I'm interested and trying to learn. Not really a NASCAR fan but the technology is certainly fascinating.

Anyone tested aero on Roadsters? I'd guess that there's one set of mods for AutoX and a slightly different set for road courses.

My build plan will include a larger hood scoop just not sure about the orientation. Might turn it around and pick up air from the windscreen. I hope to have a half-height windscreen for the track & fun. The full-height might be more efficient for getting air to the intake system, the half-height should be better for aerodynamic drag.

I'm looking at front splitter and rear spoiler options. A few conceptual plans but noting started at this time. The splitter should reduce the under car pressures by moving air to the sides and may guide more air through the radiator & oil cooler openings. I expect that the oil cooler air path will go under the car, the radiator is directly into the engine compartment. The latter may be counterproductive but should help the radiator cool, albeit not necessary once moving. More air through the oil cooler is a good thing when on the race track.

I believe that vents in the hood will help evacuate the hot under-hood air but I think that the pressure over the hood is greater than under the hood. This may cause an issue with recirculation of hot air depending on hood scoop orientation. The design of the vents will affect the efficiency.

I have no clue as to the value of the side vents. Anyone ever tried to test to figure out what they do?

I expect to use the front brake ducts for their intended purpose and will run hose to the brakes. Secondarily there will be hose to the interior for fresh air.

Just my thoughts, I could be way off base, happened before.

Jim

 

A couple of thoughts for you Jim. Check in w/ Trevor. He has been doing track stuff w/ his FFR for many years. I forget who but someone has done a reversed hood scoop. To me it is a given that there is pressure at the base of the windshield. The only question is how far forward it goes. I have noticed that some scoops extend rearward of the rear hood edge to overlap the cowl a bit. If nothing else, 99% of production cars get the air for the heat/AC systems there. A great friend who had a detached retina that got him out of cars, had put a small screen in front of him, kind of a half moon shape. He picked up a significant lap time improvement at a local track. So, yes, minimize the windshield. There have been a couple of guys who reduced the radiator opening size. I don't remember details but cutting off the top 1/4 or 1/3 height apparently helped. And shaping it to add some downforce is a good thing too. I haven't seen much on front splitters (a horizontal piece I mean) but pretty much anyone who does track stuff runs a front spoiler. Someone makes a nice fiberglass piece that looks good on the car. Others just use some material to make a vertical spoiler and hang it as low as they dare. Overall, traditionally Cobras have had front end lift=light steering at speed. So keep that in mind when thinking about rear wings. Talk to Trevor who has a rear wing on his car.

 

There are a few things you can do that do help. The trip is making the changes easily reversible, so it can become a street car again.

First thing to address is the nose. Horrible aerodynamics there. That wide mouth acts like a big parachute, and contributes to the lift a lot of people notice. I learned this trick from the Shelby Spec series. It was easily removable, and only had a few screws holding it in place. One removed, the screws holes were only visible if you were lying on the ground. This helped with a little more top end speed. But I don't think it applied any down force at slower speeds.

Second, put some down force on the car. This was obviously made for a full width roll bar. But it could be easily done on dual roll bars.

Finally, I tried this. This worked OK. It helped with down force in the faster corners. But created so much drag that it increased lap times a smidgen. And it created a dead zone behind the air dam, which increased oil and water temps.

Years ago I tried a simple angled air dam, like the '69-'70 Mustang had. Created a lot of drag and no real down force.

 

Craig & Bob,

I hope others participate in the topic. I certainly don't want to hog the whole deal, there's a lot to discuss and learn. Looking at the computer models and wind tunnel results is interesting, wish there was more on Cobras.

Bob, I really like the rear spoiler, never thought about connecting exclusively to the roll bar. My thought was to support it to the quickjack mounts and restrain it to the roll bar. This would put it further back, not sure if that would be good or bad. The added nose piece must be one of those items that grows on you. You splitter is similar to what I had envisioned. I've gone to a few Lemons races, those guys will hang plywood on their cars.

Craig, per your comment on running a splitter as low as would dare. I've thought about a design that would allow vertical adjustment, high for the street and low for the track. Per our conversation earlier this week, one would need to be aware of suspension compression during hard braking.

Windshields. I have the racer screen that comes with the Challenge Car. I'll probably fit it and make it removable, it's just a few holes from what I can tell. I hope I don't ruin the paint.

Jim

 

I have a hood vent, front splitter, rear wing, flat under pan and diffuser. I can't figure out how to post pictures anymore.

