Forced induction effects on MPGs

[DAVECS1]

There are a ton of variables that go into the real world fuel milage of a Gladiator that is supercharged.

The pentastar has a control system that works a little different than what many hot rodders are used to. It works very hard to keep the AFR at stoich no matter the situation, it does this by utilizing timing, gearing, and throttle opening. It also works to run at 100 kpa or zero pumping losses.

With all that said the shift schedule on an automatic can be tuned much better than it came from the factory. A manual much less so, but still gains to be made

With a supercharger and a competent tune there are significant gains to be made supercharged. As mentioned above, you can run at positive manifol pressures with eliminated pumping losses, and this can be done with a positive displacement blower, almost right from idle. On an automatic you van then tune the shift schedule to use higher gears sooner and supplement power with a slightly higher enrichment rate. This allows you to keep the rpm down and utilize the lug curve and ultimately burn less fuel.

With 35s and 4:10s i can hold 7th and 8th gear pretty regularly. This puts me at about 4 or 5 lbs of boost at 2000 rpm and 75 mph. I get about 14.8 mph interstate with wind and family on board. Not bad for a lifted jeep.

My original tune that came with the SC netted about 13.4. so like I said there are many factors that play into it.

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[dcmdon]

I would suspect, an educated guess, that with a proper tune, a SC engine can be more efficient because you can use less throttle to achieve the same HP.
It takes xx HP to move a JT 70 mph on the level. If you can get that HP with less throttle, I'd expect no loss in MPG.
But - Dave can speak to that - the wizard of tune, the duke of supercharging, the Pentastar whisperer.......

manifold pressure is manifold pressure. It doesn't matter if its a wide open throttle in a normally aspirated engine or a supercharged engine forcing air around a partially closed throttle plate.

In either case you have the same mass of air being pushed into the cylinder.

And then you have the parasitic drag of the supercharger and the heating of induction air.

I guess we'll just have to agree to disagree.

Where forced induction can save fuel is if its used to allow a smaller, lighter, engine with fewer cylinders and reduced friction to replace a larger engine. But that's not what we're talking about here.

 

[DAVECS1]

Actually pumping losses from pulling air in can and does use up quite a bit of work. The big wow factor of the TVS supercharger pack was the fact eaton created a rotor design that actually took less work to compress air than what is created by the pumping losses of pulling air in. With that design there is less air heating during compression and it takes less to cool it when sized properly. Not all air compressors are created equal.

 

[ShadowsPapa]

Actually pumping losses from pulling air in can and does use up quite a bit of work. The big wow factor of the TVS supercharger pack was the fact eaton created a rotor design that actually took less work to compress air than what is created by the pumping losses of pulling air in. With that design there is less air heating during compression and it takes less to cool it when sized properly. Not all air compressors are created equal.

That's why early variable displacement engines closed valves to prevent those pumping losses when those cylinders were disabled. Then the air was more like a spring in the closed cylinder. They found the pumping losses to be substantial enough to be concerned with.

manifold pressure is manifold pressure. It doesn't matter if its a wide open throttle in a normally aspirated engine or a supercharged engine forcing air around a partially closed throttle plate.

Not sure what you mean by that - I was responding to the comment that a NA engine can't get better than 100% pumping efficiency.
They can and they do. It's a matter of intake design, exhaust design and cam profile. Not all intake manifolds are built equally. Runner size and length and more go into it. (Then there are dual plane intakes - that's a different matter)
I run stacks on my carburetors because it lengthens the effective length of the "pipe" going into the chambers increasing any "ram" effect.
When designing for performance you tune intake and exhaust designs keeping in mind that the pipe starts at the air horn and ends at the exhaust outlet (although really it's up further than that)

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