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Flow Power

Posted in How To on April 22, 2003
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One of the quickest and easiest ways to improve your truck's performance is to modify the intake system to increase airflow and reduce pumping losses. This allows an engine to produce more power because it is now able to ingest more air with less effort. Most intake systems involve replacing the factory airbox with an open element air filter. The better ones offer a replacement airbox that shields the filter from debris and prevents the intake from pulling heated air from under the hood and into the engine.

GCA Industries took a different approach when designing its True Flow system. The True Flow system retains the factory airbox in order to draw in cool air while protecting the filter from debris and moisture. A high-flow foam or gauze reusable lifetime filter replaces the factory filter. The factory air tube, which can have restrictive mufflers or resonators, is replaced with the firm's high-flow powdercoated mandrel tube to maximize velocity.

For most truck owners, making more power and protecting their engine have equal priority. Making more power is good, but not if you have to sacrifice engine service life. This is especially true if your driving environment is dusty. So in regard to air filter choices you have to ask which is better, foam or gauze?

Should You Use Foam or Gauze?

Gauze filters offer superb airflow with a good dust-holding capacity. They were originally designed for race cars with the goal of maximum airflow and engine protection for the duration of the race. For a race car or for a high-performance vehicle driven occasionally, a gauze filter will allow the engine to develop the most power. The down side is they don't filter as well as other materials, so you have to trade between maximum power and maximum service life. The up side is that a properly designed foam filter will offer a good blend of filtering performance and power-making airflow.

Foam filters typically combine great airflow capability, a huge dust-holding capacity, and very high filtration efficiency for extremely small particles. They are considered by many dirt bike riders and buggy drivers as the filter of choice. High-performance foam filters are made up of tiny interlocking cells that trap and hold dirt particles throughout the entire volume of the foam and thus are often referred to as full depth filters. As GCA Industries marketing materials explain, "the cell strands of the foam stop the dirt while the oil holds it until the filter is cleaned."

GCA Industries tested the airflow capacity of a racing-type gauze filter, one of its foam filters, and a factory paper element on a Super Flow S.F. 600-flow bench. The company tested each in clean and dirty conditions using a flow range between 6 and 4 inches water resistance. According to GCA's tests, in both the clean and dirty tests the gauze and foam filters far outperformed the factory filter. And when clean, the gauze out-flowed the foam. However, under dirty conditions, the foam out-flowed the gauze. The superior flow of foam compared with gauze when loaded with silt is wellknown to off-road performance enthusiasts and it's why many use this type of filter extensively.

So What Did We Observe in Our Test?

Our test rig is a '99 GMC Sierra with a 4.8L engine backed by the four-speed automatic. It's totally stock with 60,000 miles on it. The factory says it makes 255 hp at 5,200 rpm and 285 lb-ft of torque at 4,000 rpm. We won't see those numbers on the dyno test. We expected power values at the rear wheels approximately 25 percent less than the factory flywheel stats due to rotational inertia and driveline frictional losses, and that's what we got.

The baseline test generated 192 hp at 5,100 rpm and 218 ft-lb of torque at 3,700 rpm. Those figures equate to about 75 percent of the advertised net power figures, so we're reasonably confident the GMC's powertrain and the Dynojet chassis dynamometer are functioning correctly.

With the True Flow intake system installed, we saw peak horsepower improve from 192 to 203, an increase of 11 ponies. Torque went from 218 lb-ft to 230 lb-ft, an increase of 12 lb-ft of torque. Furthermore, the True Flow intake improved the average power out put from 3,400 to 5,100 rpm by 8 hp and 12 lb-ft of torque. Keep in mind these values reflect the power losses mentioned above. An estimate of the flywheel horsepower assuming losses of 25 percent reflected in the measured values would give us an average increase of 10 hp and 15 lb-ft of torque with a peak increase of 14 hp and 15 lb-ft respectively.

The increase in the average output indicates a substantial real-world power increase from this intake package. In addition, we also measured an increase of a little more than one mpg in our fuel economy. The kit definitely made a positive improvement in the performance of this truck. Considering we didn't test the truck with the True Flow filter installed until it had several hundred miles of dusty driving through the Santa Ana winds in Southern California, the performance of the new True Flow filter is even more impressive.

