A strut brace ties the tops of the suspension towers together. It works by carrying load between them, which means it has to be stiff and it has to be bolted down hard. Anything that sits between the towers is inside a structure that is doing real work.
That matters for an intake, because the space above the engine is exactly where a brace wants to run and exactly where a filter wants to sit. The two are competing for the same volume, and the brace usually wins because it cannot be moved without losing its function.
A cold air intake wants a short path, a cool air source and a filter with room around it. In most bays the shortest path from the throttle body to the front of the car runs straight under the brace. So the pipe gets bent down, the filter drops lower, and the routing gets longer.
The alternative is to run the pipe forward along the inner wing and turn in behind the headlight. That is longer and it has more bends, but it puts the filter in the cold air stream and leaves the brace untouched. Extra length is cheaper than a compromised brace.
A brace bolted to the towers moves with the body, not with the engine. So an intake that clears it when parked can touch it under load, when the engine rocks and the shell twists. The gap you need is the gap measured with the engine running and loaded.
Check with the car on the ground rather than on stands, and have someone load the engine in gear against the brake while you watch. A brace that has been touched leaves a polished line on its paint or a scuff on the pipe, and that line shows exactly where the gap closed.
A metal brace lying across a hot engine bay becomes a hot object, and an aluminium intake tube near it picks up heat by radiation. That is a small effect next to a filter breathing air from behind the radiator, but it is the one owners notice at a standstill.
The larger factor is where the filter draws from. A filter tucked behind the brace and above the exhaust manifold is breathing bay air. A filter fed from the grille or from inside the wing is breathing outside air, and no amount of shielding turns one into the other.
Dropping the filter low to clear a brace puts it closer to splashed water and to the road. A filter that sits behind the liner can be soaked in heavy rain, and a wet element flows far less air than a dry one.
If the only clear space is low, a shield around the filter helps with splash but not with immersion. The decision rule is whether the filter can be submerged at a kerb-height puddle. If it can, the position is wrong however well it clears the brace.
Fit the brace first and tighten it as it was designed to be, then build the intake around it. Doing it the other way round means the brace ends up spaced up on washers to clear a pipe, which loads the towers unevenly and defeats the part.
Then check the whole assembly with the bonnet closed. A pipe that clears the brace can still touch the bonnet lining, and an air intake kit that has rubbed through its own tube on the underside of the bonnet is a common and avoidable finding.
