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 was told that I could have two programs available, and toggle between them using a switch. 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 the "stock" switch setting would be a "stock/fuel economy" setting. I guessed injection timing and possibly the fuel rate curve received a tweak. 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 felt pretty spunky, I thought, so why add more power if I didn't need it. Plus, I wanted the new head gaskets and injector cup reseal plenty of time to "settle in" before "putting the wood to 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 and I began using one of his ECMs with his big power programming. 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). Murphy said I had a 50/50 chance of getting it right, if I ever forgot...

Since replacing the head gaskets in Lil Red (in late 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... Turns out... All of the Lil Red 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... To add a little spice to a YouTube video... Actually, the beginning of this video: https://www.youtube.com/watch?v=nvKLtiGF-50

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 after considering my mistake for a few minutes a question formed in my mind about whether fuel economy would improve if the "Fuel Economy" switch position was active... So I filled up about 10 days ago, selected the "stock/fuel economy" switch position, then drove the truck another 375 miles over about a week or so - some local and some a little longer distance driving. The prior tank in Lil Red, with similar driving produced just over 20 mpg, which I thought was pretty good for a local biased tank of fuel.

So, what was the result of the most recent tank of fuel? 375 miles, 15.708 gallons = 23.873 mpg.

Maybe there is something to the "Fuel Economy" switch setting after all... I'm looking forward to more Interstate driving to get a better comparison, but for now, it looks like the improvement could be at least 2-3 mpg better... when using the "stock/fuel economy" power setting. Would an improvement of 2-3 mpg be a worth losing 100-hp?