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2nd gen aero modifications

12076 Views 38 Replies 16 Participants Last post by  Aus78Formula
I've been working on some aero mods as part of my rebuild. This is a car I built and raced over 25 years then tore down for a complete frame off rebuild. I figured some of you might be interested even if you'd never do these things to your own cars.

One of the aero changes I wanted to make involves the fender vents. I'm planning on a splitter and pan under the engine compartment. So I need to evacuate the under hood air that comes through the radiator and reduce high pressure air under the hood that causes lift. Many have experienced the effect called "float" at high speeds (over normal highway speed) in regular cars and some models are worse than others. The 2nd gen TA fender vents help reduce that and I want to maximize the benefit.

So I began by doing some tuft testing on the stock vent with the screen removed to see how it performed. Then I made cardboard modifications to the vents and tested again. I spent more than a day on this process testing various configurations and came up with a couple modified vents that should help keep the air pressure lower under the hood.

The stock TA vent has a hole with surface area about 15 sq. in. The screen in the stock vent blocks off about 5 reducing it to 10 sq. in. and creates turbulence as the air tries to exit through it. As I went through the testing process I changed the angle of the leading edge, added wicker bills of varying heights and expanded the opening. The modified vents now have openings about 3 times the sq. in. with steeper leading edge and the design of the housings seem to draw a lot more air from under hood. One set will be used for Land Speed racing type events (less drag) and the one with the wicker at the leading edge will be for road course use (more drag but also more evacuation).

As I mentioned it was a long process and lots of variations were tuft tested. Here's a few pics to show a couple of the differences.

Stock vent with screen removed.


Modified vent below with steeper leading angle and stock opening.


Modified vent with wicker and extra slot opening below.


This version seemed to get the best results for evacuation with reduced turbulence. But it wasn't enough "better" to warrant all the extra effort I'd have to put in to incorporate strakes into my design.


Here are the designs I came up with and made. Will tuft test in the real world once the car is back on track. Top pic below is process. Then stock vent, LSR vent, and track vent.






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Very interesting post. I admire anyone who takes the scientific approach with "form follows function" changes for increased performance in some way. While reading this I was wondering at what speed wound you say your testing simulated, and did you do any modifications to keep air that is not going through the radiator from getting under the hood in the first place? I have always wondered about the twisted path the airflow must take to get around the inner fender well to finally escape through the vents. Again, nice work !
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Can't wait to see the real world driving tests.
My main goal with this small part of the aero project was to design and make vents that would pull a much larger volume of air out of the vents at high speeds. I started off using several large shop fans in an attempt to create normal driving speeds to see what the stock vents showed. The rest of the testing was done using a high speed hand held leaf blower in front of the vents just out of the picture. So there was only wind on the exterior of the fender passing by the vent being tested. I'll guess the wind speed was 100-150 as it passed the vent since the blowers are capable of 200 and it was a couple feet away.

The core support will be sealed so the only air entering the engine compartment from the front will be through the radiator itself. I am planning on making a flow straightener for the inner fender that will smooth the path the air follows before it exits the vents to help increase the volume of air that moves through the vent by increasing the speed.

The pics below give you an idea of how the core support will be sealed to the hood and fenders. Top pic is the underside of hood and top of core support without seal and lower pic has a seal just placed in position for mock up but not attached yet. When I attach the seals I'lI write a post about them.


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Good work on this!

I actually opened mine up a little as well.

I really like the look and function you have come up with!

Keep up the great work!!!
Thanks Steve! Did you notice any difference with engine temps?

Moving along with aerodynamic modifications I'm currently working on the front end treatment.

The splitter/tray/air dam combination I've got in mind is a bit unusual from those I've seen on other cars.

A. Hinged to allow the splitter to be pushed up if I hit corner curbing or something. Splitter could rise till it hits the stock air dam. I've never whacked the stock air dam and I'll probably only loose maybe 1/2" ground clearance.

B. Two piece splitter/tray so I can have various splitters that stick out more or less with the biggest reaching out as far as the leading edge of the bumper and out as wide as the wickers on the wheel flares.

C. Height adjustable so I can use for street, LSR, Drag strip, road course, or open road with various height air dam extensions.

D. Various air dam extensions that will fold up if the splitter gets pushed up. Probably three versions, small for drag race & street , medium for road tracks, and a deep air dam extension with minimal ground clearance for LSR with no splitter but supported from behind by the tray section.

