BadAss SRT-Z - 2.4L / A568 - Update!!!

[Reaper1]

Ah, I didn't realize you were running race inserts, JT. That will definately make a difference.

Good to know about the rebuilding on our Koni's. I think the set I have on my car right now is going to need it. How much was it?

[Shadow]

The theory I think JT would be going for with more in the front is that for any given load there is less spring compression or vertical displacement. When you launch and the front suspension unloads there will be less body movement with a stiffer spring. This will help control the pitch and some rear weight transfer along with it.

Agreed, now the opposing veiw is obviously that even though there will/should be less spring compression, it will unload at a faster rate + unload a greater amount. (if there's a greater amount to be had in lbs transfered)

That's why I think this will be interesting, never know till you try and I've not heard of this being done before on a FWD.

[shayne]

Good to know about the rebuilding on our Koni's. I think the set I have on my car right now is going to need it. How much was it?[/QUOTE]

cost of rebuilding my struts is pending still, its a little spooky, they dont say what it will cost until after the work is all done, base cost it $150 per strut plus whatever else it needs. i will post up the cost and what work was done so anyone else who may need a rebuild can see approx what it will be based on a set that was in average but in need of rebuild shape.

[turboshad]

Agreed, now the opposing veiw is obviously that even though there will/should be less spring compression, it will unload at a faster rate + unload a greater amount. (if there's a greater amount to be had in lbs transfered)

That's why I think this will be interesting, never know till you try and I've not heard of this being done before on a FWD.

The opposing view in my opinion is a misunderstanding of how the forces are at work. Very simply there are two forces acting on the car during acceleration and we'll call it low speed so wind resistance isn't a factor and I think we are most concerned with a launch. There is the static weight of the car acting down at the CG which goes through the suspension and then the wheels to the ground. Then there is the dynamic forward acceleration acting on the vehicle mass at the point of the CG going backwards. This acceleration is above the contact patch of the wheels so it acts to rotate the car about the rear contact point. The vertical distance from the CG to the rear point multiplied by the acceleration and vehicle mass gives a torque that tries to flip the car over backward. The higher the CG, the larger the torque hence a lower car will have less pitch than a higher car. A simple FBD would show that the addition of the acceleration force increases the force at the rear contact and decreases it at the front contact. This acceleration force is completely independent of the spring rate used. The force on the front or rear wheels could care less what springs you use and as such the force in the spring is purely reactive and not active. Body shift will raise the CG and increase the moment arm for the acceleration force which will then transfer even more "weight" rearwards. It will probably move it back some too which adds to the bad situation. I see a spring change as being a way to settle down the CG movement so it doesn't make what the acceleration is already doing to unload your front wheels even worse. I'm not sure if that makes sense but that's how I understand the dynamics in this situation.

In short, even if we had solid suspension there would still be "weight transfer" which will always plague the FWD crowd. The only way to battle the acceleration transfer is to lengthen the wheel base like Slowe did or use wheelie bars. This gives the CG more to work with as it's moment or torque arm is in the horizontal plane and the acceleration is in the vertical plane. If you move the point the body needs to pivot around further away from the CG horizontally then there will be less unloading of the front.

[SebringLX]

In short, even if we had solid suspension there would still be "weight transfer" which will always plague the FWD crowd. The only way to battle the acceleration transfer is to lengthen the wheel base like Slowe did or use wheelie bars. This gives the CG more to work with as it's moment or torque arm is in the horizontal plane and the acceleration is in the vertical plane. If you move the point the body needs to pivot around further away from the CG horizontally then there will be less unloading of the front.

Well now the wheelie bars I once saw on a Cavalier at the track don't seem stupid to me. :P I wondered why anyone would put wheelie bars on a FWD car.

[Reeves]

Just so you know, JT, I've ridden in and driven a car with 450#/in springs with Konis and it was on the very edge of what I could consider "acceptable" for the street. On a long drive you would be feeling it for sure. 600's are going to be ROUGH! I'm also not sure the stock Koni's have enough jounce adjustment to control them. You may have to look at different dampers, or send yours out for revalving (though some have claimed Koni won't/can't do that for our dampers any more).

