I recently purchased a cold air intake kit from Injen (SP1305P, seen below) at the recommendation of my mechanic and am planning on installing it in my 2001 Honda S2000. However, it is my daily driver, and I will occasionally need to drive it in the rain. While I would certainly be a responsible driver and avoid big puddles and the like, I'm wondering how likely it is that this intake kit would suck water into the engine if driven in the rain?

Injen cold air intake kit

Can I drive in light rain, but not in heavy rain? Or should I make sure to never drive the car in any level of rain at all under any circumstances after doing the install?

An installed version can be seen below (front of the car is to the right of the picture):

Injen cold air intake installed in an otherwise stock S2000

  • A picture of the engine bay could help to determine what you could do. On most of the car a CAI doesn't cause trouble in rain. Also viewing the form of the CAI it shouldn't get too mutch rain in the engine.
    – Rémi
    Sep 25, 2013 at 13:36
  • Thanks; I've had a few people tell me to beware of driving in the rain after installing it, but it's quite possible that I just misunderstood and the fact that it's not a short-ram or something means it's okay. I found this picture of a car with one already installed online, and another of a (more or less) virgin engine bay.
    – user3729
    Sep 25, 2013 at 13:47
  • Picture I posted in the previous comment was wrong. See the updated post.
    – user3729
    Sep 26, 2013 at 13:07
  • Why would a mechanic recommend a cold air intake for a daily driver? Sep 27, 2013 at 3:59
  • 1
    Not familiar with S2000 layout and only have anecdotal evidence. I'm pretty much worst case with my turbo DSM with a filter on a stick. It sits just under the hood, right at the level where spray can get between the hood and the body. I also have run it in rallys and rallyx, sometimes in tremendous downpours, sometimes with mud flying all over. Never the slightest issue in my particular case. YMMV of course, but I've only heard of a couple cases of hydrolocked cars and they both involved submersion of the CAI while going through flooded streets. Sep 27, 2013 at 11:51

2 Answers 2


tl;dr: your car will be more vulnerable to hydrolock. Don't use full throttle in deep puddles. In the rain, you should be fine in most situations. All that said, you'll still be able to ruin your car if you try hard enough.

If you submerge a running car in water, it's going to damage the engine, cold-air intake or not. One of the worst possible scenarios is hydrolock. From Wikipedia:

Hydrolock occurs when a volume of liquid greater than the volume of the cylinder at its minimum (end of the piston's stroke) enters the cylinder. Since most common liquids are incompressible the piston cannot complete its travel; either the engine must stop rotating or a mechanical failure must occur.

Among other things, this can lead to catastrophic damage to engine internals. For example, here's what a tragically compressed connecting rod looks like:

Don't submerge your car in water.

The cold-air intake does one or both of the following:

  1. It moves the air intake point to one far away from the hot engine bay. This is often down inside a wheel well.
  2. It provides a smooth path for the air to move from the primary opening to the intake manifold with minimal turbulence or loss along the way.

Remember also that your engine is an air pump. A normally aspirated engine can create a vacuum at its primary intake point that approaches a negative atmosphere (relative to base atmospheric pressure). That means that you'll see approximately 15 psi of suction across that air intake's cross section.

This gets more exciting with a forced induction car. My car can easily generate an additional atmosphere of boost. That means that my intake is seeing 30+ psi.

So, considering the weight of water is one gram per cubic centimeter, it sure does seem like it wouldn't be hard to slurp up enough water to fill every cylinder simultaneously (my 2000 cc engine would hold about four pounds of water).

Now, a reality check: all of the above assumes full throttle and a smooth pipe-based intake that is fully submerged. What can you do to avoid damage?

  1. Don't use full throttle in deep puddles. If the engine is in a vacuum situation (i.e., closer to idle), it won't be sucking so hard on the straw.
  2. Don't use a cold-air intake. I don't but you can if you want. It's your car.
  3. Don't drive into super deep puddles / ponds / lakes. Maybe you shouldn't do this regardless.
  4. Keep your splash guard in place. That should rule out sudden high volume splashes of water right on the intake.
  5. Try an air bypass valve. There are a variety of vendors that sell a piece that goes in line with the intake that looks like a foam collar. It opens up when there's a severe vacuum in the lower intake (i.e., if it's trying to injest a bucket of water). The result is that the car continues to receive air and not water (until things get deep enough to cover that valve as well).

On the intake that you show in your picture, the air bypass valve would go right in place of the silicone collar that joins the two main sections.

  • Thanks, this is exactly what I needed. Looks like I won't have a problem after all (I certainly don't plan on driving it through any deep puddles), but I'll look into air bypass valves anyways.
    – user3729
    Sep 26, 2013 at 17:29
  • @SamWhited For reference the bypass valve look something like this amazon.com/00-09-Honda-S2000-Bypass-Intakes/dp/B0056K33BM Be sure of the size of your intake before you order one. You could also check with the vendor that sold you your current intake
    – Rémi
    Sep 26, 2013 at 19:08
  • @SamWhited, you're welcome - CAIs are fun. I had one on the Integra which badly needed the smoother airflow. I installed the bypass valve very early on and never had a problem myself. The WRX, on the other hand, has never asked me for a CAI so I haven't bothered to spend the money.
    – Bob Cross
    Sep 26, 2013 at 19:59
  • @BobCross I'm looking forward to it; the S2000 really doesn't need one under normal conditions, but I wanted a bit more power in this for autocross; looking forward to sticking it on the rolling road and seeing the difference.
    – user3729
    Sep 26, 2013 at 20:59
  • I had one fitted on one of my old Subaru Imprezas and while it may have given me a bit more mid range, the only real benefit was that it became a bit smoother and progressive below the turbo spin up point, so wouldn't bog down quite so much in slow traffic = so I figured it wasn't worth it for a turbo car.
    – Rory Alsop
    Sep 27, 2013 at 8:09

Try hydro shields. Other are nylon covers for your intake filters made by injen. It fixed the problem on my Audi tt

  • Yeah, consider something like this if it worries you. But it should be fine anyway, as long as you don't actually submerge the filter while driving. Jun 1, 2014 at 12:39

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