Doing some searching around for silencer ring threads I think I've found that the grooves they're covering are MWE groves. From this site this describes the grooves on a Borge Warner:

Map Width Enhancement Grooves

These grooves allow air to be pulled and fed directly into the second set of blades on the compressor wheel outside of the main inlet.
This most notably increases the efficiency of the compressor as well as overall air flow, hence the name, Map Width Enhancement Grooves:
it produces "wider" compressor maps.Along with the increased efficiency, feeding the second set of blades directly helps decrease spool time.

Tim's Turbos - Turbo Rebuilding - Borg Warner S366 Turbocharger

Is this the same on our turbos?

This kind of explains something. I took my stock silencer ring and sanded down the edge that faces the compressor wheel. It's shaped like a code so the more I sanded the larger the diameter got exposing more of the slots and making more whistle. I reduced it by 50%.

After running that for a while I decided to put a stock one back on. Right after that my mileage dropped by 1 to 1.5 MPG. I thought it was just driving conditions but my mileage has never been as good as with the 50% silencer ring.

Any thoughts on this? I'm going to take it out completely and see what the mileage does.

 

Correct. Some pulling sanctions even have rules on the width of the mweg.

 

Do the grooves on the hy35 go all the way through to secondary blades like the borg warner above?

 

yes they do

 

Turns out they do not. I pulled the silencer ring and the grooves are cast in but are just closed off pockets.

 

Why would you just grind down the silencer ring rather than just removing it. Seems pretty pointless...?

 

I have been looking inside my HX35, trying to see if there is open passages behind the silencer ring. I really didn't see anything with my eyes, however I was going to take some thin mechanics wire and try to see if there is actually passages there to allow air flow.

 

What is, is not always what it seems.

 

I don't think the HX or HY has the grooves opened up. It's been a while since I had an HX on my truck, but I don't remember it being open.