This page details testing a cold air intake and standard filter for pressure loss at speed in inches of water.

I tested a homemade cold air intake and a new genuine air filter. Used a U-tube manometer to measure pressure loss at three different points in air inlet tract in inches of water. The points were between the throttle and Air Flow Meter, just after the air filter and just before the air filter.

In summary the standard paper filter flows well and the biggest improvement you can make is to remove the intake snorkel.
A dirty filter had a pressure loss of 2 inches of water while a new one had a loss of 1 inch of water.
Homemade cold air intake developed a positive pressure of 2.5 inches of water at 100 kph.
Cold air intake was made from 100mm stormwater pipe - same circumference as the intake snorkel. Used two 88 degree bends (the smoothest in the range) and a short piece of straight pipe. Heated pipe to mould to shape.
Removing the headlight made hardly any difference.
Removing the intake snorkel made the biggest difference, although not as good the cold air intake I made.
Testing was done on road at full throttle in 2nd gear. Measurements were taken at 3000, 4000, 5000 and 6000 rpm.
Also measured the pressure loss after the air flow meter - this is by far the biggest restriction - but you can't do anything about it - don't even think about touching the screen in the meter - it is an integral part of the measuring device (generates vortices in air to by measured by downstream LED).
Was able to reduce the restrictions in the total air intake system by 30% by changing the filter for a new one ($48) and fitting a homemade ram air cold air intake ($9).
.

This idea of measuring the intake at different points came from Autospeed.

http://www.autospeed.com/A_0629/page1.html

The original article from Autospeed. Five parts – all free. Read this for background info. A great site and a good read.

http://www.mkiv.com/main/index.html

Terrific Supra site. Go down to basic performance upgrades, then cone filter test results. Big difference between pod filters for flow and filtration.

http://www.fordmuscle.com/archives/2000/01/airfilters/index.shtml

Comparison of different types of filters including paper. Most paper filters rated between 80 % and 90% of the cotton gauze types (K&N type). Amount of dirt stopped by the filter, paper is in the 98-99% range when new, cotton gauze will best around 96%, while some foam filters are as bad as 50%.

Testing took over three hours and half a tank of fuel. My Nephew Steven took the readings (while I yelled out the revs), didn’t complain and came up with plenty of good ideas and proper scientific procedures. Multiple runs were made.

Date: 14/7/2001 1:45 pm

Temperature: 14 degrees celcius

Relative humidity: 77%

Pressure: 1017 millibars

300 m above sea level.

These figures were measured inside the airbox before the filter. They all show a negative pressure (suction) in inches of water (27.68 inches of water equal to just 1 psi).

Pressure Loss before filter in inches of water, full throttle, 2nd gear

El cheapo stormwater inlet gives good pressure. This is the first working prototype – will try others to see how high I can get the pressure. Will post photos of intake soon.

Pressure loss measured across air filter with standard system in place

Pressure loss measured across air filter with standard system in place.

With a maximum pressure drop of only 1 inch of water for a new filter it is hard to justify a "high flow" after market filter that does not filter as well as the standard item. I will definitely be keeping my standard filter and box – hard to beat.

Pressure loss measured for whole system (between AFM and throttle)

If any one has one of the fancy after market cold air intakes I would be interested to see how they measure up.

I made a U-tube manometer out of 5 metres of 5mm clear plastic tube (70 cents/m at hardware store). Found a 30 inch long piece of timber (20 is fine) and three inches wide out in the backyard.

Mark off inches on timber from say 1 to 20.

Attach one end of clear tube to timber in "U" shape. One end stays open just above timber, the other end goes out the car window, in the bonnet and attaches to intake. I attached tube to timber using those white plastic holders for electrical cable that you nail to wood.

Suck some water and blue food colouring into tube. Suck on the long end, put short end in bottle or something. I kept on sucking and blowing J until the blue water was at the 10 inch mark in both tubes when at rest. This made measurements easier later on.

Drill 2.75mm hole in airbox ( I know it brings tears to the eyes – the irrigation dept also sells neat little caps to cover hole later – or use a grommet – pick a spot out of sight).

Insert a piece of 3mm clear plastic hose – it is a tight fit.

Connect 5mm hose to 3 mm hose – it slips right over.

If both tubes are at 10 inches of water when resting and the one connected to the intake goes up to 11, the one open to the air in the car will drop to 9 inches. They always go up or down the same amount on each side. So if one goes to 11 and the other drops to 9 then this is 2 inches of water.

You are now ready to measure suction and pressure.

This is what you should do:
Buy a genuine replacement air filter.
Remove the intake snorkel to the air box.

(To do this you have to remove the drivers side front wheel, the inner plastic guard, remove the headlight and then remove the intake snorkel. Make sure you replace the plastic inner guard otherwise you're engine bay will fill up with crud).

This won't make any difference:
Removing the headlight.
Replacing the standard filter with an aftermarket filter.
.

Would you buy it? Probably not. So do yourself a favour. Go down to the Toyota dealer and get yourself a standard airfilter:
Here's the part number:
17801-46060
.

