Asphalt Modified With Dirt Setup
I have a '97 Ellis IMCA Modified. I can get the car very fast and I've been the fastest qualifier, but the problem I've been having is my car falls off very fast by 5 to 10 laps. I can't seem to find a balanced setup that stays consistent for 30-50 laps. I usually qualify at a 15.06 and at the end of the race I'm typically running a 15.50. I race a 3⁄8-mile asphalt track, with about 8 degrees of banking. I run Goodyear Eagle Short Track Special tires.
My spring rates are: LF 500, RF 550, LR 175, RR 125. I've tried a lot of different rear springs, as much as 200 LR and as light as 100 (and the same on the right).
I run Pro Shocks and my shock rates are: LF 735, RF 75, LR 93, RR 94.
Panhard bar: left axle 14, right 15¾, roll center 3.0 inches high and 2.0 inches to the left of center, and with dive and roll moves to 0.7-inch high and 4.8 inches to the left.
My scale weights are: LF 685, RF 545, LR 815, RR 508, for a total of 2,552. This makes left 58.7 percent, cross 53.2 percent (with bar), 51.9 (without bar), sway bar (175 pounds) is preloaded seven turns from neutral, and rear is 51.8 percent.
The problem you have is that you're running a dirt setup on asphalt track. This will never work because it's badly out of balance. For starters, your spring rates, Panhard bar height, and crossweight are all wrong.
The rear spring should be matched and I would go with a pair of 175s. Lower your Panhard bar to around 12 left side and 13 right side. The crossweight is low for your higher rear percent and should be more like 56 percent.
Never preload a sway bar that much. One to three turns is plenty, even for a small thread adjuster. I wouldn't go more than two turns and usually snug it up and that's it. Adjust your crossweight with the sway bar preload in. That way you know you have the correct cross.
Look closely at your left-side tire temperatures. When the car gets balanced, they should be nearly even. Your LF should have been cool compared to the LR. The suggestions I have given are for a generic Modified and may not perfectly match your car. So, to fine-tune the setup, move the Panhard bar up or down to adjust for left-side tire temperatures and at the same time, adjust the crossweight for handling balance.
Email me and let me know what's happening and how the changes worked. I'm always curious as to the outcome of these changes. Remember that there are other considerations beyond setup that influence the car, such as front and rear wheel alignment and Ackermann.
If you have comments or questions about this or anything racing related, send them to my email address: Bob.Bolles@sorc.com, or mail can be sent to Circle Track, Senior Tech Editor, 9036 Brittany Way, Tampa, FL 33619.