2014 / 2017 airbox snorkels

[SportsterDoc]

If you are implying this part is strictly for sound deadening, I can assure you there is more to it than that.


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No, this part serves several purposes:

1. It reduces sound. With the top of bowl sliced off on mine, the airflow is louder than my stock exhaust.

2. It serves as a snorkel, in that it (a) draws air from a location less likely to drown the motor in heavy rain and (b) that air may be cooler than closer to the motor (think cold air induction).

3. Properly designed, it should also direct airflow to pass through the air filter evenly. On my 2016 Nissan Frontier (4.0) the air box internal deflector should have done that, but one section of the flat air filter was getting dirtier than most of the pleated area, until I modified the deflector.

To determine if the sound reduction is at a cost of flow efficiency, measure the area of the snorkel intake in comparison to the filter inlet.

A typical V8 in the sixties and seventies had a silencing tube feeding a round filter with the silencing tube inlet smaller than the carb throat. A high flow intake could be easily achieved by simply using a taller air filter, so that air flow came from the entire circumference.

On pre-04 Sportsters, a high flow intake was easily achieved by using a filter backplate which allowed the ham can more space around the air filter. There may also be an increase of CFM with a different air filter. Instead of spending over $100 for a Screamin' Eagle high flow intake (which came with a K&N, pre 04), the same/close to the same results came from drilling the backplate with several 3/4" holes around the outside perimeter of the air filter.

For the CB1100, 171 CFM is required at 8,500 RPM.
1140 cc x 8,500 RPM (redline) = 9,690,000 cubic centimeters
Divide that by 2 for a 4 stroke = 4,845,000 cc = 171 cu ft per minute.

I contacted Hi Flo to ask if they have a CFM rating on their HFA-1932 and if they have a comparison to the stock Honda air filter. I found no CFM rating on the K&N site for their HA-1301.

A K&N HD-900 is rated 203 CFM. A CV40 carb on a pre-04 Sportster will handle 185 CFM. The 1200 cc motor will draw 131 CFM at 6,200. A 1250 will draw 165 CFM at 7,500 (very high revs for a push rod motor).

I suspect that the stock Honda filter does not impede flow. If that is correct, air flow will be maximum if it enters the air filter with minimum interference (negatives include smaller inlet, turns, surface friction).

Intake manifolds (carb to heads) can be designed for different requirements. For example, the old Edlebrock SP2P manifold for small block V8s was designed for torque and fuel efficiency, but not particularly effective over 4,000 RPMs. This is where plenum configuration and runner design has an effect. A "high-rise" intake manifold allows flow with less turn interference.
Received this response from Hi Flo:

All our HFA air filters are designed to be functional duplicates of the stock filter they replace. I do not have the individual specs for each filter as we are not selling them as better than OE but as direct replacements.

So, still no CFM info.
If the CFM rating for stock Honda 17210-MEJ-981 or HFA-192 exceeds the 171 CFM that the 1140 cc can pull at 8,500 RPM, then there would be little, if any advantage to a K&N.

K&N response:

Thank you for contacting K&N. That filter is flowing 498.64 CFM.

Thank you,
K&N Customer Service & Tech Support
tech@knfilters.com
http://www.knfilters.com
Phone: (800) 858-3333