Those funny things tee’d into intakes…
One of the unheralded changes that has occurred in engines of the last decade is the use of resonant volumes on the intake. You know, those odd blind-ended boxes and tubes that you can see under the bonnet, tee’d into the intake. Sometimes they’re long and thin, other times they’re short and fat. Often they’re in full view but every now and again they’re hidden inside a guard or under a radiator cover plate. So what are these resonant volumes for?
And how do they work?
As the name suggests, they’re part of the ‘tune’ of the intake system. As more commonly understood with exhausts, the opening and closing action of the valves creates a rapid starting and stopping of gasflow in and out of the engine. Each time the inlet valves close, the columns of gas rushing in towards each cylinder are abruptly stopped. This creates a high pressure wave that gets bounced back along the intake runner. When it reaches the beginning of the runner, it’s reflected back towards the intake valves. If the intake runner is of the right length, the reflecting high pressure wave will arrive just as the intake valves are again opening – which will help jam in more air.
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