This was a hard list to compile. It could be put together based purely on historical significance, or era-specific performance, reliability, or even units sold and longevity of production. In the end, we took all of the above into account and picked out the engines that we hold in the highest regard as an all-around package. You may believe another engine or two deserved to make the list and, if so, do feel free to let us know which engine and why.

Porsche Flat-6

Porsche's air-cooled flat-6 was born into the world in 1964. Using the opposed piston design of the boxer engine, Porsche took the original VW Beetle's engine concept and put it into the crucible of performance cars and motorsport. Power started at 130 hp but, with help from turbochargers and with the transition to liquid cooling, by 1997 Porsche 911 models could be bought for the street making over 400 horsepower.

Ford Flathead V8

Ford's Model T wasn't the first car, but it was the car that brought personal transportation to the masses by making it affordable. Similarly, Ford's flathead V8 wasn't the first V8, but it was the V8 that brought 8-cylinder power to the masses by making it affordable. The name Flathead comes from the valves being seated in the block so the head is, effectively, a flat lid. It wasn't the most efficient solution for an engine, but the lack of complexity is what made it affordable as well as the hot rodder's engine of choice for over 20 years.

Duesenberg Straight-8

If Duesenberg hadn't been trying to sell the most regal and expensive cars of the early 20th century as America entered the great depression we would be talking about these engines more. Because more would have been made and sold. Unfortunately, the company folded in 1937 but not before making a 6.9-liter straight-6 engine that made 265 horsepower before the addition of a supercharger. The supercharged version made 320 horsepower. If that isn't crazy enough for a car built before the Nazis were conquering all but a small island in the Atlantic, two cars were built for Clark Gable and Gary Cooper that made 400 horsepower.

Chevrolet Small Block V8

In 1955, Chevy took a leaf out of Ford's book of V8 power and cranked things up a notch or ten. The original small block V8 goes down in history as one of the most durable and efficient V8 engines ever produced, making it into all kinds of cars and small trucks across GM's range until 2003. Although GM discontinued the original small block for production cars in 2003, the automaker carried on building them to sell as a crate engine. Chevy has now built well over one hundred million small block engines if you count the clean-sheet-designed LS generations of small block engines built since 1995.

Rover V8

The Rover V8 started out as the Buick 215 engine. It was small, light, and reasonably powerful. However, it suffered from issues with coolant and oil sealing as well as the radiator clogging from use of coolant not compatible with aluminum. Rover's head of American operations, J. Bruce McWilliams, saw the value of the engine and secured the rights and the tooling. Rover then hired a Buick engineer about to retire called Joe Turley to help make the engine work properly. Through its epic production run from 1967 to 2006, the Rover V8 powered British icons such as the Range Rover, the MBG GT, the Rover SD1, several TVR models, Land Rover's Defender, and Discovery models. It also became the tuners engine of choice for swapping into other cars and holds the same affection in the UK as Chevy's small block V8.

Cummins 6BT

The reason the 6BT found its way into the engine bays of Dodge trucks is due to being designed originally for farm and construction equipment. It was literally an agricultural engine, and that meant it could do the hard work that working truck owners need to do reliably. With that market in mind, Dodge wasn't too worried about refinement in its late 80s and early 90s big trucks, and with a turbocharger bolted on the 6BT was a relentless worker while making between 400 and 440 lb-ft of torque depending on the engine's variation. The engine was built to go 350,000 miles with the absolute minimum of maintenance.

Volkswagen Flat-4

Whether you love or hate the original Beetle, Volkswagen's air-cooled flat-4 engine had a 70-year production run, and that alone puts it up there as one of the greats. Somewhere north of 20 million and south of 30 million of the simple yet effective engines were made between 1936 and 2006. This wouldn't have happened if control of the VW factory hadn't have been handed over from American to British hands, and if the unexploded bomb Major Ivan Hirst had to have removed from the factory had gone off. German's needed jobs and the British Army needed cars, so Hirst persuaded the military to order 20,000 Beetles. The rest is well-documented history.

Jaguar XK

The straight-6 engine that provided the foundation for Jaguar's success was also born of World War II. Legend has it that the idea for the engine was conceived by Sir William Lyons and William Haynes as they sat on a rooftop as part of a fire watch team while German bombers dropped their loads on Coventry in the UK. The headlines for the engine are that it powered five Le Mans victories for Jaguar and powered the iconic E-Type. However, it also had longevity and remained in production until 1992.

