When I learned that my friend needed help setting up his dirt hobby stock car, I jumped at the opportunity. This little project allowed me to apply some of the technology we provide in CT to a car with limited adjustment capability. Once we got into the car, I was surprised by our discoveries. What we do to this car can also be done to a Street Stock or similar type of car.
The problem with this car that was had built late last season was that it would not turn well and as a result would push on entry and go loose on exit. There are probably a few thousand or more teams in this country that have the same problem. So, I saw an opportunity to jump in there, do an evaluation to try to fix it.
The car is a 1985 Monte Carlo and has the metric four-link rear suspension, a stock frame throughout and must use stock type springs in their original positions. The shocks are mounted in the stock positions and the car has retained all stock suspension parts.
As with most “stock” classes, teams are allowed to trade stock pieces from other model year cars as long as the brand is the same. This class also runs large Hoosier racing tires all around where-as the street stock classes are only allowed one racing tire on the RF.
Breakdown – The first order of business was to weigh the car on the scales and measure and record the ride heights and the spindle heights for future reference. We wanted to maintain the original ride heights after installing new springs so the geometry would be the same and we needed to know the spindle height so we could check for proper clearance and make sure there was no bind of the ball joints while the car was on jack stands.
We then proceeded to break the car down and remove the springs and shocks to see what we had. To get the front springs out, we had to remove the upper ball joints. This gave us a chance to inspect everything up close. My helper, Kenny Hellyer, was very familiar with the mechanics of these cars and was a definite asset in all of our re-design work.
The first problem we noticed was that the shocks on both sides in the front were rubbing on the inside of the height adjuster that was put into the car not to jack weight, but to create the ride height that was necessary to avoid bottoming out. The rear of the car had legal spring height/weight jacking, adjusting bolts.
The shock contact was so bad that one shock was leaking and both housings were bent severely. These were aftermarket twin tube shocks and still seemed to be working. I tried the standard method of checking them by placing one end on the floor and pushing in from the top. The shocks were so stiff that they barely moved.
I don’t know if someone chose really stiff compression numbers or if the shocks might have been bent, but these units were not helping the situation. On dirt, we must have shocks that will allow the car to run over the holes and bumps and move fairly easily. They must control the springs, but not be so stiff as to cause the tire to skip or bounce.
Front Geometry – I inspected the front geometry and noticed that the car builder had used the taller Impala spindles which reduced the lower control arm angles. He also had lowered the upper control arm mounts to gain more upper control arm angle. Both of these changes are highly recommended for this class. Using taller spindles actually improves both upper and lower arm angles.
The geometry I saw looked a lot like previous cars I have fooled with in the stock classes and I knew the moment center was close to where it needed to be, at or very near the centerline of the car. Had this work not been done, we could have expected the MC to be somewhere outside the car making the front end overly stiff.
The cambers were not what I would have expected or chosen. The LF was a little less than one degree and the RF was around 5 degrees. This is typical of a car that transfers a lot of load to the RF as that tire is forced to carry most of the front load and work hard to turn the car. The LF doesn’t need camber because it isn’t working very hard anyway. We needed to make camber changes to reflect how the front end would work after the redesign.
We reset the cambers to a positive (+) 2.0 on the LF and minus (-) 3.5 at the RF. Once we re-spring the car to allow a more balanced setup, the LF tire will definitely be working harder and take some of the load off of the RF tire. So, we would end up needing more LF camber and less RF camber. Our tire contact patch will be optimal with these changes.
Inspection of the caster settings revealed that the RF caster was in the negative range (upper ball joint forward of the lower ball joint) and the left side was positive. That would cause the steering to want to turn right, maybe good for sliding the car through the turns, but we were going to make this car turn well, so I opted for a different plan.
We moved the right upper ball joint back to create about two degrees of positive caster and that matched the left side caster. This way, the steering would be neutral and the driver could steer both directions without feeling a difference in resistance.
We were a little worried about possible binding of the ball joints with the increased upper control arm angles. So we cycled the spindles beyond what they would see on the track and found we had plenty of clearance. Always check to see if there is any binding or tightness in your suspension while you have the springs and shocks off the car.
Spring Rates – We next checked out the spring rates that were installed in the car. The fronts were marked as: LF = 1100 lb./in. and the RF was 1200 lb./in. The front springs had a half round of the coil cut off, so the actual rate, although we did not measure them, was obviously higher than they were marked.
The rears springs were: LR = 225 and the RR = 150. The rear had too much spring split, even for a Metric 4-link rear suspension with a high roll center. With the front spring rates being so high, this combination in the rear caused a lot of load to transfer to the RF on entry and through the middle of the turns overloading that tire. That would definitely help cause a push.
After careful consideration, we installed the following springs: LF = 900, RF = 850, LR = 225, and RR = 175. The front reverse spring split with the softer RF spring helps corner entry and promotes front roll angle while the reduced spring split in the rear facilitates the high Metric moment center to help control the rear roll while not going too far.
