Best Products bored-out Cobra

Best Products Bullet

Best Products 77min Pro-M

Vortech/C&L MaxFlow

First, an explanation of mass air meter operation. The mass air sensor's purpose is to assess engine load by measuring the quantity of air coming into the engine. All 5-liter Mustangs built from 1989(1988 in California) to present use a Hitachi-sourced sensor element attached to a cast-aluminum meter housing.

The sensor element is comprised of two heated filaments that are maintained at a temperature that is 2000 C. over the ambient air temperature. As air speed over the element increases, a correspondingly larger electric current is required to keep the sensor at the same temperature. The sensor itself is not located in the main stream of airflow, but in a smaller side channel known as a sample tube.

Air flowing through the smaller sample tube is proportional to air flowing through the main body of the meter Thus, the entire amount of air passing through the meter can be accurately sampled without causing damage to the sensor element or undue restriction to the incoming air.

The chief manufacturing advantage of using a mass air meter metering over speed density is that regardless of production differences in volumetric efficiency between engines, the air/fuel relationship may be reasonably maintained as constant From a performance standpoint, relatively large improvements to volumetric efficiency can be made without reprogramming the EEC control module.

As an integral part of engine management, the mass air meter doesn't actually do anything except measure the mass of air. But the meter's effect is felt in the fuel delivery department as it is the greatest determiner of injector duty cycle. How ironic it is then that the mass air meter measures air but controls fuel, an often misunderstood role?

We say "misunderstood" because much of the public focus on aftermarket mass air meters is on how much air one passes (its diameter), not on how accurately it measures air. Thankfully, all the manufacturers involved in our test understand this role and have designed their products accordingly (if our test results count for anything). Thus the axiom "bigger isn't necessarily better" applies in this case.

The nagging question is, "Is there any discernible difference in the performance of aftermarket mass air meters?" To answer this we constructed a test as close as possible to real-world conditions using a Dynojet model 248 chassis dynamometer, five different mass air meters and two 5-liter Mustangs.

We opted to test those commonly available meters that are strictly stand-alone units. Both the Kenne-Bell 80mm Mustang mass air system and the SVO 70mm Mass Air Induction Kit (part Nos. M-9000-C52, manual; M-9000-D52, auto) were omitted because both employ enhanced spark and fuel progr&nm1ng that could tilt the playing field and otherwise mask the performance of the lone meter.

Those units tested were the Auto Specialties 71mm, the Vortech/C&L 73 mm Ma~ow, Best Products' bored-out 70mm Cobra, Best Products' 75mm Bullet and Best Products' 77mm Pro-M. We also obtained a Vortech/C&L 8Omm MaxFlow unit for photographic purposes but did not test it because it is designed to operate with larger injectors (30 lbs./hr. and up) than our test cars were equipped with.

The meters were tested on two different Mustangs, a bone-stock '89 GT and a modified '93 LX. The showroom-mint '89 GT 5-speed had a scant 9,000 miles on it and belonged to Mike Pasternak of Quakertown, Pa. Still equipped with its original tires, air silencer, and air filter, the '89 is about as unspoiled as they come.

The '93 LX of Pierre Cornelius (Chester, Pa.) is a good example of a seriously warmed-over daily driver with a stock short-block. The 43,000-flilie 5-speed is equipped with such goodies as Edelbrock Performer 5.0 heads and intake, an SVO E303 cam, 1.7 rocker arms, BBK 7Omm throttle body, MAC l 5/8-inch equal-length shorty headers, MAC high-flow converter H-pipe, How Master 2-chamber mufflers and 3.73 gears. Pierre uses a 77mm Pro-M mass air unit with 19-lb./hr. injectors and an SVO 155-ph in-tank fuel pump.

The test was performed at Second Street Speed in Perkasie, Pa. Second Street Speed specializes in fuel-injected performance and has two dynamometers, a SuperFlow 901T set up specifically for electronic fuel injection, and a DynoJet model 248 chassis dyno. Bill Hunsberger and Lon Moyer performed the dyno chores efficiently and professionally. Ml mass air pulls were made and backed up accurately at least once with time to spare.

The primary goal of the test was to measure relative out-of-the-box performance, just as a consumer would in the real world. As such, we did not make any attempt to maximize the performance of each unit through ignition timing tweaks, fuel pressure changes or excessive cooling time. (It is our assumption that each consumer will do this anyway.) To preserve the integrity of the test, we made sure that engine operating temperature was consistent from pull to pull. Also, the time increment between pulls was kept reasonably consistent, that is between 5 and 10 minutes.

After each meter was installed, the computer was given a brief time to become familiar with the meter (both idle time and a few runs through the gearbox). All meters, with the exception of one, settled into a nice idle without undue prodding from the gas pedal. A full-blown learning period consisting of several cold start/warm-up cycles (i.e., several days per meter) was impractical. Fairness dictates that a complete learning period be given for each; in light of this fact, we will refrain from divulging the identity of the offending meter. It is our experience that an ample learning period will eliminate a poor idle 90 percent of the time.