E. Breakaway provisions so if something bad happens, damage to the car would be minimal and hopefully confined to the splash pan and stock air dam/wheel flares.

F. Cheap/replaceable using as many pieces of scraps left from other projects and junk people gave me as I can. I gathered all the stuff I've been collecting and figured I could make something out of it even if just a prototype. It'll get the scraps out of my way and hopefully save me a few bucks.

While today lots of folks use CAD I still use DIG (Draw In Garage) for projects like this. Here's the basic concept drawing. The tray section the various splitters will be attached to has a smaller footprint than the stock air dam/wheel flare section.


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So how much are you gonna sell these for?


I want a left and a Right...
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Others are also interested in some of the aero bits I'm making. I may try to see if it's financially worthwhile to recreate using molds etc. To just make from scratch like I do is too expensive because of the hours involved. To make one set of vents like you want is about $50.00 in materials, a set of core vents to work with, plus the time involved. The vents have to be cut up and fiberglass carefully built up to eliminate bubbles. Then the outside gets ground into rough shape and the inside gets ported using the same tool & bits used for porting iron heads. Once the vents are roughed in then bondo type filler is used to smooth inside and out followed by repeated block sanding and primer till they're ready for sealer & paint. Lots of hours involved.
so without a mold your looking at 500-600 or so.

With Mold would be what around a 150 a set or so?
man Make a mold and go aftermarket with
Here's the hinged splitter I'm going to test. If it works out well I'll make a nicer version with different materials that's prettier. In the pics below the car is set up (with no front springs) as if it were in full dive under threshold braking smashing the bumpstops. The bottom of the tip of the splitter is 1 1/4" above the track surface. I'll loose another 5/8" or so for rub strips I'll be putting underneath the leading edge.

There is 4" upward travel at the tip and 2" travel where the tip of the original spoiler is. So if this hinging thing works, in theory I could drive over a ball about an inch in diameter smaller than I could without the splitter. 3/8" for the plywood and about 5/8" for the rub strips. If I have to use solid splitter supports I'll loose 3" + where the tip of the original splitter is plus whatever is lost because the splitter sticks out so far.

The cables are strong. With only the two center cables attached I'm able to stand on the tip of the splitter. I'm working on plastics to extend the air dam and wheel flares now.





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Great work John. It's very impressive how you can take a well engineered car (for its time) and do so much to improve on it. I know you do most of your contouring by hand but if you ever need the use of a large CNC I would be glad to donate some time for you.
Great work John. It's very impressive how you can take a well engineered car (for its time) and do so much to improve on it. I know you do most of your contouring by hand but if you ever need the use of a large CNC I would be glad to donate some time for you.
Thanks David! You have a PM.

I've learned since starting the aero upgrades on my car that the Pontiac engineers used the wind tunnel testing information Chevrolet had collected (but didn't use) when they designed the TA bits for the 70 cars with the intention of racing and the quantity of 70 TA 's built was to meet homologation requirements of a sanctioning body. So ya, for it's time it was well engineered compared with the competition.

I've always done a lot of design and light fabrication which I enjoy. Not just for automotive applications but other things as well. One of my current projects is for a public waste water application which is about as far removed from cars as you can get ahahaha.

Thanks for the CNC offer! As for the hand sculpting, I'm currently making plastic body panels to blend the splitter into the existing TA front air dam and fender flares.


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Thanks Robert! Worked on more aero stuff today.

One of the ways to reduce the under hood air pressure that causes lift is to limit the air entering. I'm sealing the core support so the only air that passes through is for radiator cooling and brake cooling.

The cavity behind the bumper in front of the core support has a higher air pressure at speed than the engine compartment. Because the whole cavity becomes pressurized the air tries to find a way to get to the lower pressure area behind the core support. As built, there's a gap on the sides of the core support and between the top of the core support and the hood. The faster the car goes the higher the air pressure becomes in front of the core support and it finds it's way around the core support which raises the air pressure under hood. This is one of the factors that contributes to "float" experienced in a lot of cars at high speeds. The higher the air pressure raises under the hood the less grip the tires have so we want to keep the unwanted air from getting under the hood. For high speed Auto X and road course activities we want all the traction on corner turn in we can get.

Adding a splitter to reduce the airflow under the car and increase down force also increases air pressure in the cavity by stacking up more air in front of the car which increases the air pressure in the cavity in front of the core support.

