Author Topic: 2nd gen TA aerodynamics and modifications  (Read 60201 times)

NOT A TA

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Re: 2nd gen TA aerodynamics and modifications
« Reply #80 on: September 02, 2015, 09:37:49 AM »
The next part of my aero project is making the front splitter, tray, and air dam extensions along with wickers for the wheel well flares. Cardboard & paper mock up for the road race track set up in the pic below below.



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.

John Paige
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1973klrbrd

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Re: 2nd gen TA aerodynamics and modifications
« Reply #81 on: September 02, 2015, 09:43:43 PM »
John, love the DIG design. (Made me laugh)

First "Z07" option on a TA I've seen. Very cool. Are you or have you considering/ed side skirts or any underbody aero tricks for additional downforce? In addition, what s your opinion of incorporating brake cooling mechanisms into the aero design? You may already have this covered with other functional pieces I am unaware of but was curious. 
Jay & Amy
1973 Trans Am

NOT A TA

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Re: 2nd gen TA aerodynamics and modifications
« Reply #82 on: September 02, 2015, 10:35:56 PM »
John, love the DIG design. (Made me laugh)

First "Z07" option on a TA I've seen. Very cool. Are you or have you considering/ed side skirts or any underbody aero tricks for additional downforce? In addition, what s your opinion of incorporating brake cooling mechanisms into the aero design? You may already have this covered with other functional pieces I am unaware of but was curious.

I've got better DIG diagrams I'll post up. There's a list of things I'm doing in the first post of this thread.

Side skirts, check.
Flat bottom, check.
Rear diffuser, check.

Pic below shows where I'm currently planning on pulling the air from for the brakes. Brake duct tube is here, need to fashion pieces to mount to the spindle. Will cover the brake ducts fully in a later post. Still debating on inline blowers.



« Last Edit: September 02, 2015, 10:38:26 PM by NOT A TA »
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NOT A TA

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Re: 2nd gen TA aerodynamics and modifications
« Reply #83 on: September 03, 2015, 09:24:19 PM »
Here's some better DIG diagrams.

This shows how I plan on hanging the rear mount of the splitter to the frame. The height will be adjustable and the whole rear of the splitter will act as a giant piano hinge from fender flare to fender flare. The PVC listed at the bottom should have read 1/2" PVC pipe not 1".

Top two pics are side view and pic below is from front or back. I can MIG the steel pipe into the frame but need to find someone who can TIG the aluminum or figure out an alternative.







Pic below shows the mounting and adjustment of the support cables for the front of the splitter. No scale so proportions are all off. The cables will allow the splitter to rise if I hit a dip in the road/track or road course corner curbing. The splitter will come up and whack the bottom of the stock style air dam. I'll loose about 1 1/4" ground clearance compared with the stock air dam height but it may save the splitter.

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NOT A TA

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Re: 2nd gen TA aerodynamics and modifications
« Reply #84 on: September 03, 2015, 09:40:16 PM »
With the extremely accurate (chuckle, chuckle)  DIG diagrams to follow it's time to make this thing!

First step, get out some BIG pieces of cardboard to DIG on and cut up. I like appliance boxes. Sturdy, thick, and big.



I used another rough cardboard pattern I'd made before taking the car apart and along with more accurate measurements created a new cardboard version of what I wanted the whole splitter assembly to be shaped like when done. The leading edge is even with the nose of the car for the biggest version (for road courses). Then I started laying out a frame for the sturdy tray section that will be hidden behind the air dam. Most of this is being made with stuff I've had hanging around so although some materials may not be the lightest, or most applicable material it's cheaper and quicker if I just use what I've got and get it out of my way.

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Re: 2nd gen TA aerodynamics and modifications
« Reply #84 on: September 03, 2015, 09:40:16 PM »

NOT A TA

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Re: 2nd gen TA aerodynamics and modifications
« Reply #85 on: September 03, 2015, 10:05:55 PM »
Since I want to have a 2 piece splitter so I can have different sizes I decided to Use sections of 1 1/4" box tubing I had for sections of the tray part so I could use 1" aluminum box tubing to slide into the 1 1/4" to align and support the rear of the front sections. 1" tubing into 1 1/4" tubing is kinda tight and too close of a tolerance for easy insertion /removal so I split the top side of the 1 1/4" and widened it a bit.





Next I cut the sections of the cardboard apart to mock up the pieces that will connect them and keep them sturdy. The PVC pipe will go through the box tubing on the ears of the front section of the splitter and keep the two pieces joined while also being the pivot for the giant piano hinge at the rear of the splitter.

« Last Edit: September 03, 2015, 10:08:56 PM by NOT A TA »
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NOT A TA

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Re: 2nd gen TA aerodynamics and modifications
« Reply #86 on: September 04, 2015, 09:02:09 AM »


Seen in the pic above is a large sheet of 14 gauge aluminum a buddy gave me that came out of some kind of large blueprint machine or something. Perfect for the tray section of my splitter but too short to make the whole splitter out of it even if I wanted to which I didn't. So I cut it up and taped all the box tubing in place.



The pics below show how the engine tray will also be attached to the piano hinge at the rear of the splitter tray and a bracr for the sheet aluminum will be used to support the aluminum sheet in front of the engin pan notch.



