FORDMUSCLE.com FordMuscle Nav

Restricted Airway
The heavily touted 4.6L 3V motor in the new Mustang GT comes with a big jawbreaker stuck deep in its throat. The factory has it choking on its' own air inlet system. Restrictive air boxes and silencers have become the Achilles heel of Mustangs. The previous generation had the rubber fender insert and the 5.0L era Mustangs had the funky looking plastic contraption. The practice of immediately removing these things has became so notorious it is classified as a "free horsepower mod". Even the most green of Mustang enthusiasts know to rip their silencers out the minute they turn the corner from the dealer's lot.

For the '05 the restriction comes in several areas. First and foremost is the 2" square opening from which air enters into the air-box. How the car can lay down over 250 horsepower to the wheels sucking air through this swizzle stick of an inlet is mind blowing. Once the air makes it past the filter and mass-air meter (integrated into the air-box lid) it encounters the most severe restriction we've seen to date on any Mustang, the carbon filter. This rigid plastic piece resembles a tightly rolled up piece of corrugated cardboard. It performs an emissions function of trapping gasoline fumes that might be in the intake system.

The final restriction is the harsh bend in the throttle body duct. Ford has always used the pre-formed accordion shaped bellows to connect between the mass-air meter and throttle body. In our experience there has always been some power to be found by straightening this out, and perhaps even increasing the diameter - especially once you start adding other mods.


What separates the new Mustang's breathing problems from that of past generations is that on the '05 you can't just pull out the silencer or slap on a big conical air filter for decent power gains. The mass air meter and computer in the new Mustang is so sensitive to airflow changes that even removing just the carbon trap from the inlet tube results in a significant leaning out of the air-fuel ratio. Do that and a K&N filter and the engine will go lean enough to throw a check-engine light and trouble code.

If this sounds like a nightmare just talk to Lee Bender, owner of C&L Performance, the mass-air meter and inlet specialists. Usually C&L's products bolt right on, yield impressive gains, and require no tuning of the engines PCM. However, early on in their R&D process and dyno testing they realized the '05 was a different beast. The slightest changes in the factory air intake system would change the air-fuel ratio significantly. To make matters more complicated, the first couple dyno pulls immediately after a change would show no ill effects. Subsequent pulls would however show undesirably lean conditions, as if the engine management system was picking up the airflow change and improperly adapting to it. It didn't matter how slight the change, the engine ultimately didn't like it and power gains were less than optimal- and keep in mind C&L is using the same diameter mass-air meter housing and the factory sensor.

After beating their head against the wall the C&L team realized the '05 required some computer re-tuning to go along with the hardware upgrade. They teamed up with Diablosport who had also been at work developing an '05 tune for their Predator tuner product. The Trueflow system consists of a cast aluminum inlet tube and mass-air meter, a big K&N conical air filter and heat shield, and is bundled with a Diablo Predator tuner with a specific C&L 2005 Mustang tune. We had the opportunity to play with this kit on the dyno and at the track, here is how it performed.


With the '05 Mustangs mass-air meter integrated into the air-box lid, removing the entire air-inlet system is merely a five minute process.

Using a 10mm socket, remove the single bolt securing the air filter housing to the fender.

Disconnect the mass-air sensor plug as shown.

Squeeze to release the PCV system hose connection.

Loosen the clamp securing the stock rubber inlet bellows to the throttle body.

The entire factory air-inlet system can be removed now as a unit.

Using the provided Torx security bit remove the screws securing the mass air sensor cartridge.

Carefully transfer the sensor into the new C&L mass air meter and secure with the factory Torx screws.

We prefer to pre-assemble the C&L system on the work bench, then simply connect it to the throttle body. The filter shield is secured to the fender using the same bolt removed in step 2. C&L includes a bracket to further secure the mass-air housing to the motor if desired. Reconnect the mass-air connector and PCV hose.