The 35% improvement to the intake system with a cold air intake is best represented by this graph:

The mould looked like this;

The first paper mache scoop looked like this;

The inlet to the airbox is too small. The space under the headlight is a bottleneck. While the headlight was in place I filled the cavity with expanding foam. Once this had set I removed the headlight and had a nice mould. I then cut across the mould through the minimum cross-section between the headlight and the metal panel beneath. This is the maximum cross-section available to get air through.
I then compared this maximum available area with the current hole in the airbox. It was 50% bigger!! 50% bigger area with same velocity means 50% bigger flow (Q=VA, or Flow=velocity times area). So the next air intake will be 50% bigger under the headlight, and the hole in the airbox will be bigger again (nice smooth venturi effect after headlight). Other projects on boil are a 3.5 inch mandrel bent polished intake pipe (9.6 inches square versus current 7.1 square inches - 36% bigger) and smooth connector to replace corrugated rubber hose between AFM and intake pipe.

This is not a scale diagram. Use your own intake snorkel to scale it. I measured the circumference of this minimum cross - section and it was very close to that of a 150mm diam stormwater pipe. I'm going down to the local hardware shop to buy 0.5 m of the stuff. Then I will fill it with cotton rags to stop it wrinkling when I heat it and try to squeeze it under the headlight. Then I will be time to cut a larger hole in the airbox to fit the other end of it - the airbox hole is too small. May also be able to use smooth bore (relatively) duct work of same diameter - save a lot of mucking around heating stormwater plastic pipe.

BFD (Big Duct) is a replacement for the standard V8 intake duct between AFM and throttle. The standard duct is squared off to plumb into the resonant chamber (reduces noise). The BFD is the same diameter as the AFM and reduces down to the throttle body at that connection. The convoluted rubber connector between AFM and standard duct also needs to be replaced with a larger 3.5 inch smooth wall rubber pipe. The BFD combined with the BFI (Big Intake) results in a BFPI (Big Performance Increase). The BFD is available in a chrome finish with BFD engraved on it or in a black powder coat finish for that sleeper look. I asked AutoSpeed editor Julian Edgar about the chamber

"The devices are resonant chambers, forming part of the tuned intake system prior to the throttle butterfly. In addition to aiding volumetric efficiency (ie breathing) they are also sometimes used to reduce intake noise. If you are replacing the duct into which a resonant chamber is connected with a pipe size much larger than the original, we wouldn't bother reconnecting the chamber."

Looks like 3.5 inch mandrel bent polished stainless steel will be the go. Dearer than mild steel but saves on chrome and looks a bit better. Can't get the whole made from 1 pipe - will have to be a 90 degree bend, a small straight bit and a 45 degree bend. This will be a direct bolt on replacement for the standard duct. The convoluted rubber connector will be replaced with a silicon smooth bore 88 mm internal diameter rubber hose.

Of course you should construct your own out of 90 mm stormwater pipe and some suitable 90 degree and straight through silicon rubber hose and test it yourself using your own u-tube manometer.( which I will also be doing- results posted later.

Quotes for a stainless steel duct were about $200. But couldn't get a 90 degree mandrel bend with a radius small enough to fit inside the active suspension tower. 90 mm PVC stormwater pipe is the cheapest way to replace the duct. Two 45 degree bends have a smoother radius than one 90 degree bend and still fit nicely. 90mm (3.5 inch) rubber hose is hard to get with a smooth bore. I did get some high pressure suction hose but it is way too stiff and very heavy. Even 90 mm radiator hose is hard to get and relatively expensive - $38 for a 90 degree bend with clamps. Two 45 male-female bends, one 22 degree M-F bend, a few inches of 90 mm pipe, and a short length of 90mm rubber radiator hose should do the trick. Sometimes the radiator hose is a minimum of 1m long at $62 - a better bet is a 80mm standard rubber hose joiner from hardware store in stormwater pipe section- $20 with 2 clamps - heat in boiling water then squeeze on to AFM and male end of 22 degree bend. The two 45 degree bends are $1.20 and the 22 degree bend is $3.20. The M-F 45 degree bend fits onto the throttle body using the rubber ring from the standard intake duct - no problems there. Including the plumbers 80mm rubber hose gives a much larger intake duct for about $25. No testing done yet. Will post a couple of pics and do some on road testing to see if it is worth it.

A - the outline the injected foam mold up against the airbox. This is the maximum size hole in the airbox that still flows nicely under the headlight.

B - this is 150 mm diam pipe. Same size circumference as the minimum cross-section under headlight. This size pipe will crush to fit under headlight.

The standard airbox hole is a restriction and has to be enlarged. If your Soarer breathes through the standard airbox hole you are losing horsepower - the biggest ramair cold intake in the world will not overcome this restriction. On full throttle the engine is always out sucking any ram air device.

You can use 150mm (6inch) stormwater pipe or rubber ducting with a wire helix running through it.

Peter G Scott.
ALSC - Adelaide S.A.