Here’s why you won’t see any performance benefits adding hood spacers or hood risers to your stock hood.
The idea behind hood spacers (or hood risers) seems intuitive, by adding a larger gap towards the back of your hood, hot air trapped in your engine bay vents out allowing cool air to rush in.
Vital engine components cool faster and your intake sucks in more of that dense, cooler outside air.
At less than $15 for a legit set of hood spacers or, if you go the DIY route with washers, less than $5, it’s one of the best “bang for your buck” mods with all the cooling and performance benefits you get.
Thankfully for you, the hood spacer window shopper, the elders of the internet, aka car enthusiasts on forums, already argued, dissected, and presented their own inconclusive evidence of the ineffectiveness of hood spacers.
Here’s why hood spacers, as an engine cooling aid, do not work like you think it does.
Doppelganger explains in detail how your car in stock form is already aerodynamically optimized for maximum cooling effectiveness.
Your car, in motion, creates an area of high pressure up front as air “slams” into your front bumper. Your car’s radiator, inside your engine bay in a lower pressure zone, is a heat exchanger that allows higher pressure and cooler air to flow through its aluminum fins, cooling hot liquid coolant.
Fast moving air rushing underneath your car aids in moving hot engine bay air out.
At idle, if engine bay temps get past a certain point, electric fans kick on, artificially forcing air through the car’s radiator and out from underneath.
Doppelganger concludes that hood spacers decrease the cooling effectiveness of your radiator.,
“Adding a second “feed” of high-pressure effectively reduces the flow of the other high to low pressure zone because now the low-pressure area of the engine compartment is not as much of a low-pressure zone.
“This means the air at the opening of the bumper has more resistance to getting through the heat exchangers and into the engine compartment, and finds a lower path of resistance either over or under the car….but NOT through the heat exchangers. Reduced flow over the exchangers means less heat is removed from them.”
Youtuber Chris Sadowski’s own analysis corroborates the above. At 6:08, his surprisingly effective DIY test with a bit of string shows how hood spacers suck air in, not vent air out.
But, what about at idle?
Surely, hood spacers might be able to vent out hot engine bay air better than stock.
At idle, with his stock hood, it took 20 minutes for his engine bay temps to go from 95 degrees to 156 degrees.
With hood spacers, it took 21 minutes, one minute longer, to also go from 95 degrees to 156 degrees.
Both ways, with and without spacers,IAT readings topped out at 156 degrees, no discernible drop in engine bay temps.
MJRN took it one step further and measured his IAT readings at 80 MPH with and without hood spacers. He found his air temperature readings were three degrees hotter WITH hood spacers.
Hood spacers make your engine bay run hotter.
The only practical reason to add hood spacers is for what they’re actually intended for, to add…space.
If you’ve done an engine swap and your stock hood needs slightly more clearance, adding hood spacers might give you that extra bit of space to make closing your hood possible.
For any other reason, hood spacers are not worth your time and money.