A new turbo/exhaust system for the HMMWV’s 6.2-liter diesel

By Bill Fedorko

In the May ’93 issue, we road-tested the civilian Hummer. While we agreed it’s a ball to drive off-road (and gets a lot of attention on-road), we felt the HMMWV suffered from a lack of speed and acceleration. The Hummer’s GM-sourced 6.2-liter V-8 diesel is a proven, economical engine, but its relatively low, naturally-aspirated 150 brake horsepower has always been its shortcoming. We decided to do something about it.

Gale Banks Engineering of Azusa, California, has experience in turbocharging 6.2-liter diesels and volunteered to make the Hummer a more powerful runner. Although the company hadn’t turbocharged one of these behemoths yet, Banks was more than up to the challenge.

The turbo system chosen for the Hummer is a new version of the recently released Sidewinder series. The kit, specifically tailored for 6.2-powered Hummers, is the first of its kind in the country. It’s smaller and enlists the duties of an optional wastegate.

Most turbo systems have had to be matched in size to a specific application–usually, towards the peak rpm range. The problem with the match system is that it doesn’t work well in low- and midrange throttle positions. If a turbo was chosen for good low-end torque, it suffered at wide-open throttle (WOT) and vice versa. Now a smaller turbine can be used, which is faster to spool up, so the turbo boost comes om more quickly. When boost gets quicker, elapsed-time figures drop on this 10,300-pound-GVWR rig. The wastegate comes into play by limiting boost at the top end, which also leads to cooler intake air temperature. In addition, some of the turbo’s components, such as the radiator overflow tank and air conditioning lines, are rearranged to accommodate the starboard-side exhaust manifold–the side in which the turbo mounts.

When we first rolled our test Hummer to the race track for some testing, the engineers at Banks hadn’t changed the exhaust system. They felt the stock system likely had sufficient free-flow characteristics to support the turbo system. Initial gains in zero-to-60mph and quarter-mile acceleration times–from a stock 25.3 seconds at 58 mph to 18.71 seconds at 67.5 mph with the turbocharger–were pleasing, but Banks felt more power yet could be had from the 6.2 diesel. Back to the shop we went.

After Banks’ engineers dug into the Hummer’s powerplant once again, with a tweak here and there and the installation of a Banks PowerPak “Stinger” exhaust, our results were even more impressive.

At this point, quarter-mile acceleration figures couldn’t represent true performance gains, since the turbo Hummer with Stinger exhaust reached its approximate max speed just before the end of the quarter-mile: 70.9 mph. With the Sidewinder turbo and Stinger exhaust, zero-to-30 mph times were chopped by more than two seconds, and zero-to-60 mph times dropped by more than 10 seconds from stock.

Banks’ Dynafact, an onboard dynamometer, was then used to measure horsepower gains, which were dramatic. Horsepower at the rear wheels–we should say all wheels since the Hummer is a full-time 4×4–jumped from 100 to 151, a 51-percent increase. Even exhaust backpressure was reduced to 8.0 inches of mercury (in.Hg) down to 2.0 in. Hg.

Noise-level gains were not appreciable–the Hummer is a relatively noisy vehicle to start with (huge, aggressive tires and minimal hood insulation), and the Sidewinder system adds very little noise other than a little turbo whine. The Stinger exhaust added a great-sounding tone, which helps you forget about the under-hood noises.

The price for the substantial power increase doesn’t come cheap, but it’s certainly not excessive for a vehicle with a $50,000 price tag. The complete Banks Sidewinder turbo system, including the Stinger exhaust, has a suggested retail of $3,500, not including installation.

For kicking around off-road and in rocks, the turbocharger might not matter much, but when it comes time to head home after a great weekend of four wheeling, freeway drivability and mountain-road traversing is greatly enhanced with this newly-found performance.