09-14-2018, 07:08 AM
Posted this last May:
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.
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).
K&N claims a flow capability of 498.64 CFM for the HA-1301 CB1100 air filter (source: email from K&N)...but it cannot be anywhere near fully utilized by an 1140 cc motor with a 8,500 RPM redline.
I suspect that the stock Honda filter does not impede flow.
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.
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.
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.
I had K&N on one Sportster and one Jeep.
The Screamin' Eagle high flow kit, pre-04 came with a K&N, but the major advantage was more space behind the ham can for flow to the filter.
On my second Sportster (1200 Sport), I modified the ham can back plate with a stock filter and the improvement was about the same as the SE with a K&N.
If cleaned and then not sufficiently oiled, the K&N does not filter well. When dirty it filters fine, but flow drops quickly.
K&N reminds me of the oil bath air filter stock on my 1955 Mercury. It was a late model year with a 312, instead of a 292 V8. Very effective filter , but I quickly replaced it with a tall, large diameter cartridge 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.
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).
K&N claims a flow capability of 498.64 CFM for the HA-1301 CB1100 air filter (source: email from K&N)...but it cannot be anywhere near fully utilized by an 1140 cc motor with a 8,500 RPM redline.
I suspect that the stock Honda filter does not impede flow.
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.
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.
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.
I had K&N on one Sportster and one Jeep.
The Screamin' Eagle high flow kit, pre-04 came with a K&N, but the major advantage was more space behind the ham can for flow to the filter.
On my second Sportster (1200 Sport), I modified the ham can back plate with a stock filter and the improvement was about the same as the SE with a K&N.
If cleaned and then not sufficiently oiled, the K&N does not filter well. When dirty it filters fine, but flow drops quickly.
K&N reminds me of the oil bath air filter stock on my 1955 Mercury. It was a late model year with a 312, instead of a 292 V8. Very effective filter , but I quickly replaced it with a tall, large diameter cartridge filter.