Picked up a new daily driver a few weeks ago, naturally I wanted to get a baseline so I strapped it down and made some pulls. Truck has a 4.8L with a 5spd, unknown shorty headers and a drop in Filter and Flo-Pro muffler (possibly cat back kit or just muffler not sure) more or less stock as far as I'm concerned.

I was quite surprised it only made 130hp out of the gate, with already a quick tune in it. I knew it wasn't a rocket or anything but man that seemed low. So I started tuning on the dyno and added as much timing as it would take and ended up at a whopping 150hp at the wheels. At this point I knew something was wrong. Air Fuel was good, I swapped plugs right before the dyno so I knew spark was good and it has low miles and doesn't smoke so I am reasonably sure the motor is healthy. I suspected exhaust was plugged.

I ordered a "off road y-pipe" from eBay, I have previously had good luck with the Jegs version but there price jumped from $125 to $188 recently so I bought the kit from eBay for $160. All in all it was a good kit, required trimming the crossover pipe other than that it fit well. I used a boroscope on the old cats and the driver side was plugged bad, Passenger side however looked fine.

Strapped it back down and power jumped to 180, then I gave it some more timing (27deg at 5k) and ended up at 211hp. So all in all it picked up 61 hp, quite surprised.


After cat delete (off road y-pipe)

Before (stock y-pipe) with tuning

 

that's quite the difference!
wander what it'll do with some real headers... but you did just buy a new Y-pipe.

 

Holy crap, nice!