What is The Deal with New Cars that Shut Down Cylinders for Better Fuel Mileage?

Reader Question I have been reading about these new vehicles that can “turn off” cylinders to save on fuel. From what I have read, these engines will actually turn off the valves and everything.

I was wondering if there would be any fuel savings on a standard engine to just disconnect 2 of the 8 fuel injectors, thereby turning the engine into a V6 instead of a V8. I realize that the engine would run rough, but would there be any actual fuel savings? And would it cause any dammage to the engine to run it with 2 cylinders not firing?


Good question, but your idea will not work. The whole concept is not new though.

Quick story about the Cadillac 368 engine

368 and V8-6-4

In 1980 the 425 was replaced with the L61, which was the same basic engine de-bored to 3.80 in (96.5 mm) for a total displacement of 368.3 in³ (6.0 L). The reduction in displacement was largely an effort to meet CAFE requirements for fuel economy. Fuel injection (which would be known to GM as throttle-body injection after 1985) was now standard except for Fleetwood Limousines and Commercial Chassis.

Cadillac refers to the fuel injection system as digital fuel injection; this particular induction system was later adopted by other GM division except Oldsmobile V8s.

Power output dropped to 145 hp (108.2 kW) @ 3600 rpm and torque to 270 ft·lbf (420.7 N-m) @ 2000 rpm. This engine was standard on all Cadillacs except the redesigned Seville, where it was optional.

For 1981 Cadillac introduced what became the most notorious engine in the company’s history, the V8-6-4 (L62). The 368 had not provided a significant improvement in the company’s CAFE numbers, so Cadillac and Eaton Corporation devised a cylinder deactivation system that would shut off fuel to two or four cylinders in light-load conditions like highway cruising, then reactivate them when the throttle was opened.

A dashboard “MPG Sentinel” gauge could show the number of cylinders in operation, or instantaneous fuel consumption (in miles per gallon). The L62 produced 140 hp (104.4 kW) @ 3800 rpm and 265 ft·lbf (412.9 N-m) @ 1400 rpm. Cadillac hailed the L62 as a technological masterpiece, and made it standard equipment across almost the whole Cadillac line (the Seville retained its standard Oldsmobile-based 5.7 L diesel V8).

While cylinder deactivation would make a comeback some 20 years later (with modernized technology), Cadillac’s V8-6-4 proved to have insurmountable teething problems, both mechanically and electronically. The biggest issue was that the engine control computer was simply not fast enough or powerful enough to efficiently manage the number of cylinders in operation, so many of these engines had their variable-cylinder function disabled by dealers, leaving them with permanent eight-cylinder operation.

The 368 was dropped for most Cadillac passenger cars after the 1981 model year, although the V8-6-4 remained the standard engine for Fleetwood Limousines and the carb 368 remained in the Commercial Chassis through 1984.

Austin C. Davis

Posted in: Reader Questions

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