recently bought a k&n air filter and am concerned about the size. the part number (IPD) 2c2043 is correct for my car, but the height is about half that of what would normally be in the air box. what are the chances that the filter will move around allowing particles to bypass the filter?

if the filter's length and width are the same as the old one, then when you put the top of your filter box back on, it'll press the filter down securely in place on the rubber trim of the K&N filter and prevent it from moving.
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Kenric Tam
1990 Volvo 740 base sedan (B230F)
My Volvo 'Project'

HI: I would call there 800 number and simply ask them what is the correct stock number for your car. If it is the same than you have the correct air filter. I put one on our 88 740 wagon and it fit like a glove. When you put it in it should fit snugly into the air box, and when you put the top back on it should fit go around the air box lip perfectly. When you clamp down the air box cover it should all most snap shut. Good luck,Dan...
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Dan's 88 Volvo 740 GLE WAGON non-turbo