When you're being dumb and playing around water and decide to go WOT through a hole no deeper than half your tire... Engine is asking for a lot of air and will suck in whatever is around/near it. Ask me how I know... haha.
Our trucks have an active air flap. Without sealing and disabling this, you'll suck in water no matter what.
Here is the entire system:
Background:
The Cummins does have whats called an "Active Intake Box" (none of the other engines have this). The idea is that the box normally takes air from inside the fender where it is relatively well protected from dirt, dust and debris. The box has a motor and air flap as well as another air intake port in the front of the box located in the grille of the truck.
When a Cummins is subjected to very heavy loads in very high ambient temperatures, the computer will begin to de-rate the power in order to keep the engine running correctly. By opening the front valve, there is a chance it can get colder air and delay derating the power.
From what Ive been told by Ram, most trucks will go their entire lives without opening the valve. For those of us out west pulling large grades with heavy loads in high ambient temps, we will be the ones using it.
There is a lot of logic that determines just when this flap will open, for instance not when its raining, not in 4 Low, etc.
What it means for the Raised Air Intake System:
We call it a Raised Air Intake System for a couple of reasons:
A) We are trying to get the point across that its people who live in dry environments that need "snorkels" more than in wet environments. After all you might use a snorkel once a year to cross water (unless you live in Costa Rica or similar) but you'll use it everyday in the dryer environments.
B) The small flapper door does not seal fully in the Cummins Active Air Box. Now, with a very small amount of work, you certainly CAN seal the box off and make it work for water.
On the 5.7/6.4/3.6/3.0CRD, none of this is an issue and the box is sealed to the intake system.