Is there any benefit (or any problem with) removing the restrictive air inlet duct from the factory air cleaner box?

 

There are many benefits and no problems with that as long as you want to hear a little more turbo whistle. The less restrictions you have the better your truck will run.

 

I run a OEM style K&N filter, took out that bridge between the Air box and the fender, and lost the silencer ring (noise difference). The filter gets a little more dirty but not bad, Engine breathes a lot better. Race Techs thinks its a stock airbox but I think preformes like a Cold Air intaks.

 

I've read a lot of post that said that through testing , the only large change [ performance ] is a good filter , stock air box .
That said , I made a box out of blue plastic cardboard , open on fender side , I like to hear the turbo [ some passengers do not ] , it dose get dirty faster .

 

I left my tube to fender in on my 98 with the ring out, after going through all kinds of different set ups and filters on my 02 I decided that a stock truck gets more than enough air from the fender , don't have to worry about warm air or water getting on your filter (BHAF)and with the ring out and tube to fender it gives just the right amout of turbo whisle , not like my 02 with BHAF and no ring its a little too much on the highway. The outterwares cover on my BHAF really cuts down air flow , if ya don't belive me take it off after ya had it on a while ya can notice a big difference for those of you with the cover. Then the down side is water hitting the BHAF and worrying about the falling apart , and yes water does get on it . I think I will get rid of the BHAF . On my 97 I have the air box swiss cheesed , no tube and ring in , truck is stock also and the filter gets dirty reall fast and the turbo whisle is the least of the 3 trucks but its still there.

 

It is generally known that a stock CTD engine gets more than enough air through the stock inlet setup. Just use a high quality standard paper filter. You can test this, rather than believe statements from those who simply repeat what they have heard from friends: Measure your performance by whatever means you have available (timed accelleration, top speed, dyno, etc) and then remove your filter and leave the filter box cover off for another performance run. Any difference? Probably not, unless your filter was really dirty. You could try it again with no filter, cover on, to test the fender tube.

You could even check out different filters this way, for instance, K&N versus Napa Gold pleated paper. You will find they both supply enough air for a stock engine, no difference in performance.