6" to 4" inline fan reduction a no no?

setting up my grow tent after taking a few years off and remembered I had a hydrofarm 6" 400cfm inline fan.

My problem is that my new setup requires me to use 4" duct and I'm not sure if reducing the duct size is a bad idea with the inline fan? I don't recall ever running the fan at it's highest power even with a carbon filter attached but I don't want to set it up if it's going to be an issue reducing it.

thanks for taking the time

shouldn't be an issue, get a speed controller if you don't have one, and make sure you aren't running the fan faster than the filter is rated for. unless you're trying to run 2 1k lights in a small closet, you shouldn't have any issues

I have a 6" 400cfm fan that is reduced to a 4" duct and it works fine.

I have a 10" reduced to a 6" no problem at all you should be fine

what size grow tent??
i have a 12ftx12ft room seperated with my veg area being a 3ftx6ft closet..in a basement so i could only drill 4inch holes for intake and exaust.. i have a 6 inch inline reduced to a 4inch duct,, seems to work fine if using it to exaust but if i flip it and pull air in from outside its hindered by the reducer..

Thank you everyone for your replies

I will be using it to pull air through a carbon filter and exhaust out of the room

for centrifugal motor fans which most growers use, it is okay. I use the regular warehouse exhaust type fan which do not have pulling power, and therefore a minor reduction in size diminishes venting by a lot. on the bright side, i get to vent my room with 35 watts for 10" fan and i have to downsize in winter because it is too much. Oh and a fan controller breaks the motor quite fast on my type unlike the centrifugal, but i get it for 30$ and it lasts years

some motors are made to be adjustable, and some aren't, they'll say two stage or something like that if they're adjustable, single stage are unadjustable.