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.

Our first step after dreaming up what our cold air box would look like was mocking it up with cardboard. A simple Amazon delivery box lying around the shop worked perfectly.

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.

After we shaped our cardboard mock-up, it was time to trace it with a Sharpie onto the aluminum material we would use to create our cold air box.

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.

Once we knew what shape we wanted it was time to head to the band saw and work diligently not to cut our own fingers off.

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.

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Our cardboard mock-up had two separate 90-degree bends in the material. To get those bends perfect with our aluminum we used weight to hold the aluminum flat on a bench and a mallet to fold the aluminum where we wanted it bent.

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 the piece was cut and bent, it was time to test the piece in place and use a Dremel to trim the edges for tight fitment.

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.

To keep temperatures down inside the cold-air box, we used thermo tape from DEI. This stuff is easy to use. Simply stick it on and trim it to fit.
Once all of the thermo tape was in place, the cold air box was starting to look good. We only placed the thermo tape on the heat side (side closest to the header) of the cold air box.

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.

To ensure no hot air slipped past our cold air box into the air filter, we added weather stripping to the edges of our piece to seal off the hood and other parts of the engine compartment.
With the aluminum cut and bent, thermo-taped, and weather-stripped it was time to install it and do the final fitment testing.

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.

The cold air box went in smoothly (after a few more trims here and there). The next step was to ensure the hood closed.

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.

With the hood closed, I couldn’t see if the cold air box was tight to the top of the hood. I decided to drop a shop light and a GoPro camera into the cold air box and record closing the hood.
A screen capture from the GoPro recording with the hood shut shows the weather stripping is touching the bottom of the hood when it is closed helping seal off warm air from the air filter. Success!

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!

To test the difference in heat near the header versus the heat near the air cleaner with the cold air box in place, we used a laser thermometer. The header was at 403 degrees while the air filter was only at 89 degrees (on an 85 degree day).

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!

The do-it-yourself cold air box was a success. Made with a piece of aluminum, thermo tape and weather stripping, it is lowering air intake temperatures on our Honda Challenge car. The whole project only cost about $50 in materials and took a single afternoon to create.

Rob Krider is a NASA Honda Challenge 4 National Champion and the author of the novel, “Cadet Blues.”

Image courtesy of Rob Krider

3 COMMENTS

  1. So…we are dying to know…were you able to measure a difference in performance either in a better lap time or in measurable HP?

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