Cars of Circuit Showdown Round 9: Honda Civic EK Hatchback by Cabspeed

Pictures by Edward “Hazardboy” de la Rosa

Check this out! Flaming exhaust and red hot brakes, driving a Honda Civic couldn’t get as manly as this.

But I’m feeling a bit nerdy today and would want to get into the technical side of the aerodynamics of this car based on what we could visually see. I would like to hear your comments on what I have to say below. Maybe this will satisfy our curiousity.

First of all, we all see that this Civic features a rear spoiler, as well as a diffuser under the rear bumper. And we all know that this provides downforce to improve cornering ability.

Second, it is pretty obvious that on this car, the exhaust terminates underneath, instead of somewhere under the rear bumper. The shorter exhaust pipe, the higher the resonant frequency. The opposite goes for longer exhaust pipes. This also means that higher-revving engines would benefit the most from shorter exhaust pipes. And since this is a Honda, it is safe to say it has a high-revving engine.

Now, aerodynamicists have always known that injecting the exhaust into the rear diffuser enhances the downforce effect, because the fast-moving exhaust gases aid in quickly evacuating air from the underside, causing the pressure underneath the car to drops even more, which in turn creates more downforce. This is known as Bernoulli’s Principle. The only downside to this is that the amount of downforce becomes dependent on engine speed.

But if the exhaust gases start to come in from underneath the car, such as on this ride? How do you think this will affect the downforce? It is a fact that an increase in temperature also increases the air pressure. So by reducing the pressure underneath the car, it also reduces the downforce.

However, the exhaust gases can also increase the velocity of air flowing underneath the car, as it is angled towards the rear. So this time, it pushes more air towards the diffuser, enhancing it downforce effect.

So by running it in this setup, does it increase downforce or decrease it? Your thoughts?

Also, check out the rest of the photos of this awesome ride…

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