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2ndGenTeg · 10-24-2002, 09:35 PM

It is generally agreed upon that the AEM Cold Air Intake (CAI) is one of the best dollar for dollar modifications you can make to your car. Its design places the filter in the fender well of your vehicle, allowing the engine to ingest cooler air, increasing power output.

However, by placing the filter element in the fender well, the filter becomes more prone to being submerged, ingesting water into the engine, and causing hydrolock. Contrary to popular belief, hydrolock is not the inability of the engine to ignite due to moisture in the combustion chamber. Hydrolock occurs when enough water is ingested into the engine that the cylinder is unable to compress the contents of the cylinder on its upstroke (water is much more dense than air), effectively locking the crankshaft. Nine times out of ten, this results in lots of things breaking and, inevitably, a complete loss of a motor.

As a solution, AEM introduced its air bypass valve. This valve is a plastic exoskeleten encompassing foam and rubber "flanges," and is placed on the intake tube closer to the throttle body. When the filter is submerged, the vacuum created causes the flanges to open, and air is ingested through the valve rather than the filter. This relieves the vacuum on the water, and water is not ingested into the engine.

It works. Sport Compact Car conducted a test in which the designer of the bypass valve put his own Acura NSX on the line. In this test, the intake tube was rerouted to the outside of the car, bypass valve installed, and the filter was actually submerged in an aquarium. The testers did everything they could concieve of to attempt to get the engine to ingest water, including revving the engine to redline, and rapidly submerging and removing the filter from the aquarium. The bypass valve did its job, and the NSX's engine remained intact, unscathed.

Seems like a worthwhile investment, right? $40 insurance against a complete engine rebuild? Seems like an easy call. It depends. True, the bypass valve is insurance against hydrolock. However, it's a lot harder to hydrolock an engine that most people realize. The filter must be completely submerged- for most of us, around a foot of standing water. Driving in the rain is insufficient- you'd have to drive through a flood. Dyno tests have shown a 2-3 horsepower decrease after installing the valve- a product of the disrupted air flow, primarily drops in velocity and density created as the air flows past the valve. Finally, I have seen more than one valve (including my own) break in half. This leaves the intake tube completely exposed and is extremely hazardous to particles and debris being ingested, particularly pieces of the broken bypass valve. I consider myself extremely lucky.

Personally, I did not replace my valve after it broke. I installed a rubber coupling, identical to the AEM piece. If you're that worried about hydrolock, buy a bypass valve. It is cheap insurance against an engine rebuild. However, if you're smart enough not to drive through water more than a foot deep, you don't need it.

10-24-2002, 09:35 PM	#1
2ndGenTeg 4th Gear Join Date: Aug 2001 Location: Boulder, CO Age: 43 Posts: 830	AEM Bypass Valve Debate It is generally agreed upon that the AEM Cold Air Intake (CAI) is one of the best dollar for dollar modifications you can make to your car. Its design places the filter in the fender well of your vehicle, allowing the engine to ingest cooler air, increasing power output. However, by placing the filter element in the fender well, the filter becomes more prone to being submerged, ingesting water into the engine, and causing hydrolock. Contrary to popular belief, hydrolock is not the inability of the engine to ignite due to moisture in the combustion chamber. Hydrolock occurs when enough water is ingested into the engine that the cylinder is unable to compress the contents of the cylinder on its upstroke (water is much more dense than air), effectively locking the crankshaft. Nine times out of ten, this results in lots of things breaking and, inevitably, a complete loss of a motor. As a solution, AEM introduced its air bypass valve. This valve is a plastic exoskeleten encompassing foam and rubber "flanges," and is placed on the intake tube closer to the throttle body. When the filter is submerged, the vacuum created causes the flanges to open, and air is ingested through the valve rather than the filter. This relieves the vacuum on the water, and water is not ingested into the engine. It works. Sport Compact Car conducted a test in which the designer of the bypass valve put his own Acura NSX on the line. In this test, the intake tube was rerouted to the outside of the car, bypass valve installed, and the filter was actually submerged in an aquarium. The testers did everything they could concieve of to attempt to get the engine to ingest water, including revving the engine to redline, and rapidly submerging and removing the filter from the aquarium. The bypass valve did its job, and the NSX's engine remained intact, unscathed. Seems like a worthwhile investment, right? $40 insurance against a complete engine rebuild? Seems like an easy call. It depends. True, the bypass valve is insurance against hydrolock. However, it's a lot harder to hydrolock an engine that most people realize. The filter must be completely submerged- for most of us, around a foot of standing water. Driving in the rain is insufficient- you'd have to drive through a flood. Dyno tests have shown a 2-3 horsepower decrease after installing the valve- a product of the disrupted air flow, primarily drops in velocity and density created as the air flows past the valve. Finally, I have seen more than one valve (including my own) break in half. This leaves the intake tube completely exposed and is extremely hazardous to particles and debris being ingested, particularly pieces of the broken bypass valve. I consider myself extremely lucky. Personally, I did not replace my valve after it broke. I installed a rubber coupling, identical to the AEM piece. If you're that worried about hydrolock, buy a bypass valve. It is cheap insurance against an engine rebuild. However, if you're smart enough not to drive through water more than a foot deep, you don't need it.