highway fuel mileage in a large pickup comes down to aerodynamic drag, heat losses, , pumping losses and rolling resistance. 10spd and AL body panels do nothing for either of these factors so you can expect the results to be less than stellar.
How does Cylinder Deactivation actually save fuel?
- Thread starter Voltwings
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highway fuel mileage in a large pickup comes down to aerodynamic drag, heat losses, , pumping losses and rolling resistance. 10spd and AL body panels do nothing for either of these factors so you can expect the results to be less than stellar.
Get a good tune. Not an AFM piggyback or a handheld POS. Good tuning will turn off the AFM yet still provide better economy. It will also eliminate the possibility of a collapsed AFM lifter, but the cam lobes are still prone to pitting with maintenance neglect.
Even city fuel mileage is disappointing. A '14 F-150 that is much heavier and down 4 gears is only down 2 mpg in both categories.
Well it can be turned off. The above is correct. So it won't function any longer. But the ultimate goal is to go to the more reliable non-afm lifters and remove all of the crap in the first place.
My personal vehicle is a 15 Lariat 5.0 with the 6 speed on 34.5" KO2s. It gets significantly better mileage than my work vehicle, a base model 16 Tahoe 4WD with the 5.3 on stock size tires.
Every 100 lbs is only a ~2% increase in mpg. Even being down 500 lbs you're talking best case scenario of 10% improvement in mpg, and on a vehicle that only gets 15-20 mpg to begin with...
That's such a small piece of the puzzle though as others have said; gearing, rolling resistance (tire width and treadwear), wind resistance, lifts, driving style, etc...
Corvette is marginal improvement. 2-3 mpg maybe..
What he said. Dead on 100% correct.
An engine of a particular displacement has to have a certain amount of fuel to meet the air-fuel ratio requirements for good burning. Too lean or too rich, and emissions go right through the roof, and too lean also makes the engine run hot. Fuel economy falls off, as well, almost as much when lean as when rich, ironically.
So, your Chevy 350 V8 has to make 20hp to make you go 65mph. But since those 350 cubic inches of volume require a specific minimum quantity of fuel to ensure the proper air fuel ratio, you have an engine that makes 150hp, 130 more than you need. The only way to reduce the quantity of fuel is is to reduce the amount of displacement to which you need to add enough fuel to hit the magic air-fuel ratio number.
Now, there is a better way to accomplish the same thing, with real-world improvements in fuel economy far better than cylinder deactivation:
For normally aspirated engines, it's the Atkins-cycle, for supercharged engines, it's the Miller cycle. By altering the intake valve timing you can leave the intake valve open at different times in the intake cycle, so that some of the air your cylinder just took in is pushed back out. When the intake valve closes late, you have a correspondingly smaller charge of air to which to add fuel to get the proper air-fuel ratio. The only loss here is a slight plumping loss, with a long list of benefits, including keeping the whole engine up to operating temperature.
These cycles both require variable cam timing and direct cylinder injection of fuel to be truly useful. Now that both of those items are reality, many automakers are incorporating them into their engine management systems.
Oh, then I see.
But still, 5-10% on 10'000 vehicles is a number that's scary to even count on.
So I understand why the manufacturers do this. But I also understand you point of view.
Fun fact, your engine will actually get better mpg at run COOLER at a 16:1 AFR than it will at 14.2, but 14.2 is where there are the least combination of harmful emissions, which is why it is targeted by manufacturers.
I do some recreational tuning, i wont call myself a professional by any means, and was playing around with lean burn on my old mazdaspeed3 and was doing a lot of research on it.
I attached the emissions bell curve, and im sure if i looked a little harder i could find the heat one as well, but i need to get back to work haha.
Attachments
But how much air has each cylinder ingested when at part-throttle? Running at steady state on the highway will have an engine constantly under vacuum. Or am I thinking about this wrong...?
Not wrong at all, and a very good point! The other part of the equation, though, is that part-throttle is a net pumping loss. The higher the vacuum is a direct indication of how hard the engine is working to get air. The engine has to work harder to get a smaller breath, so what you gain in reduction of volume of air to which to add fuel, you lose in the effort it took to get it.
That is the other nifty trick of the Atkins/Miller cycles that absolutely demands variable timing to achieve: when you control the amount of air the cylinders get with the valve timing, you can leave the throttle wide open and eliminate those pumping losses.
Interesting. Are you familiar with the piston engines used in light aircraft? Those guys routinely cruise at something called "lean-of-peak," Is what you were doing here a similar sort of thing? The aircraft guys can get away with it because emissions are not a concern for them (for now).
No idea, i'll have to check that out though.
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