chrismc wrote:
warp2diesel wrote:
Mods that increase MPG include going to narrower tires that can hold more pressure and opening up the exhaust at the choke point that includes the stock muffler and the stupid 2 1/8" ID rear cat flange. I ran all the tests with a pressure gauge tapped into the pipe between the CAT and Turbo before and after and posted them. Extra oxygen allows all the fuel to burn and puts more power to the rear wheels, regulate the power with your foot and you will get more MPG. SIMPLE
Warp- I missed that post and I'd be curious to see those numbers (I'll search for it). I had always heard that the CRD had a relatively open exhaust and that upgrades didn't help much unless you had an upgraded turbo that moved more air. I'm not sure that a more open exhaust will get significantly more air into the cylinder for combustion on a positively-pressurized turbo engine like it would on a naturally-aspirated engine, but it will definitely help keep exhaust temps down (especially while towing). Lower EGT=cooler engine=better mpg.
A brief summery; I got as high as 5 PSI back pressure with the stock system when towing a trailer. After I opened up the system the back pressure dropped to 0.0PSI. I removed the gauge and put it back on the shelf in the garage. My boost pressure climes much faster and I can get 20 PSI boost measured at the manifold after it droops going through the intercooler.
Conclusion, removing the CAT is a waste of time and is illegal, replacing the crap stock muffler with a straight through 2 1/2" and opening up the 2 1/8" choke point on the back of the CAT is all you need with any tune that the 2.8L can handle.