The question comes up from time to time: How do you folks at WardsAuto, when running a 10 Best Engines entry through its paces in daily driving, isolate an engine from the rest of the drivetrain, particularly the transmission?

In truth, it’s not easy. An engine is only as good as its transmission, and vice versa, and it’s also true that unpleasant sounds or vibrations could be traced to the gearbox rather than internal combustion.

In this year’s 2-month test cycle, we experienced both fabulous and disappointing transmissions that made all the difference in a few hotly contested battles.

For example, both the Cadillac ATS and BMW 328i are powered by 2.0L turbocharged 4-cyl. engines. The Caddy beats the Bimmer on paper with a higher specific output and torque rating.

But the 8-speed automatic in the BMW gives it a considerable edge in real-world driving over the 6-speeed auto in the ATS – several miles per gallon better.

The Environmental Protection Agency rates the 328i at 23/33 mpg (10.2-7.1 L/100 km) city/highway, 2 mpg (0.8 km/L) better in both driving modes than the Cadillac.

Both engines made the list, but the 328i has a definite fuel-economy advantage.

Some of us also had high hopes Jaguar’s all-new 3.0L supercharged V-6 would seriously challenge Audi’s excellent 3-time Ward’s 10 Best Engines winner, also a 3.0L blown V-6.

The Jaguar engine in the XF makes more horsepower and torque, and its 8-speed automatic should have an advantage over the Audi S5’s 6-speed manual.

In our comparison, the Jag beats the Audi by several miles per gallon, but the XF’s transmission spends too much time hunting for gears and, as one WardsAuto editor writes on his score sheet, “sucks the fun out of the engine.”

It fails to deliver a knockout punch, so the Ingolstadt V-6 returns for a fourth year.

Another example: The Mazda Skyactiv 2.0L earned a trophy last year in the Mazda3, but this year’s pairing with an automatic transmission in the heavier CX-5 all-wheel-drive cross/utility vehicle makes this fine engine feel poky.

With a manual transmission and front-wheel drive, the Skyactiv 2.0L is more entertaining.

The new Nissan Altima has a solid 2.5L 4-cyl, but the continuously variable transmission makes the whole experience fairly lackluster. A week after driving the Altima, a Honda Accord arrived with the re-engineered 2.4L direct-injection 4-cyl. mated to an all-new CVT.

On paper, the Honda 2.4L has a slight performance edge over the Altima, but the Accord’s CVT is superior – quiet, smooth and even sporty under hard acceleration. The driver can select between two modes, Drive and Sport, and they’re both good.

Honda has delivered what arguably is the best, most enjoyable CVT yet, one that distances itself from the staid applications in numerous hybrids.

Thanks in part to the CVT, the Honda 2.4L earns a trophy this year, and it doesn’t hurt that a 6-speed manual also made a favorable impression during our evaluations.

A great engine needs a great transmission, in the same way a Hall of Fame pitcher needs an outstanding catcher.

tmurphy@wardsauto.com