Tom Wilson
October 5, 2006
Bolt-ons, a chassis dyno, and a V-6 Mustang are a perfect fit. Thecurrent 4.0-liter V-6 has the smoothness and punch to make it as a dailydriver. And with a few easy mods you can have 20 more horsepower.

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

If you're a senior Mustang enthusiast--not to mention a plain, old seniorlike some of us--today's 4.0-liter V-6 Mustangs are especially wonderful.For decades, the entry-level Mustang has made do with either hopelesslyoutclassed four-cylinder or fairly agricultural V-6 engines. The resulthas been a justly earned "V-8 or bust" attitude in the Mustang ranks.

But now, that's a shame, as today's smooth, revvy 4.0-liter SOHC bentsix is a great fit for daily duty Mustangs. Its advantages areimpressive. Not the least, the V-6 is considerably less expensive. It'sless expensive to purchase, less expensive to fuel, less expensive toinsure, and maybe even less expensive to keep tires and brakes due toless weight.

Here's the full monty: C&L's cold air intake and pre-programmed Predatoroption. GTR offers this complete kit for $614.99, which includeseverything shown. If you already have a Diablo Predator, the C&L intakekit is $284.99 by itself. Another option if you don't have a Predator,is to purchase the C&L intake kit by itself and continue to run the caron 87 octane fuel. It's a smaller power gain, but less money, too.

Give the V-6 Mustangs the top score in front-end weight and overallchassis balance, and there's no contest when it comes to working roomunder the hood. The V-6 looks great and can be purchased with a manualtransmission. Not only that, but all of the chassis mods that work sowell for V-8s work even better on the lighter, better balanced V-6s.

Of course, the V-6 doesn't sound like a V-8, doesn't have as many speedparts available as a V-8, and just doesn't have the power potential ofthe V-8. If it's rippling masses of V-8 power you want, then sell theV-6 and get a V-8. There's no replacement for displacement.

But there are many of us who don't need all the rippling mass of V-8power. Most of us aren't sparking up their household's second Mustang,or simply can't swing the money a GT requires. For those so inclined,there are V-6 bolt-ons. Bolt-ons make good sense for the 4.0-liter V-6Mustang. If it's big speed you want, get a V-8 and go crazy, but don'twaste time trying to make a 4.0-liter V-6 respond like a 4.6-liter V-8.It can be done, but at major cost. Just ask the Europeans.

The V-6 is a great real-world car, and bolt-ons retain the highlydesirable man-about-town persona while giving that little more urgeeveryone wants.

So, this story is all about the real and practical V-6 bolt-on. To seewhat was up in this corner of the Mustang market, we asked Ricardo andGonzolo Topete at GTR what pieces their V-6 customers were buying. GTRmails large volumes of mild-to-wild Mustang parts, and recently openedan installation center with dyno services. Now, they know what'sactually going on the new 4.0-liter cars.

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

One thing we noticed immediately is the ample elbow room surrounding theV-6. Considering the six has only 600 cc less displacement than theThree-Valve V-8, or a massive Four-Valve Shelby 5.4 for that matter, thespacious working conditions are impressive and appreciated.

We'll also note the 4.0-liter V-6 uses cast-iron exhaust manifolds. Theengineers tell us the massive castings help with emissions (it keepsheat in the cats), but they'll also end any worries about headercracking. That is an issue with '99-'04 Mustang V-6 passenger-sideheaders ('96-'98 V-6 cars do the same thing, but not quite as often)when air-conditioning condensation water drips onto the header andcracks it. That won't happen with the new car. The cast-iron manifoldsappear reasonably shaped from a flow standpoint, too. They probablydon't hurt power much.

Before getting into the dyno testing, we have to disclose that we ranall the tests in third gear. We started with Fourth gear pulls butimmediately ran into the V-6 Mustang's 111-mph (4,750 rpm) speed limiterdictated by the tire's speed rating. We had a DiabloSport Predator flashtuner on hand, and it claimed to be able to switch off, or clip, thespeed limiter. However, it repeatedly put the engine into limp-home modeinstead. Curiously, we found out after installing the cold-air kit thatyou could clip the speed limiter when the Diablo was running its ownsport tune, but not when running in stock Ford tune. It's just a glitchthat has probably been eradicated by the time you read this; it was anissue for our testing.

