Ram-Air Revelations

The biggest problem with an exposed forward-facing intake snorkel is vulnerability to water, bugs, stones and other debris.

If you live in an area affected by locusts, dust storms or where wind-driven rain is common, you should keep a very close eye on the condition of air filter element once your new snorkel is installed. You should also check to see what is deposited in the bottom of the airbox – if, for example, there’s alarming number of stones, we advise you to re-think your pick-up location. If there's lots of snow or flood waters often on your roads, we suggest you don't use this approach.

In any case, regular air filter inspections become a high priority with a forward-facing intake snorkel.

Installing the Ram-Air Snorkel

We wanted a cheap and easy approach to the intake of our VR4.

PVC pipe is great stuff for making intake snorkels but, in this case, it would have been very difficult to route a large enough pipe from the fog light area to the airbox. The problem is the limited selection of angles available in PVC bends.

An easier option is flexible pipe. But note that not all flexible pipe is the same - many have a near-smooth inside wall (which helps maintain airflow) while others are very convoluted (which restricts air flow). Cost also varies massively so shop around. Our 3 inch flexible pipe had been sitting in the shed for several years so it cost nothing...

With the original intake snorkel removed, we could fit the end of our flexible pipe to the airbox. This was easy in the case of the VR4 – our flexible pipe slipped tightly over the snout of the airbox. We even re-used the original cable-tie to hold it in place...

Now comes the task of routing the flexible pipe to the air pick-up location.

In some vehicles you might be able to run the flexible pipe from the airbox to the front of the car without cutting any metal. However, in the VR4 we were forced to put a hole through a difficult to access section of the inner guard alongside the battery tray. Note that there’s plenty of support structure in this vicinity, so you can get away with creating a 3 inch hole.

Due to space limitations, we were unable to use a holesaw to buzz a hole through the inner guard. Instead, we made series of holes using a drill and punched out the centre. A template (seen here) was used to mark the placement of the hole. The edge of the hole was then painted to prevent corrosion.

Once a suitable hole was created, we passed our flexible pipe through to the opposite side of the guard and routed it to the area of the driver’s side fog light. Cable ties were used to hold the pipe in place.

The next step was to remove the driver’s side fog light (we also removed the passenger’s side fog light to maintain a symmetrical appearance). Note that the cut-out for the fog light is quite large – it gives a cross-sectional area around 3 times that of our 3 inch pipe. This allows us to create a flared inlet to the pipe to further improve the ram-air effect.

In the space normally occupied by the driver's side fog light, we were able to integrate an 80 x 100mm plastic downpipe adaptor (as available from most hardware stores). This plastic adaptor slips almost perfectly inside the VR4's fog light cut-out and gradually tapers into a 75mm round fitting on the opposite end. Our flexible pipe could stretch just enough to slip over the round end of the plastic adaptor (as seen here).

After trimming the plastic adaptor to a suitable length, we secured its front edge directly to the bumper using Liquid Nails. A thin strip of rubber was then used to fill the gap around the edge of the plastic adaptor and the inside of the fog light cut-out. This photo shows our completed ram-air pick-up - a coat of black spraypaint gives it a stealth appearance

Ram-Air Results

With our new ram-air snorkel installed, we took to the bitumen with a couple of pressure gauges to check the results.

The first pressure tapping was in the new snorkel near the airbox. When cruising at 100 km/h, this showed a ram-air effect of 4 inches of water (1.0 kPa). This positive pressure build-up gave a noticeable improvement in throttle response.

And what about intake restriction at maximum power?

Well, the ram-air intake certainly gave an improvement – albeit not huge. Compared to standard, we saw a reduction from 27 inches of water (6.7 kPa) pressure drop to around 23 inches of water (5.7 kPa). Note that reduced restriction is from the combined effect of the ram-air pick-up and the oh-so slightly larger diameter snorkel.

Granted, these gains are relatively modest but they do highlight the effect that a ram-air induction system can create.

The most important lesson we’ve learnt is that a ram-air system can provide positive pressure inside the airbox at cruise. This gives a distinct advantage in terms of throttle response compared to a big diameter snorkel mounted in a low pressure area. But when it comes to making power, our old saying still applies – bigger really is better when it comes to snorkel diameter.

Still, if you’re up against space limitations or you’re reluctant to chop up the standard airbox you can find gains with this approach. We’ve proven it!

For more on ram-air induction set-ups see More on Siting Cold Air Intakes and Eliminating Negative Boost - Part 5

Interested in do-it-yourself car aerodynamics? You’re sure then to be interested in the Amateur Car Aerodynamics Sourcebook, available now.