TLDR: What is everyone seeing for fuel economy with the elgin 1840, especially compared to a smaller cam like the elgin 1838 ?

i have a awd silverado i built 8ish years ago that got 16-18 mpg with normal driving.
aluminum 5.3, 706 heads, elgin 1838 camshaft, twin ebay 66mm turbos, p01 ecu with efilive cos5 OLSD
4l80e, FTI converter
np149 awd transfer case, 3.73 gears

I sold the truck as a roller and then bought it back as a running truck a few years later. i have put several tanks of gas through it and cant get better than 10.5mpg
changes:
iron 5.3, flat top pistons, 243 heads, elgin 1840 cam, single on3 88, p59 ecu running boostos OLSD, tune is pretty good in cruising and driving around
4.10 gears
same trans, same converter

i checked that brakes arent dragging, commanded timing is accurate to actual timing, all spark plugs are tight, firing and dont look way off, no signs of exhaust leaks
the truck drives fine, cruise is 15.2ish afr, it feels slower than id expect down low but seems ok once its up in the rpm range, especially considering its has 4.10s now.
according to the previous owner its a real elgin cam, he paid $300 for it several years back, so its very low probability of an ebay fake.
the only flex coupler on the hot side is between the wastegate and the downpipe

i did not expect the larger cam to make that big of a difference, especially the fuel economy. i bought the truck back to use as a daily but my 454 crew cab dually gets better fuel economy lol. 10mpg is just not sustainable for me.

im having a hard time believing this is normal fuel consumption with a combo like this, but if its what others are seeing ill at least know where im at and stop looking for problems.

 

Forgot to mention I did a compression test and all holes were 150-160psi

 

No reply in 2 days, so let me take a shot....
Of course the 4.10 gears are going to hurt somewhat, but not that much.
Have you looked at the long term fuel trims to see if its running super rich?
Any chance you could put an AFR gauge on the exhaust and see where its cruising. \
Is this a lockup converter?
As a quick guess, the 4.10 gears, hotter cam, cruising at a super rich 12AFR and non-locking/slipping converter could get you down to 10mpg.

 

thank you for your thoughts and reply. I’ll try to answer all your suggestions.

I inspected everywhere around all joints on the exhaust and can’t find any signs of leaks. There is a wideband in the downpipe which I log and use for tuning.
stft and ltft are disabled, I am running full open loop but collect a large amount of logged driving. The tune is close enough that it is within 2-3% of where it should be pretty much everywhere below about 5psi of boost.
I pulled all plugs to make sure it wasn’t obviously way off due to the wideband being wrong. I have not continued down the rabbit hole of validating my wideband yet but I haven’t found any evidence it is suspect.
The truck has a 4l80e with triple disk converter that locks only in 4th, though my tune at low throttle input is quite conservative and gets through the gears and into lockup pretty quick.
for one full tank of gas I drove very conservatively back and forth to work which is only a few stops, mostly cruising 40-60mph so the converter was locked almost the entire time. That tank netted me 10.5mpg.
I have calibrated the speedo using gps and it is less than 1mph off at 70.

The next thing I want to try is sending the injectors out for cleaning. They are deatschworks 78s that are a few years old with lots of time sitting around installed in the truck.

 

If your looking for fuel economy, That's not the cam to run...
The smaller 1838 would be a better choice especially in a 5.3L

I have an Old Comp XR265HR in my 5.3L.
Stock L59 <-Factory Flex Fuel
Ported 706 Castech heads with 2" intake 1.57" Exhaust and Milled .025 to 58cc

Now depending on driving conditions and what type of fuel, It can be as low as 12MPG all street or as high as 17MPG steady cruising and all highway.

 

Trend,

I have a SS2 in a 77 c10 with twin turbos, th350, 308 gear, and a 28 inch tall tire. It cruises 70 at 2800 and it got 16 MPG on my recent 3500 mile trip. I still dont have the VSS hooked up and it was gangster rich on decel but still did well. I cruise around 12.8-14.0.

 

Good data point, thank you.
I still haven’t given up but I also haven’t found much yet.