Plenty of flow. If you can find the Donaldson version get it as its hydrophobic. The best flow one version of these and is washable is the aFe Big Boost Filter 24-91042. Its the same dimensions as the 6637 but also has a conical top media with their 5R media. Goes for about $90. Should last indefinitely with washing and oil re-charge. AFE Power 24-91042 - aFe Pro 5R Air Filter Elements - Overview - SummitRacing.com You will be fine with any of these though.
Many times you will see relabeled Donaldsons. But some are different. On my fleet account at Carquest I have seen their boxed filter for that cross reference actually come from WIX one time and then Donaldson on another. Things get very blurred sometimes with how intertwined the supply lines get. What I do know for sure is the Donaldson is hydrophobic (I believe that is the correct term i.e. repels water) I have seen others that were not. Maybe many of them are made by Donaldson and badged differently for the companies which is quite common.
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