Ok Street Stockers, I am not an expert on this series having never raced it. The closest was Hobby Stock class where we had a whole lot of latitude in car modification. Raced a 64 Ford 390 and was a blast when I was 15.The Street Stock class is very limited on modifications you can make LEGALLY. Most rules cover Midsize Metric cars made by GM from 1978 to 1987. Monte Carlo, Chevelle, Camaro, Firebird, Nova, Malibu, Cutlass, Grand Prix, Regal. The Full size Metric cars are Cadillac Impala, Caprice. Can be a good choice but so heavy not worth it on the crummy spec tires we have to use. We will concentrate on Monte Carlo and the Camaro.To win we need a very good edge and the front roll center is the number one thing we can change to give us that edge. We have to relocate it and make it work to plant the hard spec tire so the car will turn.
A subset of this is the camber build for optimum tire contact patch. Once we rework the front suspension to get these two we are on the way to max handling Street Stocker. These modifications are labor intensive but pretty cheap compared to dollars spent elsewhere.You need chassis software. Buy it. Map the front end and find out what you have with Roll Center location. Do not pass GO and collect the Win $$ if you are not doing this.
When you plug in your stock chassis numbers in the software program you will to find the present Roll Center.
Next you need to start gaming the software by changing BJ heights and locations.
Two things we need to know. Lower A-Arm lengths and spindle height. It is assumed the rules let you use aftermarket ball joints and aftermarket bushings in the A-Arms. It let's you use custom Upper A-Arms as long a location is stock. Let us assume you have the talent to ream out taper holes for bigger tie rod and ball joints and i assume you can modify the drag link to get proper bump steer. If you do not know how, learn to or be happy with being a back packer. Racers are innovative mechanics, not part replacers!GM short light metric spindles that came on all midsize GM cars from 78-87 and 2wd S-10 trucks are 7 ½” tall and these spindles have 4 3/4 bolt pattern and 11” brake rotor.
All of the short spindles dimensions are same relative to ball joint location and tie rod centers. Pay attention to the differences in outer bearings depending on what year and model. Tie rod taper may not be the same so ream it.All of the Full size Metric cars have the 5 on 5” bolt pattern and 12 inch rotor. Came on heavy duty applications like limos, station wagons, and mid-70s full size cars like Cadillac Seville , Fleetwood, Buick Riviera, Oldsmobile, Pontiacs Chevrolet, Buicks.
These are way too heavy sprung weight and not worth the effort.The Chevy Impala spindles are the " hot set up " on a mid-size metric chassis. Big Chevy Impala and Caprice 1980 to 1990 full size metric spindle is 8 3/4” tall used 11 diameter brake rotor on 5 x 4 ¾” bolt center.
Options I found are Ford Granada, Mustang II , Ford Pinto spindle is 7. 625” height. These are E mod options not recommended for heavy Street Stocker.Let’s look at a 4th generation 1981- 88 Street Stock 1986 Monte Carlo.
Stock chassis suspension mounting points front and rear, stock lower A-arms. After market upper A-Arms.
We add aftermarket longer ball joints in lower A-arms to raise the spindle .75" and we add longer upper ball joints to add up to an inch more height to the upper tube A-arm. This raised the front Roll Center to about 3 to 3.5 Inch we wanted but only moves the RC to the right about 1.5 inch. We need at least 3 inch offset to plant the right front tire.
The other factor was our camber build curve was pretty poor and bump steer needs fixing. The car is drivable and a lot better than the way it was but not as good as we can make it with these lame rules.Lets look at a project car in Steve Smiths books “Street Stock Chassis Technology”. Stock 1978 Camaro has front Roll Center of 0.487” above the pavement. Bad negative camber gain 2.9° in 4 inches of bump and neg. 1.17° in 4 inch rebound (droop).
Bump steer needed work too. After lowering the car 1 inch and adding 1” longer ball joints to stock Right side upper and lower A-Arms the RC was 2.75” height and better camber change. Next the right front lower BJ was moved out ¼” and the left lower BJ was moved in ¼”. Lowering the right front upper A-arm inner pivot points .5 inch each and lowering the right front tie rod end down 1 inch got us front RC of 3.375” height and right front camber gain is 1.47° per inch. They added a taller AFCO lower ball joint on left front lower A-arm to put camber gain in ball park, We still have bump steer to fix and need rework drag link and the front Roll Center location is left about 3 inches. A lot better but not as good as we can make it with a little more work.Goal – move Roll Center to 3 inch height and 3 inch offset to the right (paved track) 4 inch offset to right on dirt.Looking at the stock A-arms on GM metric cars we have 14.25” length from the frame mount to the ball joint center, this is for 1978 and up GM metric cars like Monte Carlo,
1978-1987 Metric Impala lower control arms are 16” length , 15.31” wide and these work on 73 to 77 Chevelle, 70 to 81 Camaro and 75 to 79 Nova.
1967 – 69 Camaro, 1968 – 1974 Nova lower A-arm is 16” length but 13.25” wide.The Nova lower A-Arm conversion on a Metric car will move the lower ball joint out 1.75 to 2 “ and forward 1.5" to 2" to correct camber gain. You will make the front end wider by about 3 inches. You need a full custom upper A-Arm with adjustable upper A-Arm screw in ball joint or similar. It is possible to retrofit the Nova 16” center to center lower control arm to a Metric frame using proper control arm bushings. You will need to modify and change several things on your car to use these. These control arms use 5" OD springs, longer tie rod ends (which get very close to the control arm. Use custom fab Upper A arm as the typical metric upper control arms will not work. The stock Metric ball joint cannot be used with this control arm so reaming of the spindle for different upper and lower ball joints will be necessary as well. Installing these control arms on a Metric car is a complete front suspension redesign and certainly not a bolt on swap. Be prepared to move the lower ball joints toward the frame or away from the frame before you weld in the screw in ball joint thread ring.
Finally, you need to use Impala spindles to compete the camber gain and end up with the 3 inch roll center offset. The 1 inch taller spindles mean you can run level lower A-arms and angle the upper A-arms for the proper RC offset and still have good camber build.Tips for the metric rear end. Figure out how to put some rear roll over steer in the car. You want the wheelbase to shrink on the left side and grow on the right side when the body rolls in the turn. Start with left lower trail arms a little uphill on the low left side and right side level. Soften the bushings in the trail arms so the left side moves forward and the right side moves to the rear. Rubber bushings can be drilled so they collapse in the direction you want. The rules may say you can use metal bushings here but the obvious advantage means you use rubber bushings. Put in 5 to 8 ° pinon angle down.I might have missed something in the research but this is as good as I can do without building one in the garage.
RM
