It also depends on what state your in, they are not legal in WA as far as i know.
They don't filter the air, and they are rarely used on the street.
You will also find that below the trumpet is a throttle body, per cylinder
That is a fuel injection setup, each trumpet is the intake for a cylinder, with a butterfly (or slide throttle) and injector at the bottom. No air filter. The trumpet shape is used as it gives better airflow than a bare pipe. A more modern approach is to enclose the trumpets in a plenum, which can then have a filter or duct to a ram/cold air intake. The Boss motors have a setup like this, except the upper manifold has the trumpets cast as one item and they are angled rather than vertical. The set up pictured would not be legal as it is through the bonnet.
it was the old school 'injection' setup...before they had ECU's and injectors, a pair of trumpets was the air intake for a weber that feed two cylinders per carbie.. ie quad webers on a V8.. very similar to using the triples on a 6 potter
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