LC9 Fuel Economy

Blue Chevy Truck 20657 · March 17, 2014

The Table below is a part of a calculation spreadsheet I created to improve my understanding of fuel economy for the LC9 drive train on my 2010 Chevy K1500.

I was unable to upload the spreadsheet so the best I could do is the table below. The websites used:

1. http://www.chevrolet.com/performance/crate-engines/lc9.html

2. http://www.mk5cortinaestate.co.uk/calculator3.php

3. http://www.ehow.com/how_8697811_calculate-volumetric-efficiency.html

4. http://www.mp3car.com/engine-management-obd-ii-engine-diagnostics-etc/75138-calculating-mpg-from-vss-and-maf-from-obd2.html.

The calculator uses all the available inputs to estimate MPG by RPM/Speed:

Engine Displacement, Tire size, Rear Gear Ratio, Transmission Ratios (6-speed) & Air flow rate.

The outputs are RPM v Speed v MPG for each gear combination with Volumetric Efficiency. The output does not include the effect of AFM Cylinder Deactivation, maybe one of you can help me model that.

What did I learn?

1. The most efficient speed is 73 MPH (~20 MPG), I rarely (almost never) get to go that fast.

2. The model confirms that around town driving should yield ~17 MPG.

Questions and comments welcome.

Blue Chevy Pick-Up

6th Gear

RPM MPH MPG

750 31 17.1

1000 42 16.9

1250 52 16.8

1500 62 18.2

1750 73 19.9

2000 83 16.6

2250 93 16.4

2500 104 17.1

karlde · March 17, 2014

Using the DIC in my Sierra and using Instant MPG on my daily drive up I-71 for about 30 minutes I have found driving 70-73 MPH, I get 18 to 13 MPG depending on wind and the grade of the road. Going up hill it get less than on flat land or going down hill. A strong head wind or side wind will decrease overall mileage usually below 15 MPG.

I don't know how scientific this is or how is compares to your algorithm but it make sense to me.

Karl

Blue Chevy Truck 20657 · March 17, 2014

I don't have the benefit of a DIC display as the dash & interior is very basic. It's no surprise head winds and hills make a big impact on fuel economy. The model was tuned to the ~20 MPG that really did happen on a ~75 MPH drive from North Carolina in January.

Thanks,

Blue Chevy Truck

Cowpie · March 17, 2014

Since aerodynamics also plays into this, and we have 6 gears in these transmissions now, I would take a look at various RPM's and speeds in 5th gear. There is no government or manufacture mandate that the top gear always be used. The 18 speed in my commercial truck hasn't ever been in the top gear since I bought it new 237,000 miles ago, and it has seen speeds of 85+ mph several times.

Aerodynamics have a negative effect on a rising curve as the speed goes up, especially above 55 mph. And there are instances where lugging the engine at say 1750 RPM would have a negative effect on economy compared to running 2100 RPM. Load on the engine plays into this as well. And rotational inertia plays into it. At lower RPM's, the engine may be fighting rotational inertia more than at a slightly higher RPM.

There are just too many factors that can effect fuel economy to narrow it down to a spreadsheet. It is fun to play "what if" games with this kind of stuff, but it takes some very serious processor time on a heavy hitter computer system to model all the various aspects that affect fuel economy.

Rear end ratio also plays into this. Are you basing your assumptions on a 3.08, 3.42, or what? Must be 3.08, as 3.42 at 1750 RPM with the 6 speed trans and factory rubber yields about 68-69 mph.

Was looking at the first link and playing with the slider and watching the gauges move. Interesting that the chart shows max torque at around 340 ft lb, but the gauge goes well over 400 ft lb when one moves the slider.

Blue Chevy Truck 20657 · March 18, 2014

I have the 3.42 rear, as the table indicates, the truck goes 62 MPH at 1500 RPM. I've often wondered if I couldn't get better MPG by driving in 5th gear (M-mode) and forcing the throttle into a higher volumetric efficiency.