Here's what I'm doing to limit air from entering the engine compartment by sneaking around the core support. The idea is simple rubber flaps pop riveted to the core support in such a way that as pressure in the cavity increases the air pressure pushes the rubber flaps tighter against the inside of the fenders and other sheet metal creating a better seal so the faster you go the tighter the seal. Unless, the speed increases the pressure soo much that the seal blows back, in which I'll replace with thicker stiffer rubber.

In the pic below you can see how much open space there is for air to get past the core support on the sides. The white areas are where air can normally pass through between the core support and fender as well as the large hole the bumper supports/frame pass through.


Pic below shows how flat rubber sheet is used to block the air. Will be pop riveted in place before fenders are installed during final assembly. The rubber will be trimmed a bit more after install around the side marker light and slots will be cut where the headlight wiring etc. needs to pass through.


Pics below shows how the bumper support hole is sealed. I'd considered trying to use the frame itself for the brake duct like a lot of the 4th gen track guys do but after examining it carefully decided it was easier to just run brake duct hose on my 2nd gen.



A lot of air can go over the top of the core support inside the fender. First pic below is from the front and second shows seal placement on the backside.



There's a gap of at least an inch between the top of the core support and the underside of the hood. Thats over 55 sq. in. that air can easily pass through so I want it sealed. A 2" strip of rubber across the width of the hood solves that problem!


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Front brake duct cooling system is kinda aero related so here it is!

The Baer brakes are large by huge 14" rotors with 6 piston calipers. The rotors are the curved vane type which are designed to move air from the rotor hat through the hollow vanes in the rotor to cool the rotor as long as it's turning. I want to have additional cooling ducts ta aid cooling for several reasons.

A. The aero changes I'm making will reduce the air exchange in the wheel wells. So that might contribute to the rotors, pads and calipers heating more than without the aero changes.

B. I'm running 285 front tires on 18" X 10" wheels that just barely clear the calipers. So the calipers and rotors are kind of shrouded by the wheels which might reduce cooling.

C. With the Yokohama AO 48 DOT R sticky tires I can brake harder during threshold braking before lock up than I would be able to with higher tread wear tires so more heat is generated.

D. Keeping the rotors and pads cooler should extend their life.

E The car is is stock bodied with no lightweight fiberglass or carbon fiber and propelled by an iron headed Pontiac engine so at 3500 lbs + it's no featherweight race car, yet I'll treat it like one on track.

Here's the basics of what I've done.

1. Remove the speed sensor mount to open up more space for a 3" brake duct hose.

2. Make backing plate for the rotor hat that has minimal clearance with a tube to attach the hose.

3. To attach the backing plate I used a threaded boss in the spindle (supplied by Baer with their package) and drilled then tapped two bolt holes in the caliper abutment so the backing plate has three bolts holding it.

4. Modified a couple dashboard vent ducts from mid 80's GM trucks so the 3" brake duct hose would fit on them. They're slightly too big for the duct hose stock so a few V cuts and they can be squeezed just enough to get the hoses on.

5. Mounted the duct opening vents in the core support up high right next to the radiator on each side. This is a high pressure area behind the grills which isn't affected by the bow wave at the very front of the bumper or air dam. I'd originally planned on using the park/turn signal openings however a discussion with Ron Sutton about the bow wave influence and the reduction of pressure on the splitter just below the signal opening caused me to change plans.

6. I've built everything using 3" 300 degree brake duct tubing. It's a tight fit by the outer tie rods and sway bar ends snaking a 3" tube in there with such wide wheels/tires. I checked turning radius, suspension travel considerations, and such but I may find that I need to downsize to 2" tubing. So I'm going to test with the 3" and if all's good make a prettier set of backing plates welded instead of riveted. If there's clearance issues I'll move down to 2" ducts and add inline fans.

Here's the pics!

Spindle with speed sensor mount in pic below.


Speed sensor mount removed (but opposite spindle).


White line in pic below shows how much of the rotor hat is blocked by spindle arms, caliper brackets, and abutments.








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wow man. ...just *wow*.
That is an amazing idea. Hopefully all of these modifications aren't going to add any signifigant amount of weight. Weight is definitely something to think about when taking high speed turns.
I've been trying to reduce weight where I can during the rebuild and had removed weight in the past. The biggest weight gain was installing the 200 lbs of tubing that now look like a roll cage. Car has no heat/AC, sound deadener, etc. and some parts replaced with lighter weight like intake, exhaust etc.
They say it's toughest to lose weight once past 40 yrs old? ;)
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