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NOT A TA

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Re: 2nd gen TA aerodynamics and modifications
« Reply #87 on: September 04, 2015, 09:15:31 AM »
I had most of a sheet of hardboard (really inexpensive stuff) left from making a rear package tray for my Malibu so I figured it'd make a great pattern to use (and keep for future use if replacement front sections are needed) for the various size front sections. Using the DIG cardboard pattern I transferred and cut. This will be strong enough and stiff enough to mock up the attachment pieces and front supports more easily than cardboard and I'll have the piece left over as a future pattern.



Searching around for something with the right curve to make a nice corner for the leading edge of the splitter I decided on a 74 Jensen Healey wheel (anyone wanting to buy a set let me know) . Started with my coffee cup and kept finding bigger things. Thought it'd make a cool pic to see the various things I'd considered using.

« Last Edit: September 04, 2015, 09:20:02 AM by NOT A TA »
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mrbandit

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Re: 2nd gen TA aerodynamics and modifications
« Reply #88 on: September 04, 2015, 09:20:25 AM »
Can you use an actual flare to get the correct curve?

NOT A TA

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Re: 2nd gen TA aerodynamics and modifications
« Reply #89 on: September 04, 2015, 09:28:19 AM »
The curve I was making is for the leading edge of the splitter under the headlight. It will be changed again later anyway since I made the hardboard template oversize in width so it can be trimmed later to the width of the outside edge of the wheel well wickers that stick out past the wheel flares. I'm not sure exactly how far out I'll have the wickers stick out so I planned ahead by just making the splitter pattern extra wide.
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NOT A TA

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Re: 2nd gen TA aerodynamics and modifications
« Reply #90 on: September 04, 2015, 09:37:27 AM »
Mocking up the pieces in pics below. The white vertical PVC pipe is slid through the holes in the frame where the steel and aluminum pipes will be mounted to support and provide height adjustment for the splitter. The PVC will NOT be used to support the weight. They're just in the frame so I can line things up and measure.





« Last Edit: September 04, 2015, 09:39:59 AM by NOT A TA »
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Re: 2nd gen TA aerodynamics and modifications
« Reply #91 on: September 04, 2015, 09:47:48 AM »
In previous pics you've seen bicycle spokes in the positions I want the supports for the front of the spoiler. They will be made with turnbuckles and steel cable lanyards (made to suit) so I can fine tune the height and angle of the splitter while allowing the splitter to raise up hinging on the giant piano hinge if the leading edge of the splitter hits the ground. I'll be sourcing something similar to the plastic rails used on the bottom sides of skateboards in the 80's to be attached under the leading edge of the splitter to take the abuse should the splitter touch the road surface.

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NOT A TA

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Re: 2nd gen TA aerodynamics and modifications
« Reply #92 on: September 04, 2015, 09:58:20 AM »
So now I wait to receive some pieces I need to complete this from McMaster (aluminum pipe and fittings)and need to decide exactly what material I will use for the front sections of the splitter. Meanwhile I've got plenty of things to work on. Patterns for smaller versions of the splitter, plastic air dam extensions, and wickers for the wheel flares are at the top of my "to do" list. Will post them once I've got something worthwhile to show. Final assembly of the splitter will be done later when I have all the pieces ready to bond, rivet, weld, and bolt together.
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Re: 2nd gen TA aerodynamics and modifications
« Reply #93 on: September 04, 2015, 10:15:36 AM »
I've always thought it would look better if the bottom lip and flares were flush with the face of the car instead of sitting back.  Looks better and functional, hard to argue with that.

NOT A TA

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Re: 2nd gen TA aerodynamics and modifications
« Reply #94 on: September 04, 2015, 08:29:25 PM »
I've always thought it would look better if the bottom lip and flares were flush with the face of the car instead of sitting back.  Looks better and functional, hard to argue with that.

Here's one of the other front sections. Being smaller it looks a little less like an all out race car or caricature to  me.

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Re: 2nd gen TA aerodynamics and modifications
« Reply #94 on: September 04, 2015, 08:29:25 PM »



NOT A TA

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Re: 2nd gen TA aerodynamics and modifications
« Reply #95 on: September 08, 2015, 10:35:26 AM »
I mocked up a flow straightener for the fender vents. Although the pieces would work well for a car with only one set of modified vents (purpose built race car) I'm not thrilled with the design for my particular application where I'll be switching among 3 sets of fender vents. As pictured below they would require that the vent be installed in the fender, then the flow straightener installed, and then the inner fender be put in. I don't want to remove the inner fender to switch fender vents every time and I don't want to spend the time finding a way to modify things to use a different type of vent installation fastening system. I considered something like the pop on headlight fasteners new cars use but that modification, combined with making the flow straighteners, is more time than I want to spend on this now. Perhaps at a later point I'll try one of the other flow straightener designs I've considered. Right now I need to move on with the build in general and not get too bogged down with any one thing.

I figured I'd post this up for anyone wanting to build something similar. I do feel it would increase air speed through the fender vent thereby evacuating a larger volume of air in the same time period compared with just a vent without flow straightener. If this was for a race only application I'd use it.

