What is the most important improvement that makes today’s gasoline engines last longer?

All of the above, with better engine oil probably being the greatest factor.

I started using synthetic oil in 1985 in my mother's Mercury Grand Marquis. She gave me the car when it had 70k miles, and I kept it to past 100k miles. I had it in the shop at a Ford dealership for fuel injection work at 100k miles. The service manager took of for a test drive after the work was done. He asked me if the car had a new engine, because he'd never seen a "302" run that good after 100k miles. A few years later, similar things happened with my 1992 Sentra SE-R (104k miles), my 1996 200SX SE-R (127k miles), my 2000 Silverado 1500 (74k miles), and my 2007 Chevy Cobalt SS (123k miles).

Cobalt's are supposedly notorious for burning oil when they get old. Mine still only burns about a half quart in 8k miles. But, most current Cobalt owners aren't willing spend the extra money on synthetic oil. That's money they'd rather spend on meth' or crack.

I'd say that the difference is lead free gas. Close second would be better fuel management with EFI.

The biggest change in oil has been longevity. Older oil formulations may not have been as durable, but the OCI was 2000 miles. So modern oil saves money and time, but the engines aren't lasting longer as a result.

None of the above. Improved oil and air filtration.

All of the above. Better ring seal=less blow by and contaminated oil. FI=cleaner oil. Improved ring and piston material. Modern engines generate much less heat. Compare the size of a modern radiator to a vintage one.

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Tony H
W111 280SE 3.5 Coupe
Manual transmission

Past cars:
Porsche 914 2.0
'64 Jaguar XKE Roadster
'57 Oval Window VW
'71 Toyota Hilux Pickup Truck-Dad bought new
'73 Toyota Celica GT

BINGO!!! This, along with improved cylinder wall-to-piston ring design virtually eliminates oil contamination from unburned fuel.

Do some research on "trumpet honing"...….interesting stuff

Virtually everything mentioned by the posters here are elements that CONTRIBUTE to longevity, but the question was about which is the most important.

Fuel control. Less over fueling. The cylinder rings dont have to deal with excess soot and raw fuel flushing the oil out.

Very good! That is indeed part of the winning answer!

Which engines? As compared to what? Old Mercedes Gasoline engines lasted way longer than their contemporary gas counterparts. So do they get thrown in to the comparison?

- Peter.

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2021 Chevrolet Spark
Formerly...
2000 GMC Sonoma
1981 240D 4spd stick. 347000 miles. Deceased Feb 14 2021
2002 Kia Rio. Worst crap on four wheels
1981 240D 4spd stick. 389000 miles.
1984 123 200
1979 116 280S
1972 Cadillac Sedan DeVille
1971 108 280S

Here's how I became enlightened about synthetic oil in 1976. My car at the time leaked and burned oil, and my parents' car at the time was all sludged up and not a candidate.

https://books.google.com/books?id=FAEAAAAAMBAJ&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=onepage&q&f=false

During WWII, the Germans created synthetic oil to improve the performance of their war machinery. WWII German tanks were found years after the war and yet their engines started right up!! The German company Lubro-moly still makes some of the best synthetic oils available. Amsoil, an american upstart, created a synthetic for the American market around 1972.

I consider both to be the top two synthetic oils for anything that travels on land.

My 36 hp 59 beetle has documented oil changes since new, 3k miles +/- apart. Engine has never been out for a rebuild. Dino oil all along, about 175k miles on it. VW geeks don't believe untill I pull out the two three rings binders

I think oil change frequency has something to do with longevity

my DAD used rpm delo,in his motor's. his 390 went over 320,000 miles .If anything belt drive timing sucks.New aluminum blocks bite too.

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1999 w140, quit voting to old, and to old to fight, a god damned veteran

Im gonna vote for: 4) Manuf. precision.

There is no way that WW2 era machine tools could repeatedly hold the tolerance that modern tools can. No matter how good your oil is, if the cylinder is out-of-round (and the inspection process doesnt catch it - you can't "inspect quality in") then the engine will wear and consume oil.
I'm leaving out any kind of production rate - yes an old hand on a lathe can cut anything to within .0001", but can he/she do 60 of them an hour ?

Better oils, better materials, smarter design engineers: these all help, but imo if you cant cut something to the 'correct' length, repeatedly, you end up with quality issues and shorter lifespans every time.

-John

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2009 Kia Sedona
2009 Honda Odyssey EX-L
12006 Jetta Pumpe Duse
(insert Mercedes here)

Husband, Father, sometimes friend =)