Yeah, my car is pretty rough riding with 450's up front and 600's in the rear. Want to go to 250's up front.

Koni can still do the fronts AFAIK. They are very close to my work.
On the rears of an L, they have to use Mustang parts, which are bigger shafts to begin with.
I'm not sure about the rears of a K based car.

[RoadWarrior222]

I don't suppose you're allowed to launch in reverse and J turn into second?

[Shadow]

Yeah, my car is pretty rough riding with 450's up front and 600's in the rear. Want to go to 250's up front.

Is that with the Koni's turn right down to "soft" with the 450's?

[turbovanman²]

Well now the wheelie bars I once saw on a Cavalier at the track don't seem stupid to me. :P I wondered why anyone would put wheelie bars on a FWD car.

We have the same issue as RWD but for them, it plants the rear tires, for us, it lifts the front tires, wheelie bars, which I believe some FWD racers preload them, will stop or try to stop the front from lifting,

So yeah, I always thought it was a good idea.

[Shadow]

The opposing view in my opinion is a misunderstanding of how the forces are at work. Very simply there are two forces acting on the car during acceleration and we'll call it low speed so wind resistance isn't a factor and I think we are most concerned with a launch. There is the static weight of the car acting down at the CG which goes through the suspension and then the wheels to the ground. Then there is the dynamic forward acceleration acting on the vehicle mass at the point of the CG going backwards. This acceleration is above the contact patch of the wheels so it acts to rotate the car about the rear contact point. The vertical distance from the CG to the rear point multiplied by the acceleration and vehicle mass gives a torque that tries to flip the car over backward. The higher the CG, the larger the torque hence a lower car will have less pitch than a higher car. A simple FBD would show that the addition of the acceleration force increases the force at the rear contact and decreases it at the front contact. This acceleration force is completely independent of the spring rate used. The force on the front or rear wheels could care less what springs you use and as such the force in the spring is purely reactive and not active. Body shift will raise the CG and increase the moment arm for the acceleration force which will then transfer even more "weight" rearwards. It will probably move it back some too which adds to the bad situation. I see a spring change as being a way to settle down the CG movement so it doesn't make what the acceleration is already doing to unload your front wheels even worse. I'm not sure if that makes sense but that's how I understand the dynamics in this situation.

In short, even if we had solid suspension there would still be "weight transfer" which will always plague the FWD crowd. The only way to battle the acceleration transfer is to lengthen the wheel base like Slowe did or use wheelie bars. This gives the CG more to work with as it's moment or torque arm is in the horizontal plane and the acceleration is in the vertical plane. If you move the point the body needs to pivot around further away from the CG horizontally then there will be less unloading of the front.

I'm not 100% sure on what point your trying to make here? (my bad?) It Almost sounds like your trying to say that the springs/spring rates have little or No effect on how one of these cars reacts during launch.

IF that is the case and the point your trying to make, I would have to dissagree. Other than that, I believe that the rest of your analogy is accurate.

It would be like saying if you had a 2500lb brick that was 15' long/ 5' wide and 3' high, resting on two 600lb springs on each front corner (a$$ end lying on the ground) and another identicle brick with two 250lb springs and you took a big pry bar and tried to lift them that it would take the same effort.

The springs Are active because they're laoded and when the weight shifts they will unload........No?

[Reeves]

Is that with the Koni's turn right down to "soft" with the 450's?

Ah, you are right.....no they are not. They are full stiff on the front and full soft on the rear. Forgot to add that and I haven't changed them. Need to try that sometime! Doh!

We have the same issue as RWD but for them, it plants the rear tires, for us, it lifts the front tires, wheelie bars, which I believe some FWD racers preload them, will stop or try to stop the front from lifting,

So yeah, I always thought it was a good idea.

The FWD's with wheelie bars haven't been able to pre-load them for years now. Have to be off the ground.....at least until they drop the hammer!

[turboshad]

it will unload at a faster rate + unload a greater amount.

