Callaway built body kits that fixed that problem. Unfortunately, you needed the whole kit as the body was body was wider due to their pieces that attached to the doors above the side ground effects. The whole kit was 5K too. I tried about a decade ago to have them produce while in germany but was too expensive and not enough interest. I still wish I had the kit minus their nose. I was hideous.

 

Looks like a 80's Porsche

 

I was thinking the same thing, this video shows what I mean about our sloped spot under our spoiler/wing, it's twords the end of the video when it shows how the Ferrari's rear wing works.
https://youtu.be/QVRCqLRgZRQ

 

Actually srz the Callaway kit would aggravate the problem. The back of the car should be squared off not made more round.

I remember that car tho. It looked good.

 

I've been kicking around some idea's with my brother, and with an aero engineer here at work.

Going to try and kinda "flat bottom" the bottom of the race car out of a sheet of aluminum and dzus fasteners. Might make a front splitter, but it have to keep a minimum distance of 3" to the ground, so maybe just a splitter and not a chin spoiler.

Want to try and implement things to reduce drag, make it more slipperier and pick up downforce. Will be interesting to see what I/We can make happen. Any little bit helps, just gotta keep from upsetting the air and making it unstable at speed.

 

I know it's not 4th gen related, I have some rather interesting results/mods that I have implemented to my 2006 single cab short bed silverado.

At one time the truck did not have a bed cover or wing of any kind and I run it with the tail gate up. Once I started reaching 130-140 mph at the drag strip the truck would start to get a little lift in the back and actually spin the tires a little. Not white smoke spin, but just enough to get it upset to the point that it started taking out the 1000' and 1320'/mph cones. At the time the rear tire was an M/T ET Drag 29.5" x 10.5" mounted on a bead locked 12" wide wheel.

I had to stop racing it cause it was only a matter of time before I crashed it so I had Madman build me a bed cover and wing set up for it. The frame for the bed cover was made with light weight aluminum and real carbon fiber. The wing was also made of carbon and I think about 16" long with side spill plates a wicker bill that is about an inch tall. It was also supported by struts down to the tailgate. I also make the switch the same size ET Drag tire, but switched to a stiff side wall and added tubes to give the tire a little more stability. Ever since I did those two things the truck drives itself. Straight as an arrow so far to 154 mph.

Just some real world aero tech I thought I would share.

 

Regarding what Project Reaper addressed, it's pretty damn good info! Most of my experience is coming from aeronautical aerodynamics study and practical use (CPL) and motorcycle aerodynamic knowledge and real world testing.

The exhausts are best to point towards the centre of low pressure, e.g in a low exit dual configuration where they are a few yards apart, tuck them slightly facing inward and upwards towards the centre of pressure as shown in the diagrams earlier. Or simply, like pagani does, put them all in the middle!
This is also the same concept used in base bleed projectiles in artillery, extending range vs unequipped shells around 30%. They are not a rocket stream, merely a gas released, reducing the negative pressure creating drag on the flat chopped back shape often used on shells.

Cd is affected by many things. People taping gaps up on body to produce a more laminar flow, frontal area - simple things like smaller wing mirrors, or running the legal minimum one mirror, as I used to often on my superbikes.
Lowering your car also reduces drag slightly. Angle of windscreen is a biggie though, it's pretty much the biggest surface area on most consumer/passenger cars. From memory the 4th gen has one of the lowest window angles in production history, so you're pretty well covered there. My S2000 being a tiny convertible coupe, sucks donkey ***** with window angle department. Seen someone who cut the damn front window off one and put a cage in with a flat body like an old canam car! That would do wonders for Cd on my ride.

