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  Topic Review (Newest First)
04-24-2019 11:53 PM
Galla4 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
04-24-2019 10:10 PM
Jim1855 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
04-24-2019 03:32 PM
UrQ
Quote:
Originally Posted by Jim1855 View Post
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 ?
04-24-2019 02:11 PM
Derald Rice
Quote:
Originally Posted by CraigS View Post
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.
04-24-2019 01:34 PM
trevor 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!
04-24-2019 01:20 AM
Jim1855 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
04-24-2019 12:15 AM
Chepsk8 I have about 25% of the grille taped off with no affect on the cooling. Kinda like NASCAR.
04-23-2019 11:21 PM
CraigS 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?
04-23-2019 09:35 PM
Galla4 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).
04-23-2019 11:54 AM
Chepsk8
Quote:
Originally Posted by Danner View Post
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?
Nope, still has the seams! High speed directional stability!!

Yes, like Trevor, I did have heat issues. I actually cooked a tranny when I was too aggressive with the skirts and front spoiler, as I had probably eliminated under-car airflow, thus achieving my goals, but it got very hot in the cockpit.

So, raised up the skirts an inch, slightly smaller front spoiler plus the winglets, car is stable and goes where I point it.

Many different kind of vents for the hood. I just ultimately went with the open mesh, nothing tricky, no re-painting.

You'll have to come and look at the car if you can make it work.
04-22-2019 11:45 PM
chrisarella
Quote:
Originally Posted by trevor View Post
Chrisarella, the red cobra in one of my pictures has the Trufiber splitter. Looks very nice.


Excellent. Thanks Trevor.
04-22-2019 09:17 PM
trevor Chrisarella, the red cobra in one of my pictures has the Trufiber splitter. Looks very nice.
04-22-2019 05:34 PM
Danner
Quote:
Originally Posted by Derald Rice View Post
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.
04-22-2019 04:28 PM
Derald Rice 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 ??
04-22-2019 04:01 PM
Danner
Quote:
Originally Posted by Chepsk8 View Post
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?
04-22-2019 10:33 AM
trevor 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.
04-22-2019 01:42 AM
Chepsk8 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.
04-21-2019 11:34 PM
Jim1855 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
04-21-2019 11:31 PM
chrisarella 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-fi...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-fac...ood-vents.html
https://www.ffcars.com/forums/17-fac...ood-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/cor...rt-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.
04-21-2019 11:05 PM
trevor here is a few pictures of the undertray, diffuser and hood vents
04-21-2019 10:48 PM
trevor more wing pics
04-21-2019 10:20 PM
trevor Hopefully this works
04-21-2019 04:52 PM
chrisarella
Quote:
Originally Posted by trevor View Post
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
04-21-2019 03:19 PM
Jim1855 Chepsk8,
I like it. Designed and built for a purpose.
Jim
04-21-2019 12:27 PM
Chepsk8 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.
04-21-2019 12:14 PM
Chepsk8 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.
04-21-2019 11:51 AM
trevor I have a hood vent, front splitter, rear wing, flat under pan and diffuser. I can't figure out how to post pictures anymore.
04-21-2019 12:32 AM
Jim1855 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
04-20-2019 11:32 PM
Bob Cowan 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.
04-20-2019 09:51 PM
CraigS 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.
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