Here is a further explanation of this. For a balanced setup, we need for each end of the car to desire to roll to about the same angle in the turns. We have discussed this concept many times in Circle Track. A high rear moment center reduces the desire to roll, so if we don’t soften the RR spring, the rear will be stiff and not allow proper compliance.
That would overwork the RR tire and cause a loose off, if not totally loose, condition. Running a RR spring that is too soft compared to the LR spring would have the opposite effect. The rear would want to roll over more so than the front and the car would be tight, or tight/loose off. There is an optimum spring split, RR softer, that will keep the car close to a balanced dynamic state and help the car on entry, through the middle and provide more bite off the corners.
Shock Installation – Because the front shocks were hitting the spring height adjuster, we needed to make a correction. We noticed that the stock hole where the top of the shock was anchored was positioned at the factory well towards the outside edge of the spring on both sides of the car. With stock shocks and springs, this would work for clearance, but with our setup and equipment it was not.
The fix was to create a new “stock” hole farther inward and closer to the center of the spring. We reinforced this new hole by welding a washer on top of the frame. This provided a good bit of spacing between the spring spacer and the shock body.
To make sure we were good with the rules against using front weight jackers, we welded the height adjuster so it would not turn. This made it a spacer rather than a weight jacking device. We also installed a new set of gas pressure “stock” replacement shocks that were made for racing and more like what should be used on this type of car.
Tire Pressures and Sizes – I reviewed the existing tire sizes versus the tire pressures they had been running. The sizes were LF = 83.75, RF = 83.75, LR = 84.5 and RR = 85.0. This only allowed a half inch of stagger in the rear, not nearly enough for this track. This too would facilitate a tight car.
The cold tire pressures they had been running were: LF = 17psi, RF = 23psi, LR = 15psi and RR = 14psi. The RF was high and the RR was low on pressures. The fix was to try to change the tires around while re-pressuring the tires so that we could get front and rear stagger.
I traded the RF tire and the LR tires. This put a larger tire at the RF and a smaller tire on the LR. We re-pressured the tires to: LF = 18psi, LR = 16psi, RF = 22psi and RR = 16psi. With those pressures, we now had a front stagger of 1.00 inch and a rear stagger of 1.50 inches.
Weight Distribution – When we weighed the car before making any changes, the cross weight was at 53%. After installing the new springs, changing the front caster and camber, moving tires around and adjusting tire pressures, we re-set the cross weight at 48.5%, or about 75 pounds of left rear weight.
With only 48.2% rear weight, the car did not need the 53% cross which represented 216 pounds of left rear weight. This was yet another reason why this car was way too tight. It was cross weight tight and was driving off the left rear tire under acceleration.
Another thing I noticed and corrected was the placement of lead in the rear of the car. The car builder had placed a considerable amount of lead well behind the rear end, on the rear hoop that protects the fuel cell. Although fairly common, this tends to create a cantilever effect and increases the polar moment. Polar moment is defined as a force trying to rotate or swing the rear end to the outside wall during cornering.
Some teams will experience a more neutral car by placing lead well behind the rear end, but this is more like a crutch for a tight car and although it helps the car into and through the turn, it will make the car loose off. It is much better to set up the car correctly and get the front to turn with a balanced spring setup and proper moment center and cambers. That way, you get into and through the turns better and still have more bite off.
It is always a good practice to keep all lead mounted inside the axles. We may decide later on to move it out, but for now we remounted the lead in front of the rear end and high in the car. A higher center of gravity is desirable on dirt cars for dry and slick tracks.
The Results – Once we got the springs installed, the tires mounted, the cambers set, the air pressures set and the ride heights and weight distributed like we wanted, we stood back and took a look at the car. It just looked better right away. I’ve seen lots of hobby stocks and this one looked like it was ready for the track.
The first chance we got to run the car, the driver noted that this car was now even better than his original Hobby Stock. The difference was that it turned better which allowed him to maneuver past guys that were hanging it out trying to point the car to get off the corners. And it had much more forward bite than before due to the more straight ahead attitude.
With his smooth and relentless style, this car was just what he wanted. If you prefer to sling the car in sideways, fight to get control and then hope for some semblance of bite off, then you might not want to copy us. Good luck and good racing.
Sources:
Afco Racing
www.afcoracing.com
800-632-2320
Allstar Performance
www.allstarperformance.com
269-463-8000
AR Bodies
www.arbodies.com
615-643-8827
Capital Motorsports Warehouse
www.cmwraceparts.com
800-278-2692
Five Star Bodies
www.fivestarbodies.com
262-877-2171
Harbor Freight
www.harborfreight.com
800-423-2567
Moser Engineering
www.moserengineering.com
260-726-6689
Optima Batteries
www.optimabatteries.com
QA1
www.qa1.net
800-721-7761
Quick Performance
www.quickperformance.com
515-232-0126
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