C15 acert

In a 05 freightliner, 18 spd. Suppose to be 550/1850.
At about 1200 rpm this puts out about 25 psi of boost. I thought this was normal until the elbow off the turbo came loose and fell off ( basically the y pipe off the turbo, one stack is blocked off - what ever no big deal ), I drove for about 15 minutes till the next truck stop and this thing pulled like a bat out of ####ing hell with that exhaust separated. Like nothing I've ever seen before, about 35psi at the same 1200 rpm pulling steep hills.
So I assume the muffler was plugged, mechanic said he didn't replace it because it's only baffles and can't be plugged.
Is this right? Doesn't seem right to me.

 

Is what im expaining even feasible? Machic said turbo over spool. But j don't see how that's possible with the muffler separating from the rest of the exhaust. What I think when I see that is a non restricted turbo spooling how jt should.

 

Truck has been nothing but problems lately. I told machic to just straight pipe it as I'm sure my boss is sick of this money pit. But he didn't want to
Doubt he even took it off tool look. Put a piece in myself ######

 

Twins yes. It used to hit 50 like my very first run of two. Barely see it over 40 now, and that take like 16-1700 rpm. I never really take it up that high

 

Yea. Barely seeing over 40 psi at any rpm.
How do I know what the exhaust actually is? Baffles, scrubbers or cat.
I pulled the tip off and looked down there. Was little holes along the sides with a plate and a #### load of rocks on it lol. This was only a foot or so down from top of the muffler. I assume it's layered?

 

Wish I could get a picture of it. Talked to the machic again trying to tell me it's a 4 inch straight hole all the way down. Tried telling him there was a plate or some sort covered with rocks and a holes around the outside. Similar to what baffles look like, just real small holes