Autocross Falcon Suspension Tuning Advice

[NorthFalcon]

Hey all,

I am hoping on getting some advice on my suspension setup on my falcon. I've done quite a bit of research on the forums, and I have read all of the information I can get from some of Ron Suttons post. I'll lay out my setup and some of the issues I am having.

Setup:
1963 Ford Falcon (2700lbs with a full tank of gas, no driver)
331 stroker motor approximately 400 whp.
Falken FT615k+ 245/40/18
Falken FT615k+ 275/35/18
Street or Track front coilover system running Bilstein coil-overs "Race" valving with a 600lb spring/ with shelby drop.
Street or Track 3 link with watts link running Bilstein coil-overs "Race" valving with a 325lb spring
Front sway bar is 7/8"
no rear sway bar.

Issues: Now the biggest issue I am having is in the corners, for example a left hand turn on throttle the drivers side front wheel will pick up off the ground. I wish I had photos but at the last auto cross event multiple people said they thought it was 8" off the ground. (yikes) Despite the car picking this wheel off the ground, the car maintained insane traction. I have never had the car push and has an enormous amount of turn in. After the first two laps I pulled the car into the pits, and raised the rear ride height by 3/4". This improved how far the front wheel was coming off the ground but I still know something is off. The car is rolling over on itself and causing the rear end to bottom out so the only thing the car can do after bottoming out this right rear, is to raise the front left. I would assume the front right is close to the bottom of the stroke as well. I realize my front sway bar is not big enough for the driving that I am doing but I still believe there are other factors involved. Currently I have my watts link pivot in the middle position and believe I may be able to adjust some of the body roll by moving the watts link pivot up slightly. (roll center) This may help but I don't think it is the right corrective action. After reading Ron Suttons post, I have two plans of attack with some median in between: 1 stiff front springs, soft springs in the rear, with a small sway-bar in the front. (This is what I imagine is my setup currently, and what Shaun at Street or Track has designed intentionally) 2: Soft front springs, stiff rear springs, Stiff front swaybar, and a soft rear swaybar. I would like to find a medium to this and maybe the most cost efficient method to this.

My thinking: The motion ratio of the front suspension is should be around 81%, Shaun mentions on his website that his front coil-over design improves stock motion ratio by 50%, stock motion ratio is 54%. The rear motion ratio according to my rough calculations should be around 88%. I do not think the spring rates are balanced well. With out a rear sway-bar there is not a way to counter act this rotational force, so the car blows through the travel. As for the front, I think a bigger front sway bar could be beneficial, although I do not think this is the main source of my problems. I would like to see my car remain very level in the corners, overall ride quality is not a main concern.

I would like to hear your opinions on where I should start, and maybe setups for mustangs that others have run. I think I should throw more rear spring at the car, somewhere around 550lbs. I will see how this affects it and go from there. Springs are cheap enough to test and tune with.

Thanks guys,

Nick

[Steve Chryssos]

Are your coilovers adjustable? You may be exceeding your shocks' valving -- particularly as it relates to compression force and velocity. I say that because you state that the car still hooks and handles well. If that's the case, your combination is happy in most load scenarios. Given a magic wand, the very first thing that I would do is remove my shocks and get them over to a shock dyno. I would seriously do that before even messing around with springs and stabilizer bars. Just as you know your current spring rates, you should know your shocks' calibrations. The good news is that if your shocks' valving is the issue, you will have really good baseline data from the shock dyno to help dial them in. You'll know which direction to go when revalving. If your shocks are adjustable, you will then be able to fine tune compression and rebound around the new baseline.
Thanks
Steve

[stab6902]

Some quick back of the napkin math, which should be in the ballpark assuming your springs are close to vertical:

Front wheel rate = 600(0.81)^2 = 394 lb/in
Rear wheel rate = 325(0.88)^2 = 252 lb/in

By conventional street car wisdom, your front/rear spring rates are mismatched. You usually see rear rates greater than fronts. As a point of reference, here are the rates for a 2013 Mustang GT:

Front wheel rate = 155 lb/in
Rear wheel rate = 188 lb/in

Based on the above, I think your idea to stiffen up your rear spring rate would be a step in the right direction. If we desire a similar front to rear spring rate balance as the modern Mustang (while holding your front spring rate constant) you'd need a rear spring rate of around 600 lb/in. It's clear when comparing your wheel rates to the heavier modern Mustang that your suspension setup (ride frequency) is on the race car end of the spectrum.

