The Mazda has a grille opening large enough and placed properly enough to pull in a lot of air through the radiator. They even have an undertray to help facilitate that airflow.

In regular production street cars, the angled footwell portion of the firewall is enough to direct under-hood air out from the engine compartment and out the bottom of the car, but that can begin to fall short of what’s required for racing. That dynamic also can create lift on the front of a car, which is less than desirable, particularly for high-speed cornering where front grip is essential.

One simple solution is the addition of hood vents, which relieve under-hood pressure and also remove heat from the engine bay. That’s true for any car, but we happened to know a guy who needed to do the job on his Miata, so we followed along for the most important part of the job: finding the right place to put them.

As air travels over the hood of a car at speed, it creates areas of low and high pressure. Low-pressure areas are better place for locating the hood vents because they “pull” air out from under the hood through the vent.

On a Miata, the low-pressure areas best suited for removing hot air are pretty well established. You just need to figure out which vents you like, or which are legal for your class, and where to put them.

The kit from Flyin’ Miata came with instructions that outlined where the low- and high-pressure areas are on three generations of Miata hood designs. On the second-generation Miat, the areas of lowest pressure are on the edges of the hood, but that’s probably not the best location for removing under-hood heat and pressure.
To get a more precise idea of where to place the vents, we decided to tape a grid on the hood as outlined in the instructions.
The squares on the hood measure 10 inches from center to center.
One consideration you must include is how much of the under-hood bracing you’ll need to cut to create the openings for the hood vents. Miatas are nice because the hood and bracing are made of aluminum, which is easy to cut.
With the grid taped out like those in the instructions, you can begin to experiment with the placement of the vents.
The locations of the vents meant cutting some of the under-hood bracing.
Now for the fun part. Using a center punch and a hammer creates an impression keeps the drill from walking while you’re drilling the fastener holes for the vents. For fasteners, pop rivets are the quickest solution.
Wrapping a drill bit with tape can help keep the drill from penetrating too far and into something delicate under the hood.
With everything mapped out, you can cut the holes in the sheet metal and bracing underneath to permanently mount the hood vents. In theory, coolant temperatures should come down and front grip should improve a little as a result.
Image courtesy of Brett Becker

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