[Randy_the_Hack]

Originally Posted by Lazarus

Welcome to the site. Really nice job with the truck. But why unplug and remove all the emissions control? Does it really help that much and at what cost?

The '04.5 LLY was the first year for emissions equipment on GM's diesel trucks. It may or may not have been the first year for that type of equipment on any diesel engines; I just don't know. The rationale is as follows:

1. The cat reduces exhaust airflow, which increases exhaust gas temps, which in turn threatens the turbo when the truck is under load, e.g. towing a trailer in the summer up a long hill. By increasing the exhaust diameter, ditching the cat, and replacing the muffler with a flow-through (sort of like a Flowmaster or Cherry Bomb on a gasser), you increase horsepower by 15-35 hp (depends on the system, phase of the moon, alignment of the planets), and decrease EGT's significantly. Bottom line - much more efficient use of the fuel.
2. The PCV, as routed by GM, feeds direclty into the suction side of the turbo, pre-intercooler. As a result, when you're running under boost, the engine is actually having the engine oil mist being positively sucked out of the valve covers, and then pressurized into the intercooler. The net result is that the intercooler gets coated with this oily mess which can result in the intercooler boots being blown off, leaking, etc. Amazingly enough, if you reroute the PCV and cap off the intake to the turbo, almost nobody ever sees any oily discharge from the rerouted hose. I know I haven't. And... the intercooler is cleaner and you don't run the risk of blowing the boots off under heavy use, which leaves you with no power.
3. The EGR takes exhaust soot and blows it right back into your intake. Even a few thousand miles of this can and does literally cake the intake tubes with thick layers of soot. Worst case is that you end up with clogged equipment, which is extremely expensive to replace... plus it again works against you as it increases overall exhaust gas temps. By blocking the EGR, you run cooler and more efficiently; most people see quicker response and better fuel economy. You will notice that the newest diesel engines use a DPF to deal with accumulated soot in an enterly different method. The EGR was a good idea gone amok on this particular diesel engine.
4. The resonator is another good idea in theory gone amok. Supposedly it makes the engine quieter, but by blocking it you avoid unfiltered air getting into the intake if the sucker ever develops a leak (and they do), and by blocking it you increase hp a little.

There is a method to the madness. My truck now smokes less than it did when it was stock... and runs way more efficiently (16-17 mpg v/s 21-22+ mpg) while putting down an extra 150+ RWHP and 100-200 extra ft-lbs of torque.