The other way to achieve a good balance would be to hold the rear spring rate constant and soften the front. If you're hurting for front suspension travel (which it kind of sounds like you are if you're lifting a wheel 8"), stiffening the rear is probably the way to go.

Hopefully this helps. Bear in mind I'm speaking in generalities, and I have zero real world experience with that platform (or any Ford for that matter).

[Rod]

to me with out really seeing the car and knowing the set up, its seems you answered your own question, you need a rear roll bar and possible progressive bump stops on the shock shafts (i would start with softs)

The car is rolling over on itself and causing the rear end to bottom out

[NorthFalcon]

@stab6902
Thanks! I have had a lot of good replies on here and my build thread. The consensus is to stiffen the rear as well as work on chassis stiffness. I ordered some 550# springs to start out with that way I can run them on the front to soften it if I want too.

@Rod
I have quite a bit of stuff to work on but a rear bar isn't really an option with the packaging of the 3 link/watts link. I also have progressive bumps stops already. I spoke to Ron Sutton and he suggested to work on total roll stiffness. We'll see how it goes. Ive been reading as much as I can on suspension dynamics, and relating any of the suspension tuning I have learned through racing rc cars to this car.

[groho]

Been awhile since I've been on here. Just tossing my .02. This look familiar? In summary, couple things are happening at the same time, your front sway bar is helping to pick up the inside tire as the outside tire is under load, and you're back end is too soft squatting as you accel helping to pick up the front end. For me, I went up to a 1 1/8" front bar, and went to a heavier rear leaf setup. For you, likely a stiffer rear spring or at least adj the shock compression. Also raised my panhard a touch to remove some of the body roll, in your case adjust your watts link. The solution is to stiffen the rear, and reduce the body roll without creating a scenario where the car is snap/loose in the corner. Take care, good luck.

[NorthFalcon]

Been awhile since I've been on here. Just tossing my .02. This look familiar? In summary, couple things are happening at the same time, your front sway bar is helping to pick up the inside tire as the outside tire is under load, and you're back end is too soft squatting as you accel helping to pick up the front end. For me, I went up to a 1 1/8" front bar, and went to a heavier rear leaf setup. For you, likely a stiffer rear spring or at least adj the shock compression. Also raised my panhard a touch to remove some of the body roll, in your case adjust your watts link. The solution is to stiffen the rear, and reduce the body roll without creating a scenario where the car is snap/loose in the corner. Take care, good luck.

Looks very familiar, Do you have any chassis strengthening? I am going to start with rear springs and I think it should help a ton.

[Turbo6inKY]

Looks very familiar, Do you have any chassis strengthening? I am going to start with rear springs and I think it should help a ton.

My Grand National packed wheels all last year. Everybody whose brain I picked (had several long conversations with the guys at AFCO) sent me down the road of much stiffer rear springs and appropriately valved shocks. Adding rear bar wasn't advised because it would lead to picking up the inside rear tire.

More rebound stiffness in the front shocks could also help slow the front end rise, but it'll be easier for you to try out stiffer rear springs before pulling the shocks and mailing them off for are revalve.

[groho]

Yes, and the early mustang and falcon share similar chassis. I'm running subframe connectors, torque boxes, HD cross member that ties into the LCA, boxed shock tower braces, etc. The car is very stiff, which likely contributed to my suspension lapses. You might want to take a look at Craig Johnson's 63 falcon to get some ideas, watched it in person and it's a very well built, flat, fast, falcon. Please realize you don't have to have the most expensive parts to have an effective autocross car. I've gotten great ideas from people here, and on the course.