With the engine off connect the Diablo Predator to the vehicles OBD-II service port. On the '05 it is located directly under the driver side dash. Follow the on-screen instructions to program the vehicles computer with the C&L specific tune. Further enhancements to the tune can also be made, as we detail in this article.

Track Gains
The first opportunity to test the C&L system came at a Wednesday night Bracket event at our local track. We generally don't prefer testing at bracket events because you typically get very few runs before you are into elimination rounds. To make matters worse our plan to run the '05 on slicks fell through due to the 15" steel wheels not clearing the disc brake calipers. So we did the best we could on the stock radials.

2.5mph gains at the track gave quick confirmation the C&L/Diablo air intake and tune was for real.
With only a total of three runs to acquaint ourselves with the new car we managed a best run in bone stock form of 14.42 @ 99.68 mph. This came on an embarrassing sixty-foot time of 2.39. Disappointed that we didn't achieve the stock-13's-on radials that so many '05 owners around the country are reporting, we chalked it up to the poor traction and lack of seat time in the new platform. With elimination rounds looming we quickly installed the C&L kit and reprogrammed the computer with the Predator.

We only got one pass with the C&L system in place, however the results proved to be a clear indication this was no ordinary duct and filter kit. With a slightly better 2.10 sixty-foot time the '05 tripped the lights at 13.86 seconds and 102.54 mph. We were dying to make another all out pass to see if we could get the ET lower, however the announcement came that it was time to dial-in and begin bracket rounds. We played it safe and dialed in at 13.8, and managed to run a 14.0@102. At least we backed up the trap speed gains with the C&L.

In This Article:
Ford has always put a choke hold on the Mustang via a restrictive air-inlet system. The 2005 Mustang is no different, except in that a free flowing air box is alone not sufficient. The computer must be re-tuned. The C&L Trueflow package addresses this by including a C&L specific Diablo Predator tune. We test its worthiness in this article.

Also See:
High Five
Sound Thinking

The C&L Truflow system (below) consists of a re-designed cast aluminum mass-air to throttle body pipe. A cast aluminum mass air sensor housing replaces the stock plastic unit integrated into the air-box cover. A big K&N conical filter is sealed off from the hot motor via the included sheild.
Diablo teamed up with C&L to create a specific Predator tune for the C&L Truflow air inlet system.

Shown is the restrictive carbon filter trap which resides in the factory air-intake duct. This corrugated piece serves to trap any raw fuel vapor from the intake manifold. Removing this piece is good for a several horsepower gain, however often yields to wacky air-fuel ratios.











































Dyno Testing
We spent the better part of a day at Custom Dyno Tuning in order to test every possible combination of the C&L TrueFlow system. To keep the playing field level we used the Predator's data-logging function to ensure our intake air temperature (IAT) and engine coolant temperature (ECT) were consistent run to run. We aimed for starting IAT of 72-76°F and ECT between 180 and 190°F. When ECT's climb above 190° the 05's computer retards timing to avoid engine damage. Therefore, as an added measure of consistency we also monitored spark advance at 4000, 5000, and 6000 rpm. If we observed any pull back in timing we'd repeat that pull.

We made over 16 dyno pulls, with the first and last pulls made with the C&L kit installed and computer upgraded with the Diablo tune. This way we also covered any potential of the '05 needing to "learn" the new modification. Below we have detailed the three most interesting comparisons from our testing.

How much better than stock?
The first test, and the one of most interest, is the straight forward comparison against the stock setup. We knew from our impressive track gains that there was going to be no false sense of the butt-meter with this product. The dyno confirmed that with no uncertainty. With the stock air box and factory tune the '05 Mustang made 255 peak horsepower at 5100 rpm. Peak torque measured 277 lb-ft. at 4300 rpm. With the C&L air inlet system and matching Diablo tune the power improved in single digits up to the same 5100 rpm peak. However it is what occurs after that point that is noteworthy. Whereas our '05 drops off after 5100 rpm, the effects of the C&L/Diablo kit allows power to climb another 1000 rpm, with the new peak horsepower being 270. From 5700 to 6100 rpm the C&L/Diablo is up over 30 horsepower and nearly the same on torque versus the stock curve.

