Forward-Facing Snorkels – the Downside...
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
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
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
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
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
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
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.