It’s all about marginal cost and benefit. If the marginal benefit – in terms of higher sales price, perceived value, brand reputation for innovation, etc. – exceeds the marginal cost (R&D cost, manufacturing cost, warranty cost, etc.), the thing will be added.
Dimpled pistons probably only improve efficiency and performance by a small amount, but it’s more than enough to justify the lifetime cost of having them.
This is a very old debate most of us have moved beyond.
Engines with timing chains can also be interference engines. We own 2 of them. My Dad owned a 71 Toyota Corona with a timing chain and it was an interference engine.
You are garunteed lower horsepower and lost MPGs if rhe engine is not an interference design. High lift variable camshafts, high compression ratios and all the efficiency that goes with it will be lost if enough clearance is created to make the engine a non-interference design.
This is preferrable, in my opinion, to making the engine mistake proof.
@Mustangman. I will take the lower MPG and less power than the interference engine. In fact, I would prefer the flathead engine to an overhead valve engine. I have a couple of colleagues where the overhead valve engine ‘swallowed’ a valve and the engine was destroyed. That can’t happen when the valves are in the engine block. Give me the old time flathead engine, preferably a Continental Red Seal engine in a Checker.
And how many times in the first 100k miles will you have to change the head gasket?
On the flat head Dodges and DeSoto my parents owned, they never had a head gasket blow. It wasn’t a big deal to replace a head gasket. I pulled the head on my flathead 1947 Pontiac 6 when I thought the head gasket was bad. It turned out to be a crack in the engine block around a valve seat. I slapped the head back on, poured K&W seal in the radiator and drove on.
The Hudson Hornet with its 308 cubic inch flathead 6 won a lot of stock car races back in the day. Of course, the superior handling of the Hudson also contributed to the many victories as well as great drivers like Tim Flock and Marshall Teague. Those were the days when the cars were practically driven from the showroom to the race track. The drivers didn’t have to pull into the pits to change a timing belt on an interference engine.
There was also a 1949 Plymouth flathead 6 coupe that was very competitive in the stock car races. The Plymouth could go further on a set of tires and didn’t need a pit stop for new tires.
I bet a flathead engine would torture a catalytic converter.
All those nooks and crannies would hold lots of unburned HC each cycle.
A wood-burning boiler with secondary combustion might be cleaner. 
Among the odd fleet vehicles that I have maintained a few had Continental flat head engines and they were usually pushed to the max when operated although they were so under powered they didn’t get many miles but I never saw one require a head gasket. Similarly many flat head stationary engines came across my floor and likewise they never had head gasket problems.
And the L79 Corvette engine was 11:1 and had dimpled pistons
You will have to drive the older models, then. The government regulations effectively outlawed those designs in new cars.
Same for ABS, TPMS, airbags and more.
While it’s true that in extremely rare cases an interference engine which has been properly maintained from a timing belt perspective can still end up being damaged by a faulty/poorly-installed belt, the same can be said about a lot of car parts.
Screw up the brake job and hit a tree. Screw up the transmission fluid exchange and roast your gearbox.
Look at oil changes. That drain bolt is a single point of failure. All it takes is for the dope at Iffy Lube to leave it off or loose, and you’re looking at destroying your engine. This should not lead to the conclusion that we need to pursue oil-less car engines.
The bottom line is that if you get the timing belt changed on schedule, you will probably never experience the down-side to owning an interference engine, and meanwhile you have more power and better fuel economy for the entire time you own the car.
As you get more into cars (or airplanes, or rockets, or anything else that moves under its own power) you realize more and more that everything is a compromise. Want your rocket to go higher? You’re gonna need more fuel. And then you’re gonna need even more fuel to lift the extra fuel you need.
Want your airplane to take off in a shorter distance? You’re gonna need more wing, less wing sweep, etc, which will limit your top speed. Conversely, if you want your airplane to cross the Atlantic without stopping for fuel, you give up the ability to land on very short runways because you end up with an airplane that has to go faster in order to fly than the Piper Cub you replaced.
In cars, want an easier to maintain engine? You’re gonna sacrifice performance, and possibly longevity.
Sure, @Triedaq’s engines were very easy to maintain, but how many of them accumulated more than 200,000 miles? I can still remember as a little kid in the early 80’s, our neighbor coming over and insisting on seeing the odometer in dad’s Corolla. He just couldn’t believe the thing had more than 100,000 miles on it and still ran well. Sure, you can find outlier engines from the 40’s (maybe) that got close to quarter-million-mile territory, but now it’s as common as water. Heck, you can still sell vehicles with 200,000 miles on them. Like, sell them, for real money, not pay someone to haul them away.
And power? If I recall that Plymouth flathead 6 didn’t hit 100hp until the 50’s. More like 97hp before then, hauling a 3,000 pound car around which means the 0-60 time would be “yes, eventually.”
Meanwhile my former Acura with its physically smaller interference motor and timing belt got better mileage while putting out 250hp, and it had 180,000 miles on it when I sold it.
