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Power Play - 2007 Hummer H3

More muscle for the '07 Hummer H3

Zipping around in the Hummer H3 just got even more fun thanks to the introduction of a new, more powerful 3.7L five-cylinder engine. This new powerplant boasts a welcome 22 more horsepower and 17 lb-ft of torque than the engine it replaces. This translates to 242 hp and 242 lb-ft of torque.

How They Did It

Hummer's Daryl Ehrlich, Development Engineer, Energy and Drive Quality, summed up the goals of the project by saying: "Our goal was to improve acceleration performance and driveability with the new 3.7L engine, yet minimize impact to fuel economy by implementing new technologies like Regulated Voltage Control and a high-efficiency alternator." With goals set, the team increased the cylinder bore from 3.66 inches to 3.76 inches. Of course, this increase in diameter necessitated bigger intake and exhaust valves, so larger 1.52-inch intake valves replace the previous 1.45-inch intake valves, and larger 1.32-inch exhaust valves replace the previous 1.18-inch exhaust valves. Engineers also revised the profile of the dual overhead camshafts to optimize valve lift and duration in accordance with the larger valves. Naturally, these modifications require more airflow, so engineers increased cylinder head airflow to match the demand of the larger valves and revised camshaft. Major attention was paid to creating a quieter engine too. The list of noise-reducing changes includes a connecting-rod oiling system, aluminum camshaft cover, and tighter-clearance balance shaft bushings. Finally, as stated earlier, fuel economy was also a major concern. With that said, the team integrated Regulated Voltage Control into the mix. Quite simply, this system shuts down the alternator when voltage isn't needed, thus elimin-ating drag on the engine. The result is a larger engine that makes more power than its predecessor but suffers no decrease in overall fuel economy.

How It Drives

We figured that the best way to gauge the power of the new engine was to compare the current 3.5L and the 3.7L engine back-to-back. With that said, we borrowed a 3.5L-powered H3 from the Chicago press fleet and we drove it to the Hummer Homecoming in South Bend, Indiana. We then hopped into a 3.7L-powered H3 for a run from South Bend to Silver Lake Sand Dunes near Mears, Michigan. After testing on the dunes, we jumped back in the 3.5L-powered rig for the return trip to our Four Wheeler Midwest Bureau.

On the road, we immediately noticed two things about the new 3.7L engine. First, it definitely seems quieter, both at idle and under load, thanks to the host of noise-reducing changes. Second, the new I-5 engine generates a power-to-weight ratio that is more in line (no pun intended) with the vehicle's 4,700-pound curb weight. It won't take your breath away, but it doesn't stand out as obviously needing more beans. As we wound our way north on Highway 31 toward Muskegon, we noticed the 3.7L's 242 hp also kept the Hydramatic 4L60E four-speed automatic transmission happier-it wasn't demon-strating the propensity to shift out of overdrive to hold highway speed on hills as often as the 220hp 3.5L-powered H3.

The fact that Hummer turned us loose on the soft, power-sucking sand of Silver Lake Sand Dunes says a lot about their confidence in the performance of the new 3.7L engine. Of course, the first thing we did was head for the tallest hill we could find. With the transfer case in 4-Hi and the auto trans in Second gear, we easily climbed to the top of Silver Lake's tallest dune. Over the course of three hours, we Baja'd the H3 over every obstacle we could find. It never exhibited a gross lack of power, though on long hillclimbs it seemed to be happiest yowling near its max horsepower-making rpm of 5,600. Throttle response was very good and the tuning of the drive-by-wire system was excellent, even on the roughest of terrain.

Bottom Line

Overall, we were impressed with the new 3.7L engine. It eagerly yanked the H3 through fast-moving traffic and tire-sucking sand. Not only is it more powerful than its predecessor-an engine we called "unimpressive" after last year's Four Wheeler of the Year testing-it's also more refined. When factored in with the H3's outstanding off-highway resume and darn respectable highway fuel mileage, we think it makes a great package even better.

Engine Specs

Type: 3.7L I-5
Displacement (ci): 223
Bore & stroke (in): 3.76 x 4.0
Block material: Lost foam cast-aluminum
Cylinder head material: Lost foam cast-aluminum
Valvetrain: Dual overhead camshafts, continuously variable exhaust valve timing, four valves per cylinder, dual balance shafts
Ignition system: Distributorless electronic spark, coil-on-plug, platinum-tipped spark plugs
Fuel delivery: Multipoint sequential fuel injection
Compression ratio: 10.0:1
Horsepower @ rpm: 242 @ 5,600
Torque (lb-ft) @ rpm: 242 @ 4,600
Recommended fuel: Regular unleaded
Maximum engine speed (rpm): 6,300
Emissions controls: Dual "split converter" design; LEV II
Fuel economy (mpg city/hwy): manual 15/20, automatic 15/19

Hummer News

When our nose isn't to the grindstone, our ear is to the ground. Here's some hot Hummer news we've heard lately.A high-ranking Hummer official says that Hummer wants to be GM's Diesel Division.Hummer is negotiating with an unnamed source to provide a diesel engine for the H3. Rumor is that diesel-powered H3s will be exported overseas initially and eventually offered in the U.S.Don't look for a diesel in the current-generation H2-it isn't going to happen.A Hummer pickup truck may materialize before an H4.The '08 H2s will get an all-new interior mid-year, as well as an all-new powertrain and electronics.