Questions on aerodynamic enhancement

Correct me if I'm wrong, but I think what most of us have found is that aerodynamics are not super important with these cars due to their small size.

It mostly comes down to good rolling wheels. I've seen big rigs beat supercars many times.

Agree with Maniac that aerodynamics is not the biggest factor, however, it does also depend if you're talking about straight drag racing or a road course. That race sounds like its on an open track at which point a lot of that minor tweaking matters far less than wheels, axles, and weight.

I just seal the side windows to let the air flow around the car and not enter and collect at the back of the windshield aka parachute effect, and then paint the patch black.

After calculating the average airspeed velocity of an unladen swallow (European) I'd say from atop the grandstands you're throwing maximum effort towards minimal results 

Elite performance axles & wheels, good lube, proper casting selection for the track involved, and balanced weight distro are what really pay off 

1:1 or 1:64, the side windows matter IMO and if it's even .005 faster etc., speed is speed. 

If you're going to go that far, may as well kick the rear window out of the car, too, for maximum airflow.

I personally don't see a benefit to this, especially since the inside of the car is going to be filled with weights, anyway, but I'm willing to be proved wrong. If it works, more power to you. You never know if you never try, right?

We did some testing on our drag track with the same car, same lane did 5 runs as it was then taped a huge cardboard flap to the roof of the car, like a giant sign but facing forward for max drag, ran it another 5 times and it made no difference to the average times. At this scale and speed aero doesn't really play a big role, it's about friction in the axles/wheels, body dragging on sidewall etc that will give you a far bigger advantage

Hmm, just looked up the race event in question. Yes, the ZigZag Street Track. Lots of turns. Maybe instead consider the Mercedes-Benz 500 E, if you're keen on the manufacturer? 

Your current chosen casting, the rear axle is slightly wider than the front, and the assymetry gives me pause. I see the same in Porsche castings that like to spin out. The 500 E's stance doesn't have that quality, just my two cents

I really think more importantly is the chosen paint scheme.  To many racers paint their cars with stripes when we all know that little dots are faster and more wind resistant that stripes.  Stay away from giving your car stripes in the paint.  Choose dot patterns to more effectively combat wind as you are cruising through the track.

Red cars always go faster.  : )

I generally looked to guidance from pinewood derby sources... Top 5 performance items ranked are

1. Lubrication

2. Axle polishing and straightness

3. Wheel alignment

4. Weight placement

5. Aerodynamics

With aerodynamics being such a small percentage of the overall dynamics, I wouldn't worry about it until you have sucked out all the speed available after deploying and maximizing the first 4 criteria.

sources:

Pinewood Derby Physics Lectures

Maximum velocity

*Disclaimer

I'm not fast or consistent...

Per Stoopid, here's a past article talking about various factors. Mark Rober's pinewood derby science is helpful. www.redlinederby.com/topic/the-science-of-downhill-racing-video/2184

And TLDR: weight > wheels

But again...this is for pinewood racing that is straight with a known track. Anything not straight will differ and I always chalk up to a healthy amount of luck.