 

trevor,

Click Quick Reply > Go Advanced > go to the Drag and Drop File Upload or Attach Files sections > follow instructions > Submit Reply.

HTH

 

I have the reversed hood scoop, and when properly made, works great. It mates to an air box on the carb, so it's sealed and the carb only drinks fresh air. Posted many pics of this over the years. My scoop is based on a 1969 Camaro Z-28 cowl scoop, but sectioned and shortened to fit the Cobra hood.

It has been universally agreed that the original hood scoop acts more like an exhaust vent, it does not pull in air. It is located in the laminar flow area, so has no "ram" effect.

I also have a host of other aero aids, including front spoiler & winglets, side skirts underneath, rear diffuser, hood vents, fender vents.

Our Cobra bodies are bricks with rounded corners, so above 85 mph, they are pigs, and try to fly. The goals are to either use a front splitter and rear wing to push the car downward onto the track, or undercar aero to create a low pressure area under the car to suck it down to the track. I went undercar, still developing it, but it works to some degree.

Definitely search out the threads, do alot of research. No matter which way you go, the look is immediately un-traditional.

adding any kind of rear spoiler on the trunk will be purely ornamental. That's what the wings are mounted high up to get them in the air. No air on the trunk area.

 

Some more pics.

Each part is a big discussion.

My Roadster is behind the black one, but shows my current hood with all the vents. One centered and above the radiator for that hot air, one either side above exhaust to vent that hot air. I have also experimented with the hood vents adding a truncated "Gurney" flap. The concept is to "trip" the air passing over the hood, so as to create a low pressure area behind it, and aid in evacuating air from the vent.

 

Chepsk8,
I like it. Designed and built for a purpose.
Jim

 

Hopefully this works

 

more wing pics

 

here is a few pictures of the undertray, diffuser and hood vents

 

Since my build is a departure from traditional, I've planned a few mods that are functional and serve a purpose. I prefer going with a low-pressure under-car solution over adding a giant wing as a starting point.

trevor, I like the flat aluminium panels you added under the car to remove some potential turbulence. That was one idea I had as well.

Chepsk8, any more pics of the diffuser from under the car or a write-up?

Been looking at the Trufiber front lip that Mark Gearhart has: https://trufiber.com/cobra-carbon-fiber-air-dam-factory-5-mk4/

Also going to add hood vents. Lots of discussions on here about hood vents. Here are two I found quick:
https://www.ffcars.com/forums/17-factory-five-roadsters/287280-real-hood-vents.html
https://www.ffcars.com/forums/17-factory-five-roadsters/636036-hood-vents.html

These are the hood-louvers I'm going with from vraptor speedworks:

Here are those same vents from a different angle on Galla's car:

Available here: Mk4 Roadster Hood Louvers

I might even try to lose the factory hood scoop entirely and go with something like this at the front of the hood (similar to how the GTM aero is on the hood): https://www.summitracing.com/parts/tak-t1hl-b/overview/

Or event a carbon fiber Corvette hood vent: https://www.southerncarparts.com/corvette-real-carbon-fiber-hood-vent-insert-p-6378.html

Like I said, it's a departure from traditional. I'll mock it all up in Photoshop first before I commit to this route though.

 

Anyone try to evaluate the benefits of the mods? Wind tunnel, pressure sensors, yarn tufts?

Lap times will show changes/improvements but there are many variables to contend with that can account for the change.

I've run my previous cars on the dyno many times, we've seen consistency and changes. Wish there was an easy way to test aero. Anyone have a wind tunnel in their garage?

Has there been any info from FFR on flow simulation? They use SolidWorks CAD and flow is available. The add on software is probably $5-10k. I have SolidWorks, but not the cash or CAD models. This would provide some or all of the flow info shown in the NASCAR model that Craig started this with.

Toys are cool.

Jim

 

Here are some from the diffuser build. I first mocked it up from cardboard, then build from aluminum. Had to make sure it all was mounted securely, as the "elephant ears" used to blow out all the time at speed on the track. Now they are used as part of the diffuser mount, so no more issues.

How well does it work? No clue. But, the car as a whole is steady and secure at 150 on the back stretch at VIR, and I can run through the esses at Watkins glen as fast as the tires will hold the car.

Just remember, as others have said, it is a whole package, achieving a balance, always in flux.

 

You've sanded down those fiberglass seams by now, right Chepsk8?

