Whether or not they are needed, a (well-installed) set of hood vents looks rad on just about every car.
Photography by David S. Wallens
After a Lucky Dog endurance race at Carolina Motorsports Park, it was clear that our Miata’s cooling system needed some attention.
[What you learn from your first time racing a new car]
Why? Well, blame us: We swapped a LFX V6 under the hood with a V8 Roadsters swap kit, meaning we were now cooling 300 horsepower with a radiator space originally sized to cool just over 100.
Thanks to the upgraded radiator and ducting we installed with our Nine Lives Racing air dam, the situation wasn’t terrible. At full pace, our Miata’s coolant would run about 225 degrees in clean air, and rise to 235 degrees in traffic. And once the car got hot, it stayed hot, taking half a lap to cool back down after completing a pass.
We know, we know–that’s warm. But it’s not actually dire.
In the Camaro this engine was originally installed in, the factory fans don’t turn on until 222 degrees. Modern engines are simply designed to run warmer than those from 50 years ago thanks to better materials, oils and tolerances. The benefit? Cleaner emissions and–more importantly for us–more efficient horsepower.
But our fans weren’t set to 222 degrees. Instead, we tuned the car to activate them at 196 degrees in hopes of getting ahead of any traffic-induced coolant temperature creep. It wasn’t working, and running this engine for extended periods at 235 degrees would shorten its life. We needed a more efficient cooling system.
So we looked at the options on the table: A bigger radiator would mean diminishing returns, as we already installed almost as much radiator as you can stuff into an NA Miata.
And with both big OEM fans already attached, we didn’t think more fans would solve our problem. In fact, we figured they were a temporary fix at best for a lack of natural airflow through our big radiator. Fans are really meant for low-speed driving, while we were trying to solve overheating at 100 mph. We already had the nose of the car fairly well ducted, too.
There was one option left on the table: Cut some holes in the hood!
In theory, hood vents would reduce underhood pressure, meaning more air through the radiator. They’d also increase front downforce and reduce the likelihood of lighting a plastic hose on fire from heat soak after parking the car for the day.
So we ordered a pair of massive hood louvers from Race Louvers, choosing their Miata ’90-23 XL Side Hood Louvers in the RX Extreme Trim.
Why spend $380 on hood louvers? Because we’ve used this brand in the past and were stunned by the fit, finish and completeness of the kit. And unlike the cheap crap we’ve bought on eBay before, these are mostly empty space, rather than being mostly sheet metal that blocks airflow.
The louvers included a hood cutting template and hardware for installation. Don’t want to spend $380? Hood vents aren’t hard to make, just time consuming, so feel free to use ours for inspiration.
In theory, these would solve our problem. But in practice, we needed to test.
So before cutting any holes, we loaded our Miata onto the trailer and headed over to the Florida International Rally & Motorsport Park, our official test track, for a day that left our paddock neighbors shaking their heads.
Our experimental setup was simple: Go out for a session and monitor coolant temps. Then come in, install the louvers, and go back out for another session. We figured this was the best way to control variables and test in as equal of conditions as possible.
When V8 Roadsters owner Shandelle Leonard went out for this first session, the Miata behaved as expected: Coolant temperatures of about 225 degrees, rising to the low-230s whenever he encountered traffic and staying there for an annoyingly long time.
So we opened the hood, broke out the toolbox, and started cutting. Twenty minutes later, and our Miata looked meaner than ever thanks to its massive hood vents.
We then sent Shandelle back out on track and, in short, they worked. Coolant temperature settled at 217 degrees, and traffic no longer had nearly the same impact on it.
In short, we’d drug our LFX back out of the danger zone–if only slightly. At Shandelle’s and Race Louvers’ recommendation, we’ll pull one radiator fan off for our next test day in hopes of lowering temperatures even further.
Whether or not they are needed, a (well-installed) set of hood vents looks rad on just about every car.
I did the SuperMiata 3 vent set on my turbo NA and installed them from the underside. It's MUCH more of a PITA to do with all the webbing underneath the hood skin that needs to be trimmed back but I like the way it looked afterward. It makes a huge difference in keeping it's cool on hot days, I don't love that rain can get in and the noise from the engine bay is much more noticeable now.
Miata hoods are a dime a dozen, y'all could have saved track day time by having the louvers installed already and simply swapping hoods in the pits for the back to back comparison.
That's a good idea for a stock car, but a Miata hood won't fit on ours--it interferes with the swap. This is a fiberglass swap hood from Treasure Coast Miata.
Colin Wood said:Whether or not they are needed, a (well-installed) set of hood vents looks rad on just about every car.
The problem is that they are so frequently installed for looks, not function. Usually the best place is up front, right behind the radiator level, but people seem to prefer them further back and in many cases far enough back to get into the high pressure region in front of the windshield and then they actually take air in rather than venting it out.
In reply to wspohn :
I hear on the looks. I feel like hood vents fall into a similar category as a rear wing. If it's not making your car faster/handle better/etc., it tends to look a little out of place.
KyAllroad said:I did the SuperMiata 3 vent set on my turbo NA and installed them from the underside. It's MUCH more of a PITA to do with all the webbing underneath the hood skin that needs to be trimmed back but I like the way it looked afterward. It makes a huge difference in keeping it's cool on hot days, I don't love that rain can get in and the noise from the engine bay is much more noticeable now.
Miata hoods are a dime a dozen, y'all could have saved track day time by having the louvers installed already and simply swapping hoods in the pits for the back to back comparison.
I was looking at photos of a first-gen BRZ with some of these earlier and I would do the same as you - mount them from underneath. They look too square and clunky on most modern cars. That said I can't argue with their functionality, and the manufacturing looks really simple and clever. I'm assuming they are either laser cut or water jetted from a single sheet and then the flaps are bent to their final position.
Some hood vents do look better mounted from underneath and the same goes for some hood "pins" like Aerocatch latches. The less on the surface of the hood, the better. For pure function, however, does it really matter? I don't think it does. I like the fact that the Miata hood vents are black, which contrasts nicely with the red paint, just like the wheels, etc. Sweet little track car that.
Vents on the hood look sexy but the hood tends to be an area of positive pressure
You want air in through the grille and out underneath or through the wheel openings.
An extractor vent in the fender with a duct if needed works well.
You can also make the front edge of the wheel arch protrude further than the rear edge to create a low pressure area to draw the under hood air out.
On the Fieros some used to put small vents (c. 3" across) right behind the radiator level on the hood - very effective.
ShawnG said:Vents on the hood look sexy but the hood tends to be an area of positive pressure
You want air in through the grille and out underneath or through the wheel openings.
An extractor vent in the fender with a duct if needed works well.
You can also make the front edge of the wheel arch protrude further than the rear edge to create a low pressure area to draw the under hood air out.
Depends on where on the hood, it varies quite a bit. Also, what matters is if the pressure on the upper surface is lower than the pressure in the engine bay, because it's that pressure differential that will drive airflow. I think we have a pretty solid body of knowledge that venting out the top of the hood can work.
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