A short radius to smooth the fastest moving air is at the top of the vent inside the fender. Air (coming over the inner fender inside the fender) will be pulled from the top inside the fender (reducing lift) and air flowing from the main engine compartment area would speed up flowing to the vent past a gentle radius at the rear by the firewall (due to reduced turbulence).





« Last Edit: September 08, 2015, 10:37:59 AM by NOT A TA »
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Re: 2nd gen TA aerodynamics and modifications
« Reply #96 on: September 08, 2015, 01:09:21 PM »
Great work and innovative ideas John!

1973klrbrd

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Re: 2nd gen TA aerodynamics and modifications
« Reply #97 on: September 21, 2015, 11:55:56 AM »
Very cool fender vents John. This is a great thread you have going. A bunch of innovative ideas at work here. Thanks for sharing. 
Jay & Amy
1973 Trans Am

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Re: 2nd gen TA aerodynamics and modifications
« Reply #98 on: September 22, 2015, 07:45:49 AM »
Thanks guys!

Jay, can you post up some pics of your splitter? Height from track surface? Mounting? Experiences?

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 bump stops. 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.









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Re: 2nd gen TA aerodynamics and modifications
« Reply #99 on: September 22, 2015, 08:30:36 AM »
While waiting on materials for the splitter I got busy making the brake cooling duct backing plates for the brake rotors. The Baer 14" set up for 2nd gen F bodies includes a new spindle which has a speed sensor mount cast into it. The speed sensor mount is right where I wanted to put the brake duct hose so it had to be removed.

The backing plates for the rotors are just a bit smaller than the rotor hat and fit almost flush inside the rotor hat when mounted. This creates a pressurized plenum of cool air to flow through hat and then the vents in the rotors. Without the backing plates hot air that's passed over the outside of the rotors would be mixed with the cool air from the ducts before entering (or re-entering) the rotor hat and still wouldn't be forced through the rotor vents relying only on the vent design to pull air into the hat as the wheel turns. Without any modifications almost half of the rotor hat area is blocked by the spindle and caliper bracket/abutments. The whole thing is shrouded by the smallest diameter (18") and widest tire (285) I can fit. Pressurizing the hat with cool air will also help keep bearing temps down.

The Baer spindle is fully assembled and adjusted with hub, calipers, rotor, pads etc.and is ready to bolt on out of the box (which I did initially). To install the brake ducts everything had to come apart to make the backing plate for the spindle. In the pic below the spindle is bare and the speed sensor mount is still in place. You'll see in following pics the speed sensor mount is gone.



the white line in the pic below shows the size of the rotor hat. As you can see a lot of it is blocked off by the caliper brackets etc. even though the speed sensor mount is gone.



Pic below shows how the backing plate fits into the rotor hat.



Hose routing below checking for steering and suspension interference. It's a tight fit so actual track testing may lead to changes.





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RatOne

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Re: 2nd gen TA aerodynamics and modifications
« Reply #100 on: September 22, 2015, 08:52:44 PM »
Looks great!  Looking at your pics It makes me wonder if the c5 z06 brake ducts would retrofit on the trans am?

1973klrbrd

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Re: 2nd gen TA aerodynamics and modifications
« Reply #101 on: September 23, 2015, 06:24:23 AM »
John, this is great stuff. Informative as well. Where did you research all the info about the brake ducts. I look forward to reading your next update.

Here is a few pics of the splitter. They are not great detail. I need to get into my photo archives fro the TA build to find more detailed fab and build photos.

Finished look. Couple angles. It is not nearly as adjustable as your design. We get approximately 3/4" - 1" of adjustment from the turn buckles so typically the splitter is left in place as you see it in the pic. Plus, the splitter does not do a whole lot for aero on autocross which is where my wife enjoys driving the car the most.





Pic of the splitter fitment to the front flare.


I do not have any good detail dimensional pics like yours John, yet you can see from this photo, we have 3-4" of ground clearance at speed and in the neighborhood of 2-3" at full brake.


I need to go back through my photo archives to find more detailed build pics of the splitter. If I can track them down I'll post a couple up. The install was fairly simple and not nearly as functional as your design from a racing need. The design we installed does add downforce on the nose at speeds over 100mph but we rarely are getting the car above those speeds these days.   
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Re: 2nd gen TA aerodynamics and modifications
« Reply #102 on: September 23, 2015, 07:53:50 PM »
This is one of the coolest posts I've ever seen. My goal is autocross, so I'm digging all of the race tech.

NOT A TA

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Re: 2nd gen TA aerodynamics and modifications
« Reply #103 on: September 23, 2015, 09:45:11 PM »
Jay, I think your splitter probably helps more on auto X courses than you realize. It's certainly cool looking and blends well with the car better than mine which looks like a fat lip. ahaha

I'd like to see the bottom of it and how it's attached.

EDIT: You have a PM.
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NOT A TA

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Re: 2nd gen TA aerodynamics and modifications
« Reply #104 on: September 23, 2015, 09:51:54 PM »
This is one of the coolest posts I've ever seen. My goal is autocross, so I'm digging all of the race tech.