Auto Specialties 71mm. The folks at Auto Specialties have offered this low-cost alliterative for the past five years. Milled from billet-aluminum stock, the unit takes on a plain, utilitarian appearance but works well nonetheless. Small adjustments to sensor calibration are made via a small screw on the side of the unit. This changes the rate of flow over the air sensor (which the user supplies) within a small range. For our test, the screw was adjusted all the way out to put it at its max rich setting.

Best Products bored-out Cobra. The '93 Cobra Mustang came equipped with a larger 7Omm sensor housing (LX and GT models were equipped with 58mm units). In spite of its larger diameter, the bore of the unit is usually obstructed by a wide post that reduces airflow to the engine significantly (this is also the case with the SVO 7Omm Mass Air Induction Kit). Best Products removes the bar, which frees up another 28 percent airflow and recalibrates the electrical sensor accordingly. Customers may order the unit calibrated for any size injector.

Vortech/C&L MaxFlow. The cast-aluminum 73mm MaxFlow design is jointly marketed and sold through C&L Performance and Vortech distributors. It's unique in that calibration changes are affected by changing an aluminum sample tube inside the unit (The user supplies his own sensor element) By changing the diameter of the trailing portion of the sample tube, flow over the sensor element can be altered for compatibility with different-size injectors. A larger 8Omm unit that requires a larger-than-stock inlet tube is available. Primarily designed for high-output supercharged applications, sample tube calibrations on the 8Omrn unit are only available for 30-lb./hr. injectors or larger.

Best Products Bullet. The Bullet unit measures 75mm in diameter and is the only aftermarket piece not made of aluminum. The chrome-plated steel tube is attractive and comes (like the bored-out Cobra and Pro-M) with its own custom-calibrated sensor element Each unit is provided with its own signature flow bench data sheet (as is the bored Cobra and Pro-M).

Best Products 77min Pro-M. The granddaddy of all mass air meters, the Pro-M is the only meter comprised of multiple aluminum castings. It's the largest of the meters we tested (in length, weight, price and opening diameter), and its OEM appearance is impressive as a result The meter is available in long or short configuration (for naturally aspirated and blown applications) and commonly comes in 19-lb/hr., 24-lb./hr., 30-lb./hr. and 36-lb/hr. injector calibrations.

We baselined the stock '89 GT with the stock mass air element, air filter and airbox. As an intermediate step, we also tested the GT with the stock mass air meter and a conical 6x9-inch K&N filter that was later used for all meters except the Vortech/C&L and the 77mm Pro-M (they came with their own conical K&N filters). These are the results of the '89 GT baseline test and follow-up filter substitution:

Stock ’89 GT
Baseline w/OEM filter, box, & silencer
Peak HP: 192.7 (4200 rpm)
Peak TQ: 269.2 lbs.-ft. (3000 rpm)
Avg. HP: 187.9 (3500-4900 rpm)

Stock ’89 GT
w/K&N 6x9-inch filter element
Peak HP: 198.2 (4300 rpm)
Peak TQ: 272.0 lbs.-ft. (3000 rpm)
Avg. HP: 192.0 (3500-5000 rpm)
Gain: +4.1 Avg. HP

In this and all subsequent comparisons, we have noted peak torque, peak power and average power for all examples. The average power figure is by far the most consequential, as it has the most impact on vehicle performance-both on and off the track. In a few cases, you will note that the average power figure is taken from a smaller set of data points (e.g., stopping at 4900 rpm). This is because some dyno pulls were terminated before the computer was able to take the last data point (this has an insignificant elevating effect on the average).

The air filter test was performed to give you an idea how much performance improvement can be attributed to a high-flow filter and the elimination of the intake silencer restriction. In the stock '89 GT, this accounts for an additional 4.1 average hp. All mass air performance graphs of the stock '89 GT use the OEM filter/airbox/silencer trim as the baseline trace (the thinner of two lines). In comparisons of meters on the modified '93 LX, the baseline trace (the thinner of two lines) consists of a stock mass air meter with a conical 6x9-inch K&N filter (not the stock airbox/filter/silencer).

Modified '93 LX-Stock Mass Air Meter
baseline w/conical 6x9-inch K&N filter
Peak HP: 275.4(5500 rpm)
Peak TQ: 307.6 lbs.-ft. (3800 rpm)
Avg. HP: 268.0(4300-5800 rpm)

The horsepower average is taken from the range that yields the highest average. In the case of the '93 LX, we found that to be between 4300 and 5800 rpm. For the stock '89 GT the range was significantly lower (3500-5000 rpm) due to the induction-limited nature of its engine (i.e., stock throttle body, EGR spacer, intake manifold, cylinder heads and exhaust). In both cases, the indicated 1500 rpm range is the one that will produce the best quarter-mile results for that engine.

