IF..! his piece of pipe worked it could be for 2 reasons:
1: Most likely the stock air intake was sucking in warm, less dense air.
2: He was in fact getting air rammed into the pipe and the airspeed squared law was playing a small role at speed. Unlikely without a correct bell mouth.
NB that properly designed (Elliptical) Bell mouths everywhere the plumbing cross sectional area decreases dramatically are key, regardless of whether the 1st one is facing into the wind or in a relative vacuum somewhere under the bonnet.
ie: A bell mouth on the intake
AND
a bell mouth after the air filter, on the pipe to the intake manifold
AND
Bell mouths on each intake tract to the cylinders. ( now often called Velocity stacks)
NB that these last intake tracts' length (and diameter) are tuned to give extra power in a narrow rev range of around 1000 rpm and are normally tuned in combination with the cam profile.
Look at the RAM air intake bell mouths on F1 and other performance cars etc:
They are NOT huge funnels. The bell mouth is small. The throat after the bell mouth is smaller than the 'box' after, where you want to slow down airflow (= increase pressure) and get it through the restrictive filter, preferably without causing turbulence in the air (filter) box.
They are also mounted high and away from other influences and surfaces.
You can also make sure that the intake is the 1st thing to arrive as the car moves through th air, and in a high pressure area.
Elliptical bell mouth:
http://www.profblairandassociates.co...mouth_Sept.pdf
rotarygod here speaks sense IMHO:
https://www.rx8club.com/series-i-aft...ly-work-77909/
https://www.enginelabs.com/engine-te...ing-air-inlet/
https://www.onallcylinders.com/2015/...op-technology/
To totally confuse yourself see under testing here:
https://mygolfmk7.com/2020/02/air-in...w-bench-tests/
IMHO on warm air intakes:
2 things:
1: The more you can get the fuel to evaporate (gas vs mist) the better it burns.
So what you are actually doing is increasing the rate of evaporation of the fuel.
The 2 ways to do this are to increase air temperature OR increase fuel temperature.
Air is easier as you get gas bubbles forming in the fuel, at around 80C IIRC.
If the gas bubbles are before the pump/s; the pumps cavitate=stop pumping.
Doing so after the pumps works, but requires warming multiple high pressure fuel lines = to the number of cylinders you have.
That's not so easy, nor is it light: (NB that kw/kg is king until you're cruising at constant speed)
It's also only works on fuel injection, not carbs.
2: Warmer air is less dense so there's less air to compress during the compression stroke.
Sure; pressure causes heat but that's basically a function of how much closer together the air molecules are:
There are less of them in the cylinder before compression, so, for the same stroke, they are further apart after compression = less heat gained from compression.
Then there's the Delta T thing where: the bigger the difference in temperature between the air and hot engine surfaces; the faster the air warms up.
So; smaller delta T: less heat up for the same amount of heat up time.
So it takes takes less energy from the engine to compress warm air than cold. Kinda like the Atkinson cycle but easier to do, + the extra evaporated fuel vs mist...
You also need to consider the type of airflow meter:
If its a hot wire, cooled by airflow:
Warm air will look like less air to it because the hot wire is cooled less for the 'same' flow and less fuel will be injected. resulting in a leaner mixture.
That there
is most likely t
he real trick behind why "it works so well!" here.
Apparently other (newer?) types employ manifold pressure sensors. Probably to avoid this confusion in the engine management system..?
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