V-6 Mustang Bolt-Ons - Oh Six

Horse Sense: East and West Coast readers are often left wondering about each other's octane. That's because East Coast premium is typically 93 octane, while West Coast premium is only 91 octane. For bolt-on cars such as the one tested here, it doesn't matter, but East Coast blower cars can often eke out a few more horsepower on pump gas.

Bolt-ons make good sense for the 4.0 V-6 Mustang. Sure, if it's big speed you want, get a V-8 and go crazy, but don't waste time trying to make a 4.0 V-6 respond like a 4.6 V-8. It can be done, but at major cost. Just ask the Europeans.

No, the V-6 is a great real-world car, and bolt-ons retain the highly desirable man-about-town persona while giving that little more urge everyone wants.

This story is all about the real, the practical, the V-6 bolt-on. And to see what was up in this reasonable corner of the Mustang market, we asked Ricardo and Gonzolo Topete at GTR what pieces their V-6 customers were buying. GTR mail-orders large volumes of mild-to-wild Mustang parts and recently opened an installation center with dyno services, so they know what's actually going on the new 4.0 cars.

It turns out to be a short list, namely cold-air intakes, mufflers, and underdrive crank pulleys. Additionally, we wanted to see if the new V-6 engines responded as favorably to octane increases as the V-8 engines do. So GTR scheduled a customer's five-speed,manual-transmission '06 Mustang for some bolt-on work, and we brought the camera.

One thing we noticed immediately is the ample elbowroom surrounding the V-6. Considering the six is only 600cc less displacement than the Three-Valve V-8, or a massive Four-Valve Shelby 5.4 for that matter, the spacious working conditions are impressive and much appreciated.

We'll also note the 4.0 V-6 uses cast-iron exhaust manifolds. The engineers tell us the massive castings help with emissions (keeping heat in the cats), but they'll also end any worries about headers cracking. That is a real issue with '99-'04 Mustang V-6 passenger-side headers ('96-'98 V-6 cars do the same thing, but not quite as often) where air-conditioning condensation water drips onto the header and cracks it. That won't happen with the new car. The cast-iron manifolds appear reasonably shaped from a flow standpoint, too, so they probably don't hurt power much.

Stuck In Third
Before getting into the dyno testing, we have to disclose that we ran all the tests in Third gear. We began with Fourth-gear pulls but immediately ran into the V-6 Mustang's 111-mph (4,750-rpm) speed limiter dictated by the tire's speed rating. We had a DiabloSport Predator flash tuner on hand, and it claimed to be able to switch off, or clip, the speed limiter, but instead it repeatedly put the engine into limp-home mode after several attempts. Curiously, after installing the cold-air kit, we learned you could clip the speed limiter when the Diablo was running its own sport tune, but not when running in stock Ford tune. This was just a glitch that's probably been eradicated by the time you read this, but it was an issue for our testing.

Faced with either running in Third, the next closest gear, or sticking with Fourth and having the runs end before the power peak, we choose Third gear. Because the V-6 Mustang's Third-gear ratio is 1.41:1, there isn't a big correction factor to worry about, at least for horsepower. We ran some calibration runs to see what the dyno thought of the difference between Third and Fourth gears, and in the upper rpm range it was only about 3 hp in favor of Third gear. Torque was up 10 lb-ft or more at the peak.

Ultimately we decided not to monkey with the data, and we are presenting it here just as it came off the dyno. You'll have to subtract just a few horsepower, or more so torque, if you're trying to horseback a comparison with some other Fourth gear test. But for comparing with all the tests we're showing here, no correction is needed.