cars news 10: Tech Deep Dive: GM 1.6-Liter LH7 Turbodiesel

Volkswagen’s Dieselgate scandal has clouded the crystal ball used for predicting passenger-car diesel futures, but GM has worked so long and hard on its new Medium Diesel Engine family 1.6-liter that it’s rolling the little “Flüsterdiesel” (Whisperdiesel, as the German press dubbed it) in the current Cruze sedan and hatchback and in the forthcoming 2018 Chevy Equinox and GMC Terrain. It’s already on sale in much the same state of tune in Europe’s Opel/Vauxhall Astra.

A truly international engine, the design was engineered in Turin, Italy, at a facility that started life as part of the Fiat-GM powertrain alliance, was developed and validated in the U.S., and is assembled in Szentgotthárd, Hungary. To achieve the obvious goals of high fuel economy, strong torque delivery, and low noise, the ingegneri kept everything that was good about the old Family B LUZ 2.0-liter Cruze engine (a variable-nozzle turbine that greatly reduces lag from the BorgWarner turbo, a variable-swirl intake manifold, cooled EGR, and a variable-displacement oil pump) and then obsessed over the LH7’s combustion chamber and fuel injection designs to optimize efficiency. Replacing the LUZ’s piezo injectors are new state-of-the-art solenoid injectors that typically shoot six to 10 squirts of fuel at (29,000 psi) out of eight precision-drilled holes during a single combustion cycle. This technique ramps the fuel burn up much more gradually, preventing the single loud bang that produces all that diesel clatter in older oil-burners.

Even with the fancy fuel injection, diesels make more noise than gassers. To make it whisper, GM uses loads of foam surrounding the entire fuel rail, an insulated clamshell lid covering the whole engine, and a structural aluminum bedplate and oil pan, and the cam drive is relocated to the rear of the engine so most of the gear and chain noise can be absorbed by the transmission bell housing. The hood and dash pads are unique to the Cruze TD, and it gets a belly pan, but Chevy claims that when mounted on a chassis dyno with microphones measuring engine noise directly under the hood, the sound coming off the engine is reduced by 50 percent at idle and 68 percent at 4,000 rpm under load as compared with the previous Cruze diesel.

Relative to that older 2.0-liter engine, this one upgrades from iron to aluminum block construction, which saves roughly 50 pounds. Compression drops slightly from 16.5:1 to 16.0:1, but improved combustion allows it to produce nearly the same torque—240 lb-ft at 2,000 rpm (90 percent of which is available from 1,500 to 3,250 rpm) versus 264 lb-ft at 2,600 rpm (95 percent of which was on tap between 1,750 and 3,000 rpm). That engine offered a temporary overboost function to produce 280 lb-ft for brief periods, but this smaller, more highly stressed engine doesn’t offer this feature. Power drops slightly from 151 hp at 4,000 rpm to 137 hp at 3,750 rpm. The bigger news, of course, is the fuel economy: 31/47/37 mpg city/highway/combined when coupled with GM’s new nine-speed automatic, or 30/52/37 mpg with the six-speed manual. The former leverages auto start/stop to gain that extra city mpg, and the latter qualifies as the most efficient nonelectrified vehicle in the EPA books. Oh, and ultra-greenies can run it on B20 biodiesel.

The 2017 Cruze TD model starts at $24,670—that’s $2,795 more than the LT with the Convenience package it’s based on. Little else changes on the rest of the car. The engine only weighs 33 pounds more than the base 1.4-liter turbo, so no serious suspension recalibration was needed. Oh, and if you’re fretting about the emissions, this one runs an oxidation cat, a diesel particulate filter, and selective catalytic reduction (SCR) for NOx, meeting the Tier 3 Bin 125 standards that will be phasing in through 2025. We’re assured that with all the scrutiny diesel emissions are drawing now, GM won’t be buying any of these back. How many will it sell? That’s anybody’s guess, but the Chevy folks say they’d be thrilled to get the same 9 percent take rate the Colorado 2.8-liter diesel is currently earning. We’re betting it proves more popular in the CUVs, but what do we know?