Talk Me Out Of ...

... Punching a Hole In My Spare Tire Well, Adding 50 lbs to My Racecar and Collecting Salt in My Trunk

My Daewoo Nubira is getting close to the point where it's only for racing. I need to gut the interior, lexan the windows and do the car's second motorswap (70 whp 1.5 Aveo engine-> 105 whp 2.0L Daewoo engine -> 160 whp 2.0 Hyundai Beta with large cams).

In the class I plan to run, I'm never going to lead the field for power. Honestly, as long as I'm within 30 whp of the diesel guys, I'll be thrilled. As such, I'm depending on handling and aerodynamics to make up the power gap and, hopefully, more than compensate.

I'm currently very happy with my oddball suspension setup, so I don't think I'm going to change it much, except to get more caster. However, I'm just scratching the surface with the aerodynamic stuff.

I've already got an experimentally verified air extractor hood. I've also built an aluminum front half flat-bottom and fender vents to keep air from escaping the wheel wells by going under the car.

These aero modifications have, in my experiments, improved drag. Or at least, that's what I infer from higher top speeds. While I can't verify it except by feel, they've also cut lift. This means that, from a racing standpoint (if not a cosmetic or NVH standpoint), I've given up nothing and improved in both drag and down force.

I've been thinking about ways to continue this process and figured it might make sense to do something like this:

1. Build a splitter (rules don't allow more than 3 inches of protrusion) in the front. Experience a worsening of the already frightening frontward aero-balance.

2. Remove the OEM radiator, leaving only the oil cooler up front. This will hopefully increase the in and out airflow created by my flat bottom and air extractor hood and thus, fill in the low pressure area over the hood (lowering drag) and create a little down force.

3. Continue the flat bottom all the way to the rear bumper, with a hole where the spare-tire well used to be. This will hopefully further cut drag.

4. Use that excised chunk of spare tire well as a scoop to feed air into the trunk.

5. Mount the radiator vertically in the trunk, abutting the trunk lid.

6. Vent the trunk with many louvers along the vertical surface of the trunk lid. This will hopefully allow the air flowing into the trunk to escape into the lowest pressure zone behind the car, increasing down force and reducing drag.

7. Install a funnycar style spoiler on the rear trunk, increasing the camback effect, helping trunk/radiator flow and making down force with very little extra drag. Like this

So, before I do anything stupid, please let me know if this is a solid plan.

do it!!!!

I think this is a cool idea, but because I am a complete noob about aerodynamics I have a couple of questions.

My first question is, "Is the spare tire well located symmetrically (middle of the trunk floor) or off to one side?" If the latter, will that new route for airflow cause the car to vary from its intended path, aka handle weird?

Secondly, I'd want to know how to deal with the edge of the "scoop": smooth edges? edges with little vertical vanes on them? Should the scoop edge (viewed from above) be perpendicular to the nominal direction of airflow, or should it be angled/rounded, and, if so, should it look swept forward or swept back?

Thirdly, once you've got your airflow eagerly heading into your trunk, at what angle do you mount the radiator? My guess (which is worth about 1 won, because noob) is that the airflow aspect is going to be worth more than the actual cooling, especially if you get a big enough rad. (That is, one that's big enough to cool the engine even if the airflow is optimized for overall vehicle aerodynamics rather than radiator function as such.) Do you shroud the intake area somehow, or would the air see that as a restriction and/or cause for turbulence? Heck, for all I know you could use angled vanes on the front of the the rad to "focus" the incoming air and direct it to your designated exit route.

I'll be watching this with interest!

Build a splitter (rules don't allow more than 3 inches of protrusion) in the front. Experience a worsening of the already frightening frontward aero-balance.

I know you were having a problem with this already. Is this a good idea? Was it a splitter or diffuser problem before?

N Sperlo,

If it gets too crazy, I'll break down and buy a wing.

Stealthtercel wrote: I think this is a cool idea, but because I am a complete noob about aerodynamics I have a couple of questions. My first question is, "Is the spare tire well located symmetrically (middle of the trunk floor) or off to one side?" If the latter, will that new route for airflow cause the car to vary from its intended path, aka handle weird?

It's dead center in the trunk. It's basically a cylinder. I figure if I cut off the front half of that cylinder, the remainder is a crude scoop, I think.

Secondly, I'd want to know how to deal with the edge of the "scoop": smooth edges? edges with little vertical vanes on them? Should the scoop edge (viewed from above) be perpendicular to the nominal direction of airflow, or should it be angled/rounded, and, if so, should it look swept forward or swept back?

I am going to try something like this, except upside down.

Thirdly, once you've got your airflow eagerly heading into your trunk, at what angle do you mount the radiator? My guess (which is worth about 1 won, because noob) is that the airflow aspect is going to be worth more than the actual cooling, especially if you get a big enough rad. (That is, one that's big enough to cool the engine even if the airflow is optimized for overall vehicle aerodynamics rather than radiator function as such.) Do you shroud the intake area somehow, or would the air see that as a restriction and/or cause for turbulence? Heck, for all I know you could use angled vanes on the front of the the rad to "focus" the incoming air and direct it to your designated exit route.

In the beginning, I'm just going to stick it straight up and down and depend on the fans. If it works, I'll probably build a tunnel with proper shrouding.

I'll be watching this with interest!

Sweet!

The air going into the radiator needs room to expand and slow down for the most efficient cooling. I would mount the radiator so it aims at the exit path. How much suction you get at the back will determine how big the scoop should be which seems very hard to measure. It sounds like you will need trial and error testing to get it optimal.

Adding a camback might reduce the hole you are trying to fill with hot air. I would test the rear radiator before testing a camback. A splitter might reduce the under car air to the point of a vacuum making the under car scoop useless.