Sorry for Hijacking the thread,
alcooker, where did you get your GTA snorkel from? every week i'm pestering autolusso's second hand parts department but it seems impossible to get hold of a used one without paying £40+ for a new one from the dealer.
Just a quick one, the 'cone' that's fitted inside the air filter housing is known as a venturi cone. its designed to increase pressure after the restriction. if you take it out you will increase the volume of air entering the engine, but you can't get the cold air into the engine quickly without the 'venturi' because there is no pressure to force the cold air in.
the venturi cone is there also to give an even dirt wear across the air filter, if you take it out then dirt will build up in one place where the air enters the air box and hits the filter because that's the shortest path as there is no cone there.
that's what iv'e learnt that what the venturi is for and what it does, any one that has a better explanation on what its for i'm all ears.
Hi Chris. Venturi tubes are used to create a low pressure area at the constriction rather than a high pressure area after the constriction. A carburettor (anyone remember them?) is a venturi and the low pressure generated by air passing (accelerating) through the 'throat' or throttle of the carb sucks fuel into the airstream through a selection of jets (precise diameter holes) at hopefully the correct ratios.
The pressure after the venturi (in this case the alfa cone) is always less than atmospheric pressure before the venturi (within the air box). If it wasn't the air would be going the other way and blowing out into the airbox. Air always travels from high to low pressure areas - the engine is creating a vacuum and the air at atmospheric pressure is rushing in to equalise the pressure.
The purpose of the cone has been touched on before. I think it has two purposes. One, it is a bell-mouth for the induction system. The curved and radiused bell mouth opening will flow a lot more air than a 'straight cut' pipe opening. I've attached a couple of pics and a graph to show what I mean. I don't think it is the great impedament to air flow that lots of people think it is as the it would greatly reduce turbulence (drag) of air entering the induction pipe. The cone is an extension of the curved induction pipe which suggest it is designed to deliver smooth laminar flow (unturbulent air) past the MAF to provide accurate fuel metering. Turbulence
kills airflow and effectively reduces the diameter of the tube the air is travelling through (see blue areas of dead air adhering to the walls of the pipe opening below).
Two (although a long shot due to the attenuation caused by the modular manifold), it may act as pulse reflector/inverter. When inlet valves open they create pulse negative wave that travels back through the airflow at the speed of sound. The taper of the cone would refect positive pressure waves back up the pipe, effectively harnessing the resonance within the system to increase pressure at the inlet valve.
Removing the cone may or may not
give you a small boost at peak rpm depending upon whether the cone is bigger bottleneck (from a fluid dynamics perspective -see turbulence above) than any other component in the induction system at full flow. Then again its is likely to provide no benefit at the speeds and rpm that you do 98% of your driving (where the biggest constriction is the throttle butterfly) and may
negatively effect power and fuel efficiency.
Remember the most inaccurate dyno on earth is usually located in a driver's ass.