Glad you like it! Keep checking in for new info and if you try anything on your own car or have questions just ask. We'll be discussing the later 2nd gens and the aero differences between early and late cars very soon.
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Re: 2nd gen TA aerodynamics and modifications
« Reply #105 on: September 27, 2015, 09:15:41 PM »
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 between the top of the core support and the underside of the hood. It's 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!






« Last Edit: September 29, 2015, 02:48:26 PM by NOT A TA »
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NOT A TA

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Re: 2nd gen TA aerodynamics and modifications
« Reply #106 on: September 28, 2015, 10:09:53 PM »
I'm going to ramble a bit about things that are relevant to posts coming up.

As mentioned in my last post the air pressure in front of the core support is higher than the air pressure in the engine compartment when the car is moving. Besides reducing lift, another reason for sealing off the core support so the least amount of air can get around it is so that we can create the biggest difference in pressure possible to aid engine cooling. The greater the difference in pressure the easier it is to cool the radiator because the air in front is trying harder to pass through the radiator to get to the low pressure area regardless of fans or shrouds. By creating a pressure difference between the front and back of the radiator the air is being forced/sucked through the radiator as long as the car is moving.

Conversely the higher the air pressure is in the engine compartment the harder it is for the fan to create a pressure difference which draws air through the radiator. This is why there is an air dam under the core support of many cars even though they're not considered performance cars. The air dam increases the difference between the air pressure in front of the radiator and behind it when the car is moving. The simple style air dams were used on regular Firebirds during the later years of the 2nd generation.

With a good difference in air pressure between the front and in back of the radiator a fan isn't really needed, the air will flow through naturally on it's own. A fan just creates a lower pressure behind the radiator which causes air to pass through the radiator trying to equalize the pressure. In our 2nd gen birds a thermal clutch fan was used on most models which allows the fan to just freewheel at highway speeds when there is enough of a pressure difference front to back of the radiator causing enough air flow to cool the radiator. The bimetal coil on the clutch that causes the clutch fluid changes which engage and disengage the fan operation senses that the radiator is being cooled enough and the fan freewheels. The clutch fan saves gas, reduces fan noise, etc. Remove the TA air dam or the small air dam used on the late 2nd gen birds and Formys and the clutch fan will keep the fan engaged at higher speeds than with the air dam in place because the smaller difference in pressure between the front and back of the radiator (without the dam) will reduce airflow through the radiator at a given speed. Thermal clutch fan explanation here http://www.howstuffinmycarworks.com/Fan_clutch.html

Increases in engine power also require an increase in cooling because increased heat is a byproduct of increased power. So often times the first thought is to use an aluminum radiator and an electric fan(s) to deal with the additional heat generated by a more powerful engine combination. Makes sense right? Engine temps still too high? Use a bigger fan or maybe a two speed fan, and if that doesn't work step up to twin fans and perhaps a larger core radiator. Still can't cool the radiator enough? Try an additional pusher fan in front of the radiator also... I've seen many people go through this scenario when their problem isn't really a mechanical one it's an aerodynamic one. What they need is a bigger difference in air pressure between the front and back of the radiator and other factors are causing the air pressure in the engine compartment to be so high that the fans have a tough time creating a big enough pressure difference in front/back of the radiator to get enough airflow to properly cool the radiator. The air pressure under hood is so high it prevents the fan(s) from functioning well. This is often caused by modifications someone has done to the car without realizing the additional consequences of the modification other than what was originally intended.

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Re: 2nd gen TA aerodynamics and modifications
« Reply #107 on: September 29, 2015, 04:02:17 PM »
So one might wonder what kinds of modifications would increase the air pressure under the hood of a 2nd gen?

Adding a transmission or oil cooler to one or both sides of the radiator by cutting a hole in the core support next to the original radiator opening.

Swapping to headers that might change the airflow under the engine by slowing it down with all the tubing before the collector and hanging lower than the stock exhaust.

Inner fender removal.

Removing or not replacing deteriorated "splash guards" on the inner fenders around the upper control arm.

Installing a radiator that doesn't fit quite as well as the original leaving gaps on the side or top between the radiator and the core support.. This happens pretty often with aftermarket aluminum radiators that aren't "exact fit" but rather "fits most" and are sold by core dimensions and inlet/outlet size.

Deteriorated or removed shaker seal to hood.

Open shaker scoops that are strapped to the hood with nothing to seal them below. Most often used with an open aftermarket air filter.

Open Formula hood scoops that aren't used with a Formy air cleaner base.

Low hanging aftermarket oil pans.

Low hanging remote oil filters or oil coolers.

Aftermarket dual exhaust mufflers under the front floor pans that hang down blocking air flowing under the car.

Aftermarket cowl induction hoods without using a carb pan that seals to the hood when it's closed.

Aftermarket forward facing hood scoops without using a carb pan that seals them.

Deteriorated or missing cowl to hood seal.

Deteriorated or missing inner fender extensions.

Now I'll be the first to admit I've done a few of these things in the past. The worst was removing the shaker scoop completely on certain road tracks because it blocked my view and I couldn't see the apex of certain corners at Road Atlanta and Sebring. And guess what? Engine temps were higher to the point that on one hot day at Sebring  I had to run the heater full blast on high while on track  plus take a slow lap in the middle of each 20 minute session to cool down the engine. Eventually I made a seat pad to raise me up a bit so I don't need to remove the scoop.