The five meters tested fell in an extremely narrow performance range. The spread between the highest and lowest performers was only 2.9 horsepower in the case of the modified '93 LX and only 2.1 hp in the stock '89 GT. The results are as follows:

Stock '89 GT

1. Best Products Bullet, 198.1
2. Auto Specialties, 197.5
3. Vortech MaxFlow, 196.2
4. Best Products Cobra, 196.2
5. Best Products Pro-M, 196.0

1. Best Products Bullet, 275.6
2. Auto Specialties, 274.8
3. Vortech MaxFlow, 273.8
4. Best Products Cobra, 273.2
5. Best Products Pro-M, 272.7

Stock '89 GT

1. Best Products Bullet 205.3
2. Auto Specialties, 205.1
3. Vortech MaxFlow, 203.0
4. Best Products Cobra, 203.0
5. Best Products Pro-M, 202.9

1. Best Products Cobra, 285.6
2. Best Products Bullet, 283.9
3. Vortech MaxFlow, 283.1
4. Auto Specialties, 283.1
5. Best Products Pro-M, 280.7

MASS AIR TEST DATA:

*As of this test, the suggested retail price of the Pro-M was reduced to $449. Some advertisers had yet to incorporate the new pricing in their ads. This is the reason for the discrepancy in suggested retail price and average retail price.

These results are almost too close to count, and given the closeness of the outcome, we can characterize the test only as a virtual tie among all five. All were capable of admitting enough air for the engine without imposing any restriction. The difference in power would then be a result of the meter's calibration with the EEC-IV computer.

Beyond this, we can surmise that the meter with the highest power output put the air/fuel ratio at the engine's sweet spot, which is just before the onset of detonation. It would've been nice to monitor air/fuel ratio during the test with a wide-band 02 sensor, but DynoJet has yet to implement this parameter into its data acquisition software.

Nonetheless, if this is true, then the results should not be held in strict hierarchy, especially if your individual induction hardware differs from our test cars' significantly. For example, a supercharged or turbocharged application may run quicker (or for that matter, safer) with a meter that puts the air/fuel ratio a little more on the rich side. Of the five meters submitted for testing, only those from Best Products were accompanied by bench test flow figures.

These figures show measured test stand flow and actual metered flow (from the sensor element) in 10 discrete points on the flow curve. When compared, it is possible to measure the meter's error in either direction, rich or lean. In the case of our test Bullet meter, airflow at the top end of the range produced (according to manufacturer data) a lean condition, while the Pro-M produced a rich condition.

We can't put the same weight on Best Products' flow data as on the dyno results, but it is supported by the dyno results. It is then reasonable to assume that other cars with other combinations of equipment could produce different dyno results, but they wouldn't vary significantly, as the close clustering of our test supports.

Of particular note was the unexpectedly small gap in performance on the modified '93 LX between the stock 58mm sensor and the aftermarket units. The restriction of the stock mass air meter doesn't appear to be fatal. It's only down 7.6 hp from the best performer By the seat of your pants, this wouldn't amount to an improvement you could really feel (especially at normal engine speed), but at the track it could account for a sizable lead at the finish line (.07 or .08 second in ET). Still, the improvement is far less than some manufacturers have claimed, as we indicated at the outset.

Our only suggestion is that before you purchase a mass air meter, you negotiate with your dealer to retain the option of returning the unit if there is an unexpected mismatch with your computer and injectors. In many cases, a retailer will allow you to return the unit for credit or swap it for another if there is a problem. The ability to upgrade the meter to a larger injector at a later date may also come into play, so discuss these options with the dealer before you buy.

Should you buy a larger mass air meter? It depends on where you are now. Adding a larger meter would certainly make economic sense before an item like a computer chip or a set of roller rockers. But by the same token, we'd go with a set of equal-length shorty headers before a mass air meter (on a stock 5-liter) because they have a higher performance payoff for the dollar (around 15 hp for $200). No matter, because if you've got bigger plans for the future, you'll need the meter anyway. As induction improves, the benefit of the meter only becomes larger

The bottom line is that we feel good about recommending any of the meters we tested. The real-world performance gain is enough to warrant the cost, providing all the fine and cheap performance mock (like bumping the timing and replacing the engine oil with synthetic) have been made. And unlike some quick tricks, the performance benefit will pay greater dividends as other induction and exhaust parts find their way onto your car.

Auto Specialties
13313 Redfish,#106
Stafford, Ix 77477
713/721-8056
7lmm mass air meter

Best Products
(Professional Flow Technologies)
25760 John R. Rd.
Madison Heights, Ml 48071
810/399-9223
7Omm Cobra, 75mm Bullet, and
77mm Pro-M air meters

C&L Performance
13015 S. Memorial Pkwy.
Huntsville, AL 35803
205/882-6813
73mm and 8Omm MaxFlow air meters

K&N Engineering
561 lowa Ave.
Riverside, CA 92502
909/684-9762
K&N Filtercharger filters

Second Street Speed
109 South 2nd St.
Perkasie, PA 18944
215/257-3724
Dynojet chassis dyno

Vortech Engineering
5351 Bonsai Ave., Suite 405
Moorpark, CA 93021
805/529-9330
73mm and 8Omm MaxFlow air meters