BMW Inline-6

Another long-lived legend was built in the aftermath of WWII as BMW sought to rebuild and then compete with Mercedes. In 1968, the brand was ready and added two cylinders to its already successful 2.0-liter 4-cylinder engine. The BMW straight-6 has endured since as just about every other manufacturer switched to the more compact V6 arrangement, giving up on the smoothness the inline powerplant had to offer. Since 1968, BMW has built legendary variations including the M1's M88 race car engine that went on to power the first M5 models and the iconic E46 M3's S54 engine. To this day, BMW is using the straight-6.

Lexus V8

When Lexus dropped the 1990 LS 400 on the world, the new marque served a notice to the entrenched European luxury brands. Part of that package was a V8 engine that used every technical advance Lexus engineers could cram in to build a powerful V8 so smooth that you could pile glasses of champagne on the hood and not see them drip all the way to redline. Toyota realized how much engine they had and made sure it got used in trucks, sports cars, SUVs, and sedans.

Honda CVCC

In 1975, manufacturers making cars in or for the United States found themselves needing to meet strict fuel emissions standards. GM had already worked out catalytic converters and declared Honda's new CVCC technology as having no potential outside of a "little toy motorcycle engine". Having started in a shed, Soichiro Honda now had one the largest motorcycle and automobile companies in the world and he didn't appreciate the CEO of GM being an arrogant and patronizing ass. So, Honda had a 5.7-liter V8 Impala shipped out to Japan, had his engineers build a CVCC system for the V8, then shipped it back for testing by the EPA. It passed the emissions standards with no loss of horsepower.

CVCC stands for Compound Vortex Controlled Combustion, and it was the predecessor to VTEC, the system that helped Honda earn the Accord the first Super Low Emissions Vehicle certificate in California.

Honda B-Series

While the CVCC engine took care of emissions standards, Honda's first VTEC engine put the brand on the map for enthusiasts and tuners. The engine was reliable, economical, easy to maintain, and VTEC kicked in. VTEC stands for Variable valve Timing and lift Electronic Control and, in essence, allowed for lower fuel consumption at low RPM and higher performance at higher RPMs. It was also the first mass production engine to generate 100 horsepower per liter.

MoPar Street Hemi

The Hemi engine was born out of NASCAR racing. The design uses hemispherical combustion chambers that allow larger valves to be fitted while adhering to regulations that only allow for two valves per cylinder. The Hemi was a big lump of an engine, and in 1965 you could only special order one if you knew the right words and the right people to say them to. It stayed in production until 1971, although the basic concept was first used in the Chrysler FirePower engines through the 1950s.

Ferrari Colombo V12

Gioacchino Colombo also designed engines for Alfa Romeo under Enzo Ferrari, but Ferrari had used a Fiat straight-8 in his own first car. Ferrari's first homegrown engine was a V12 though, and he brought Columbo in to design it. The first iteration was the 125 that had just 1.5 liters of displacement in order to be eligible to use in Formula 1 racing where it claimed six victories in its first year. Eventually, the V12 grew to 4.9 liters and gained notoriety in the 250 GTO. If you've ever heard one scream with the staccato firing of the cylinders then you know that's enough to put it on this list alone.

Ford Ecoboost

While it may be a little early to declare, Ford's Ecoboost V6 has all the makings of a classic, whatever the internet commenters may say. Truck builders have been avoiding forced induction, but Ford has happily been putting its torquey turbocharged V6 into trucks, including the phenomenal and game-changing Raptor. It's an engine that can be a workhouse, a powerplant for a sports car or an SUV, and its tuning potential is exceptional. The V8's days might be numbered and the Ecoboost is showing that there is a replacement for displacement.

On the other end of the performance scale, the 1.0 liter 3-cylinder Ecoboost engines have been earning award after award in Europe based on just how engaging they are to drive while still being remarkably economical.

Ferrari 3.9-liter V8

Also a little early to declare, but we are confident here. Ferrari's twin-turbocharged masterpiece has already picked up two International Engine Of The Year awards and shows Ferrari's mastery of balance between keeping its character while unleashing an absolute screamer that also features razor-sharp throttle response at the low end.