Many of the things mentioned above also reduce performance in other ways besides making it harder for the radiator to cool the engine.

Pic in the pits at Sebring. Note missing shaker and the hood open a bit to help the car cool between sessions.



« Last Edit: September 30, 2015, 08:24:59 PM by NOT A TA »
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Re: 2nd gen TA aerodynamics and modifications
« Reply #108 on: September 29, 2015, 06:00:00 PM »
Moving along,  Jay "1973klrbrd" has consented to allow me to use his and Amy's car (seen above) as a sort of case study here. Although I've never seen it in person I've known about it and followed it for many years from the beginning when Albert the owner of Carbon Kustoms created it. The car is a great example of a beautiful top pro touring car with lots of modifications to the body, drive line, and suspension. The modifications have increased the speed and mechanical grip available making it a much more capable car than it was stock. I suspect,  (based on what I've seen in pics) that a few aerodynamic changes could make it even more competitive at PT events.

The PT cars have gotten very advanced the past few years and there are now competitive events for them to run at. With the competition all maximizing the power and suspensions available and the rules that set limits on things like tire tread wear ratings I think we'll see more efforts to use aerodynamics to increase grip. The 2nd gen birds are a natural for these types of competition because they have advantages right from the start compared with a lot of other models of muscle car era cars.

When Albert built this car he was concentrating on the prototyping and eventual production of Carbon Fiber hoods, fenders, shakers, inner fenders and other parts to lighten the cars. I for one would love to have some of the pieces for my own car, but I digress. I noticed that there were a couple things I thought should have been retained or better modern versions of made that were (are?) missing that are key aerodynamic parts. In particular there was no cowl seal or inner fender splash guards.



Both parts help keep under hood air pressure down and in so doing make the car stick better. The splash guards reduce the amount of air that can get in from the high pressure area in the wheel well. It can't be actually sealed off very easily but simple splash guards would reduce the volume of air that can get in.

The cowl to hood seal is actually a much bigger deal because the air pressure at the base of the windshield is very high. That air is being forced under the rear edge of the hood and moving forward entering the engine compartment because the seal is missing. Many folks think of the seal as a weatherstrip to keep water in the cowl area (and out of the engine compartment) so it will go down the cowl openings and drain out, however it's main function I believe is to keep high pressure air from entering the engine compartment. Lots of people don't replace the cowl seal because they aren't planning on driving in rain or using a hose to wash the car and the cars are now toy cars that spend most of their time in a garage. However that's not the main purpose of the seal.

The hood doesn't have the grills in it like a regular 70-76 hood (will talk more about the hood grills later) so the full force of the highest pressure air at the windshield base is forced into the engine compartment. This increases the air pressure under the hood increasing lift at speed (less front wheel grip), making it harder for the radiator to be cooled, and adding a large volume of air which needs to escape the engine compartment. Since most of the air will go out under the car it will increase lift under the car and as speed increases the rear wheels will have less grip. I suspected that at high speeds the rear was "light" and the car had a tendency to over steer.  Then I saw this pic which leads me to believe I might have been right.



The addition of a splitter on the front of the car may have exaggerated the effect because it's forcing the front end down while cantilevered (tipping the rear up) and the air being blocked by the splitter is being replaced by the air coming into the engine compartment from the cowl. While at lower auto X speeds the splitter may be helping it may be hurting at very high speeds. My guess is that at high speeds over 100 MPH the rear has less grip than it should for gentle sweepers, when threshold braking, and also during initial turn in at the end of high speed straightaways on road tracks the rear probably wants to slide out. If an effective cowl seal can be used I'd bet the bias valve for the rear brakes could be adjusted to add more bite on the rear calipers and there would be better overall braking with less dive. This would shorten braking distances and make initial turn in on high speed corners at the end of straights smoother (including auto X). Smooth = fast.





« Last Edit: September 29, 2015, 07:55:14 PM by NOT A TA »
John Paige
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Re: 2nd gen TA aerodynamics and modifications
« Reply #109 on: September 29, 2015, 07:20:42 PM »
The 70-76 hoods had grills in them above the openings in the top of the cowl but 77 & up hoods do not have the grills. All of the aftermarket fiberglass 70-76 hoods I've seen exclude the grills.

The grills in the early stock style hoods allow the air pressure above and below to remain more equalized as the air pressure increases with speed. If there is a good cowl seal on the car the hood remains as we think it should. If there's an aftermarket  hood without grills used and the seal is good the hood may start to vibrate, burping the high pressure air built up under the hood above the cowl into the engine compartment. This is because the highest pressure air closest to the windshield at the base is being forced under the rear of the hood and the air pressure above the hood is lower allowing the hood to be pushed up.