Graph 1: Stock Air Box and Tune vs. C&L/Diablo System
Stock HP C&L HP
Stock TQ C&L TQ

While this test clearly shows the worthiness of the C&L system, the gains may be a bit inflated. This is because we know from our original dyno testing of this particular '05 that we may have a Ford PR "dud" on our hands. Other than this '05 we have not seen another produce a horsepower peak as low as 5100 rpm. Most five-speed manuals are making peak power around 5700, and the factory rating is at 5750 rpm. We believe this particular car from the media fleet to be one of the first off the production line, and therefore it may have an early PCM flash or a deliberately fat air-fuel curve to avoid media mishaps. Take note of the A/F ratio before and after the C&L tune. In stock form our test vehicle dips into the low 10:1 range - drowning in fuel even by forced induction standards. The Predator tune brings the ratio into a more acceptable mid 12 range.

Can we improve with a leaner A/F ratio?
The next step in the dyno testing process was to use the Predator's built-in capabilities to fine tune the fuel and timing parameters. With the canned tune putting A/F ratios at 12.4:1 after 5500 rpm, we suspected there may be a bit more by approaching 13:1 across the board. The Predator offers two possibilities to alter the A/F ratio. One way is to decrease the fuel by going a certain percent in the lean direction. This yielded no gains in our testing and we actually observed very little change, if any, to the air fuel ratio. The other method to lean up the A/F ratio is to add timing or spark advance. Using the Predator's "Global Spark Adjust" parameter we played with varying degrees of advance over the base Predator setting until we found peak power. While the gains were not massive, with the maximum 4° additional advance allowed by the Predator we picked up some single digits here and there.

Graph 2: C&L/Diablo Tune vs. C&L/Diablo Tune 4° Spark Adv.
C&L HP C&L (+4° Spark) HP
C&L TQ C&L (+4° Spark) TQ

How does the competition stack up?
Manufacturers may hate when we do this, but readers love it and that's what counts. Since Custom Dyno Tuning has a Super Chips Tuning system in house we figured it'd be worthwhile to see what sort of numbers we could generate with SCT's X-calibrator product (see side bar.) We cleared the Diablo Predator tune from the computer and then loaded on SCT's base "cold-air" tune. This is a canned tune from SCT aimed at '05 Mustang's with any type of aftermarket CAI (cold air induction) kit. This tune actually lost power across the board compared to the Predator tune. In fact, the SCT cold-air tune put A/F ratios in the mid 13's above 4k, something the '05 clearly does not like.

CDT's owner Arlee Taylor then went into the SCT X-Calibrator tuning software and modified the tune to add 3% more fuel than specificed in the SCT cold-air tune. The tune was then uploaded to the '05. This time the engine responded with an average gain of 4 HP and 4 lb-ft across the
board over the best Predator tune. The gains are minor but clearly due to even finer finessing of the air-fuel ratios across the power curve.

Without a doubt the 2005 Mustang GT is gasping for air. Open up its' airway, make the appropriate fuel and timing adjustments, and you've unleashed some significant horsepower.

Graph 3: C&L/Diablo Tune vs. C&L/Diablo Tune +10% Spark Adv.
C&L/Dabble HP C&L/ACT HP
C&L/Dabble TQ C&L/SCT TQ


Custom Dyno Tune's Arlee Taylor straps the '05 in for a long days worth of dyno testing air-intakes and tunes.

Using the Predators built-in capabilities to adjust spark advance and fuel we tried to pick up power by further leaning out the A/F ratio.















The SCT X-calibrator is similar to the Predator in that it is a EEC-V tuning device via the OBD-II port, however it is not nearly as refined. There is no user interface to make on the fly tuning changes, and no logging or scan tool built in like the Predator. You can only use it to transfer tunes which have been placed on it via a PC.



Tech Archives Project Cars Readers Cars Feature Cars