That’s not to say that the old flathead 6 wasn’t a good motor for its day, but sacrificing some ease of repair is not automatically a bad thing if you gain efficiency, power, and longevity.
There were good reasons that Checker Cabs replaced the Continental flat head with a small block Chevrolet and the manual transmission with a Turbo-hydramatic and it’s unlikely the move was to be fashionable. But there is a great deal of peace of mind holding on to well proven machinery rather than jumping at every new gimmick. Rolls Royce was one of the last manufacturers to drop manual transmissions and mechanical brakes and look at the reputation they had.
The most interesting application of a flathead engine I ever saw was on a Jaeger air compressor that was being used to power jack hammers. I was sitting in my office with the window open and a crew was busting up the concrete in the street to get to a water main. The engine in the compressor sounded like it wasn’t running on all cylinders. I was curious, so I went out to investigate. The engine really wasn’t running on all cylinders. It was a Chrysler 6 flathead. The engine ran on the back three cylinders and air was compressed by the front three cylinders. The engine had one cylinder head for the power section and another head for the compressor section.
@Rod-Knox. Continental wouldn’t renew its contract with Checker, so Checker had to find another supplier for engines.
Continental did offer two types of engines for Checker. One was a flathead 6 and the other an overhead valve 6. When Continental no longer supplied engines to Checker, Checkers were available with either the Chevrolet 230 cubic inch 6 which replaced the ‘stovebolt’ 6 in 1963 or the small block Chevrolet V-8.
It seems my only knowledge of the changes were the ones I saw under the hoods and Checker automobiles were and still are rare around here. But all that I have seen were the very old flat heads and the small block Chevys. They were great automobiles when you consider how well they suited the needs of a taxi.
I recall tuning up Freightliner Continental flat heads and setting the idle so slow that you could count the fan blades. But pulling an empty tandem axle trailer was about all they could handle. And traffic would stack up behind on long stretches of 2 lane with no safe place to pull over.
Guy I worked with owned an old flat-head Ford. He kept spare head gaskets in his trunk.
Those Ford flat heads were a curiousity to me @MikeInNH. With the exhaust being ported through the block it was necessary to have 2 thermostats and 2 water pumps I guess. I never had any hands on experience with them though.
@Rod-Knox. You are right about the Ford flathead V-8. These engines also had a tendency to overheat. In 1941, Ford offered a flathead inline 6 cylinder engine. Up to 50 mph, it supposedly would out accelerate the flathead V-8, and it didn’t have the problems of the flathead V-8. In 1952, the flathead 6 was replaced with a modern overhead valve inline 6. This engine really outperformed the flathead V-8, yet Ford charged more for its flathead V-8. For a company known for its V-8 engine, the 6 cylinder was probably the better engine back in the days.
While today’s cars and rheir engines are much more efficient and require less maintenance, for me the trade-off has been the ease of maintenance and repair. I always looked at things in terms of time. If I could do the job in the same time or less than scheduling an appointment and taking the car to a shop, I did the job. As things became more demanding as a university professor in terms of publishing and writing grants, and cars became more difficult to service, I did much less work on my own cars. I have gotten involved in so many things after I retired 9 years ago that I still don’t have time to do repair jobs either on our vehicles or on our house.
The situation for younger people in higher education is even more demanding. Our son is a college professor. He sold his three bedroom house that was 35 minutes from his campus and bought a two bedroom condo a five minute walk from his residence to his office. He not only gained an hour a day in getting to his job, but doesn’t have to take care of a yard. This way he can meet the demands for his job and have time with his family…
As to the interference engines, I would choose a today’s vehicle with the modern engine over a vehicle from the old days with a flathead engine. I just like to reminisce about the good old days when I was more competent in doing things myself.
While I wouldn’t leave for the west coast in a 60+ year old car I do have a great deal more appreciation for them than most people and if I could find a nice old clunker for every day driving around town I’d seriously consider buying it. Maybe an old slant 6 Valiant with a floor shift manual or a 4 cylinder Chevy II stick shift. Bare bones models though. But those cars weren’t considered collectible and have mostly been scrapped.
@Rod-Knox. I think of the Valiant with the slant 6 engine and the Chevy II as modern cars. One of my fellow graduate students when I went to graduate school in 1962 bought a new Chevy II with the 4 cylinder engine and the three speed column shift manual transmission. He hated that car. It did vibrate when idling. If you bought a cup of coffee at a McDonald’s which didn’t have indoor seating in those days and added sugar to your coffee, you didn’t have to stir. All you had to do was start the engine. Consumer Reports described the feel of the car as “something from the early days of motoring”.
The slant six was a much better engine than the 4 cylinder Chevrolet engine and it was around for a long time. My aunt had a 1964 Dodge Dart with that engine. She gave it to my brother sometime in the mid 1990s. He drove the car from Florida to Ohio, advertised it in the paper, and had a string of buyers lined up bidding on the car.
I like cars of the 1940s and 1950s as long as someone else owns them.
