Truck MPG/towing question.

On the topic of small motor work hard vs big motor work easy, I have three data points that might be of some interest. All three vehicles towing the same ~2500lbs 18ft open trailer to the same track with the same ~2300lbs miata onboard.

2014 Acura MDX (DI 3.6, 6spd) - 17mpg

2015 Chevrolet Silverado 1500 (DI 6.2, 8spd) - 14mpg

2018 Ford F150 (Direct+Port Injection 2.7tt, 10spd) - 16.5mpg

 This over a 5 hour round trip from Greenville SC to atlanta motorsports park and back. Moral of the story is that it's kind of a crap shoot, but NA engines working hard seem to be more efficient. Peak BSFC is usually somewhere in the middle of the operating range and at higher load. 

morello159 said:

NA engines working hard seem to be more efficient. 

That's to be expected.

Tuning a forced induction engine to a point where it doesn't melt the pistons or the valves requires running rich, using the fuel to cool the combustion chamber.

That wastes gas. Lots of it if you're really beating on it.

2014 Acura MDX (DI 3.6, 6spd) - 17mpg

2015 Chevrolet Silverado 1500 (DI 6.2, 8spd) - 14mpg

2018 Ford F150 (Direct+Port Injection 2.7tt, 10spd) - 16.5mpg

What i'm about to say wouldn't be useful to the OP since he had a truck he loved and wanted to keep, but my experience towing has been that cars that are more efficient not towing are also more efficient while towing. I.e. I towed with a midsize car that got 26 empty and got 17 towing another car. I towed with a 4100 lb hybrid sedan that got 30mpg highway and it got 20mpg towing another car.  I've towed with multiple trucks and never approached the same mileage towing the same small car as i got while towing the cars with other cars!  Obviously some situations dictate a large tow vehicle and that's fine. But if all i ever had to tow was a miata on a small trailer (or in my case usually <3k lb vehicles on a dolley) i wouldn't necessarily seek out anything bigger than that MDX.   

As far as non turbo engines getting best mpg at high loads, it's substantially due to getting rid of the pumping losses it takes to make the intake manifold vacuum. Gas engines don't benefit from intake vacuum in any way, but it's a necessary side effect of limiting the airflow enough to have a rich enough mixture to be able to actually combust it at low loads. If you only want to burn a certain amount of fuel, you can only mix it with a certain amount of air, thus the need to limit airflow which creates the unpleasant side effect of the pumping losses. In diesels you have the whole cylinder so hot that you can inject at any 'air/fuel ratio' and it will burn. Gas engines on the other hand have to stay in a narrow AFR range to run properly.  Stock turbo setups are all built so that you have boost at any kind of high load. It is possible to build a turbo setup that won't make boost until past a certain RPM even at WOT and it would get the same or better mpg as the non-turbo under the same conditions, but that's not how factory setups are spec'd. 

In reply to ascott :

Actually, if the OBD2 data is to be believed, the AFR readings for my F150 and the MDX were not all that different under load. Ford must be using some serious fuel/ignition timing witchcraft with their knock control strategy to keep the truck from blowing apart at 15psi and 14.0:1. Generally, it runs pretty lean. 

If the ford is direct injected that makes sense. In my experience you can run .5-1 point afr leaner in di vs port injected with all else being equal until the power level is very high. 

In reply to morello159 :

They're using all kinds of EGR dilution tricks to cool the chamber, along with way less timing.

That's why you can throw a tune on that truck and pick up 150hp. Add the timing back in and ramp the fuel to 12:1.

ascott said:

In reply to morello159 :

They're using all kinds of EGR dilution tricks to cool the chamber, along with way less timing.

That's why you can throw a tune on that truck and pick up 150hp. Add the timing back in and ramp the fuel to 12:1.

What's that do to longevity? 

bobzilla said:

In reply to WillG80 :

This goes back to the same problem I have stated numberous times before, the 6.0 was ONLY offered in 2500 and larger trucks with a 4L80 and 3.73 or taller gears. My original proposal was the 6.0L engine in the lighter truck with the 3.23 or 3.08 gears. A 6.0 at 1800rpms makes significantly more torque than the 4.8 or even the 5.3 and the slower engine speed and load would theoretically improve economy. 

Maybe someday I'll find out. If this 4.8 ever pops I'll snag a 6.0 to replace it. 

If you have any interest in trying a tune for your truck I have an ECU from Black Bear performance, that might fit that truck. I'd be happy to get you the info off of it if you wanted to call Black Bear and see if it would be compatible.

I bought it to go on a 2005 Avalanche 5.3, then sold the truck before installing it. Black Bear offered to take it on trade for a tune for the '07 2500/6.0/6 speed I bought, but I never did anything after speaking to him.