Faced with either running in the next closest gear, Third, or stickingwith Fourth and having the runs end before the power peak, we chooseThird gear. Because the V-6 Mustang's Third gear ratio is 1.41:1, thereis not that big of a factor to worry about, at least for horsepower. Weran some calibration runs to see what the dyno thought of the differencebetween Third and Fourth gears, and in the upper rpm range, it was onlyabout three horsepower in favor of Third gear. Torque was up 10 lb-ft ormore at the peak.

Ultimately, we decided not to monkey with the data, and are presentingit here just as it came off the dyno. You'll have to subtract just a fewhorsepower, or more-so torque, if you're trying to horseback acomparison with a Fourth gear test.

Our testing regimen had us bouncing back and forth between 87- and91-octane pump fuel. We found no power in the higher-octane gasolineunless the engine was tuned with advanced ignition timing.

Our first official test was to baseline the car in showroom conditionusing 87-octane gasoline. Ricardo reports his customers almost alwaysrun 89 octane due to their preference. This car is rated for 87-octanefuel, and we were interested in spotting even a small power increaseattributable to octane; we went with regular gas to start.

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 HO V-8 putsout (assuming it's in sound mechanical condition). Of course, the V-8puts out substantially more torque and the old 5.0s weigh much less thanthe newest Mustangs. The little 4.0-liter has some snort.

To see what 91 octane would do, we pumped out the remaining 87 octaneand added a splash of 91 octane. The result was about a 3 hp loss, whichwe're attributing mainly to normal variables such as water and oiltemperature, the dyno, and so on. True, higher octane fuel burns moreslowly than low octane, and in race engines theoretically you'll see apower loss with excessively high octane fuel (for what the engineneeds), but the 4.0-liter in showroom condition isn't that highly tuned.

More practically, we determined that Ford doesn't really have apremium-fuel strategy lurking in their engine management software, sothere 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 gain5 rwhp when stepping up from 87 to 91 octane.

87 Octane

91 Octane

C&L, 87 Octane

RPM

POWER

TORQUE

A/F

POWER

TORQUE

A/F

POWER

TORQUE

A/F

2,400 88.17 192.93 14.99 87.07 190.52 14.97 98.9 216.44 14.41
2,500 95 199.68 15.02 94.14 197.77 14.94 104.01 218.52 14.26
2,600 102 205.76 15.18 100.34 202.68 14.87 108.43 219.02 14.18
2,700 108 210.02 15.29 105.4 205.03 14.83 113.16 220.13 14.13
2,800 116 216.63 15.32 112.9 211.75 14.88 117.37 220.16 14.08
2,900 121 218.53 15.26 118.6 214.8 14.82 121.44 219.93 14.03
3,000 125 219.06 15.18 123.18 215.66 14.77 125.58 219.86 14.01
3,100 130 219.84 15.08 127.59 216.17 14.85 129.53 219.46 13.97
3,200 133 219.02 14.76 131.66 216.1 14.37 133.78 219.57 13.93
3,300 137.47 218.79 14.04 135.92 216.32 13.9 138.31 220.13 13.9
3,400 141.98 219.32 13.64 140.17 216.53 13.58 141.85 219.12 13.9
3,500 145.75 218.72 13.43 144.13 216.28 13.35 146.16 219.32 13.92
3,600 149.23 217.72 13.34 148.47 216.61 13.23 150.36 219.37 13.94
3,700 152.85 216.98 13.25 151.78 215.45 13.16 153.97 218.56 13.93
3,800 155.98 215.59 13.16 155.48 214.9 13.08 158.09 218.51 13.87
3,900 159.87 215.29 13.08 158.91 214.01 13.01 160.35 215.94 13.8
4,000 163.37 214.52 13.07 162.19 212.96 12.92 164.86 216.47 13.72
4,100 166.71 213.56 13.03 164.6 210.85 12.82 168.03 215.25 13.6
4,200 169.31 211.72 12.96 166.46 208.17 12.76 171.62 214.61 13.54
4,300 172.38 210.55 12.87 169.35 206.85 12.73 174.09 212.64 13.55
4,400 174.53 208.34 12.83 172.25 205.61 12.74 177.92 212.38 13.52
4,500 177.54 207.22 12.82 175.43 204.75 12.75 180.47 210.63 13.51
4,600 180.41 205.98 12.78 177.28 202.41 12.67 183.1 209.06 13.51
4,700 181.86 203.23 12.71 178.72 199.72 12.71 185.48 207.28 13.52
4,800 183.23 200.49 12.75 180.67 197.69 12.72 187.8 205.5 13.48
4,900 184.45 197.7 12.73 181.25 194.27 12.72 190.05 203.71 13.43
5,000 185.46 194.81 12.75 182.98 192.21 12.72 190.92 200.54 13.45
5,100 186.66 192.23 12.78 183.32 188.79 12.7 191.29 196.99 13.51
5,200 186.47 188.34 12.74 183.4 185.25 12.77 191.94 193.87 13.51
5,300 186.12 184.44 12.8 183.03 181.38 12.79 192.39 190.66 13.5
5,400 185.76 180.68 12.77 183.45 178.43 12.77 192.42 187.16 13.51
5,500 184.93 176.6 12.74 182.6 174.37 12.75 192.57 183.9 13.56
5,600 183.47 172.08 12.78 181.07 169.83 12.75 191.07 179.21 13.55
5,700 181.76 167.48 N/A 179.35 165.26 12.78 186.44 171.79 13.55
5,800 n/a n/a n/a 176.5 159.82 n/a 185.01 167.53 n/a