This part is wrong. In fact with less body movement the 600lb spring should unload less as the CG will have less movement which transfers to more contact force at the front wheels. I'm assuming you are meaning you think the higher rate spring will unload quicker and more because it is easier to unload due to the higher rate. If not then disregard the rest.

An unsprung spring has zero potential energy. A 600lb/in spring compressed 1" has the same potential energy as a 300lb/in compressed 2" b/c they both have the same 600lb load compressing them. The only reason the spring was compressed to begin with was because of the weight force of the car acting on it and that is why I call it reactive and not active. There is no internal energy other than that stored by the applied weight that acts on the system.

They would both unload at the same percentage rate but the softer spring would have more displacement. Your analogy with one end sitting on the ground doesn't quite work since the angles will be different making the loads on the springs different. When you switch springs in a car with coil overs you adjust them so the ride height is the same. So if you had adjustable perches on your concrete block springs and assume the angle when lifting them was small enough to be negligable then it would take equal force to lift the block off the springs for each case though the 250lb version would see more displacement before this happened. Once again the compression comes from a force applied to the springs and in the case of acceleration this force is independent of the spring rate as the spring potential comes from the body mass.

Of course different rates will effect the how the car reacts and as I stated the effect will be in body/sprung mass/CG movement which is the only downward vertical force on the front tires neglecting internal suspension geometry forces.

[Shadow]

This part is wrong. In fact with less body movement the 600lb spring should unload less as the CG will have less movement which transfers to more contact force at the front wheels. I'm assuming you are meaning you think the higher rate spring will unload quicker and more because it is easier to unload due to the higher rate. If not then disregard the rest.

An unsprung spring has zero potential energy. A 600lb/in spring compressed 1" has the same potential energy as a 300lb/in compressed 2" b/c they both have the same 600lb load compressing them. The only reason the spring was compressed to begin with was because of the weight force of the car acting on it and that is why I call it reactive and not active. There is no internal energy other than that stored by the applied weight that acts on the system.

They would both unload at the same percentage rate but the softer spring would have more displacement. Your analogy with one end sitting on the ground doesn't quite work since the angles will be different making the loads on the springs different. When you switch springs in a car with coil overs you adjust them so the ride height is the same. So if you had adjustable perches on your concrete block springs and assume the angle when lifting them was small enough to be negligable then it would take equal force to lift the block off the springs for each case though the 250lb version would see more displacement before this happened. Once again the compression comes from a force applied to the springs and in the case of acceleration this force is independent of the spring rate as the spring potential comes from the body mass.

Of course different rates will effect the how the car reacts and as I stated the effect will be in body/sprung mass/CG movement which is the only downward vertical force on the front tires neglecting internal suspension geometry forces.

I missed the part where the springs became different lengths? I was assuming the length of the spring would be the same so the angle would be identicle - the 250's being compressed more by the weight.

I still can't wrap my head around a 250lb spring having the same unloading force as a 600lb when the weight is the same? I'll think about it some more and see if I get more than just smoke. (insert cool guy with pipe and cap)

[BadAssPerformance]

I still can't wrap my head around a 250lb spring having the same unloading force as a 600lb when the weight is the same? I'll think about it some more and see if I get more than just smoke. (insert cool guy with pipe and cap)

Think of it this way...

Different rates, but both springs are the same length. Set 1 is 250 lb/in each (500 lb/in total), Set 2 is 500 lb/in (1000 total)

The torque applied to the body while launching puts 500lbs of lift into the front (reduces weight on front by 500 lb)

Set 1 lifts 1" while set 2 only lifts 1/2"

The spring rate is a rate, so dependant on both force compressing it and resultant deflection, not a value of force that it can apply

...or maybe I'm smoking crack LOL

[Shadow]

Think of it this way...

Different rates, but both springs are the same length. Set 1 is 250 lb/in each (500 lb/in total), Set 2 is 500 lb/in (1000 total)

The torque applied to the body while launching puts 500lbs of lift into the front (reduces weight on front by 500 lb)

Set 1 lifts 1" while set 2 only lifts 1/2"

The spring rate is a rate, so dependant on both force compressing it and resultant deflection, not a value of force that it can apply

...or maybe I'm smoking crack LOL

Well, interestingly enough, this May be what I'm missing. I'm thinking of the springs as having a load bearing capability relative to it's rating.

