Suppressor on an AR, gas question

I'm running a can on an AR. When I was building the rifle, a trusted source of information told me to open up the gas port on the barrel. I didn't give it much thought at the time, but as I think on it now it seems counter-intuitive. He's never been wrong before, and my assumption is that he's correct in this instance, too.

Does a suppressor increase or decrease the pressure at the port? If the answer is "decrease" and you know the mechanism, please explain to me.

If it matters, it's chambered in 5.56 and uses a mid length gas system. The gun runs extremely dirty, and I think I understand that to be typical. I don't understand the mechanism behind that, either.

Gas port should be fine.

In fact, most people put an adjustable gas block on it and effectively close up the gas port a bit.

The extra filth is also normal. Goes with the over pressure that comes with the can.

When I first started running a suppressor on an SBR, my dealer told me that it was 'essential' that I have a switchblock on there, so I swapped out my existing gas block for the Noveske Switchblock. Well, the gun ran flawless in any of the three settings on the gas block. In light of that, I no longer run a switch block and the rifle (shock) runs flawlessly. I have never had a problem running a suppressor, regardless of barrel length, switchblock or not, caliber, etc. Suppressors make things quieter, that's the only change I've noticed in using them.

Back-pressure is slightly increased when using a suppressor but not enough that I feel the need to go back to having a switchblock for the gas.

Load, shoot, repeat.

the DI units run fine without any alteration. My piston guns, adjust as needed.

A can will increase the gas in the system. You would need a smaller gas port to compensate for that. Some guys use and adjustable gas block to turn the gas flow down. Most DI systems will handle it just fine, but you are likely over gassing your gun. A simple test to tell if you are over gassed and how much is to pay attention to where the brass lands. If it lands in the 1 to 3 o'clock position it is over gassed. The 3 to 4:30 position is optimal and 4:30to 6 is under gassed. This has to do with the bolt speed. Over gassed bolt moves faster and throws the brass agains the brass deflector harder. In turn the brass bounces forward further off the deflector. This is a good rule of thumb. If your are severely over gassed your gun will function fine but you will be putting more stress on your gun than needed. Entirely up to you if you need to address it. If its a range toy then you will not likely ever see any issues with it. If you plan a very high round count through it you may want to consider addressing the high gas pressures. There are several options. Adjustable gas blocks can be dialed in to suit your application perfectly. It would also allow you to have a setting for suppressed and unsuppressed. A heavier buffer and or spring will also slow the bolt down.This is a little more generic but is also cheeper. You do have to be careful not to slow the bolt down to much tho. That can cause feeding issues. What ever you do run it with and with out the can to make sure you do not have any issues. Unless you plan to keep the can on all the time. For what its worth I run a Wolff XP buffer spring and heavier buffer in my stuff. Still a little over gassed with the can but its not under gassed without the can.