The K9 Modified/Sport Modified has had an interesting life. It all started with a garage build based on a 1978 Malibu metric chassis back in ’06. Sean Stewart raced it at Mohave Valley Raceway and Victorville Auto Raceway. He wanted to sell the car and advertised it around where it finally ended up in my hands late last year.
Over the winter and in the racing off season, Mike Gibson at Victorville Auto Raceway decided to start his own Sport Modified Class. The rules for this new class were a bastardization of the IMCA Northern Sport mod and IMCA Southern Sport Mod rules. As the season approached, talk of some of the local favorites moving into the new Sport Mod class started growing and getting bigger on the message boards. Onedirt.com was just getting started then, so we got to see a lot of the internet chatter about this class. It was looking like the new sport mod class was going to be very popular. It was at that time I decided to join the cool people and convert the K9 car into a sport mod.
When the K9 car was built, the rear suspension had swing arms on both sides. According to Sean, “the car would raise the left front tire way off the ground and people loved it and started calling it the claw. The car was a real crowd pleaser with the tire up so high.” But Sean found it hard to control and even harder to see the track when the front left came up so he adjusted the car. By the time it came into our project car family, the rear end was setup in what we called a “poor man’s four link”. There was a swingarm on the left side with a Bilstein easy up coil over shock and a AFCO 325 lb spring. The right rear was a three link with an AFCO 250 spring on a perch on the axle tube and an AFCO shock. The right front had an AFCO 800 lb spring and a pro shock. The left front had a 750 lb AFCO spring and AFCO Shock.
The torque absorber or pull bar was an AFCO progressive spring pull bar and the rear end was located laterally by an AFCO adjustable J-bar. While I like the idea of a lot of really nice suspension components on the rear end, it wouldn’t fit into the rules of the new Sport Mod class which specifies that nothing can be mounted on the lower control arms and it must be either an OEM stock design, a multi leaf spring design or an aftermarket three link design. Most of the cars I have seen are using the aftermarket three link designed system which the rules also require a minimum 16 inch lower control arms (of equal length left to right), one pull bar with rubber biscuits, and a 23 inch pan hard bar located behind the rear end housing.
I understand the reasoning behind these rules. These were designed to give an older chassis car with a three link suspension a chance to be competitive in a class of their own, and to prevent racers from attempting to run the IMCA modified class and the Sport Mod class in the same vehicle. Having seen enough IMCA mod races at Victorville, I really liked the idea of a less destructive class to run in, so we decided to convert the K9 car into a Sport Mod.
Out came the “poor man’s” 4 link, the J-Bar and the Spring loaded pull bar. In order to add the long pan hard bar behind the rear end housing, I had to add an additional bar to the rear chassis frame. Unlike many of the modified chassis designs, the K9 car did not have frame rails running below the rear end (underslung). K9 was designed so that all the frame rails in the back were above the rear end housing. That was one of the reasons that I liked this car. Thinking that the weight placed up higher in the chassis would help the roll oversteer, I fell in love with the design. The only drawback to this design is, adding a long roll bar. That’s just my luck. After some cutting and welding, the bar was added and the three link conversion was completed. Now the K9 car is back in the shop for scaling and chassis setup before getting out on the track on the 25th.
Next step is to square the rear end to the chassis, set the front end alignment, and scale the car. Part of the set up that we will be checking with the rear end squaring procedure, is the lower link angles and pull bar angle. We have not had this car on scales to this point, so everything is pretty much going from scratch set up. I am staying with the shock package that Sean ran on the car Here’s my target numbers:
Target weight: Over 2,550 lbs with driver and minimal fuel load to meet the track’s minimum weight requirement after race.
Left Side weight: 54% (no left side weight requirements in the rules)
Rear Weight: 56%
Cross Weight: 49-51%
LF: 5.0 RF: 5.5
LR: 5.5 RR: 6.0
LF: +2.5 degrees
RF: +5.0 degrees
LF: +1 degree
RF: -3 degrees
1/4 inch initially for stability. Second run at the track we will reduce the toe to 3/16ths of an inch.
We’ll see how close we can get and how she does on the track.
Additional photos of the suspension additions: