had the same thing explained without such definite numbers, funny how the latest Suck for your Buck ad touts a 21% increase in HP???? in conjuction with what other components? You think you would have to state that, or it shows - in my pea brain anyways - how easy you can skew a dyno's figures. Truth in advertising:roflback:

Cheers,
Dirk

Check out the Harley air cleaner set up at www.freedomcyclereno.com.

I know of some people who run their K&N oil filter dry, I barely put any oil on mine, just enough to know it has some.

A over capacity CFM filter will probably get you the maximum needed after some dust accumulation, just a thought.

Dan, one other factor not considered at least on the bikes with farings (newer ones) the way the flow is set up to facilitate cooling also will result in some ram compression of incoming air which even though heated as it passes the cylinders on the way to the intake will still retain some of the additional compression mass and will help compensate for the heating.

Running them dry greatly lessens their ability to filter.


Bingo! Doesn't take a lot either.

That's why I say the numbers don't tell the whole story. Often you will see an increase when you remove the filter during a dyno session -- even though the numbers say you shouldn't.

Dunno why, but suspect that while the smaller filter will flow the volume, it doesn't flow as freely. Again, haven't experimented and definitively found the reason, just doof logic.

If you're stock or a mild upgrade and / or you rarely get into it - stock or the Stage I will be all one ever needs.

OTOH, if you're beyond that, I like the Zippers because it flows really well - and fits under the stock cover. I understand the "green filter" that Hillside came up with also flows very well and fits under the stock cover. My $.02 FWIW.

I used the best science available when deciding on my air cleaner.

It was $60 for a lightly used Ventilator.

As to the very lightly oiled K&N, If you ran an oil analysis I'd bet on seeing silicon.

Abrasive.

Oh, and some extra aluminum. Again, abrasive contaminant. There's a lot of Al in the Earths crust.

I use a Ventilator as well, and I do se silicon in my oil analysis.....FWIW.