Ram air works and is proven, almost every production superbike since early 00s has employed it. It's was usually worth about 10hp on them, maybe a little more on new ones. They usually ran ITBs, big plenum/airbox, velocity stacks in short and long tuning lengths, flat ram path straight from the nose, through the frame ports and into the airbox. Ram air inlet diameter is about 6-8" typically on cars and bikes I find. I have a feeling this is the answer to the stall question - once maximum expected velocity range is known, limit aperture size and angles of edge and tract to be within optimal parameters. They also have often sharper edge angles in later motorcycle models, around the edges of the inlet. That said the GP stuff is usually smoother. I can take photos of an 06 ZX10R one.. I have part of one in my 'wall of shame'
edit: Also from memory ram air requires a decent amount of speed to be of any use, of course depending on design. From memory around 200kmh/120mph you will start to have some noticeable effect.

Appropriately angled and designed diffuser, flat bottom, splitter and the rest all will help too.

 

S2KIWI, I'm very interested in your aerodynamic information on intake designs, I hope you dont mind if I ask you a question. I have the SSRA intake which as most know is a cold air/ ram air style intake in rectangular shape that mounts to the bottom of the bumper and feeds in a low angle Z shape design going up in front of the radiator and feeding into the bottom of the factory air lid. I have the larger SLP lid and smooth bellows in conjunction as well, anyways, the question that I have is, my knowledge of intake designs is less than desired and yet im confident there is a way to improve this ram air design. Do you know of a way, Im assuming a setup like Hio has made would be more efficient as well.

 

ok this might be dumb. but ive always had this idea. the fender vents on the trans am. to cut the inner fender liner so that they are functional but to just let air escape the front wheel wells to increase downforce in the front at high speeds. like how a lot of high end cars have vents for both front and rear. not sure if this would effect CD

not sure what to do with the rear wheel wells.

 

I've thought about that myself....but camaro here. Again that wouldn't make down force. ....but it would reduce lift. Reducing lift typically lowers cd.

A gurney lip would suffice in front of the rear tires. If you look at my pic of the front of my car in this thread you will see i have a gurney lip on the front wheel wells.

 

Reaper, the factory style bottom feeder ram air design does work. To get it working optimally really only needs a few minor tweaks.
1. The larger the opening at the bottom, the better. Squared off shape works for ram air because you cannot "funnel pressure" if that makes sense. NACA ducts are rounded for smooth airflow but they do not feed pressure. NACA ducts would work for bringing outside air into the cab without drag penalty, or moving air from one area to another like the C7 rear quarter panels.
2. Be sure the entire ram air box and intake are sealed air tight.
3. Larger lid and intake tubing will increase pressure differential across the air filter.
4. Extend the radiator air dam forcing more air up rather than under the car. Composite garden edging is a good material for this.


So I stared at the Camaro fender well for about an hour the other day thinking how to release high pressure zone created by tire rotation. I think its simply a matter of cutting out a rear section of the inner liner with a basic louver in the fender, or trim the fender section that bends around and prop the lip for outer air to flow across. Really though this will reduce front end lift and overall drag for stability. If you run a duct from engine bay and Y them together I bet it would further reduce front end lift as well as high pressure/heat from engine bay. I might try something like that with black pvc duct.

 

Roger that on the SSRA intake, looks like I'm already in the right direction. As for the fender vents, something that I'm starting on is the typical corvette style fender vent with the hole cut in the inner fender, but also planning on a hole in the inner fender area with small pipe into the engine bay with a heat extractor in the hood. The plan is hopefully any air that doesn't make in out of the fender vent may be sucked out of the engine bay vent, as for the rear fenders I'm planning a slightly over the top idea on them. The car will have a full flat floor with tunnels as well as a 10 degree diffuser, and for the fenders I'm going to place a intake tunnel similar to the Ferrari 458 that has piping going into the rear hatch area that Ys into the exhaust that will exit in between the tail lights. the idea is that under throttle the Y section will cause a pressure difference not only from the high speed exhaust but from the air entering the fender intake vent which will cause a suction in the rear fender-well as well as dissipating the separation bubble behind the car lowering Cd even more. Ill draw up a diagram in case people are having trouble visualizing what I mean.

