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

Gokhan · Jul 2, 2024 at 2:48 AM

fuzzy1 said: ↑

Not quite. There have been several methodology updates over the years, and the older vehicles have been updated only part way, not all the way to the latest methods. E.g. the 1984-2007 model figures have been updated only to the 2008 method, not to subsequent updates.

IIRC, up through 2007, there were only 2 tests. 3 additional tests were added for 2008, and old ratings were 'updated' to 2008-equivalents by ad-hoc adjustment factors, not by re-testing any old models.

Also IIRC, 1983 and older models used just the original CAFE results, without any EPA de-rating.

EPA: 2017 Ratings Changes

"EPA updated its method for calculating the fuel economy shown on new-car window stickers starting with the 2017 model year.

EPA periodically updates its methodology to account for changes in vehicle technologies, driver behavior, and/or driving conditions. The 2008 changes (see below) were broad revisions to the entire methodology that affected every vehicle.

The 2017 change updates some of the calculations used to estimate fuel economy. The new calculations are based on test data from model year 2011–2016 vehicles. ...

...

Comparing New Vehicles to Older Ones
You may see 2016 vehicles with the old fuel economy estimates on the window sticker along side 2017 vehicles with estimates based on the new calculations. To help you compare vehicles with new and older ratings more easily, the estimates in Find and Compare Cars have been adjusted:

The original estimates for model year 2011–2016 vehicles have been adjusted to match the revised 2017 calculations.

The ratings for most vehicles are unchanged.

Ratings changes are small for affected vehicles. Some go down by 1 to 2 mpg.

Ratings for 2008–2010 model year vehicles are still based on the 2008 methodology.

Estimates for model years 1984–2007 have been adjusted to be consistent with the 2008 methodology.

2008 Changes
EPA updated its methodology in 2008 to account for (1) faster speeds and acceleration, (2) air conditioner use, and (3) colder outside temperatures. Since all of these factors lower fuel economy, the 2008 changes lowered fuel economy estimates for all vehicles.

See How Vehicles Are Tested for more information."
Click to expand...

Yes, but from my experience, both the updated old-methodology numbers and the new-methodology numbers are right on the money with the real-life mpg numbers. So, I believe the updated 1994 Geo Metro XFI numbers.

The Consumer Reports mpg numbers—not so much.

bwilson4web · Jul 2, 2024 at 4:15 AM

Gokhan said: ↑

The Consumer Reports mpg numbers—not so much.
Click to expand...

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

fuzzy1 · Jul 2, 2024 at 5:21 AM

Gokhan said: ↑

Yes, but from my experience, both the updated old-methodology numbers and the new-methodology numbers are right on the money with the real-life mpg numbers. ...
Click to expand...

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?

The Consumer Reports mpg numbers—not so much.
Click to expand...

Agreed there.

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

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

Gokhan Senior Member

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