Engineering The MDX: A Daily Driver Tuned at the Nürburgring

John Mendel, senior vice president, Automotive Operations, American Honda, describes Acura as "the world's first Asian luxury brand." The division was established in the U.S. in 1986. Arguably it is working to become the "world's first Asian luxury performance brand." And what's all the more remarkable is that it is working to accomplish this, in large part, with an SUV. Yes, an SUV.

Where the family vehicle is uncharacteristically introduced.

BeaveRun is a race track in western Pennsylvania. When introducing the MDX to the national press, Frank Paluch, chief engineer of the '07 MDX (he also served as chief engineer for the Honda Pilot—a vehicle which, like the MDX, is built at Honda of Canada Mfg., although the MDX is shifted to a special inspection area) and his colleagues brought the 300-hp SUVs to the track, brought along competitive vehicles including the BMW X5, Porsche Cayenne, and Volvo XC90, and said, in effect, "Go out and see what they can do." Which is to say that Paluch et. al. are fairly confident that what is probably going to be primarily put to use as a people hauler and grocery getter has been engineered such that it is capable of performing with aplomb on the race track. It's not that you would. But you could.

And what did they do during engineering development to make sure that the MDX was up to snuff? They took it—and the development vehicles that led up to it—to the 13-mile, 170-plus-turn NNürburgring Nördschleife circuit in Germany.

 

What do you do when they change the way horsepower is measured? Go back and do it again. 

300 hp was a "magic number" during the development of the MDX's all-new 3.7-liter VTEC 60° V6. 300 hp, not only a nice, round number, means that the engine has 47 hp more than the one it replaces. Paluch recalls that they had achieved the number during the development of the engine, but then something happened: the way that SAE calculates horsepower was changed. A result of this new math was that the new 3.7-liter V6 was 6 to 7 hp below 300. "So I told the team to completely change the exhaust system and get to 300." So Jeremy Hall, principal engineer, and his team set to work. Again. And, yes, they reached it. The engine in the MDX has the largest displacement of any in the Acura line up: at 3.7 liters. Not only does it provide 300 hp (@6,000 rpm), but it offers more torque: 275 lb-ft @ 5,000 rpm (which is up 25 from its predecessor).

So, where does the additional horsepower come from? Starting with the baseline of 253 hp (i.e., the previous engine), they get 20 from the increased displacement and increased compression ratio (from 10.1:1 to 11.1:1); 15 from a new intake port design (it alone is said to add 7 hp) and a tuning of the Variable Timing and Lift Electronic Control (VTEC) system (there are two modes, below and above 4,500 rpm so that at low speeds the intake valves have low lift and are open for a short period of time during cylinder filling; at high speeds, there is a high-lift, long-duration mode). Finally, there are 12 horsepower provided by the induction and exhaust system. The two-stage intake manifold is cast magnesium; it weighs eight pounds less than its predecessor. The exhaust system was modified to provide higher flow; among the modifications are an increase in catalyst diameter, a decrease in catalyst cell density, an increase in the silencer flow rate, and the use of hydroforming for the A-pipe (which results in a smoother pipe).

Overall, the engine, which has an aluminum block and heads, is 17.2 lb. lighter than the previous model's. One interesting change is the use of high-silicon cast-in-place cylinder liners in the place of iron liners; the bores are mechanically etched so as to expose the silicon particles, thereby providing a hard piston-ring sealing surface. Magnesium is used for the cylinder head covers (which saves 2.6 lb.). The camshafts are 25% lighter than their predecessors; instead of a solid shaft, they're using a steel tube onto which splined lobes and journals are pressed.

The other aspect of the powertrain that should be noted is the five-speed automatic transmission; it has lower ratios in each gear for improved performance, as well as upgraded shafts, gears, bearings, and clutches to accommodate the increased engine power outlet, as well as a strengthened aluminum case to contain it. The transmission offers sport shift capability. What's more, it facilitates the 5,000-lb. tow rating.

 

If it's good enough for the luxury sedan, then it certainly is applicable to the sport ute.

One of the key factors that allows someone to drive the MDX in places like BeaveRun—or on I-75 at rush hour, for that matter—with a higher level of confidence is the SH-AWD system—the Super Handling All-Wheel Drive system. This system is similar to that used in Acura RL (The Allure OF AWD) and the Acura RDX (Acura RDX Purpose-Built For The Urban Environment). Essentially, this system distributes torque to the front and rear axles as required, as well as between the left- and right-rear wheels, with as much as 100% of the available rear axle torque being sent to one of the two wheels. Architecturally, there is a torque transfer unit bolted to the front-mounted transaxle; a helical gear attached to the front differential's ring gear provides input torque. There is a short horizontal shaft and hypoid gear set that send power to the prop shaft, then to the rear drive unit. On either side of the hypoid gear that drives the rear axle are electromagnetic clutches; they operate either as a pair to coordinate the front-rear split or independently so as to be able to shift the rear torque to one side of the vehicle.

 

Euro styled; American sized.

During the development of the MDX, vehicles including the BMW X5, Porsche Cayenne, and Volvo XC90 were benchmarked. This may have led to what is said to be a more European body design for the vehicle than the previous generation model (even though it was designed and engineered at Honda facilities in California and Ohio, not Europe; the exterior designer, Ricky Hsu, references St. Moritz and Milan, not St. Louis and Milan (Michigan) as inspirational points of interest, he also cites the 118 Wallypower from a Monaco-based yacht company, which is to yachts what the F-117 is to aircraft), although the two vehicles are visibly related. As is ever the case with new vehicles, the '07 is dimensionally larger than its predecessor in all parameters but one. It is 190.7-in., long, so +2.1 in.; 78.5-in. wide, so +2.3 in.; and the wheelbase is 108.3 in., or up 2 in. But it is 0.6 in. lower, at 68.1 in. On the inside, John Norman says that the overall approach is one that takes into account the primary comfort of the driver and three passengers, although there is a third row, which he describes, as "occasional seating for three."

According to Jim Fusco, chief engineer, Body Design/Safety, there was extensive computer-aided engineering deployed in developing the body structure (yes, it has the Honda Advance Compatibility Engineering (ACE) body for crash energy management and to assure that the SUV won't over-ride smaller vehicles in the event of a front-end collision). They've significantly upped the amount of high-strength steel used—from 13% of the structure to 56.3%, including grades 780 and 980, which are in the "ultra" high-strength steel category. Aluminum is also deployed, representing 4.1% of the body structure (e.g., the hood has gone from steel to aluminum, which contributes to a 15.5-lb. weight reduction).

 

Depot driver.

The MDX is an important vehicle for Acura. It is second to sales in the division's lineup to the TL. It is second in sales in the mid-premium crossover utility vehicle (CUV) segment to the Lexus RX. They're anticipating the production of 60,000 units per year.

Which brings us back to the aforementioned race track. Frank Paluch admits that their research shows that the '06 MDX purchase decision was driven largely by "Family Mom." Someone looking for an SUV-cum-people mover. But for the '07, they're targeting "Driver Dad," someone who wants a sports car but needs an SUV, which explains the NNürburgring experience. Of course, with four feet between the wheelhouses in the back, it can also facilitate the functionality needed by Home Depot Dad. Who may have a heavy foot.