EXTERNAL AERODYNAMICS

[69427]

Lots of interesting items being shown and discussed. I'm enjoying this thread.
While I'm trying to figure a robust enough design for the cowl area aero flow spoiler, I've added a couple more feet of undertray to the car (about four feet total back from the Pace Car spoiler) and looking at extending the front air dam down another couple inches. Due to the long nose on a C3, a splitter shelf has to be awful damn forward to not just trap air between it and the higher bumper area, so I don't currently think extending the Pace Car spoiler horizontal surface further forward is going to be a good ROI of time and material for this car. The lower height of the air dam should hopefully reduce the amount of air entering the bottom of the car, helping cornering traction, and particularly front tire grip during braking. I reduced the front suspension anti-dive percentage a few years ago when I read about compliance issues with high amounts of anti-dive. I'm comfortable with the current level of dive during braking, and I guess I'll see if anything now scrapes the pavement.
I'm now looking at directing whatever air I can from under the bellypan/engine out to some vents in the under-door mouldings. I'm still in the design phase, trying to come up with something that won't accidentally end up trapping air in the area as well.
I hate adding any weight to the car, so I'm going at all this pretty slowly at the moment.

 

[phantomjock]

"...splitter shelf has to be awful damn forward to not just trap air between it and the higher bumper area...

Fastening an airdam could be useful, but require some mods to the Pace Car Spoiler. Maybe 'glass in a lip to blind fasten to?
I could be way-off here - sold the Pace Car Spoiler over 15 years ago. so have no real-world data to work from. But I recall the lower lip was substantial(?).
With some thought could maybe be removable for DD?

Cheers - Jim

 

[mfain]

This may be a little hard to explain, but here is what I would suggest. Add brackets to the frame behind the front fascia to support the splitter, Then attach the air dam (really a filler panel in this case) to the bottom of the spoiler but do not attach it to the splitter as a supporting member. Instead, add upward tabs to the top of the splitter behind the air dam to prevent the air dam from pushing back. This "support could be a simple piece of aluminum angle formed to the shape of the back of the air dam.. If you hit something with the splitter, or if it pulls down any with the aero downforce, it won't put stress on the air dam or spoiler. I did this with my C-1. The splitter support is fairly substantial since it supports both the splitter and the front of the undertray, but it only weighs 6#. In the first photo you can see the splitter/undertray support structure. It is bolted to the frame, and the undertray then bolts up into the structure using countersunk bolts. Then the air dam is added - it bolts to the body behind the bumperettes and to a couple of aluminum brackets inside the center cooling duct. Finally, a CF filler panel - much like you show above as an air dam - fills the gap between the air dam and the splitter. It bolts to the bottom of the air dam, but is not secured to the splitter/undertray. Hope this makes sense.

 

[phantomjock]

Pappy good fill. AND, good example on the C1. I'll use some of that on mine too.
That 6# structure - you doing your own TiG? I need to add that to my bag...
The Airdam on the C1 is exactly what I was trying to 'splain.

Came across an old pic that might show how to on a C-3:


The piece in the lowest segment could be "worked" and supported to be the gap filler.

Cheers - Jim

 

[69427]

Fastening an airdam could be useful, but require some mods to the Pace Car Spoiler. Maybe 'glass in a lip to blind fasten to?
I could be way-off here - sold the Pace Car Spoiler over 15 years ago. so have no real-world data to work from. But I recall the lower lip was substantial(?).
View attachment 57541 With some thought could maybe be removable for DD?

Cheers - Jim

That's pretty much the exact setup I've been running for several years. Last week I added an additional one inch lower strip to it for track days. It comes off with six bolts for street use. Behind the airdam I have about four feet of Lexan bellypan to discourage air from just balling up in front of the radiator or up into the engine compartment. The sides of the Pace Car spoiler seem to do a decent job of causing a low pressure zone at the wheel faces, pulling air (and brake dust) out to the sides. I've got some air directors on the lower control arms to direct some of the undercar air up into the brake rotor centers for cooling. (I felt like this was kind of a hillbilly modification until a few years later I saw a similar factory setup on C6Z06 Corvettes. ) So far I've never had any issues with overheating the brakes.

 

[SuperBuickGuy]

That's pretty much the exact setup I've been running for several years. Last week I added an additional one inch lower strip to it for track days. It comes off with six bolts for street use. Behind the airdam I have about four feet of Lexan bellypan to discourage air from just balling up in front of the radiator or up into the engine compartment. The sides of the Pace Car spoiler seem to do a decent job of causing a low pressure zone at the wheel faces, pulling air (and brake dust) out to the sides. I've got some air directors on the lower control arms to direct some of the undercar air up into the brake rotor centers for cooling. (I felt like this was kind of a hillbilly modification until a few years later I saw a similar factory setup on C6Z06 Corvettes. ) So far I've never had any issues with overheating the brakes.

GM put a deflector under the engine support on IROC Camaros that was much lower then is 'normal' - it rarely dragged and was pretty effective at helping keep the engine cool. Never considered it would help the brakes too but I'm sure it did

 

[BBShark]

Mike, interesting comment about air balling up in front of the radiator.

I'm going from memory so I am probably mis-remembering this. The lower valance (front) of my 68 has a pretty big opening on each side of the bumperettes, which pushes air into the frontend (in front of the radiator). I think those two openings were closed off on later cars?

 

[69427]

GM put a deflector under the engine support on IROC Camaros that was much lower then is 'normal' - it rarely dragged and was pretty effective at helping keep the engine cool. Never considered it would help the brakes too but I'm sure it did

I'm not following what that was (under the engine support). Are you referring to something other than the air dam under the radiator support on some other cars?

 

[69427]

Mike, interesting comment about air balling up in front of the radiator.

I'm going from memory so I am probably mis-remembering this. The lower valance (front) of my 68 has a pretty big opening on each side of the bumperettes, which pushes air into the frontend (in front of the radiator). I think those two openings were closed off on later cars?

My car has those same openings. I haven't had engine overheating issues, so I've been incrementally blocking off the air entrances to the radiator in an effort to reduce the amount that eventually finds its way under the car, increasing lift and drag. I have both front outer grilles blocked off, and those two underchin holes 50% blocked off. I keep considering completely blocking them off, but I haven't as that increases the surface area that any air pressure above the top surface of the Pace Car spoiler will push onto and increase lift a touch. I would like to block off the center grill some (or a lot), but I haven't come up with a good/strong way to fasten the blocking sheet/surface.
The frame area between the front grille and the engine is so aerodynamically dirty that I figured even someone as unqualified as me could still clean it up a touch. My hope/goal when I added a short bellypan from the spoiler to the oil pan was to prevent undercar air from leaking up into the front of the radiator (increasing lift and drag) and also from undercar air getting trapped between the engine and the radiator, slowing airflow through the radiator. And, any air that leaks from the front of the radiator or gets trapped between the radiator and the engine now has a horizontal surface that the blocked (modest) air pressure will push down on. I also have horizontal aluminum sheets between the header collectors and frame rails to reduce trapped underhood air from going under the car, and persuading it to exit the side louvers instead.

Just a step up from shadetree engineering.