SierraFlyer
Registered
Some of you might be thinking about buying the BMC race airfilter. If so, be warned that it won't fit the stock airbox. You have to do a small box mod to make it fit.
The stock filter is "D" shaped and has a foam gasket on the bottom edge that seals on the bottom of the airbox. A small raised ridge on the bottom of the airbox fits on the inside edge of the filter to guide it in place. The BMC race filter is the same size on the outside of the "D". The inside diameter is smaller though to allow more/larger filter pleats and won't fit around the ridge on the bottom of the airbox like the
stock unit does. The filter is thicker than stock. You will have to cut the ridge off or better yet use it as a guide for your dremmel tool to cut thru the bottom of the upper airbox case and around the outside of the ridge and remove the whole flapper valve and ridge. The new foam gasket fits perfectly on the remaining lip to seal the bottom from the top. After removing the flapper, I left the vaccuum motor that actuates the flap in place because I didn't have a plug fabricated for its hole. Now it pushes and pulls the rod but it is not attached to anything. Later it will be removed to lose the weight.
I haven't noticed any loss of low end torque and once tuned, it should give some top end HP. This mod WILL require remapping but is worth it. The opening into the filter is over twice as large with the whole flaper mechanism and surrounding plastic removed. Airflow has to be better now.
If you do this mod without removing the airbox from the bike (like I did), don't forget to cover the throttlebody openings with duct tape to keep the plastic particles out. I used a shop vac to suck out all particles from all areas of the box (top - including behind the throttle bodies/bottom/intake ports) before removing the tape. The whole mod took 15 minutes with my Dremmel. Better yet remove the airbox and do it right.
The stock filter is "D" shaped and has a foam gasket on the bottom edge that seals on the bottom of the airbox. A small raised ridge on the bottom of the airbox fits on the inside edge of the filter to guide it in place. The BMC race filter is the same size on the outside of the "D". The inside diameter is smaller though to allow more/larger filter pleats and won't fit around the ridge on the bottom of the airbox like the
stock unit does. The filter is thicker than stock. You will have to cut the ridge off or better yet use it as a guide for your dremmel tool to cut thru the bottom of the upper airbox case and around the outside of the ridge and remove the whole flapper valve and ridge. The new foam gasket fits perfectly on the remaining lip to seal the bottom from the top. After removing the flapper, I left the vaccuum motor that actuates the flap in place because I didn't have a plug fabricated for its hole. Now it pushes and pulls the rod but it is not attached to anything. Later it will be removed to lose the weight.
I haven't noticed any loss of low end torque and once tuned, it should give some top end HP. This mod WILL require remapping but is worth it. The opening into the filter is over twice as large with the whole flaper mechanism and surrounding plastic removed. Airflow has to be better now.
If you do this mod without removing the airbox from the bike (like I did), don't forget to cover the throttlebody openings with duct tape to keep the plastic particles out. I used a shop vac to suck out all particles from all areas of the box (top - including behind the throttle bodies/bottom/intake ports) before removing the tape. The whole mod took 15 minutes with my Dremmel. Better yet remove the airbox and do it right.