New Fuel Economy Information site

[redpoint5]

It also increases surface area, meaning more of the combustion chamber heat will transfer to the spark plug. Probably negligible, but it's there.

[RealityRacer]

According to Fueleconomy.gov website here are the stats that seem correct:
Petrol vehicles are 12% to 30% efficient,
Engine losses: 68% to 72% (thermal losses 58% to 62%),
Wind resistance: 8% to 12%,
Rolling resistance: 4% to 7%,
Braking: 4% to 7%,

So that would make engines overall 28% to 32% thermally efficient.
Combustion losses: 3%,
Friction losses: 3%

Discounting pumping efficiencies, we can improve engines theoretically by 64% to 68% (adding thermal, combustion and friction losses).
Compare that to 8% to 12% wind resistance losses.

[mpgmike]

Back when we did the X-Prize Sonata, the EPA stated engines were 18% efficient. That was the primary reason we chose a stock vehicle and focused exclusively on engine related modifications instead of impractical carbon fiber toys that dominated the competition.

[redpoint5]

Diesel engines are about 50% efficient.

Plenty of ways to make ICE more efficient, but there are tradeoffs.

Gasoline engines could easily be run at high compression like diesels and gain a ton of efficiency, but then NOx emissions would be through the roof. We could eliminate the catalytic converter and get a boost in fuel economy.

There are no solutions, only trade-offs.

[RealityRacer]

There are solutions if you really want to find them.
The issue you all have been experiencing with engine efficiency or overall vehicle efficiency is the limitation imposed by the ECU due to EPA standards that are specified for the design of the vehicle.
For some vehicles, there is more flexibility in this imposed MPG limit. The ECU is limited in its ability to provide greater MPG than is specified on the window sticker.
If you can successfully supercede the imposed MPG limit and keep the emission feedback system unaltered, you are in a winning situation.

[redpoint5]

Originally Posted by RealityRacer

There are solutions if you really want to find them.
The issue you all have been experiencing with engine efficiency or overall vehicle efficiency is the limitation imposed by the ECU due to EPA standards that are specified for the design of the vehicle.
For some vehicles, there is more flexibility in this imposed MPG limit. The ECU is limited in its ability to provide greater MPG than is specified on the window sticker.
If you can successfully supercede the imposed MPG limit and keep the emission feedback system unaltered, you are in a winning situation.

I'm not following what you are asserting. Please be more explicit.

I know for instance that certain tuners allow a diesel engine to run more efficiently, but that comes at the cost of emissions compliance. Heck, we've now got particulate traps that simply burn fuel to generate heat to vaporize those particulates. That's an inefficient process.

There is no such thing as imposed MPG limit. Nobody and nothing stands between a driver and any MPG they wish to strive for.

[freebeard]

There are no solutions, only trade-offs.

...a Thomas Sowell might say.

Originally Posted by RealityRacer

There are solutions if you really want to find them.

And those solutions require tradeoffs. Reductio ad absurdum.

[RealityRacer]

The ECU is limited internally in its programming to not exceed an MPG due to EPA certification- see window sticker. For the vast majority of vehicles, higher efficiencies are circumvented because the vehicle is designed for catalytic converters to function at 800F (idle) to 1800F (cruise). That's a lot of fuel being burned in those catalytic converters. There is a way to gain more mechanical advantage on the piston by accelerating the burn rate. To do this we must exert more pressure on the piston between 15 degrees and 30 degrees after top dead center. If we increase the burn rate and prevent the ECU limitations, significant efficiencies can be realized.

[mpgmike]

In casual conversation with a Ford engineer, he told me that life would be so much easier if the EPA just told us (Ford) to meet these specific emissions requirements, regardless of how you do it. Instead, they tell us what emissions levels are acceptable, but also what type catalyst we must use, what fuel delivery system strategies are acceptable, that we must choose from their approved ECU manufacturers, and the list endlessly goes on an on.

I will stake my reputation, my life, and all hope for future happiness on the proven fact that engine combustion efficiency ABSOLUTELY CAN BE IMPROVED WITHOUT INCREASING EMISSIONS; perhaps not with the limited list of approved technologies provided by the EPA to OEMs, though.

[Piotrsko]

From what I know: there is no mandate for emmisions equipment to properly function, but it has to be installed and supply working data to the OBDS within parameters. If you can increase efficiency and stay below current cleanliness regulations at the tailpipe end, then by all means do so and share your results. Inho, that is the ultimate ecomodder mantra