So in my mind, and back to my "brick" scenario, if both springs start out life the same "free length" and same diam coil, so surface contact is also = (I'm Not talking about the diam of the actual steel here, obviously the higher rate spring will be thicker), the 250lb springs (500 total) will have an imaginary load carrying capacity say 500lbs as they compress. The 600lb springs will have 1200lbs load carrying capacity and will Also compress Sig Less.

The simple Fact that the lower rate spring will yield more, giving a Worse angle to pry from sugests that it Will take More force to move it........No?

When I think of your eg. it assumes that the travel Stops when the springs have "unloaded". I'm thinking the motion will continue longer with higher rate springs.

[glhs0426]

This part is wrong. In fact with less body movement the 600lb spring should unload less as the CG will have less movement which transfers to more contact force at the front wheels. I'm assuming you are meaning you think the higher rate spring will unload quicker and more because it is easier to unload due to the higher rate. If not then disregard the rest.

An unsprung spring has zero potential energy. A 600lb/in spring compressed 1" has the same potential energy as a 300lb/in compressed 2" b/c they both have the same 600lb load compressing them. The only reason the spring was compressed to begin with was because of the weight force of the car acting on it and that is why I call it reactive and not active. There is no internal energy other than that stored by the applied weight that acts on the system.

They would both unload at the same percentage rate but the softer spring would have more displacement. Your analogy with one end sitting on the ground doesn't quite work since the angles will be different making the loads on the springs different. When you switch springs in a car with coil overs you adjust them so the ride height is the same. So if you had adjustable perches on your concrete block springs and assume the angle when lifting them was small enough to be negligable then it would take equal force to lift the block off the springs for each case though the 250lb version would see more displacement before this happened. Once again the compression comes from a force applied to the springs and in the case of acceleration this force is independent of the spring rate as the spring potential comes from the body mass.

Of course different rates will effect the how the car reacts and as I stated the effect will be in body/sprung mass/CG movement which is the only downward vertical force on the front tires neglecting internal suspension geometry forces.

I understand a softer rear spring will have more jounce at launch which will unload the front suspension more. Assuming a solid rear suspension and just concerning the front suspension travel am I to understand that a higher rate spring will unload less because it compresses less? When the spring is unloaded the unsprung weight becomes sprung weight and adds mass in front of the CG helping to counter the acceleration force (vertical). To help add mass to the unsprung weight becoming sprung weight more friction would be needed in the control arm pivots, travel limiters would need to be added, or the strut would need to be in full rebound as soon as the front spring is unloaded. ??????

[BadAssPerformance]

Well, interestingly enough, this May be what I'm missing. I'm thinking of the springs as having a load bearing capability relative to it's rating.

Sure, a higher rate spring would potentially have a higher load capability, however, all else being equal for this comparisson, why would that matter as long as neither sping option was compressed to its solid height?

So in my mind, and back to my "brick" scenario, if both springs start out life the same "free length" and same diam coil, so surface contact is also = (I'm Not talking about the diam of the actual steel here, obviously the higher rate spring will be thicker),

Higher rate could be large rdiameter wire, or same diameter wire with fewer coils

the 250lb springs (500 total) will have an imaginary load carrying capacity say 500lbs as they compress. The 600lb springs will have 1200lbs load carrying capacity and will Also compress Sig Less.

Not sure what you mean by "capacity" do you mean "spring rate"? Either way, yes, the stiffer spring will compress less.

The simple Fact that the lower rate spring will yield more, giving a Worse angle to pry from sugests that it Will take More force to move it........No?

Not sure if angle comes into play if everything else is equal, so with either spring option the ride height would be set identical. With the preload force (weight of the front of the vehicle) being the same, the softer option would have longer to travel to completely unload. So when the same unloading force is applied to each, the stiffer option moves less.

