AEM Bypass Valve Debate

[2ndGenTeg]

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.

[ebpda9]

well i have the aem cai and their bpv. when i installed it i lost everything i gained from the cai. plus in the manuals for my intake it said that the filter is like 16" off the ground, but i had times whe i had to drive thru water just like that on the highway. i had no point of return.

[94_AcCoRd_EX]

I have the AEM CAI and the BPV, but I too replaced it with a rubber coupling. I ran all last winter w/o the valve and was fine, but if the weather gets bad, I think I'll stick it back on to be on the safe side.

Great write up BTW.

Or if you're like me, running at stock height I've got even more clearance before I reach total submersion.

Definitely a good write-up. I had never heard of the BPV breaking. This would concern me greatly especially for the possibility of ingesting parts from its breakage.

b

[94_AcCoRd_EX]

Originally posted by spoogenet
Or if you're like me, running at stock height I've got even more clearance before I reach total submersion.

Definitely a good write-up. I had never heard of the BPV breaking. This would concern me greatly especially for the possibility of ingesting parts from its breakage.

b

AEM did a semi 'recall' on the first ones made. Mine was included. The foam lining could get sucked into the TB, causing it to stick open. AEM supplied a plastic clip to stick inside to stop that from happening.

I think that the bypass valve would only be good for people who live where it rains a lot...otherwise theres no real point to having it b/c you are just losing HP...juss my opinion...

[2ndGenTeg]

Mine was NOT included in the recall, but the flanges did not dislodge like the ones in the recall. Mine simply fell apart at the seams, literally. Split right in half. I'm extremely lucky nothing was ingested into the engine.

[ChrisCantSkate]

Originally posted by 2ndGenTeg
Mine was NOT included in the recall, but the flanges did not dislodge like the ones in the recall. Mine simply fell apart at the seams, literally. Split right in half. I'm extremely lucky nothing was ingested into the engine.

same here. i still have mine on, but i think im going to get a rubber coupling and fix it, then keep the bypass valve in my car just incase i need to.

We had an Accord come into the shop the other day, drove through a puddle of water and blew the # 3 rod completely out of the block. I agree, the filter has to be totally under water, but remember, the normal engine runs like 20 in/Hg which means that the vaccum created will pull mercury 20 inches up a tube. Water is less dense and so the same vaccum will pull water about 20 feet up the same tube. So for ~$50.00 I'd rather loose 2 hp than the motor.


Andy

[Addict]

Not sure how I missed this debate.

Originally posted by 2ndGenTeg
However, if you're smart enough not to drive through water more than a foot deep, you don't need it.

It doesn't take a foot of water. I can testify to that. Like most you know, my car was hydrolocked earlier this summer. Maybe 7 inches of water. Like Frost was saying, it is like a big vacuum. I sitll don't get how AEM can claim the 16" of water rule. MY car is lowered only about 1".

$35 is alot less than the $5,000 plus it took to get me back on the road.