Project S2000: Part 19 – Ram Air!!! Plus Hot Air Testing!

Project S2000: Part 19 – Ram Air!!! Plus Hot Air Testing!

By Khiem Dinh

Khiem Dinh is an engineer for Honeywell Turbo Technologies at the time of this writing.  All statements and opinions expressed by Khiem Dinh are solely those of Khiem Dinh and not reflective of Honeywell Turbo Technologies.

Did I mention there would be more hood hacking? Why yes I did. Somewhere along the other 18 parts of this project, I noticed the stock air box looked relatively well sealed along with having a location ideal for ram air. Ram air is used on practically every sport bike you can buy to coax as much power as possible from the engine. Even cars such as the Corvette Z06 and Dodge Viper use ram air. Lastly, the last time I took the S2000 up Angeles Crest Highway, I got pulled over for not having a front plate. During the interrogation friendly banter with the police officer, he asked if I had an intake to which I replied no (FYI, he was digging the StopTech brakes). So, keeping the stock intake deters further police inquiry. There’s nothing illegal (I don’t think…) about chopping up the hood and adding a ram air NACA duct (plus, this is my track-only hood), so that’s what I did.

The duct in the hood of the Viper seals up against the air box providing a ram air effect.

The principle of ram air is simple: it converts the dynamic pressure of air at a high velocity into a higher than ambient static pressure. Basically, it supercharges your engine by increasing the air pressure in the intake manifold. The maximum pressure that is achievable is a simple function of velocity. The higher the velocity, the more dynamic pressure there is to convert to static pressure. Using Bernoulli’s equation, dynamic pressure is equal to 0.5 * air density * velocity^2. As total pressure along a streamline stays constant, the change in static pressure is equal to the change in dynamic pressure. So when you bring the velocity down to 0 (hence, the term stagnation pressure), you have maximum static pressure.

Using Bernoulli’s equation gives us this curve of the stagnation pressure vs. vehicle speed.

Now that we know how ram air works, it was time to figure out a way to do it. I decided to design my own NACA duct to feed the snorkel of the stock air box. There are some NACA ducts you can buy on the market, but they were too narrow or too long or not deep enough. Also, none of them would line up perfectly because of the curve of the hood. So, I designed one specifically to work for the S2000. There is actually science behind the shape of a NACA duct to draw in as much air as possible. I had no clue as to where to start in designing one, but a Google search netted a free spreadsheet someone else had already developed. All I had to do was enter my desired length, width, and depth and the spreadsheet cranked out all the dimensions I needed to design my duct. The tricky part in designing the duct was to make it match the curves of the hood.

I began by using C.A.D to locate the snorkel relative to the hood.

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