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AEM Adjustable FPR - Quick Tech

Apr 9, 2007 SHARE
Turp_0103_01_z+aem_adjustable_fpr+full_view Photo 1/1   |   AEM Adjustable FPR - Quick Tech

We don't have to tell you that too little juice to the squirters, especially under boost, is a costly proposition that could lead to serious internal surgery on your engine. Twelve years ago, when Advanced Engine Management (AEM) was still just a tuning shop and chief engineer, John Concialdi, was prepping engines for the strip, he came across many vehicles that lacked adequate fuel delivery to the injectors. This was a frequent problem back then-and one that still persists today.

Fortunately, one man's nagging observation led to a comprehensive fuel system for Hondas and other high-horsepower engines. AEM's new fuel systems include direct-fit High Volume fuel rails, High Performance fuel filters and trick adjustable fuel pressure regulators for Hondas. Currently, the company has a universal adjustable fuel pressure regulator available for any application and in the works is a race fuel filter capable of supporting approximately 1300 hp. The fuel rails and regulators for Honda applications (and universal FPR) support in excess of 1000 ponies and the direct-fit Honda fuel filter is good for 500 bhp. What makes this system different from the others, you ask? Read on and find out.

AEM Adjustable FPR
Advanced Engine Management's adjustable FPR is CNC machined from a billet extrusion of 6061 T-6 aluminum and mounts directly to the stock fuel rail or AEM's High Volume rail. A stock barb fitting is included for the factory outlet line, however the base is tapped to 9/16-18 threads that allow for the use of AN fittings and -6 or -8 line if desired.

The unit is adjustable from 20 psi to the maximum output of any fuel pump (if you want a hard number, let's use 150 psi). Fuel pressure is adjusted by a setscrew on top of the regulator that changes the preload on an internal spring that contacts the diaphragm. The amount of preload determines the base fuel pressure the regulator will allow with no vacuum or pressure applied to the top chamber of the regulator.

The AEM unit includes a manifold vacuum/pressure port in the top chamber to ensure pressure at the injectors is constant in all conditions. The top chamber of the FPR is connected to the intake manifold with a hose so that vacuum/pressure in the top chamber matches that of the manifold inlet. At idle or under light throttle, vacuum in the intake manifold is very high. In this situation, there isn't much fuel being consumed so a low volume of fuel flow at the injectors is required. The high vacuum in the regulator under low load helps to overcome spring pressure, which deflects the diaphragm off of the flow orifice allowing unneeded fuel to bypass the flow orifice and return to the fuel tank. As fuel requirements increase under throttle, manifold pressure (and consequently pressure in the regulator's top chamber) rises, deflecting the diaphragm toward the flow orifice and decreasing the amount of fuel that is bypassed to the fuel tank, allowing more fuel to be delivered to the injectors. In forced-induction applications, fuel pressure is increased one psi for every psi of boost (1:1 ratio), so the AEM regulator is boost dependent.

But the real beauty of the AEM regulator is that the company includes patented interchangeable discharge ports that allow users to precisely match both regulator pressure and flow with the output of their fuel pump, regardless of pump size.

Other "universal" regulators incorporate a fixed discharge orifice that does not allow users to control fuel flow if the fuel pump is different than stock. In cases where a larger fuel pump is used for high-horsepower applications, a regulator that has too small of a discharge orifice will not allow fuel to be bypassed when the vacuum in the top chamber is increased. This causes a momentary rich condition that, depending on the severity, can cause an engine to stumble or stall. On street cars, this condition could degrade catalytic converter performance. On the flip side, if the discharge orifice is too large it can make controlling fuel pressure within the regulator difficult since small changes to the setscrew can affect large changes in fuel pressure. A too-large orifice can also cause fuel pressure to "hunt" during fluctuating throttle conditions, which can cause a momentary lean condition. That could spell disaster in the form of detonation, which is a turbocharged car's worst enemy.

The AEM regulator includes three orifice sizes (0.100-inch, 0.150-inch and 0.200-inch) that cover 99 percent of all applications. The smallest-diameter discharge port is already installed to accommodate a stock fuel pump and the orifices are color coded for easy identification. The orifices are easily changed by unscrewing the top chamber, removing the diaphragm, unscrewing the orifice and replacing it with the desired size.

Since the sizes and flow rates of the fuel pumps you can use with the regulator are chosen based on the type of setup you have, AEM recommends the following procedure for adjusting its regulator. First, install the regulator and a fuel pressure gauge and adjust the setscrew in quarter-turn increments. If the pressure is difficult to adjust, then the orifice size is too large for the delivery system. Second, put the car on a dyno and spin the rollers. If fuel pressure remains high for more than .5 seconds at idle immediately after full-throttle operation, then the orifice size is too small. Determining the proper orifice size will ensure consistent fuel pressure and flow to the injectors and will keep your pistons, rods and sleeves from going south or cracking open.

High-Volume Fuel Rail
AEM's fuel rails are also CNC-machined from a 6061 T-6 billet extrusion and are application specific. The rails have a 1/2-inch fuel bore that is capable of flowing enough fuel for virtually any type of set-up. This larger bore also dampens the back pulses created by larger injectors in high-output applications. AEM includes an end bolt and fitting for the factory supply line; however, the ends of the rail are tapped to accept either -6 hose or a -8 adaptor can be used. The stock fuel pressure regulator mounts directly to the rail, as does AEM's adjustable unit, or it can be bypassed with an external regulator. Another trick feature is the additional NTP port next to the regulator port that can be used to mount a fuel pressure gauge or even tap in nitrous! Sweet.

High-Performance Fuel filter
The second coolest thing about this unit is that it mounts in the stock location on most Hondas and Acuras. The coolest thing about AEM's fuel filter is that you only have to buy it once. The two-piece filter housing is made of 6061 aluminum and utilizes a standard high-flow FRAM or NAPA element that can be purchased at most any auto parts store. The unit mounts using the factory lines. AEM also machined large hexes into the housing for easy disassembly and double O-ring sealed the housing to prevent leakage. What's more, the company has a Race filter in the works capable of supporting more than 1300 horses that will be remotely mountable on any car. That means you V8 guys can use it too; just don't tell your buddies it's intended for a Honda.

The Bottom Line
Fuel tuning is a tricky task made all the more difficult when you are running a high-flow pump in conjunction with a somewhat-adjustable regulator that is delivering fuel to the injectors through an anemic stock rail. AEM not only addressed delivery dilemmas with its rail and filter, but also went the extra mile to develop a patented regulator that is truly adjustable. MSRP for the regulator is $220.61, the rail lists for $174.95 and the filter will run you $124.76. For about $520, you can pump all the power you want into your engine and never have to worry about whether your fuel will run out. Plus, the pieces come anodized in blue, red and clear with a machined finish to look good under the hood as well. This is one fuel system that definitely delivers.

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Sources

Advanced Engine ManagemenT (AEM)
Hawthorne, CA 90250

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