Magazines:  Real Estate Shopping: Adult Costumes  |  Kids Costumes  |   |  Guitars |  
This Issue Archived Articles Blog About Us Contact Us

Ram-Air Revelations

We give the ram-air treatment to a factory airbox!

By Michael Knowling

Click on pics to view larger images

At a glance...

  • Easy Do-It-Yourself intake modification
  • Aerodynamic pressure testing to find the best pick-up location
  • No need for a clumsy big diameter intake snorkel
  • No need to hack up your existing airbox
Email a friend     Print article

If you’ve read our many previous articles on this topic you’ll know there’s no such thing as a ‘too big’ snorkel for your car’s airbox. Big is good - and bigger is better.

But what if there’s inadequate under-bonnet space to run a big diameter snorkel or you don’t want to hack up your factory airbox?

Well, that calls for a ram-air induction system!

In this article we’ll look at a very cheap and easy way of installing a ram-air induction system – the demo car being our ’91 Mitsubishi Galant VR4...

The Standard Air Intake

Click for larger image

This photo shows the factory Galant VR4 intake system. As you can see, the snorkel into the airbox is tucked snug against the body and extends to an unusual arrangement near the radiator support panel. An ‘air cleaner intake box’ forms a pre-airbox chamber that draws induction air from inside the wheel arch. There’s also a lid on the top of the intake box, the function of which we haven’t worked out.

Click for larger image

And here’s a close-up of the factory sticker instructing you to keep the box lid closed... Any ideas?!

With the standard air intake arrangement in place, we tested flow restriction at maximum engine power. Using a Magnehelic pressure gauge, we recorded a peak pressure drop of 27 inches of water (6.7 kPa) restriction at the PCV fitting between the airflow meter and turbocharger. Of this total restriction, 10.4 inches of water (2.6 kPa) restriction was caused by the snorkel arrangement feeding the airbox. (The higher the measured pressure drop, the greater the flow restriction. We've covered the technique in many AutoSpeed articles - do a site search under 'Magnehelic'.)

On this car, there was certainly room for improvement in this area.

Sizing a New Intake Snorkel

Click for larger image

It’s important to look at the standard intake snorkel before sizing a replacement unit. A big diameter intake snorkel is not essential because we will, literally, be ramming air through it. On the other hand, there’s no point causing an unnecessary flow restriction by using a smaller-than-standard snorkel.

In the case of the VR4, the standard intake snorkel to the airbox is 3 inches OD - and it maintains a similar cross-sectional area along its length. This means the new intake snorkel should be no smaller than about 3 inches diameter – and 3 inches is what we went for.

Finding a Ram-Air Pick-Up

The location of the air pick-up is critical.

Click for larger image

To achieve the greatest ram-air effect, you need to perform aerodynamic pressure measurement on the bodywork while driving on the road or racetrack. For this you’ll need a sensitive positive pressure gauge (or manometer) and a length of tube to probe aero pressures at various locations across the front of the car. (The frontal surface of the car is where you’ll find the greatest aerodynamic pressure.)

The ideal location for the air pick-up is where there’s the greatest build-up of aerodynamic pressure. This pressure can be harnessed to force-feed the airbox.

Click for larger image

In the case of the Galant VR4, we tested aerodynamic pressure in the frontal cooling aperture (which feeds the radiator), the fog light area, and immediately below the bottom edge of the front bumper. At a road speed of 100 km/h, we measured 2.1 inches of water (0.5 kPa) positive pressure in the cooling aperture and fog light area. In contrast, the area immediately below the bottom edge of the bumper had negative pressure.

You sure as hell don’t want to mount your air intake there!

In this case, we decided to remove the driver’s side fog light and use the cut-out as our air pick-up. Why? Well, it’s in a high pressure area, it’s relatively easy to access and the pick-up can be made to look entirely factory.

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 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.

Click for larger image

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...

Click for larger image

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.

Click for larger image

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.

Click for larger image

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.

Click for larger image

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.

Click for larger image

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).

Click for larger image

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.

Click for larger image

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.

Did you enjoy this article?

Please consider supporting AutoSpeed with a small contribution. More Info...

Share this Article: 

More of our most popular articles.
Huge lights without a roo- or nudge-bar

DIY Tech Features - 2 October, 2012

Mounting big driving lights, Part 1

Measuring analog and digital signals

DIY Tech Features - 24 February, 2009

How to Electronically Modify Your Car, Part 11

Reducing engine intake restriction to a bare minimum

DIY Tech Features - 30 October, 2007

We Have a Record!

A new low cost data logger - and how to use it on cars

DIY Tech Features - 7 July, 2009

Five Channel USB Data Logger, Part 2

One of the most amazing constructions ever

Special Features - 23 February, 2010

Building the Eiffel Tower

It changed the way everyone viewed railway travel

Special Features - 18 August, 2009

The Pioneer Zephyr

Describing how diesel burns

Technical Features - 16 April, 2013

Diesel cetane ratings

You don't need an expensive factory towbar harness - even on CAN bus cars.

DIY Tech Features - 4 August, 2009

Towbar Electronics

A press so huge it can forge titanium beams over 5 metres long

Special Features - 29 October, 2013

The Wyman Gordon 50,000 ton forging press

A new intercooler... and the series conclusion

DIY Tech Features - 22 March, 2011

Powering-Up the 1.9 litre TDI, Part 5

Copyright © 1996-2020 Web Publications Pty Limited. All Rights ReservedRSS|Privacy policy|Advertise
Consulting Services: Magento Experts|Technologies : Magento Extensions|ReadytoShip