AJ Petersen
Performance Speedtech, LLC
215 Performance Lane, Building 1
Cresson, TX 76035
performancespeedtech.com
(877) 512-5180
Didn’t get enough Viper tech tips in the November 2013 issue? Have some more.
Purchase a rear lower shock mount that changes the spring motion ratio. These run about $500-800. The geometry change corrects the motion ratio and ride frequency of the suspension.
A mono-ball suspension arm takes friction out of the suspension arms. It also gives the car a quicker response to the road and driver inputs. You will feel more connected with the road and the car. Suspension arms with spherical bearings or mono-ball bushings will cost around $3200.
The factory allows for bump steer adjustments. You can purchase the shims from the Dodge for $100. The shims will set the height of the front steering rack and the height of the inner rear ball joints to affect bump steer. We have found that it is relatively easy to get the car to have a toe change of less than 0.020-inch through 3 inches of vertical wheel travel. We measure bump steer with a plate that is the length equal to the outer diameter of the tire. Some shops use a 13” stock car plate. We increase our resolution for adjustment with the larger plate. This makes the car very predictable and easy to drive on the edge of tire grip.
Make certain that the rake and corner balance is set properly. The rake is very important to the balance of the Viper.
Change the ball joints to a low friction height adjustable type. You can change the roll center front and rear with this type of ball joints.
Set the proper rear caster setting. You can set the rear caster by adjusting the rear lower control arm position. The magic number is 1 degree or so. This will help the car transfer power to the track.
If you haven’t done it already, change the brake lines to steel braided Teflon lines.
Keep similar rolling circumferences on the tires as supplied from Dodge. The ABS is tuned for this setup. Braking performance is decreased with a smaller rear tire.
This probably should be first on the list, not last!
You must have a race seat with an appropriately installed harness to run the car with sticky tires. Expect to spend at least $2500-$3000 installing driver and passenger seats and harnesses in the car. Look at brands that promote FIA-approved seats and harnesses. We recommend Sparco, Cobra, RaceTech, Schroth, and Sabelt brands. The seat/harness will not only protect you in a crash, but also give you support to drive the car instead of hanging on. Also make certain that the installation will allow for proper use of a HANS device.
This car is hot to drive on the race track. It is proven science that the cooler your body temperature is, the quicker you can react and make decisions. This car does not like to have the air conditioning running while on track. We suggest that you install a Cool Shirt system to keep you cool and sharp for track sessions. The systems start at about $500 complete with shirt.
There are several options on tires depending upon the service of the car. The Michelin street tires are very capable on the track in the factory sizes. In fact, the ACR was sold with Michelin Pilot Sport Cup tires installed. However, the car comes alive when the front wheel size is changed to an 18x11 from the OEM 18x10. Even with all of the horsepower, the car tends to push with the narrow front wheel.
The 18x11-inch wheel will allow tire fitments up to 320mm wide. With an 18x13 or 19x13 rear, we can run tires up to the 355mm wide. We strongly suggest that if you run an 18-inch rear wheel that the tire installed be of the same height as the OEM 19-inch wheel and tire. This helps keep the rake in the car and suspension geometry as designed by the SRT engineers. It also helps systems such as the ABS stay within maximum performance. So, with the 18-inch rear, run a 345/35R18 tire. For a Michelin race slick, use a 31/71-18.
Don’t waste your time with the cheap imitations. Purchase the SRT-engineered wing elements that were designed for the car. That would be a wing from the FIA Competition Coupe or the ACR-X. These are optimized for the way the air moves around the body and the greenhouse.
The same goes for the front splitter and undertray. The SRT-engineered splitters are fit with venturi-type shapes on the underside to add downforce. Just install the splitter with care and seal the fascia to the splitter to prevent air from running over the top of it. Also, remove the grilles from the vents in the hood. They are just cosmetic parts and air will flow better without them. If you do not have vented hood, get one. It improves engine cooling and downforce.
Add the complete ACR-X dive planes to the car. They work. Make certain that they anchor well to the front fascia.
great tips, keep posting :)
Great article thanks for the tips as I'm looking to modify my viper suspension for track and this is very helpful.
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