Lil Red - Duramax 6600/Allison Conversion/Swap & OBS/NBS Dash Conversion

[More Power]

Some time ago, I announced here in this thread that I was having Kennedy reprogram Lil Red's ECM to help the truck be a little more "daily driver friendly". I asked JK for one of the two programs to be "stock". John sighed a little at hearing the word "stock", but did as I asked, though he added a little twist to the definition of the word "stock".

When delivered, John said that he programmed the "stock" switch setting to be a "stock/fuel economy" setting. This is what I thought I had been using since the ECM was returned to me - a little more than 4 years ago iirc. The truck was already pretty spunky, I thought, so why add more power if I didn't need it?

I had installed a toggle switch on the bottom rim of the dash way back when... not long after JK first began offering EFI-Live programs. I knew (or was convinced I did) that pushing the switch toggle away from me would select the "stock" setting and pulling the switch toggle toward me would select the "fun" position (a +100 horsepower setting). I had a 50/50 chance...

Since replacing the head gaskets in Lil Red (August 2021) till a couple of weeks ago I left the switch in what I thought was the "stock/fuel economy" position. I thought I didn't need the +100 position. All of the fuel economy reports I've posted here in this thread these past 4 years were actually with the switch in the +100 position, unbeknownst to me. Lil Red is 2500-lbs lighter than my crew cab, so I thought the spunk was due to that... till one day... a week or so ago, I thought I'd try the fun position... Had to shoot a Youtube video...

Much to my surprise, I definitely noticed a change in performance, but it was opposite to what I was expecting. Long story short, I had been running in the +100 position all this time - for at least the last 4 years. Funny story actually, but then a question formed in my mind about whether fuel economy would be different if the "Fuel Economy" switch position was active... So I filled up about 10 days ago, selected the "economy/fuel economy" switch position, then drove the truck 375 miles - some local and some a little longer driving.

What was the result of that tank of fuel? 375 miles, 15.708 gallons = 23.873 mpg.

The prior tank in Lil Red, with similar driving produced just over 20 mpg. So maybe there is something to the "Economy" claims... I'm looking forward to some Interstate driving to get a better comparison, but for now, it looks like at least 2-3 mpg better... when using the "economy" power setting.

[More Power]

A YouTube viewer asked recently what rear axle I was using in Lil Red. This photo shows that the truck is running a 6-lug GM 9-1/2" ring gear 14-bolt semi-floating rear axle. This axle replaced the original 10-bolt that GM used in most of their 1500 series trucks. I was told by a drivetrain expert back when this truck was in the development stage that the GM 9-1/2" semi-floating axle's input torque rating would not likely be exceeded by a programmed Duramax because traction would be the limiting factor.

So far, this axle has been great! I've been running Amsoil synthetic 75W-90 in it since the break-in period. The aluminum cover adds another quart of capacity and the fill/magnetic drain plugs make service easy.

More information about this axle along with a complete description for how it was built can be found at the following ink:
https://www.thedieselpage.com/reviews/randys.htm

[arveetek]

I'd like to have that diff cover! I installed a 14-bolt semi-float axle in my Tahoe a little over a year ago. Mine also has the factory G80, but unfortunately the governor gears were stripped out and it is not functioning. I have been having trouble sourcing replacement parts. I'm perfectly happy with the G80 for my uses, and a new locking diff of some sort is rather expensive.....

Casey