The 77 and up hoods have no grills in them. But why? Perhaps because of the national 55 MPH speed limit in effect at the time and the manufacturing cost of the grills which might not be needed at 55 MPH. In any case I've seen the later hoods pushed up by air pressure at high speeds. I don't know of a simple long term cure other than hood pins to hold the rear of the hoods without grills. I'm sure many of you have done like I do and push the rear of the hood down after highway use or high speed runs. However if the hood gets pushed up and air enters the engine compartment it increases lift etc.so for high speed activities we want the hood to stay down and the engine compartment sealed off. I have seen some guys use 2" square spongy foam to keep the cowl sealed on the 77+ cars during high speed race events. They just lay it across the cowl and shut the hood.
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Re: 2nd gen TA aerodynamics and modifications
« Reply #110 on: September 29, 2015, 07:41:08 PM »
Some of you may have wondered how much of a difference sealing off the top, sides, etc. of the core support could really make. The surface area of the gaps blocked off adds up to over 1/3 the size of the radiator opening so it's like having a hole this big in the core support allowing air directly into the engine compartment.

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Re: 2nd gen TA aerodynamics and modifications
« Reply #111 on: September 30, 2015, 10:30:08 AM »
I've always thought it would look better if the bottom lip and flares were flush with the face of the car instead of sitting back.  Looks better and functional, hard to argue with that.

Here's one of the other front sections. Being smaller it looks a little less like an all out race car or caricature to  me.



John, this is a great look for the splitter. Have n idea what the downforce or aero needs you are seeking will be with this design, but aesthetically, this is way cool.
Jay & Amy
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Re: 2nd gen TA aerodynamics and modifications
« Reply #112 on: September 30, 2015, 02:21:18 PM »
Wow John, this is excellent information.

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Re: 2nd gen TA aerodynamics and modifications
« Reply #113 on: September 30, 2015, 08:34:31 PM »
Thanks guys! I forgot about this pic I'd intended on posting early in this thread. Think it came from Pontiac back in the day. Note the blurb about the fender air extractors.

« Last Edit: September 30, 2015, 08:36:26 PM by NOT A TA »
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Re: 2nd gen TA aerodynamics and modifications
« Reply #114 on: September 30, 2015, 08:54:42 PM »
I decided to go ahead and pop rivet the core support seals in place since the core support is already painted and then I won't have to keep track of all the rubber panels. So here's a couple pics before and after.

Upper fender above core support before/after.





Drivers side fender to core support gap before/after rear, after front. Note the hole around the frame/bumper support in the first after pic.







Frame/bumper support seal.


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Re: 2nd gen TA aerodynamics and modifications
« Reply #115 on: September 30, 2015, 09:14:24 PM »
At Land Speed Races you'll often see cars with all the body seams taped up like the pic below. Rumor has it that little things that reduce drag will allow slightly higher top speeds.



I'm a long way from getting to the point that tape is going to make much difference on my cars top speed and I think it looks funny.  I'm going to use a wiper seal on the sides of my hood with the hope it keeps high pressure air from entering the engine compartment and reduces turbulence a little even if I can't quantify a difference.

This is a little piece of the seal I'm using and in the second pic you can see how it seals to the fender. There will be a couple breaks in the seal for the hood side bumpers which will be retained but the seal will butt up to the bumpers so there's no air gap to speak of.



« Last Edit: September 30, 2015, 09:17:01 PM by NOT A TA »
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Re: 2nd gen TA aerodynamics and modifications
« Reply #116 on: September 30, 2015, 09:30:22 PM »
While hunting through my Photobucket  for a taped up car I was reminded of what happened at a LSR I was at. Killer corvette with a custom intake that required a custom raised center section hood. Got up to a certain speed and the high pressure air from the windshield base raised the hood and blew it off at well over 150 MPH. Didn't have a functional cowl seal as you can see in the lower pic.



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Re: 2nd gen TA aerodynamics and modifications
« Reply #117 on: October 01, 2015, 03:00:44 PM »
Moving along,  Jay "1973klrbrd" has consented to allow me to use his and Amy's car (seen above) as a sort of case study here. Although I've never seen it in person I've known about it and followed it for many years from the beginning when Albert the owner of Carbon Kustoms created it. The car is a great example of a beautiful top pro touring car with lots of modifications to the body, drive line, and suspension. The modifications have increased the speed and mechanical grip available making it a much more capable car than it was stock. I suspect,  (based on what I've seen in pics) that a few aerodynamic changes could make it even more competitive at PT events.

The PT cars have gotten very advanced the past few years and there are now competitive events for them to run at. With the competition all maximizing the power and suspensions available and the rules that set limits on things like tire tread wear ratings I think we'll see more efforts to use aerodynamics to increase grip. The 2nd gen birds are a natural for these types of competition because they have advantages right from the start compared with a lot of other models of muscle car era cars.

When Albert built this car he was concentrating on the prototyping and eventual production of Carbon Fiber hoods, fenders, shakers, inner fenders and other parts to lighten the cars. I for one would love to have some of the pieces for my own car, but I digress. I noticed that there were a couple things I thought should have been retained or better modern versions of made that were (are?) missing that are key aerodynamic parts. In particular there was no cowl seal or inner fender splash guards.



Both parts help keep under hood air pressure down and in so doing make the car stick better. The splash guards reduce the amount of air that can get in from the high pressure area in the wheel well. It can't be actually sealed off very easily but simple splash guards would reduce the volume of air that can get in.

