Second day update:
1) It looks like I am still averaging a +2 MPG increase, even while at city speeds. Because it is a lot of stop & go traffic, I'm using the computerized average which is holding fairly steady between 25 & 26 MPG. The stopping drops the average (naturally), while steady 40 mph speeds are showing 35 - 40 MPG. With a light foot, the truck used to show 22-24 MPG averages in the city, which is reflective of the rated 21 MPG City rating.
2) Since I purchased the truck (stock), I've notice the little 4-cylinder has a definite 'sweet spot' for the best fuel mileage. In the top gear (6th) it really liked 60 mph before the upgrades. My best fuel mileage numbers have come from that cruising speed. Since the upgrades, the truck has a new 'sweet spot.' Now the best mileage for the highway is 68 mph, which is better for me since most highway driving is now 65+ mph. I've also noticed, as referred to previously, a new 'sweet spot' appearing at 40 mph. This is in a lower gear, but the truck is finding the right power to maintain these speeds at the best fuel economy. The 68 mph point is running a steady 28-30 MPG, while the 40 mph point is showing 35-40 MPG.
3) I have a little oil seepage coming from the front boot of the boost tube. According to what I've read, the oil is normal as the oil recirculates and is reinserted into the cylinders after the turbo. I'm hoping the seepage can be stopped by tightening the clap connecting the boost tube to the front boot. This is common after installing a Banks boost tube to a larger diesel engine.
4) Since I restarted the truck a few times, another difference I noticed is how the motor first starts. The first cylinder fire after the starter rolls the engine 'lurches' the truck more than any of the gas vehicles I've owned, including a previous Towanda 454 and my SSR's 6.0 LS2. My step-father's diesel does the same thing when first fired up. It makes sense due to the more violent pressurized explosion of a diesel engine vs the sparked explosion of a gas engine. Since the upgrades, the first crank over seems a little more violent. I'm leaning toward the assumption that the engine has more available free air (oxygen) at start-up to compress at ignition. This results in a slightly harder 'first-fire.' All of the other minor changes since the intake upgrades would back up this theory.
The service manager at the dealership took a little time to look at the upgrades and ask some questions. He is curious about the power numbers after the changes, too. He thought all three tubes looked really good and, when compared to the stock tubes, clearly saw the improvements in air flow over OE.
If I can give you any more updates, I'll keep them coming.
Have a great day!
My 24th Duramax is the StudeMAX drag car!!
Special Thanks to my Sponsors!!
Danville Performance, SoCal Diesel, Vibrant Performance, & ProFab Performance!!