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.

Our first official test was to baseline the car in showroom condition using 87 octane gasoline. Ricardo reports his customers almost always run 89 octane just because, but as the car is rated for 87 octane fuel and we were interested in spotting even a small power increase attributable to octane, we initially went with regular gas.

With 186 rwhp, we were impressed with the 4.0-liter's baseline output. Believe it or not, this is what a stock 5.0 Mustang's 5.0 H.O. V-8 puts out, assuming it's in sound mechanical condition. Of course, the V-8 produces substantially more torque and the old Foxes weigh much less than the newest Mustangs, but still, the little 4.0 has some snort.

To see what 91 octane would do, we pumped out the remaining 87 octane and added a splash of 91 octane. The result was about a 3hp loss, which we're attributing mainly to normal dyno variables such as water and oil temperature, the dyno itself, and so on. True, higher octane fuel burns more slowly than low octane, and in race engines theoretically you'll see a power loss with excessively higher-octane fuel than what the engine needs, but the old 4.0 in showroom condition isn't that highly tuned.

More practically, we determined that Ford doesn't really have a premium-fuel strategy lurking in its engine-management software,so there is no use in running high-octane fuel in these cars when stock. That's the opposite of the Three-Valve V-8's response, which is to gain 5 rwhp when stepping up from 87 to 91 octane.

Ricardo said cold-air kits and underdrive pulleys are the big V-6 sellers, so we opted for the cold-air kit next.

GTR provided a C&L kit, which uses the larger mass air housing (it reuses the stock electronics as C&L's always have), a larger intake tube, a large open-element air filter, and a DiabloSport Predator electronic tuner with an upgraded tune optimized for the cold-air kit.

In fact, there are various tuning options in the Predator, notably one for 87 octane and another for 91 octane. Being good at swapping gas at this point, we switched back to 87 octane for our first go with the cold-air kit and were rewarded with a solid 6-rwhp gain. Considering there can't be much, if anything, from ignition timing with the Predator's 87 octane tune, we have to chalk up most of this gain to increased breathing.

No doubt the less restrictive, open-element air filter, and smooth intake elbow casting are the main sources of gain from the cold-air kit, as indicated by the increased induction noise through the filter. It makes an easily heard, but not overly loud "tuuuuff," sucking sound when you mat the accelerator.

At this point, we did a side experiment with the hood. Open hoods are the rule on chassis dynos because they help shed heat, which is always an issue with the car stationary and making long, hard pulls no matter how many fans are pointed at it. But cars don't run down the road with their hoods open, and with the cold-air kit's air filter sealed to the hood, running with the hood open means the air path to the filter is unusually wide open and mainly fed by fanned shop air to boot. Deciding we'd like to see what happens when the hood goes down, we made several pulls to stabilize the engine temps and output at "good and warm," then ran some hood-open, hood-closed, hood-open tests. The result was a repeatable 3 rwhp drop in power with the hood closed, so engine heat, or air restriction, is a factor when chassis-dyno testing.

We ran the remainder of the tests with the hood open for cooling and continuity with our previous tests.

Next we reinstalled 91 octane fuel in the gas tank and switched to the 91 octane tune in the Diablo Predator. This picked up 3 rwhp and 3.5 lb-ft of torque; both measured slightly higher in the powerband. This is a predictable power gain, as the higher octane allows more ignition timing, which is one of the surest paths to power.

Mufflers are popular bolt-ons, mainly because of the noise, of course. And with the new Mustang, the mufflers are all the way at the rear of the car and blessed with high-quality, reusable clamps-ideal for changing, in other words.

Ricardo produced a MAC axle-back kit, which is the muffler and truncated, large-diameter tailpipe attached. The installation takes a few minutes, as three hangers are involved, along with a small-mass damper (oh, those weight-loving engineers).

Once Ricardo finished hanging the muffler the engine had a decent cool-down, and the car gained a vaguely ricer tailpipe. We weren't expecting much, if anything, from the muffler powerwise, as with cats and relatively low power to begin with, there simply isn't any meaningful restriction in the stock mufflers these days. And we were right. The muffler made maybe 1 hp, or didn't really change anything powerwise, as the "gain" is within the margin of error on this test.

On the other hand, fit the V-6 with a blower, nitrous, turbo, or other air-mover and the muffler might be worth some power. It would all depend on how much air is being pushed out the tailpipe.

But if the power didn't change with the muffler, the sound certainly did. The stock V-6 muffler is a quiet one, and the MAC is not. The sound is definitely V-6, with a bit of a rasp. Ricardo said it sounded like a hopped-up Nissan 350Z, and that was a great call. If you like the higher-pitch V-6 buzz with a bit of tear in it, you'll dig the MAC.

The 4.0, like the 3.8 that preceded it, is one of those engines where the underdrive pulley is just one pulley-the crank pulley.

Again like the 3.8, the 4.0 crank pulley is integral-one piece-with the harmonic damper. So, to install "underdrive pulleys" on a V-6 Mustang, you are really changing only the harmonic damper. But pulling that damper is occasionally a job only a dentist would love.

And, yeah, this was one of those times. It would have been fairly simple, except the bolt supplied with the damper to mate with the harmonic-damper puller was simply too short. All sorts of time-wasting effort resulted, with the final fix being the fabrication of our own bolt. This wasn't the easiest thing, as the combination of thread series, diameter, and length is oddball, but it became much easier when it was realized a modular V-8 head bolt was correct, save for the length. As GTR has old modular head bolts on hand, a pair of cuts with the chop saw and some quality time with the smoke wrench got us in business.

But we have to say, after hours of messing around, all the effort proved worth it. The power jumped to 204 rwhp, then backed up at 203 rwhp, then 203 rwhp again. We figured that must be what it runs, but we hit it again just to see what it would do when totally heat soaked. Uh, 204.5 rwhp, that's what.

So, call the pulley a 10hp gain. Impressive.

Thanks to the cold-air intake and underdrive pulley, we gained a solid 20 hp at the V-6's wheels. The muffler didn't hurt and might help with a blower, while higher-octane fuel was a waste until more ignition timing arrived thanks to electronic tuning. All told, it was a 9.8 percent gain in horsepower, and that's just right for a daily driver. It's enough power to feel, but not enough to ruin good manners.

For our tastes, we'd go with the cold air and underdrive pulley and save our muffler money for when forced induction is fitted. Considering we'd have a V-6 Mustang around for economical, yet fun, daily transport, the definite noise increase from the muffler isn't in keeping with the car's use to begin with, and without a big power gain, why bother? But we're us and you're you, and if more sound makes it more fun, then there's your answer.

Another tact would be to fit a true dual exhaust, as V-6 engines prefer two separate three-cylinder exhaust systems with no H- or X-crossovers. While more expensive, such systems can definitely aid power with forced induction and often sound more V-8-like than rasp-can given the Mustang's generous six-cylinder displacement. It just depends on what you're listening for.

In any case, bolt-ons and the 4.0 V-6 are a good thing.

For more information, call GTR Performance or visit the manufacturer's Web sites.