When I think of your eg. it assumes that the travel Stops when the springs have "unloaded". I'm thinking the motion will continue longer with higher rate springs.

Why? Even before being completely unloaded, they should only relax the displacement corrsponding to the reduction of compression force applied.

[BadAssPerformance]

Thanks to VNTES for the alignment today! At the Audi dealer the Z got a tad more attention than any of the R8's

[BadAssPerformance]

Link to last run HERE

Changes since the last runs:

-New custom front coil overs, KONI single adjustable inserts, 600lb H&R springs
-New csracer style rear adjustable spring perches, 600lb H&R springs
-Flip-flopped slicks back left to right
-Fresh alignment

Runs from Great Lakes Dragaway (Grove where SDAC-21 was) IMPORT WARS - Puerto Rico Nationals (Yesterday)

Run #1 - Right off the trailer, 30psi, spun thru 1, 2, 3, lifted and coasted

R/T: .272
60': 1.875
330': 5.261
1/8ET: 8.095
1/8mph: 84.07
1000'ET: 10.611
1/4ET: 12.659
1/4mph: 108.01

Run #2 - Better launch but still spun thru 1, 2 missed 3rd, lifted and coasted

R/T: .247
60': 1.738
330': 4.781
1/8ET: 7.562
1/8mph: 81.66
1000'ET: 10.340
1/4ET: 13.068
1/4mph: 77.65

Run #3 - Similar launch, spin 1, 2, 3 ... crunched going into 3 and 4, cut out once at the beginning of 4

R/T: .092
60': 1.741
330': 4.783
1/8ET: 7.240
1/8mph: 104.08
1000'ET: 9.250
1/4ET: 10.979
1/4mph: 131.48

Run #4 - Used 5100 rpm 2-step. More violent launch, more spin (is that possible?) spin 1, 2, 3 ... crunched going into 3 and missed 4 so lifted and coasted

R/T: 1.163
60': 1.766
330': 4.834
1/8ET: 7.229
1/8mph: 106.59
1000'ET: 9.250
1/4ET: 11.229
1/4mph: 108.29

Run #5 - Tightened up KONI's a little, again used 5100 rpm 2-step. Similar violent launch, spin 1, spin and tire shake thru 2, spin 3... crunched going into 3 & 4

R/T: 1.509
60': 1.760
330': 4.813
1/8ET: 7.208
1/8mph: 106.53
1000'ET: 9.209
1/4ET: 10.93
1/4mph: 131.79

Run #6 - Dialed in crank trigger 1/2 thread to try to see if it helped cut out. Used 4900 rpm 2-step. Similar violent launch, spin 1, spin and tire shake thru 2, spin 3 and cut out repeatedly in 3rd I had to get out of it...

R/T: .504
60': 1.762
330': 4.796
1/8ET: 7.213
1/8mph: 103.73
1000'ET: 9.461
1/4ET: 11.709
1/4mph: 95.12

Conclusions?

New suspension consistantly worth a tenth in the 60' over previous setup. Still needs tuning, maybe play with rates a little. 22Shelby got some video, no more lift in front, still squats in rear.

So.... in no particular order, still gotta:

- Trouble shoot the cut out (ordering new crank trigger tonight)
- Tear apart the trans and unfuk 3 and 4
- Trouble shoot data logging and see why it stops once in a while mid run (bad cable connection or RS-232 port?)
- Decide if I want to go stiffer in the rear or try this again
- Figure out how to fit 26" tires on it

[Reaper1]

What is being neglected here is inertia! The spring and the suspension parts will both have inertia that will cause the suspension as a whole to extend and KEEP extending in a dynamic situation. Remember that springs that hold in energy, then release it oscillate. The don't just stop at the free length of the spring when they release the energy, they extend beyond that. This is where dampers come into play, and having the ability to adjust the RATE at which the spring can release its energy, or have energy passed to it is VERY important.

Just having stiff springs might not be the sing answer here as you can end up making things worse. Providing the proper dampening to the system is PARAMOUNT to control the energy transfer.