Your aero is definitely what I'm looking at for my own. Mostly underbody stuff, plus hood vents, still trying to figure out the shape and mounting points. any suggestions for what to do around the wheels? any problems keeping the transmission or rear diff cool?

 

Jim at FFR did wind tunnel testing on the gen 3 coupe R about a year ago. He did some testing with a splitter, wing and other aero bits. I think it is in the road race forum.

Aero was the most significant change I made. I had Bobs wing (sold it to him) and the larger wing I have in the pictures now. My lap times went down 3 sec at VIR and 2 at Summit point main right out of the gate. All the "holes" I added on the car body was from parts almost flying off on the straights. Once I added the bottom tray, all kinds of "air getting out" problems arose.

 

Since all of the go fast guys are in here on this thread.......

I have always wondered whether or not the dark water air splitter is effective or not.

Dark Water Customs

Your opinions ??

 

The air splitter doesn't do anything for aero directly, because any downforce you gain by pushing down on the splitter gets offset by the pushing up on the top of the nose. Maybe a slight amount, some folks say it makes the front feel more stable, but that seems suspicious to me. It could be that there's less air in the top of the engine bay at speed, that would reduce the lift caused by the gaping maw of the cobra, since all the air is pushed under the car.

What it does do effectively is split the air and make your radiator more efficient, by causing multiple columns of air to stack up and push through the radiator, instead of is all pushing to the top of the rad. It's something that happens in air-to-air intercoolers too, from corky bell's research.

I'm putting one on because the car I'm trying to replicate had one(CSX3301) but it's for radiator efficiency, not aero.

 

Chrisarella, the red cobra in one of my pictures has the Trufiber splitter. Looks very nice.

 

Excellent. Thanks Trevor.

 

Great conversations, i run the vraptor vents and the dwc air dam with tape opening between the dam and body. Between 130-140 mph i still feel lightness in front end. I can live with it since i don't want to go any faster. If i could have a do-over, i'd lose the windshield install rear wing and rear diffuser. The front profile of the roadster is the issue imo, Maybe it's time for a coupe or gtm build or stick to smaller tracks (but i enjoy road america too much).

 

Galla, I think your thinking is right for sure. Yep, a coupe would be a huge advantage. But, sticking to the roadster, it has two problems, drag and front end lift. One huge change on the drag would be, as you know, to get rid of the windshield. Not sure where you are rules wise, and build wise(how much you want to mod your car), but that would be my goal. Just look at the front view of a roadster and it's easy to see the w/s is 20-25% of it's frontal area. Of course than you will go faster, and then the front end lift will be worse. And then....? But it's all fun isn't it?

 

But, sticking to the roadster, it has two problems, drag and front end lift. One huge change on the drag would be, as you know, to get rid of the windshield. Just look at the front view of a roadster and it's easy to see the w/s is 20-25% of it's frontal area.

If you have a chance, go back and look at some of the archival photos of the roadsters when they were racing. Many of them have the W/S laid back, some of them at a really radical angle, almost laid flat.

And laid way back, the W/S might have acted like a wing to create some downforce rather than drag.

 

I have about 25% of the grille taped off with no affect on the cooling. Kinda like NASCAR.

 

I'm with Galla4, 140 is fast enough and I don't like shifting in & out of 5th. Easily hit 140 on VIR South Track and Grattan. Been considerably faster but those were momentary lapses of reason. I'm not racing, just HPDE for fun.

I do want to thank those that have contributed to this topic. Lot's of great info, certainly much to consider. We can all benefit.

Jim

 

Why don't you like shifting in/out of 5th, is it that the shift is just awkward ?

 

yea Jim, I bounce off the rev limiter about 2/3s down the back straight doing 162 at VIR. I hit 155 on the front straight!

 

Tony,

The 4-5 shift is notchy and I guess I'm a bit weird (for so many reasons) and don't like driving w/ one hand at 140-150. Previous car w/ 3.27s, 315/35-17 and a TKO 600 would go 157 in 4th, that was about all it had, maybe 6,800rpm. Plenty fast. 140 is just fine.

I'm looking at the T56 for this build, all indications are that it shifts better and should work well with my street driving style. Don't need the weight but at least it's in the middle.

Jim

 

Jim, you aren't weird on the 5th to 4th shift in my opinion. It happens for me coming off main straights into a sweeping turn. Lots to think of: carrying speed, hitting apex, not over-cooking brakes, oh btw traffic. I wish i was a better driver but i haven't lost an instructor yet. Shifting is a secondary concern but i still wear out clutches. ?
Tim