Why did six cylinder cars mostly disappear?

Necessary Fractional Fuel economy and emissions improvements to improve fleet economy on paper to meet law.
Also the law forces manufacturers to treat each engine and transmission option as a separate completely unique designed car that necessitates 100’s of millions of dollars of extra compliance and crash testing for each engine option.
Cars also are required to get much better fuel economy than a suv/truck/cuv/minivan/wagon due to the regulatory environment which has only made it harder to produce an actual car/sedan profitably. (The real reason cars are getting rare)

These same laws convert every pickup into a larger long wheelbase short box with a passenger car layout for the cab.

Even if a A bench seat long box pickup gets better MPGs it
“hurts” fleet fuel economy by getting half the fuel economy per passenger volume on paper towards fleet economy . AKA it’s effectively double counted in the red which costs the manufacturer $10’s of thousands in pollution credits.
This is also why small fuel efficient trucks are nearly illegal even without the chicken tax. (Small trucks would need to get over 50mpg to not drive fines in the regulatory environment and would also need to be cheap, meet crash and emissions)

This same effect penalizes manual transmission cars.
Manual transmission vehicles in the real world exceed epa by about 10% consistently, automatic cars universally are about 10% under epa.
Why?
The manual transmission test for both fuel economy and pollution is dramatically different than the one for the automatic and thus invalid .

These types of meniscia are eliminating vehicle choice and options and there is no evidence that our outdated platform laws even make sense at this point (draconian and wasteful)
But the only way to fight them would be to ban Reagan era grey market laws but nobody wants to reduce automotive market protections.

At the rate we are going every vehicle from a manufacturer may one day be like a model T but always with the same engine

 

Fewer cylinders = lighter weight, take less room under the hood, have a lower parts count, and those specific parts excluded were on the more expensive side.

Today's 3 and 4 cylinder engines are easily doing the work of yesteryear's 6 & 8 cylinder engines with better fuel economy, lower purchase costs and fewer points of failure.

 

Mainly economy - couldn't imagine buying a commuter car with a 6 cylinder and paying the penalty in higher fuel cost - the math doesn't make sense.

Being used to getting 50 mpg in our vehicle a six cylinder engine is just not going to compete with that type of efficiency.

Cars are doing just fine - Camry, Corolla, Crown, Prius as well as a wealth of entries from the South Korean makers - the sedan is here to stay. Most of Toyotas sedans/cars now get over 50 mpg and this type of mpg is only going to increase as time goes on - 6 cylinders can't compete.

Now in Trucks and SUV's the 6 cylinder is having a comeback in certain sectors - these vehicles have a different job than just commuting - many haul loads, tow etc. A well-made turbo charged 6 cylinders can handle many of these tasks as well as an eight cylinder and do it more efficiently.

 

Dropping from 6 to 4 cylinders seems to often involve adding a turbo charger.

 

an important reason to keep up with maintenance and to change your oil at 5K miles intervals vs OEM's 10K recommendations. A lot of formally metal parts has been replace with composite or plastic parts - Not going to past the test of time and all those cold/heat cycles. IMHO

 

Maybe three decades ago I heard a Porsche engineer explain why they will transition to all four cylinder engines; they have less loss to friction and will be able to make as much horsepower as they will need. That sounded pretty implausible to me then.

Apparently he was right.

That Toyota and Honda still make competitive sedans doesn't mean the segment is healthy or here to stay. Those two make up a huge portion of all sedan sales. Ford and GM are primarily manufacturers of trucks/SUVs in the US market. The problem with the future of the regular car is that the people most wedded to it are old and getting older.

I was a big fan of the three door hatch; nearly every manufacturer used to make one. Cheap, fun and versatile, I bought them with manuals and never regretted the choice. That market is gone. People don't want to look poor, which apparently lots of people equate to hatchback ownership.

Sedans are currently the best cars for the dollar if you don't mind not being able to see through the Sequioa or Excursion you'll be stuck behind. As they are increasingly seen as the cheap choice, more young people to whom driving a truck doesn't seem weird will see SUVs as aspirational.

 

Sometimes, anyway.

It's no big deal to get 200ish horsepower out of a 4-cylinder engine without a turbo. Adding one gets you to 300-350hp these days.

So if you can cover the low end of 6 cylinder applications with a normally aspirated 4, and the upper end by 'simply' adding a turbo, there's a whole lot less need for the larger blocks with more cylinders.

...do keep in mind that that's a crazy amount of power for ordinary transportation. A lot of the classic old V8s that are so fondly remembered by "gearheads" were producing 90-120hp out of the factory.

 

Cars we own:

Prius c
Mazda 6

Cars we considered, on the path to getting those two:

Chevrolet Malibu
VW Passat
Ford Fusion
Mazda 2
Toyota Yaris

What do all 7 of these cars have in common?

They've all been discontinued. Somehow we have a perfect record for wanting something the industry doesn't want to make anymore.

Maybe I can take it as validation for spotting good values?

Owning some nice places to park the cars always appealed to me more than the cars themselves.

 

china cornered the market on 6 cylinders and dumped them in third world countries

 

Easy!
Math and
CAFE.

Same reason you can no longer buy a compact pickup truck.