Tom Wilson
December 6, 2010

Fourth vs. Fifth Gear
There's a "gotcha" lurking in the new 5.0 Mustang's six-speed manual transmission. Unlike every previous manual, the new Ford gearbox uses a 1:1 ratio in Fifth gear, not the industry standard Fourth gear.

This is of no concern when driving, but it definitely skews chassis dynos, which assume a 1:1 transmission ratio. In other words, if you dyno a '11 Mustang in Fourth gear-all too easy for a dyno operator to do as he's always done it that way-and you'll get numbers lower than expected.

As you've already guessed, we fell into this trap during this article, and curious as to the effects, we baselined the car in both Fourth and Fifth gears. We found horsepower was little affected, but torque was noticeably off. In our case, peak horsepower was 1.58hp less in Fourth gear (absolutely within the margin of error on this car/dyno combination, so statistically insignificant), and 11.62 lb-ft of torque less in Fourth gear.

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To save a whole day in the shop re-running tests, we've opted to present the short-tube header part of this test in Fourth gear and the long-tube header examination using Fifth. This means you can't accurately compare the short- and long-tubes directly, but the relative improvements are easy enough to spot.

In the future, we'll double-check that testing starts in the standard gear for '11 Mustangs-Fifth. In the meantime, it's something to keep in mind when considering '11 Mustang chassis dyno tests you conduct or read about.

Long On Power
After the short-tube testing, we stood down for a couple of days waiting for the first set of long-tube headers to emerge from BBK's prototype shop. But then the testing shifted into Fifth gear, with a new baseline set with the car returned to totally stock condition. This time the baseline figures came in almost square, the horsepower at 360 and the torque at 361 lb-ft.

Because the long-tube headers can't be run with the stock H-pipe, the long-tube test setup was simple-the long-tubes and their matching X-shape crossover pipe. So Mike Briggs, BBK's lead prototype tech and media liaison specialist got to pull the stock headers off for the umpteenth time and the long-tubes went on.

When the tires stopped singing on the rollers, the power had jumped 29 hp to 389 and the torque gained just a couple to reach 363 lb-ft, as shown in our charts. Actually, the absolute peaks-which naturally fell at rpm points not shown in our charts-were 391 hp and 367 lb-ft of torque. Anyway you look at it, the BBK long-tubes gained at least 25-almost 30-horsepower. That's a solid gain you can feel from behind the wheel.

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Furthermore, the torque muscled up far more than the measly 2 lb-ft the peak would indicate. Looking at the full arc of the torque curve, it's clear the long-tubes add generous torque down low-about 34 extra lb-ft at 3,000 rpm-but then the torque curve plunges back to the baseline values from 4,100 to 5,500 rpm. At 5,500 rpm, the torque shoots right back to where it would have been had it not taken its midrange dip.

Two things are notable about this torque dip. First, its unfortunate, intentional-by-Ford placement falls right across the Coyote's torque plateau, robbing it of a higher peak value. Secondly, the midrange dip is likely a result of Ford's engine management software getting its tentacles around the ignition timing or electronic throttle in order to calm the party. One wonders what ecstasies await with electronic tuning.

Finally, because the prototype cold-air intake was busy posing as a pattern for its production tooling, we were unable to test it with the long-tube headers.