Featured Gen 6 Prius engine will be a “game changer,” achieve a 53% thermal efficiency

On their mystery number, I agree. However, their highway numbers are close enough. My previous Prius experience:

• First drive wait 1 minute - it typically takes 45-50 seconds for the catalytic converter to get hot enough for feedback, mixture control. If you have an OBD device, look for the catalytic converter temperature. Just wait at idle until it leans out.
• 63 mph - matches the highway numbers. Faster is less, slower is more.
• 22 mph +/- 3 mph - peak efficiency. The slowest cruise control setting, 26-27 mph. Find your minimum and add 2 mph for longest, most efficient speed.
• one hour minimum - this is long enough to reduce the startup and initial inertial load to less than 10% of the trip

These simple rules are how I got my 1,000 mi tank. Don't fiddle with 'feathering' or 'engine off' nonsense but rolling in "N" works on very long, shallow, downgrades.

Bob Wilson

 

I find them to be sand-bagged. Pessimistic. De-rated to lower than actual, outside of foul weather.

Maybe I don't speed fast enough?

Agreed there.

 

Ran into the same. I recalled the adjustment might have started a year or so after the start of the requirement, but left it off the post for brevity,.

These energy efficiency numbers are for their thermal efficiency. It is the amount of the fuel's thermal energy gets turned into work. The lower the percent, the less fuel the engine uses to turn the crankshaft. The rest is wasted in terms of the engine doing useful work.

You are moving beyond engine efficiency into vehicle efficiency. These are two different, but related, things. An engine can go into numerous different vehicles. All with different shapes, weight, equipment, and features. Put a car together wrong, and even the world's most efficient engine will return crap fuel economy.

Without knowing the specific car, talking vehicle efficiency of an engine is pointless. Knowing an engine's thermal efficiency is important because it sets the bar for a car's potential efficiency. The air drag, rolling resistance, drive train efficiency, etc. all subtract from it to get to the vehicle efficiency. All else being the same, putting a more efficient engine into a car will yield better fuel economy. It's how the OP of this thread estimated 75mpg for a Prius using Toyota's new engine, which is going into the new Corolla.

 

absolutely agree. I am sure they are getting these figures in the the lab, but when it goes into a real car cost, pollution controls, and reliability usually drop this figure except in rare examples like the vw XL1 which never got an epa rating because all 250 were presold outside the US.