The cowl to hood seal is actually a much bigger deal because the air pressure at the base of the windshield is very high. That air is being forced under the rear edge of the hood and moving forward entering the engine compartment because the seal is missing. Many folks think of the seal as a weatherstrip to keep water in the cowl area (and out of the engine compartment) so it will go down the cowl openings and drain out, however it's main function I believe is to keep high pressure air from entering the engine compartment. Lots of people don't replace the cowl seal because they aren't planning on driving in rain or using a hose to wash the car and the cars are now toy cars that spend most of their time in a garage. However that's not the main purpose of the seal.

The hood doesn't have the grills in it like a regular 70-76 hood (will talk more about the hood grills later) so the full force of the highest pressure air at the windshield base is forced into the engine compartment. This increases the air pressure under the hood increasing lift at speed (less front wheel grip), making it harder for the radiator to be cooled, and adding a large volume of air which needs to escape the engine compartment. Since most of the air will go out under the car it will increase lift under the car and as speed increases the rear wheels will have less grip. I suspected that at high speeds the rear was "light" and the car had a tendency to over steer.  Then I saw this pic which leads me to believe I might have been right.



The addition of a splitter on the front of the car may have exaggerated the effect because it's forcing the front end down while cantilevered (tipping the rear up) and the air being blocked by the splitter is being replaced by the air coming into the engine compartment from the cowl. While at lower auto X speeds the splitter may be helping it may be hurting at very high speeds. My guess is that at high speeds over 100 MPH the rear has less grip than it should for gentle sweepers, when threshold braking, and also during initial turn in at the end of high speed straightaways on road tracks the rear probably wants to slide out. If an effective cowl seal can be used I'd bet the bias valve for the rear brakes could be adjusted to add more bite on the rear calipers and there would be better overall braking with less dive. This would shorten braking distances and make initial turn in on high speed corners at the end of straights smoother (including auto X). Smooth = fast.

John, thanks for the feedback on the aero suggestions/education using our car. We used the "theory" of getting heat out of the engine bay which is counter-intuitive (aka. counter-productive) to your explanation for increasing grip. HA! No splash guards, shaker seal, cowl seal, etc. was a concept to get heat out. Boy, did we miss the mark when considering aero for the car. Yes, the splitter really enhances the car's front end however I had n idea what the counter effect was to the rear.

Speaking of the rear, the car has always had a loose feel in the rear. In fact, I am not comfortable at all with the rear of the car at speeds over 90mph. We have no problem getting the car to those speeds quickly, but boy is the feel uncomfortable. Granted we had issues with the 4 link and frame rails and replaced the set up with complete frame rails and the 3 link/Watts link which greatly enhanced rigidity, lateral grip and forward bite BUT the car just simply feels "wobbly", loose, wallowing (insert any and all words here) in the rear at speed. We have considered a rear diffuser or wicker bill on the rear spoiler to increase downforce but after re-reading your thread, I'm wondering if we have a lot more going on than just a rear aero issue. You demonstrate issues within the engine bay and on the front of the car, yet there is more for sure.

One place we get a tremendous amount of air is through the trans tunnel, up the shifter boot and up into the cabin of the car. Makes me wonder if I have way more issues of air flow under the car than I've ever considered...which has been very little consideration until reading your thread. Would be very curious if you have any thoughts on this concern/issue.

Thanks again for the insight and education. I have way more to learn.       
Jay & Amy
1973 Trans Am

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Re: 2nd gen TA aerodynamics and modifications
« Reply #118 on: October 05, 2015, 10:46:44 PM »
John, thanks for the feedback on the aero suggestions/education using our car. We used the "theory" of getting heat out of the engine bay which is counter-intuitive (aka. counter-productive) to your explanation for increasing grip. HA! No splash guards, shaker seal, cowl seal, etc. was a concept to get heat out. Boy, did we miss the mark when considering aero for the car. Yes, the splitter really enhances the car's front end however I had n idea what the counter effect was to the rear.

Speaking of the rear, the car has always had a loose feel in the rear. In fact, I am not comfortable at all with the rear of the car at speeds over 90mph. We have no problem getting the car to those speeds quickly, but boy is the feel uncomfortable. Granted we had issues with the 4 link and frame rails and replaced the set up with complete frame rails and the 3 link/Watts link which greatly enhanced rigidity, lateral grip and forward bite BUT the car just simply feels "wobbly", loose, wallowing (insert any and all words here) in the rear at speed. We have considered a rear diffuser or wicker bill on the rear spoiler to increase downforce but after re-reading your thread, I'm wondering if we have a lot more going on than just a rear aero issue. You demonstrate issues within the engine bay and on the front of the car, yet there is more for sure.

One place we get a tremendous amount of air is through the trans tunnel, up the shifter boot and up into the cabin of the car. Makes me wonder if I have way more issues of air flow under the car than I've ever considered...which has been very little consideration until reading your thread. Would be very curious if you have any thoughts on this concern/issue.

Thanks again for the insight and education. I have way more to learn.     

Yes, you probably do have more aerodynamic issues than you thought. That's why I PMed you and asked if it would be OK to use your car as an example.  It's an awesome car but just seeing pics on the various forums, USCA commercials etc. I figured it had aero issues from the time it was built.

