The Wix 51087 is 5.477 inches long while the "stock" 51372 is 4.167 inches long. The 3 local stores I called by me didn't stock the 51087. The price they quoted was $13. BTW, according to the Motorcraft site, the 820s is 4.04 inches long with a bypass of 12.5 to 18.5 psi.