Because cars don't run around with their hoods up, we tried a few runswith the hood down to see if the cold-air kit would lose any efficiency.It did as heat built up. However, the airflow around through the enginecompartment isn't the same on the dyno as it is on the road.

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

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

In fact, there are various tuning options in the Predator, notably onefor 87 octane and another for 91 octane. We switched back to 87 octanefor our first try with the cold-air kit. We were rewarded with a solid6rwhp gain. Considering there can't be much, if anything, from ignitiontiming with the Predator's 87 octane tune, we have to chalk most of thisgain up to increased breathing.

The less-restrictive, open-element air filter and smooth intake elbowcasting is the main source of gain from the cold-air kit, as indicatedby the increased induction noise through the filter. It makes an easilyheard, but not overly loud "tuuuuff" sucking sound when you mat theaccelerator.

At this point, we did a side experiment with the hood. Open hoods arethe rule on chassis dynos because it helps shed heat, which is always anissue with the car stationary and making long, hard pulls, regardless of how many fans are pointed at it. But cars don't run down the road withtheir hoods open. 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 unusuallywide open, and mainly fed by fanned shop air to boot. Deciding we'd liketo see what happens when the hood goes down, we made several pulls tostabilize the engine temps and output at "good-and-warm," then ran somehood-open, hood-closed, hood-open tests. The result was a repeatable 3rwhp drop in power with the hood closed, so engine heat or airrestriction is a factor when chassis dyno testing.

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

Next, we reinstalled 91-octane fuel in the gas tank and switched to the91-octane tune in the Diablo Predator. This picked up 3 rwhp and 3.5lb-ft of torque, both measured a little higher in the powerband. This isa predictable power gain, as the higher octane allows more ignitiontiming, which is one of the surest paths to power.

Looking mighty shiny is MAC's Direct Fit Muffler kit. It's a $169.99combination of muffler and tailpipe. The bright look is courtesy of theunit's stainless steel construction. MAC figured that since Ford'smuffler is stainless, all of its '05-'06 mufflers would be stainless aswell.

Mufflers are a popular bolt-on, mainly because of the noise. On the newMustang, the mufflers are all the way at the rear of the car and blessedwith high-quality, reusable clamps. Ideal for changing, in other words.

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

Once Ricardo finished hanging the muffler, the engine had had a prettydecent cool-down. We weren't expecting much, if anything, from themuffler as far as power was concerned, as with cats and relatively lowpower to begin with, there simply isn't any meaningful restriction inthe stock mufflers these days. For once, we were right. The mufflerdidn't really change anything relating to power, as the "gain" is withinthe margin of error on this test.