There's a lot going on because of the many modifications and changes from stock. The way the car is set up is making it very hard for the radiator to cool the car as well as reducing high speed handling capabilities and pumping hot air into the cabin. I've got questions about certain things and would like to see pictures of a bunch of things but first lets address some of the things I've seen that are increasing the air pressure under hood.. Along with a reduction in front tire grip, I believe the under hood air pressure issues are at least partially contributing to the loss of rear grip and the trans tunnel heat. Adding a few things along with ride height adjustment should have a VERY dramatic affect.

Although we're discussing Amy's car I'm going to ramble about each topic as it relates to all the 2nd gens and include things I'm doing on my car.


1. The car needs a hood/cowl seal.  The hood doesn't have the grills cut out so the highest pressure  air at the base of the windshield is pushing the air to flow under the hood because it's easier than going up over or off to the sides of the windshield. The pinch welded "lip" at the leading edge of the cowl was rounded off when the firewall was smoothed so there's even less restriction "turbulence" as the air enters the engine compartment and there's a nice unrestricted path for a huge volume of air to enter. This large volume of high pressure air is raising the air pressure in the engine compartment. I don't know if the underside of the carbon fiber hood is contoured the same as a stock one so you may or may not be able to use a stock cowl gasket.

For those following along, the grills on the 70-76 stock hoods allow the pressure above and below the hood to become more equalized. When there is a stock cowl seal in place the air forced under the rear of the hood at the base of the windshield can exit up through the grills minimizing the pressure difference above and below the hood in the area above the cowl sealed off from the engine compartment. This keeps the hood from trying to lift up. This becomes more of a problem on the 77 and up cars without the grills in the hood because at high speeds the pressure under the hood above the cowl can become greater than the pressure above the hood in that area. This lifts the hood and burbs air into the engine compartment. Sometimes it's referred to as cowl shake but it's really the hood bumping up and down rapidly.

For a cheap way to test whether there's an issue with high pressure air getting into the engine bay of 2nd gen birds with hoods that do not have the grills some pipe insulation foam can be stuck in along the rear edge of the hood as seen below.



2. The inner wheel wells should have splash guards. Otherwise there's a big opening above the frame height the high pressure air in the wheel wells can come through into the engine bay. Increasing lift, reducing radiator cooling blah blah blah.

Shown in the top pic below is a stock "splash shield" except the small separate piece missing on the right. The lower pics are the new seals I'm making for my car out of 1/8" EPDM sheet rubber. They should seal off better than the stockers did.







3. I have a suspicion that the inner fender extensions might be missing on Amy's car. They seal off the front of the inner fender to the bottom of the core support keeping air from coming in from the wheel well. Without them the air moves as shown in the pic below.Again increasing lift, reducing cooling blah blah blah. I've shown my old stock one in the bottom pic, I'll be making new ones for my car but they can be bought from resto parts companies.






.

4. The rear of Amy's car is too low IMO. It's making it harder for the air to move smoothly and quickly under the car. So there's a pressure build up under the passenger compartment. High pressure air is trying to roll under the car along the rockers while the air that comes under the splitter, through the radiator, and all the extra air allowed because the seals are missing from the engine compartment is trying to flow under the car. The air under the car is slowed by the constriction of the narrowest point which appears to be just forward of the rear wheels. This is causing the high pressure air to try and come up through the trans tunnel while lifting the car reducing rear grip. I'd suggest raising the rear of the car a couple inches and testing. By adding "rake" to the car there's a larger area for the air under the car to flow into which I believe will make the car more stable and provide better grip for turns at speed. A rear diffuser would probably not do anything to help without raising the rear of the car first and even then a diffuser has some design requirements to actually function.  A lot of "diffusers" don't really do crap, but they look cool.

In the bottom pic we can see the height difference between the bottom of the splitter and the rear of the rocker panel. There's simply a much larger volume of air getting under the front of the car than can move through the most constricted area at the same speed. While the air speed increases right at the point of constriction lowering pressure at that point it's slowing down the air trying to enter that area increasing pressure forward of the constriction.





If you can Jay, take a whole bunch of pictures under the car, in the engine compartment by the radiator and fans, core support, the close out panel etc and just let me know when you've put them in your photobucket account and I'll look at them.
« Last Edit: October 06, 2015, 09:36:05 AM by NOT A TA »
John Paige
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Re: 2nd gen TA aerodynamics and modifications
« Reply #119 on: October 06, 2015, 09:29:33 AM »
In an effort to utilize the high pressure area at the base of the windshield/cowl area on my car (with no heat/AC) I modified a stock plastic cowl grill with 3/32 EPDM sheet rubber to seal off the cowl openings. This will increase the air pressure above the cowl (downforce)and reduce the amount of air that has to find a way out under the car through the cowl drains etc. The kick panel openings are sealed off inside the car. As with some of the other seals I'm installing as the pressure increases the seal gets tighter as it's forced against the paint.

I do not think this would be a good modification for aftermarket 70-76 hoods without the grills or the 77 & up hoods without the grills because it would only increase the difference in air pressure above and below the hood rear of the cowl seal making it more likely that the hood would be pushed up unless hood pins or some other means is used to keep the rear of the hood from rising.



« Last Edit: October 06, 2015, 09:39:03 AM by NOT A TA »
John Paige
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Re: 2nd gen TA aerodynamics and modifications
« Reply #119 on: October 06, 2015, 09:29:33 AM »
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