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#4104466 - 04/08/21 05:22 PM Feedback on Race Suspension
Traffic22 Online   content
Rookie

Registered: 05/14/12
Posts: 59
Loc: CA
So as may of you know, I'm racing my P7 in 24 hours of Lemons, and we were actually pretty successful our first time out. (50 out of 132 overall and 21 out of 62 in our Class)

Our suspension, which is stock, was very much a limiting factor. I have set out researching what will work best for our needs.

In about a week I (as soon as my trans is all back together) I am having the car corner weighed so I know what our front/rear distribution is. My rough estimate says 3700LBS, with about 53% over the front, but we'll see.

Our priorities are as follows:
1) Has to be a durable and reliable as stock. We were successful in our first race because nothing broke. We want to maintain that reliability.
2) Needs to make the handling more neutral. We had quite a bit of understeer, although not as much as you would think. I think taking 200+ pounds off the nose helped a lot.
3) Need to stiffen up the front, and make the rear less squirrelly under hard deceleration. (Our brakes are far too good for our current suspension.) We had a ton of nose dive and rear wheel lift under hard brakes.
4) All springs, front and back, MUST be linear. Progressive rate does not work well in racing.

Based on my rough measurements so far, we are probably going to need about a 600lb front spring. Not sure about the back yet.

It also seems, based on my research, switching out the rear upper and lower control arms seems to be of great help. The MDEC set up seems interesting, but I had a conversation with Maximum Motorsports, and they had this thought....

"Just like the 1979-2004 Mustang rear suspension, the P71 rear suspension is overconstrained. Given this, do not install polyurethane bushings or bearings in all eight rear control arm locations. If you do that, the ride and handling will be terrible. You must leave at least four of these bushings with rubber or very soft polyurethane material."

I'm open to suggestions, and feedback on what you guys use, your experience, and things you have used and would not use again.

Thanks,

Chuck


Edited by Traffic22 (04/08/21 05:23 PM)

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#4104470 - 04/08/21 06:02 PM Re: Feedback on Race Suspension [Re: Traffic22]
85GT Offline
Member

Registered: 10/30/13
Posts: 387
Loc: NYC
Totally agree with Maximum. The suspension will bind. There are some that think the flatter feel that comes from them is better handling. It's just the suspension can't move any further smile But that's applies to the trianglated 4 link. If you have a later model with panhard bar the action is different.


What year? Going to 600 sounds like an 03 and up model.

Adding stiffer to the front will induce even more understeer. So you need stiffen the back even more. With springs or swaybar or both. I've run some 200 lbs in the rear of the 91 caprice. But it would be too big of a diameter for a panhard set up i think.
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08 CVPI
85 Mustang GT w/4R70W
91 Caprice
95 Caprice

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#4104484 - 04/08/21 07:10 PM Re: Feedback on Race Suspension [Re: 85GT]
Traffic22 Online   content
Rookie

Registered: 05/14/12
Posts: 59
Loc: CA
Originally Posted By 85GT
Totally agree with Maximum. The suspension will bind. There are some that think the flatter feel that comes from them is better handling. It's just the suspension can't move any further smile But that's applies to the trianglated 4 link. If you have a later model with panhard bar the action is different.


What year? Going to 600 sounds like an 03 and up model.

Adding stiffer to the front will induce even more understeer. So you need stiffen the back even more. With springs or swaybar or both. I've run some 200 lbs in the rear of the 91 caprice. But it would be too big of a diameter for a panhard set up i think.


I guess I should have mentioned it’s a 2011. Yes, binding is bad, definitely want to avoid that.

When we go lower, I know that will induce a little negative camber, which for us is a good thing.

I’m having a tough time figuring out rear spring rate, because estimating weight is a guess at best. Once I know our actual rate, it’ll be easier to sort it.

It does seem for the rear, upper and lower control arms, are a must. The CHE Performance arms seem robust, appear well made, and are a little cheaper than the Heinous. Of course the Heinous are aluminum and likely lighter, which of course is a good thing.

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#4104520 - 04/08/21 10:16 PM Re: Feedback on Race Suspension [Re: Traffic22]
85GT Offline
Member

Registered: 10/30/13
Posts: 387
Loc: NYC
Lowering will 'automatically' add negative camber. That's what it's supposed to do in a turn when that side compresses. Issue at least with b-bodies, lowering you change the camber curve. When the lower arm is parallel to the ground, you've achieved max negative camber. If you're parallel at rest you have max neg. As you push down more like in a hard turn, it now starts loosing camber rather than gaining. But the uppers come into play to as to what the top of the spindle change is. Not sure how the vics arm are relative to each other. Caprices actually can handle better at near stock height. A tad lower to help center of gravity is about it. Real low is more for looks than handling.