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

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

RPM

Hood Closed

C&L, 91 Octane

Muffler

POWER

TORQUE

A/F

POWER

TORQUE

A/F

POWER

TORQUE

A/F

2,400 n/a n/a n/a n/a n/a n/a n/a n/a n/a
2,500 n/a n/a n/a 99.4 217.54 14.13 n/a n/a n/a
2,600 n/a n/a n/a 104.19 218.88 14.06 n/a n/a n/a
2,700 106.24 214.58 14.29 108.88 219.94 14.01 108.13 218.43 14.32
2,800 110.3 214.55 14.16 113.58 220.94 13.97 112.57 218.98 14.12
2,900 114.57 214.9 14.01 117.44 220.29 13.91 116.79 219.08 14
3,000 118.47 214.56 13.88 121.51 220.07 13.87 120.67 218.55 13.89
3,100 122.33 214.16 13.78 125.67 220.02 13.87 125.09 219 13.83
3,200 126.53 214.38 13.73 129.66 219.69 13.87 129.47 219.35 13.8
3,300 130.46 214.11 13.64 133.46 219.04 13.9 133.34 218.85 13.76
3,400 134.42 213.94 13.57 137.74 219.22 13.93 137.35 218.6 13.75
3,500 138.37 213.74 13.56 142.02 219.38 13.89 141.05 217.9 13.76
3,600 142.66 214.08 13.59 145.35 218.11 13.86 144.97 217.54 13.8
3,700 146.75 214.09 13.55 150.16 219.07 13.85 148.75 217.02 13.84
3,800 150.26 213.3 13.5 153.72 218.21 13.84 152.67 216.71 13.87
3,900 154.19 213.11 13.47 158.11 218.52 13.73 156.72 216.61 13.79
4,000 157.57 212.2 13.37 161.01 216.83 13.61 160.64 216.33 13.67
4,100 160.7 211 13.29 163.97 215.29 13.52 164.16 215.54 13.63
4,200 163.12 208.96 13.21 168.35 215.67 13.47 167.3 214.31 13.58
4,300 166.44 208.14 13.1 170.69 213.45 13.45 171.19 214.07 13.52
4,400 169.22 206.69 13.12 173.88 212.38 13.42 173.66 212.12 13.45
4,500 171.58 204.81 13.11 176.9 211.16 13.37 176.25 210.38 13.41
4,600 174.23 203.35 13.07 179.7 209.73 13.27 179.43 209.43 13.43
4,700 176.67 201.72 13.02 182.47 208.35 13.28 181.56 207.3 13.42
4,800 179.49 200.57 12.98 185.21 206.97 13.28 184.01 205.63 13.41
4,900 182.01 199.16 12.95 187.08 204.71 13.26 186.96 204.57 13.47
5,000 183.36 196.54 12.95 189.21 202.8 13.33 188.56 202.11 13.5
5,100 184.99 194.32 12.97 190 199.59 13.31 190.39 200 13.54
5,200 185.96 191.51 12.98 191.82 197.55 13.3 191.66 197.38 13.55
5,300 185.86 187.73 12.95 192.24 194.17 12.8 192.61 194.54 13.54
5,400 185.28 183.61 12.96 192.75 191.01 12.46 193.17 191.42 13.54
5,500 185.85 180.76 12.97 192.04 186.78 13.37 193.51 188.22 13.55
5,600 185.3 176.95 12.99 191.63 182.99 13.46 192.27 183.6 13.54
5,700 183.87 172.45 13.01 190.74 178.89 13.45 191.75 179.84 13.56
5,800 182.4 168.07 13.03 189.07 174.22 13.49 190.57 175.6 n/a

Just one pulley--the crank pulley--is underdriven on V-6 underdrive pulleykits. The one-piece pulley/harmonic damper assembly is exchanged withthe stock damper, along with a shorter serpentine drive belt. GTR sellsthe ASP Racing pulley/damper for 4.0-liter V-6s. ASP says this 25percent underdrive pulley provides charging voltage at only 850 rpm.