 

We found that tunnels seem to work better at about 7.5* on our m3 alms gt cars. 10* is pretty steep. That may work on longer tunnels but probably not so well on shorter ones like a unibody would likely have to work with on.

The pan on the back if my car is a little less than 8*. If i were to change it i would probably flatten it a little.

 

 

Lol That's a hella diffuser ....I'll take a pic of one i built for the race cars.

 

roger

 

Sorry I only just saw this!
I would imagine that the z shape could possibly cause a reduction in flow, but I don't know if it'd be enough to measure in most scenarios unless you're pulling something like 180mph with a hugely modified engine. That said, the bike intakes squeezed down to smaller ports but they always kept the path as straight as possible. The air while pressurised, isn't pressurised as much as say, an exhaust and could be a little more subject to tract shape/direction changing than e.g. a decent flowmaster exhaust which is equivalent to an open pipe..

As to a ram air solution for you, I think really you're going to have to do what you probably don't want to do - modify the exterior if you can't make use of the existing ports on the bonnets of the TAs (forgive my non domestic knowledge we simply don't really have WS6s here, my neighbor has an F-body though of all cars..) Most drag cars will simply take a headlight out, or a fog light or similar to run a ram air venturi. I'd love to see track results with one being used and not. I'd almost bet a few mph trap speed difference with very little difference until at least half way up the strip.. Most of the fastest/record holding NA drag cars I know of use them in the Honda scene and for a reason. Same with every production superbike since 00s... it's not just there for aesthetics.

Another idea perhaps more suited for an f-body without the ram air hood on the WS6;
Build a system where you can remove a headlight, swap the ports/ram air intake in (custom fibreglass perhaps if not off shelf?) and leave the SSRA system in place if possible. Then remove and drive home if regulations require. Might be a PITA though but if you really want ram air to eek out the last 5-10% of an NA build at speed... it'll be worth it for you.

If it's a drag car then no brainer. Street car - what is your tolerance for modification and pain in the assedness if you don't want to physically modifiy the car? But it seems you do.. so I'd just stick to the existing ram intakes for now.
Another idea is custom bonnet or another which would look weird - an MR2 Turbo type intake scoop, they had really weird ram air style intake on the rear window on some of the models. Not sure if JDM only as I have not seen it on stateside cars before. But fitting something like that is probably going to look dogs *****..


And regarding diffuser angle and design - there is a great deal of dependence on your ride height as to the optimal angle, along with number of strakes and width and length these sections. 12 degrees is usually getting close to maximum in applications which allow such angles (aka seriously low flat bottomed race car)
The Bimmer posted earlier will benefit from a fully flat floor being installed. Just throwing a diffuser on will help settle the rear end at speed but really shines to its fullest taking advantage of a flat floor.

If you want to learn about diffusers, here is an F1 aerodynamicists' take on it. https://www.linkedin.com/pulse/how-d...rk-willem-toet

As I don't want to do any exterior modifications (for now), fitting ram air is pretty much off the cards. I don't have the room even if I wanted to. Custom bonnet would be the only way possible.
But I am going full flat floor to avoid a 'rice wing' (although it would be amazing for trolling other people with... along with a fake ricer shopping list on the side panel) hopefully a discreet diffuser on the rear in conjunction with the flat bottom, will be enough and I won't have to resort to a wing as well. To be honest, if I get even more ***** deep into track days it could happen anyway, front and rear downforce increase is easy lap time on the table.

 

I know this is a little old, but I remember reading about gliders and small planes painting old engine oil on the surface of interest then going for a short flight to see where the flow stuck and dispersed the oil. May help give visuals to what goes on and what actually happens when changing things up. Like that work you did Hio...

 

any pics?

side note. When ever I get around to installing the MWC rear bumper support I would like to get the rear under body all sealed up with a panel/diffuser. maybe sheet aluminum. if anyone has done this. hearing that installing that rear bumper support creates a parachute effect with the rear bumper.

also any proof that the wheel well canards actually help on the f body?

 

Under the body is a big area, lots of space gaps.