Engines like cold air to make power. The question is: How do we get the coldest air into our air filters to make that power? Air is air. I can’t change the weather. However, heat from a racing engine in an engine compartment warms things up quickly, and I can do my part to keep that engine heat away from the air entering my air filter. In Honda Challenge 4, we are not allowed to cut a hole in a headlamp housing and bring in clean fresh air into the intake tube. We have to find another way to separate the hot air away from the air filter under the hood. It is time to fabricate.
There are systems you can purchase commercially for Hondas and Acuras that pull cold air from the wheel well, but we have determined during dyno testing that the intake tube length makes a difference in horsepower and torque. We found the intake tubing length we liked for power and then parked the air filter at the end of it. The problem was it placed the air filter under the hood not too far from the header, where things get very hot. Not cool.
Our air filter was shielded partially from the header by the battery, which we are not allowed to move, according to H4 rules. Careful inspection determined there were still plenty of places for warm air from the engine and header to wind up going into the air filter and rob us of power. To combat this, we decided to build a cold air box to keep the heat away from the filter.
Another thing we were interested in keeping away from the air filter was off gassing from an engine breather in the engine compartment. Our cold air box would be designed to keep heat away from the air filter and to keep anything coming out of the engine breather from going into the air filter. Based on these criteria we decided to build the walls of the box in numerous directions to keep things cold and fresh near the air filter.
We used cardboard to mock up the shape of our cold air box. We paid careful attention to the contours of the bottom of the hood so the cold air box would seal when the hood was shut. This involved a lot of trial and error and opening and closing the hood a thousand times. Scissors and lots of cardboard made this a success, eventually.
Once we had a cardboard mock-up of what we wanted, we traced the shape onto a piece of aluminum. We used aluminum because it is lightweight and better at dissipating heat than steel. To improve the heat-blocking ability of the piece, we added gold thermo tape to the warm side of the cold air box piece.
We purchased some slip-on weather stripping that would fit the edges of the cold air box. This would help in sealing the box at the edges and ensure none of the warm air from the header would get near the air filter. The trick to getting this stuff to fit under tight bends was to trim parts of the weather stripping into a V shape so it could bend appropriately.
Once the piece was completed, it was time to verify the fitment. We needed the piece to clear the mount for the battery hold down, clear the intake tube, and clear the hood when it was shut. This was a time-consuming process trying to ensure it was small enough to fit while at the same time big enough to be tight to keep warm air away from the air filter.
We couldn’t really tell how well the cold air box was fitting under the hood. So, we decided the best way to see it was to drop a camera under the hood and film the hood opening and closing. Our first attempt was a laughable failure. When the hood is shut, it is dark and you can’t see anything. We dropped a shop light under the hood with the GoPro camera and finally got the footage we needed to verify the fitment.
Once we had the piece in place, it was time find out if it worked worth a damn. We used a laser thermometer and checked temperatures in different parts of the engine compartment. The header registered 403 degrees. Our air filter was only at 89 degrees. By pointing the laser thermometer at the warm side of the cold air box and then at the inside (cold side) of the box we could see a difference of more than 50 degrees Fahrenheit. That was good news because it meant we didn’t just waste an entire afternoon building something we didn’t need and making the car heavier for no reason. Yay!
Some vehicles have cold air boxes commercially available for them. The 90-93 Acura Integra didn’t have anything on the market, so we decided to fabricate it ourselves. We slapped a Krider Racing sticker on our cold air box and made it look legitimate, even though it was a home-built piece. The next step is to go to the track and go fast!
Rob Krider is a NASA Honda Challenge 4 National Champion and the author of the novel, “Cadet Blues.”