Spark Plug Gap - Prius MPG Test

I'm testing different spark plug gaps to see if it improves mpg if you increase the gap. The test car is a Gen 3 Prius. I also show test results on a Toyota Prius C. The tires are set to 40 psi cold. This car has a K&N air filter installed. This test shows some kind of results, unlike my previous test with the tire pressures! Enjoy the scenic drive from Kailua, through Waimanalo, to Koko Marina Center in Hawaii Kai.

I don't have any video of the Prius C test, because back then when I had the car, I never thought I would ever make a video on fuel economy. I was only expecting a small gain in mpg, I was very surprised of the results! This is a free or cheap mod to do, as long as you don't break the tip off a spark plug. I just wanted to share my knowledge, especially if it can help others.

Notes:
When checking the gap on new or low mileage spark plugs, I find it to be slightly smaller than what it's listed at. For example, a 2010 Toyota Prius Denso spark plug SC20HR11 has a gap of 1.1 mm or 0.044" according to Denso's website. I measured it to be closer to 0.040" or 1.0mm. Same with the Prius C, the FK16R-A8 plug has a gap of 0.8 mm or 0.032". I measure that plug gap at 0.028" or 0.7 mm. Why such a small gap? It don't got a turbo, and it's not making a boat load of power. It must be the super high 13.4:1 compression ratio! But the Gen 2 Prius has the same motor, and comes with a 0.044" plug gap. I don't know.
The Gen 3 Prius has good driveability for both the 0.040" and the 0.045" plug gaps and one gets slightly less mpg. The 0.045" gap feels a little bit stronger at light throttle when the gas engine kicks in. Throttle response is better with the larger gap. As for full throttle acceleration, I can't tell the differences.

Chapters
0:00 - Intro
0:20 - Removing the spark plugs
2:00 - Checking and gapping the plugs
3:34 - Kailua to Hawaii Kai city test route
7:52 - Kailua to Hawaii Kai test results for the Gen 3 Prius and Prius C
8:31 - Honolulu city and highway route
11:38 - Honolulu route test results
11:48 - GoPro airbox cam, intake sound test
12:33 - Summary

Kailua, Hawaii
Waimanalo, Hawaii
Honolulu, Hawaii

Music from the YouTube audio library:
Champ - Gunnar Olsen
Dat Step - Gunnar Olsen
True Love - Silent Partner
Jah Jah Bangs - Quincas Moreira
Smooth and Cool - Nico Staf
Cliff Side - Silent Partner