And then there was the underdrive pulley. The 4.0-liter, like the3.8-liter that preceded it, is one of those engines where the underdrivepulley is only the crank pulley.

Again like the 3.8-liter, the 4.0-liter crank pulley is integral--onepiece--with the harmonic damper. Installing "underdrive pulleys" on a V-6Mustang, only changes the harmonic damper. But pulling that damper isgenerally a difficult job.

It would have been pretty simple, except the bolt supplied with thedamper to mate with the harmonic damper puller was too short. All sortsof time-wasting effort resulted, with the final fix being thefabrication of our own bolt. This wasn't the easiest thing, as thecombination of thread series, diameter and length is oddball, but it gotmuch easier when we realized a modular V-8 head bolt was correct, savefor the length. As GTR has old modular head bolts on hand, after a pairof cuts with the chop saw and some quality time with the smoke wrenchand we were in business.

We have to say, after hours of messing around all the effort provedworth it. The power jumped to 204 rwhp, then backed up at 203 rwhp, then203 rwhp again and we figured that must be what it runs, but we hit itagain just to see what it would do when totally heat soaked. It maxed at204.5 rwhp.

RPM

Pulleys

Total Gain

POWER

TORQUE

A/F

POWER

TORQUE

2,400 n/a n/a n/a n/a n/a
2,500 n/a n/a n/a n/a n/a
2,600 n/a n/a n/a n/a n/a
2,700 n/a n/a n/a n/a n/a
2,800 118.69 230.78 13.94 10.72 20.76
2,900 123.22 231.13 13.7 7.72 14.5
3,000 127.78 231.41 13.59 7.11 12.88
3,100 132.63 232.2 13.58 7.5 13.14
3,200 136.66 231.54 13.62 6.9 11.7
3,300 140.97 231.37 13.65 7.53 12.35
3,400 145.28 231.22 13.68 7.81 12.43
3,500 150.22 232.05 13.7 8.24 12.73
3,600 154.21 231.41 13.67 8.46 12.69
3,700 158.12 230.69 13.65 8.89 12.97
3,800 162.2 230.25 13.61 9.35 13.27
3,900 166.56 230.21 13.51 10.58 14.62
4,000 170.97 230.24 13.48 11.1 14.95
4,100 174.13 228.63 13.46 10.76 14.11
4,200 177.9 227.89 13.38 11.19 14.33
4,300 181.29 226.71 13.31 11.98 14.99
4,400 184.9 225.84 13.26 12.52 15.29
4,500 187.97 224.38 13.23 13.44 16.04
4,600 191.05 222.99 13.24 13.51 15.77
4,700 193.3 220.71 13.26 12.89 14.73
4,800 194.91 217.81 13.27 13.05 14.58
4,900 198.51 217.21 13.24 15.28 16.72
5,000 199.41 213.74 13.21 14.96 16.04
5,100 201.19 211.34 13.24 15.73 16.53
5,200 202.41 208.45 13.31 15.75 16.22
5,300 202.75 204.78 13.35 16.28 16.44
5,400 203.93 202.09 13.39 17.81 17.65
5,500 204.44 198.84 13.41 18.68 18.16
5,600 204.27 195.06 13.42 19.34 18.46
5,700 203.65 191 13.45 20.18 18.92
5,800 202.44 186.54 13.46 20.68 19.06

Thanks to the cold-air intake and underdrive pulley, we gained a solid20 hp at the V-6's wheels. The muffler didn't hurt and might help with ablower, while higher octane fuel was a waste until more ignition timingarrived due to electronic tuning. All told, it was a 9.8 percent gainin horsepower, and that's just right for a daily driver. It's enoughpower to feel, but not enough to ruin good manners.

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

Another tactic would be to fit a true dual exhaust, as V-6 enginesprefer two separate three-cylinder exhaust systems with no H or Xcrossovers. While more expensive, such systems can definitely aid powerwith forced induction and often sound more V-8-like than rasp-can giventhe Mustang's generous six-cylinder displacement. It just depends onwhat you're listening for.

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