Lance Purdy

Hello. New to Forum. I have a 2015 GT performance pack that I take to the track (road courses). Its highly modified, engine and suspension.

I have a recurring nightmare that has almost resulted in a high speed wreck on several occasions. The car will go snap aero loose around a moderate corner (really just a kink) at speeds over 90 mph. Not loose at all (after mods) at lower speed corners. The obvious fix is a wing. But, I still like to cruise my GT, I don't want to be the idiot with a wing at the drive-through. My question is, has anybody else had this problem. If so, has anybody installed a particular spoiler that has given just enough rear downforce and stability to stop this problem. I'm not looking for maximum corning speeds, I just want to eliminate the snap looseness.

Lance

EJ27

EJ27

MariosKITT

I prefer American Muscle's RTR spoiler, but I'm not sure how much more functional it is than a stock spoiler. Based on the size and shape, I'm assuming it adds some degree of down force.

I have the same issue at Atlanta Motorsports Park if I go a bit too quickly around the carousel, turning on to the straight can be a pucker factor of 10. I tend to just drive it more cautiously on the carousel.

Lance Purdy

Ok researched spoilers as best I could. Nobody could give me real downforce numbers and I had experts tell me that they felt it likely that it was less than 30lbs at 100 mph, even for some of the more aggressive spoilers. I was on my way to Fontana and I was getting worried since snapping loose at 90-100 mph and spinning into the grass on a road course is one thing. Snapping loose at 140mph and hitting the wall on the high banks of AutoClub is another. Love the way then new mustang fastbacks look, but unfortunately the fastback shape is just an upside down wing causing more and more lift the faster you go.

So I got APR performance wing, wing which produces over 130lbs of downforce over 100mph at less than 15lbs of drag. The tail of my stang was glued to the track. For the first time ever I was tight at high speeds, which was just fine with me.

What to do cruising around town? Well, I can take the wing off, leaving the carbon brackets on the deck lid. All it took was a few extra stainless steel bolts. It looks pretty sharp actually. People ask me about it, like it a custom accent just for looks.

But I don't recommend this option for anybody who is not a total track junkie. The big deal for me was eliminating the the "pucker factor". For the first time ever I could drive with confidence into turns at over 100 mph.

Lance

proeagles

I have a Shelby GT350 and I've been over 150 in it and it was stable as a rock. I had a 15 GT before that and it was stable at 120 with no wing. I don't get the aero loose you are feeling unless you are over steering the car.

Lance Purdy

The GT350 has several things about it that reduces aero issues or, looking at it from the opposite, makes it for aero efficient. For one, the GT350 spoiler is truly effective, creating a more typical high backed exit for the air off the car, and I have also heard adding some yaw stabilization both which would tend to keep the rear end planted. Additionally, the GT350 is more air efficient under the car, keeping the flow more laminar longer, which also reduces lift. So the comparison of a track built car to the 2015 GT which is really a muscle car trying to be a sports car, really does not work.

As for claiming that I must be oversteering, of course too much wheel and too much gas can make a car loose. However, I'm pushing the car to the max, I'm not tootling around the course. Also, my suspension is highly modified. I have much more front grip than a stock 2015 GT. The stock car can't even quite pull 1g in a corner. I'm pulling over 1.3g. So I'm bending around a much sharper corner at 100 plus than what would be possible with a stock GT. In its current configuration, without some kind of aero adjustment, the rear end breaks free at high speeds. No push, just snap aero loose. And the wing did fix the problem. There are probably additional mechanical modifications I can make to help as well.

I agree its all overkill of a 2015 GT. Probably I should have waited a year and got the GT350. However, taking a car not really truly built for a track and making it fast has been a completely rewarding experience. It takes a real driver with a GT350 to stay in front of me. Weekend warriors arn't even in my mirrors.

Cpthair

Would you mind posting a few pictures? Maybe just of the car overall? Sounds like it's a pretty well built machine.

Lance Purdy

I'll try to get some pics up tonight. Nothing on my phone that I can download at work.

Lance Purdy

slow speed corner, missed the apex slightly. Still to much front roll.
Looks decently balanced on the banks. Doing 125 plus here.
You can see the rear planted here because of the wing. First stint, only doing about 110.
Profile driveway view for the heck of it.Ok, somebody asked for pics. Here is the whole story. 2015 GT with performance pack. Early delivery 2014 Christmas present.

Suspension: Steeda bracing (you can see some of the bracing in some of the pics). Steeda bushings (not quite everywhere, but where it matters). Verticle links. AFE coilovers. AFE sway bars, Maximum Mortorsports camber plats, bigger rims and tires. I run DOT tires as I still drive to the track, Nittos or Toyos, 275 front, 305 rear. When combined, tested and balanced the difference is amazing, making it much easier to get the power down and adding .3 plus g's through the curves (30% plus gain) . Running truly sticky tires, like Hoosiers, probably tack on other tenth of a g.

Adding to suspensions mods in terms of what improves handling would be the new APR splitter and wing. The difference the wing made over 80 mph was easily felt. Not sure I could feel the splitter working but likely it was, but the overwhelming benefit of the wing overshadowed it. Can't give an g comparisons as there are no high speed flat corners at Fontana (almost anyone can pull close to 2 g on the banks). The real test will be at thunderhill, particularly turn 8.

Power: JLT intake, Kooks Headers, Cams (Made by Comp cams, but to my tuner's tuner specs, yes tuners have tuners and the cams are totally custom), Tune of course. I will also include under power, lighter rims (NOT carbon), lighter and more efficient drive shaft, and lighter brake rotors. Because I am a road course guy my tuner went for torque under the curve. The combined power difference is significant, truly producing more the 400 lb ft of peak torque at the rear wheels with a very wide power band. This gives me significantly more torque available than a GT350 through either 3rd gear or 4th gear esses. But, unfortunately, the torque still dives off quickly at 6,500 rpm, right when the 350s voodoo really makes a difference. Can't touch the 350s advantage holding good torque for another 1,500 rpm while I am forced to shift. Thinking about putting on a Cobra Jet intake to partially address this issue. My tuner swears he can give me 365 lb ft of torque (rear wheels) out to 7,500 rpm with the Cobra Jet. We'll see.

Again, the mods are overkill if you are a rational person. But damn, its been so much fun!!!! Especially the suspension tuning.