What's this?

The big one in front is exhaust.

 

You can thank California for that one.
It is the tube that the EGR gases travel through from the exhaust into the intake.

 

Off subject here, but the top of the EGR cooler on the other side is a fine place to stick a can of Hormel chili with Beans when you get parked for the day!

 

Sorry, JReding, asked and answered, but this opening is too good to pass up. Staying off topic;
Back in 1967 on the first trip to Alaska, I had a wire mesh basket affair rigged up on top of exhaust,
I had ground out a big rectangle, right over header tubes - inside of the engine lid, on the back
of my 1957 VW Bug, that I did some cooking experiments on. Tried hot dogs first, progressed to burgers,
had a stainless covered container I tried to steam vegetables on, to speed up the stops to eat. That didn't
work very well, has a disaster or two, some were great. Timing is everything, found out the hard way.
I tried several steaks, pulled into Calgary trailing a little smoke, but it smelled great!
Later I read someone had made a cook book of this type of cooking on the move.

 

Some stuff you can't work on without a degree... or an account at SnapOn

 

EGR Delivery Pipe