The Free Mod Sieres: Part VI Acing Aerodynamics - Fuelly Forums
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Old 11-22-2006, 05:13 PM   #1
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Join Date: Nov 2006
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Cool The Free Mod Sieres: Part VI Acing Aerodynamics

I originally wrote this in early 2005 for elsewhere. So I'm jsut copy/pasting it here. The sole purpose of this was to increase top speed, and if possible lower nose lift. Both of which were achived.
For anyone here wondeirng. The calculated cd drop wound up being from .32 to .28. provided that both the OEM published figures for frontal cd are correct, and that .32 minus .4 is still .28.

That would have the affect of changing horsepower lost due to aerodynamic restriction from below to:
ES 300's HP losses at X mph:
55mph = 7.8 horsepower VS 6.8 horsepower
60mph = 10.1 horsepower VS 8.8 horsepower
65mph = 12.8 horsepower VS 11.2 horsepower
70mph = 16.0 horsepower VS 14.0 horsepower
75mph = 19.7 horsepower VS 17.2 horsepower
100mph = 46.7 horsepower VS 40.8 horsepower
120mph = 80.7 horsepower VS 70.6 horsepower
140mph = 128.1 horsepower vS 112.1 horsepower

I never got around to making a full under-body.

I would like to state for anyone on this forum doing under-trays. I am NOT joking when I say that under-car openings have a gross impact on both engine bay temperature, and the airflow through the engine bay (Which affects the capacity of any cooling system).
You must NOT seal the bottom of the engine bay. Specifically the portion in the general firewall area. More than 90% of the airflow escaping the engine bay will exit at this point. And you want to maintain a large opening to facilitate a high flow rate, *and* high velocity of the air exiting the engine bay while in motion.
The velocity portion of that also is why completely deleting, or reducing an under-tray will also lower cooling capacity. The velocity of the air exiting the bay lowers.
(You can also seal any coolers to any grill work done, forcing air through the cooler instead of letting it spill out. Increasing cooling capacity.)


Aerodynamics. What can't be said? If they're better, you get better gas mileage (less resistance to moving through the air) while having the ability to accelerate faster...


A stock Camry/ES 300 is pretty good from the factory.
Gen 1 ES 300 (92-96) has a .32 drag coefficient, while having 21.88 ft ^2 of frontal area
Gen 3 Camry (92-96) is .34 drag coefficient, while having 22.27 ft ^2 of frontal area
Good, but could be better!

ES 300's HP losses at X mph:
55mph = 7.8 horsepower
60mph = 10.1 horsepower
70mph = 16.0 horsepower
100mph = 46.7 horsepower
120mph = 80.7 horsepower
140mph = 128.1 horsepower

Camry's HP losses at X mph:
55mph = 8.4 horsepower
60mph = 10.9 horsepower
70mph = 17.3 horsepower.
100mph = 50.5 horsepower
120mph = 87.2 horsepower
140mph = 138.5 horsepower

Anything we can do to cut resistance is going to and increase gas mileage, and increase top speed (if you don't have an ECU limiter)

Roughly 1/3 of the drag on a modern car comes from the undercarriage! Ever seen your undercarriage??? Next to NOTHING has been done to help it out!!!
Percentage of Total Drag
Cooling package (including radiator, intercooler, oil cooler, etc) - 33.4%Exterior - 31.7%
Front wheels - 13.1%
Rear wheels - 6.9%
Floor - 6.9%
Rear Axle - 3.1%
Engine - 3.1%
Front Suspension - 1.4%
Exhaust - 0.7%

Face it... The large front air damns on most body kits don't do crap for aerodynamics. (Let alone many people don't like how they look); while lip spoilers simply look ridiculous if you're not a Porsche running a 24 hour endurance race!
Let's decrease that by a big chunk!
Anyone that's ever changed their oil will recognize these as the tock under trays:

We are going to replace those. You have a choise to make:
Plastic sign material (i.e. the large, fluted yard sign stuff) = $2.50, easy to make. Cut it, tape it together, bolt it up. Good to just "see if this crap actually works"
A sheet of ABS plastic (1/8" thick) = $50-100 Much stronger. This is actually a permanent solution. Cut to fit, use a heat gun and bend it into the shape you want.
Fiberglass Epoxy = $20-30. Many, many times harder to use. You must build a form first, then lay your fiberglass down, then epoxy it. One chance, but nothing is going to bust this!
Both fluted Plastic, and a large sheet of ABS can be found at sign shops. Just ask for any scrape 2' in depth, by whatever the width of your car is.

The easiest way to start, is to tape a large sheet of paper under your car, and trace out the general pattern. Transfer this to the material you are working with.
At this time there is an aerodynamic warning.
¡¡¡DO NOT go farther behind than the front cross member!!!
If anything leaks from your engine, the plastic will be melted.
More importantly, what you do here DOES AFFECT your engine bay's ability to expel air. Run no covers and the temperature RISES because less air is able to pass through the radiator. Make too LARGE of a cover, and the same thing happens. Remember that some 90-95% of the air that enters your engine bay is expelled at the BACK-BOTTOM of the engine bay!

Be sure you leave extra material around the outsides. You want enough so that you can tuck it under the bottom of your body/bumper, that is rolled back plastic. Tape the plastic signs together... WELL...
If you have ABS simply take a heat gun to the ABS and get it hot. You can then bend it evenly with something like a broom handle for even leverage.
I suggest re-using the stock bolt locations on any mounting method. No need to re-use them all. That's all the more you have to take back off during a fluid change!
(I'll skip fiberglass epoxy, because it takes a lot of practice... PM/IM/EMAIL for questions/tips on that. *Definitely* create an ABS Plastic one first so you have a ready-made mold.)

Here is my fiberglass epoxy one:


It is not visible to anyone at headlight height, or above.

Shape plays a very important part. If you form the thing down LOWER at the edges (in front of the tires), and roll it inwards. It will deflect air from part of the tire (from looking in front of the car) you can take a good chunk of drag away from the front tires. The trade off will slightly decrease stability in high wind. (Not enough for me not to go back and do it later)
(Unless you're a lucky, or smart; you'll want to remake an ABS one a few times, or make a few sign versions to find a "sweet spot")

Gas mileage on a 350m one way, all highway trip improved 4mpg at 75-80 mph, while top speed improved roughly 5 mph. 28mpg trip-average on a 3vz-fe that was previously never getting more than 24mpg under it's best highway day is a huge difference.

Now for the most important question! Why it is blue!? Simply because I didn't have enough black model air plane covering, and blue was the darkest color I had on hand.
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