If you don't mind spending the bucks, last set i just got for the other caprice is the moog cvpi replacement, 81479. 82 bucks shipped and tax from amazon. Rockauto have at like 65 but then add shipping.

They work out to almost impala ss height in a caprice. These have a 160 rate. Which is one of the numbers i've heard for stock pi springs. With them as a know, you already know how to proceed figuring out what you want.


Edited by 85GT (04/08/21 10:22 PM)
_________________________
08 CVPI
85 Mustang GT w/4R70W
91 Caprice
95 Caprice

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#4104526 - 04/08/21 11:01 PM Re: Feedback on Race Suspension [Re: 85GT]
Traffic22 Online   content
Rookie

Registered: 05/14/12
Posts: 59
Loc: CA
Originally Posted By 85GT
Lowering will 'automatically' add negative camber. That's what it's supposed to do in a turn when that side compresses. Issue at least with b-bodies, lowering you change the camber curve. When the lower arm is parallel to the ground, you've achieved max negative camber. If you're parallel at rest you have max neg. As you push down more like in a hard turn, it now starts loosing camber rather than gaining. But the uppers come into play to as to what the top of the spindle change is. Not sure how the vics arm are relative to each other. Caprices actually can handle better at near stock height. A tad lower to help center of gravity is about it. Real low is more for looks than handling.

If you don't mind spending the bucks, last set i just got for the other caprice is the moog cvpi replacement, 81479. 82 bucks shipped and tax from amazon. Rockauto have at like 65 but then add shipping.

They work out to almost impala ss height in a caprice. These have a 160 rate. Which is one of the numbers i've heard for stock pi springs. With them as a know, you already know how to proceed figuring out what you want.


Thanks for the info. I’m actually having an email conversation with Chris over at ADTR. We’re kind of spitballing a game plan.

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#4104546 - Yesterday at 12:11 PM Re: Feedback on Race Suspension [Re: Traffic22]
85GT Offline
Member

Registered: 10/30/13
Posts: 387
Loc: NYC
Cool. Would love to hear their thoughts if you don't mind sharing.
Racing stuff tends to be secretive so would understand if not.

A little history for the younger viewers. Carroll Shelby for his first gen Shelby Mustangs dropped the pivot point on the upper control arms to increase the negative camber rate. It was the hot ticket for regular Mustangs to do the same by drilling new holes 1" lower in the shock tower than the original holes for the arms.
_________________________
08 CVPI
85 Mustang GT w/4R70W
91 Caprice
95 Caprice

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#4104602 - Yesterday at 07:20 PM Re: Feedback on Race Suspension [Re: 85GT]
hkerekes Offline
n00b

Registered: 09/19/20
Posts: 45
Loc: NC
The factory rear end setup will accept 2.5" coil springs so getting different rates and lengths isnt a huge deal.

I'm going to try out 3.1 degree of negative camber at our next luckydog race, as we had issues with understeer. Although its an aero it might help you with some setup ideas. We are running 2012 boss 302 rear springs and shocks, cut springs upfront with p71 shocks. 1/16 toe in and 5 degree of caster. 275/35/18 RS4 18x9.5 et10 rim and 12mm spacers. Poly bushings everywhere upfront and almost nothing left in the car. Doors are just skins, trunk is just a skin and pin on, next to go are teh wipers, hvac is all gone, interior wiring is all gone. Shedding weight should help with the understeer.

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#4104634 - Today at 02:00 AM Re: Feedback on Race Suspension [Re: hkerekes]
Traffic22 Online   content
Rookie

Registered: 05/14/12
Posts: 59
Loc: CA
Originally Posted By hkerekes
The factory rear end setup will accept 2.5" coil springs so getting different rates and lengths isnt a huge deal.

I'm going to try out 3.1 degree of negative camber at our next luckydog race, as we had issues with understeer. Although its an aero it might help you with some setup ideas. We are running 2012 boss 302 rear springs and shocks, cut springs upfront with p71 shocks. 1/16 toe in and 5 degree of caster. 275/35/18 RS4 18x9.5 et10 rim and 12mm spacers. Poly bushings everywhere upfront and almost nothing left in the car. Doors are just skins, trunk is just a skin and pin on, next to go are teh wipers, hvac is all gone, interior wiring is all gone. Shedding weight should help with the understeer.




Yep, we’re all stripped out like you. I’m actually having the car weighed soon to see what rates we need for our springs.

We’re going to slowly move to all Polly bushings.
Chris is actually recommending the Massive Traction system for the rear. (It’s very similar to the MEDC system posted here)
I’m not 100% comfortable with the idea of no bushings in the rear, My gut says this is going to put too much stress on the mounting points.

Our first step is new front and rear sway bars.
I’m leaning towards the Heinous billet upper and lower arms and watt link.
We’re likely going to do coil overs at some point.

Thanks for the alignment recommendations.

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