Cowpie · March 18, 2014

I will generally run in M5 on everything but 4 lane freeway, where I will let it kick to 6th. Main reason is that when in 6th on hilly stuff, it constantly is hunting and searching for the gear to get it done. Seems like every little molehill causes a downshift to get over the rise if the vehicle speed is below 65-70, or loaded at that speed or even a little higher. And that shifting will eat fuel like crazy. So I will run in 5th on anything below 65 mph and greatly reduce the shifting. I have found also, that even at speeds like 65-70 on the freeway, when the wind or a load is really making the engine work, it can get a mpg improvement by running at the slightly higher RPM of 5th. Reason is that at the lower RPM it actually takes more throttle to get the same job done and also that there is some rotational inertia that the engine is fighting against as well. EGT's will tend to rise higher at hard working lower RPM's which reflects an increasing restriction in the exhaust stream due to exhaust cooling along the route to the tail pipe. By increasing the flow with a little RPM, you are actually decreasing the workload on each cylinder by overcoming some of the rotational inertia, and getting the exhaust to flow a little quicker and get further down the line before it cools significantly to cause a bottle neck.

I gleaned all of the is stuff from working commercial diesels for several decades, and it seems to play out very similarly with our smaller gas engines. Principles pretty much remain the same. This is why I usually make the point, that the driver has more control over fuel economy than any mod ever could. Studies have shown the driver accounts for well over 1/3 of fuel economy variance. And this is even more pronounced when using tall ratios like 3.42 and 3.08 in the rears. You have to do more of the thinking for the engine. On a nice flat grade on a calm day, everything does as it should from the factory. But throw anything else into the mix, and things get screwed up. The ECM cannot read terrain, wind, and other factors. It just knows how to go and it will do whatever is programmed into it to make the vehicle go. If it feels it needs to downshift and floor it, it will. Yet another reason that I will remain off the cruise control on everything but 4 lane interstate/freeway running. I can see the terrain and the conditions and moderate the accelerator better than any ECM ever could. On the freeway loping along, there is a decided advantage to cruise control, unless someone is under a heavy engine load.

Blue Chevy Truck 20657 · March 19, 2014

I appreciate the info. I'll do more M-5 driving when conditions require it.

Thanks,

Blue Chevy Truck 20657

swathdiver · August 3, 2018

On 3/16/2014 at 9:29 PM, Blue Chevy Truck 20657 said:

The Table below is a part of a calculation spreadsheet I created to improve my understanding of fuel economy for the LC9 drive train on my 2010 Chevy K1500.

I was unable to upload the spreadsheet so the best I could do is the table below. The websites used:

1. http://www.chevrolet.com/performance/crate-engines/lc9.html

2. http://www.mk5cortinaestate.co.uk/calculator3.php

3. http://www.ehow.com/how_8697811_calculate-volumetric-efficiency.html

4. http://www.mp3car.com/engine-management-obd-ii-engine-diagnostics-etc/75138-calculating-mpg-from-vss-and-maf-from-obd2.html.

The calculator uses all the available inputs to estimate MPG by RPM/Speed:

Engine Displacement, Tire size, Rear Gear Ratio, Transmission Ratios (6-speed) & Air flow rate.

The outputs are RPM v Speed v MPG for each gear combination with Volumetric Efficiency. The output does not include the effect of AFM Cylinder Deactivation, maybe one of you can help me model that.

What did I learn?

1. The most efficient speed is 73 MPH (~20 MPG), I rarely (almost never) get to go that fast.

2. The model confirms that around town driving should yield ~17 MPG.

Questions and comments welcome.

Blue Chevy Pick-Up

6th Gear

RPM MPH MPG

750 31 17.1

1000 42 16.9

1250 52 16.8

1500 62 18.2

1750 73 19.9

2000 83 16.6

2250 93 16.4

2500 104 17.1