The True Flow kit comes complete with detailed and comprehensive instruction. It features durable bright-red silicone couplers to attach the metal powdercoated intake tube as well as all the hardware required for installation. You won't have to make any modifications to existing components because other than removing the factory intake tube and filter, all the factory breathers, sensors, and hoses are left intact. The True Flow kit comes complete with detailed and comprehensive instruction. It features durable bright-red silicone couplers to attach the metal powdercoated intake tube as well as all the hardware required for installation. You won't have to make any modifications to existing components because other than removing the factory intake tube and filter, all the factory breathers, sensors, and hoses are left intact.
The stock intake tube uses a series of ports and reservoirs to filter intake noise. We didn't test the efficiency of the stock intake tube, but it doesn't lend a performance look to the engine, so it had to go. The stock intake tube uses a series of ports and reservoirs to filter intake noise. We didn't test the efficiency of the stock intake tube, but it doesn't lend a performance look to the engine, so it had to go.
These are all the tools you'll need to install the True Flow system. A blade screwdriver, a #3 Phillips, and a 5/16-inch (8mm) wrench and socket. These are all the tools you'll need to install the True Flow system. A blade screwdriver, a #3 Phillips, and a 5/16-inch (8mm) wrench and socket.
First disconnect the battery. This is important because you'll be moving the mass air sensor. Also, because of the free-flowing nature of the new intake, disconnecting the battery allows the computer to adapt to the new setup. First disconnect the battery. This is important because you'll be moving the mass air sensor. Also, because of the free-flowing nature of the new intake, disconnecting the battery allows the computer to adapt to the new setup.
Remove the hose clamps on the intake behind the mass air sensor and at the throttle body. Remove the hose clamps on the intake behind the mass air sensor and at the throttle body.
There is a hose clamp that positions the heater hose attached to the underside of the stock intake tube. You need to release the hose from this clamp in order to remove the intake. There is a hose clamp that positions the heater hose attached to the underside of the stock intake tube. You need to release the hose from this clamp in order to remove the intake.
Remove the stock intake tube. Remove the stock intake tube.
Comparing the stock paper filter to the True Flow foam filter. At first glance the paper seems more restrictive than the foam. That observation proved out in testing. Be sure to remove the excess oil from the foam before installing. Blot both sides with a paper towel to remove excess. Comparing the stock paper filter to the True Flow foam filter. At first glance the paper seems more restrictive than the foam. That observation proved out in testing. Be sure to remove the excess oil from the foam before installing. Blot both sides with a paper towel to remove excess.
9. Use a #3 Phillips screwdriver to remove the fasteners from the stock air filter box. 9. Use a #3 Phillips screwdriver to remove the fasteners from the stock air filter box.
Remove the factory filter and replace with the True Flow foam filter. Be sure to remove excess oil from the foam before installing. Remove the factory filter and replace with the True Flow foam filter. Be sure to remove excess oil from the foam before installing.
You're going to need some soapy water to get the silicone couplers around the end of the mass airflow sensor. You're going to need some soapy water to get the silicone couplers around the end of the mass airflow sensor.
Slip the True Flow silicone hose end around the flange of the mass sensor. This operation requires patience, some soapy water, and a slight stretch of the coupler opening. We used the jaws of a vise as a spreader. If you follow our lead, just be careful and don't over do it. Slip the True Flow silicone hose end around the flange of the mass sensor. This operation requires patience, some soapy water, and a slight stretch of the coupler opening. We used the jaws of a vise as a spreader. If you follow our lead, just be careful and don't over do it.
Install the right angle hose end to the throttle body intake. Position the hose clamp, but don't tighten yet. Install the right angle hose end to the throttle body intake. Position the hose clamp, but don't tighten yet.
After getting the hose end over the flange of the mass airflow sensor, installing the tube between it and the throttle body hose was the second trickiest part of the installation. The angled hose on the throttle body has to be rotated to allow the entry. After getting the hose end over the flange of the mass airflow sensor, installing the tube between it and the throttle body hose was the second trickiest part of the installation. The angled hose on the throttle body has to be rotated to allow the entry.

Dyno Test Baseline
RPMHPTQ
3,400139215
3,500144216
3,600146212
3,700153218
3,800156216
3,900160215
4,000162213
4,100167214
4,200170213
4,300173212
4,400175209
4,500177206
4,600181206
4,700184206
4,800187204
4,900188201
5,000190200
5,100192198
5,200189191

Dyno Test with Intake
RPMHPTQ
3,400137212
3,500153230
3,600153224
3,700159226
3,800163226
3,900166224
4,000171224
4,100176225
4,200178223
4,300181222
4,400186222
4,500190221
4,600194221
4,700196219
4,800197216
4,900200214
5,000203213
5,100198204

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