2004 Chevy Silverado - Silver Autocross

My '04, pre-mod Silverado....        read full caption My '04, pre-mod Silverado. The key to my buildup is the optional ($375) all wheel drive AutoTrac transfer case. The AWD setting sends power to the wheels with traction just like the SS truck. While there is about a 300-pound weight penalty, it allows for phenomenal traction at the drag strip with a relatively narrow all-season tire. An additional benefit is the ability to switch over to 2WD for dyno tuning, slightly better mileage and the occasional burnout.

This view shows just how high...        read full caption This view shows just how high a stock Silverado K1500 regular cab is lifted in the rear. While this stance allows for a 9200-pound towing capacity it looks odd in person and detracts from the ultimate handling capability. I focused my suspension efforts on the rear and worked forward.

Right now, the GMHTP faithful are left with precious few options for RWD V-8 performance while we wait for a Camaro replacement. But one of them is an AWD, 325 c.i. V-8 powered, 4.10 geared, four wheel disc brake two seater that can be yours for under 30 grand--if you are willing to get behind the wheel of a truck.

Chevrolet and GMC trucks are available in just about every configuration imaginable, with the exception of the one that seems most obvious to the readers of GMHTP, a Silverado SS regular cab. For the past several years Chevrolet and John Moss have conspired to bait us with the promise of a reasonably priced Regular Cab SS model with the plan of switching us into a stylish but underpowered extended cab model. When I realized the Silverado SS regular cab shown at SEMA last year was just another tease, I decided to take matters into my own hands and headed to the Chevy dealer to option out a regular cab truck that, with a little help from the aftermarket, would satisfy my need for a reasonably priced and performing daily driver. A quick test drive in a Silverado SS provided a baseline for ride, handling, and acceleration. Choosing a regular cab 1500 model narrowed the largest engine option to the 5.3 and transmission to an automatic. Luckily 4.10 gears, AWD transfer case, locking differential, and towing package are available options. As luck would have it, the dealer had a 5.3 AWD truck optioned out perfectly for my little experiment, and after a little haggling I was driving home in a 2004 Silverado for significantly less than the $29,620 sticker price.

After leaving the dealership I arrived at a red light, and I figured it was time to see how badly the 5.3 and 4.10 gears would shred the 245/75-16 tires. The light turned green, I put the hammer down, and then...crickets chirping...nothing. I meekly crawled away from the light, and finally at about 4000 rpm the 5.3 started to show signs of life. It felt good up to the 1-2 shift, where it suddenly fell on its face for a geriatric shift into second gear. After checking the window sticker to confirm I bought a 5.3 not a 4.3, I suspected torque management was the problem. While underwhelmed by the Silverado's performance I knew it had potential, it just needed an attitude adjustment.

In this story I use HP Tuners' VCM software to remove the factory imposed limitations on the 325-inch powerplant, and make a series of systematic changes which I hope will exceed the handling and acceleration of the Silverado SS while matching its excellent ride quality and road manners. While some of my results are subjective I also intend to quantify my results at an autocross course. Many of the modifications are specific to 4x4s or regular cab trucks, but all '99 and up full size Chevy trucks can benefit from some of these mods.

In the next episode I'll install Stainless Works' new full length headers and cat-back and follow up with a wideband dyno tune session using HP Tuners' new wideband interface.

Notice the steel lift block...        read full caption Notice the steel lift block sandwiched between the axle and leaf springs. This "marketing decision" block provides about a two-inch lift in the rear and adds ten pounds of unsprung weight to the solid rear axle. Removal of the blocks require a set of 2WD U-bolts (p/n 15002781) and about an hour of work. The two-inch reduction in rear height provides a more neutral stance, eliminates axle wrap during part throttle launches, and drops ten pounds of unsprung weight. This is an inexpensive and easy mod that I would recommend to anyone with a 4x4 regular cab unless they plan on utilizing every bit of this trucks 9200-pound towing capacity.	Longer leaf spring shackles...        read full caption Longer leaf spring shackles from DJM (SH2599-2) will lower the rear another two inches. Jacking and supporting the axle correctly will make this a simple and safe mod, just be sure to follow the included instructions. These drop shackles would really benefit from a grease fitting like Hotchkis uses on its sway bars, as they started to squeak shortly after installation.	Removing the lift blocks and...        read full caption Removing the lift blocks and adding the drop shackles resulted in about a four inch drop in the rear and reduction in suspension travel. Cutting off about an inch from the rear bump stops will prevent the suspension from bottoming out.
Up front, 4x4s and some 2WDs...        read full caption Up front, 4x4s and some 2WDs use torsion springs in lieu of coil springs. The torsion spring suspension is preloaded with a key that is sometimes referred to a "pork chop". The key uses a bolt to change its clocking relative to the axis of the spring, which changes the preload on the spring and consequently raises or lowers the front of the vehicle.	To lower the front of the...        read full caption To lower the front of the truck I turned the bolts counter-clockwise seven complete turns, resulting in about a 1.25-inch drop which is just about the limit for the stock keys. Offset keys are available which will drop the front 1 to 3 inches, but keep in mind ride quality decreases as you reduce bump travel.	As torsion rods have a very...        read full caption As torsion rods have a very linear spring rate, bump stops are used to provide a more progressive spring rate as the suspension reaches the limit of its bump travel. Notice how the factory bump stop just contacts the lower control arm at stock height.
Unloading the torsion rod...        read full caption Unloading the torsion rod as stated above will require trimming the bump stop. Mine are probably a little too short for optimum ride quality.	Any time ride height is altered...        read full caption Any time ride height is altered an alignment is required. Front end alignment is an overlooked and inexpensive way to improve handling characteristics regardless if you are autocrossing or drag racing. Factory alignments are typically set up conservatively, as understeer is considered a safer condition at the limit of traction. Since Chevrolet sends the Silverado SS out the door with about one degree more caster than the K1500, I chose the SS's caster spec as a starting point. My local alignment shop, Dunivin's Corner in Woodbridge, VA, is staffed by SCCA racers and they recommended -.25 degrees of camber and 0 degrees of toe-in. This picture was shot immediately after the autocross with about 42 psi. The 60 series tires kicked ass and never rolled over onto the sidewall.	For wheels I chose a set of...        read full caption For wheels I chose a set of 18-inch Mille Miglia Mesas, as the basic shape roughly looks like the C5 Corvette Z06 wheel (seen here at the auto-X alongside a Z06). A trip to the local powdercoater for the gun metal gray finish completed the look. I chose a set of 265/60-18 Kuhmo STXs from Tire Rack. The 265mm width increases traction while maintaining competent all-weather and road handling characteristics. The 18-inch wheels and 60-series sidewall provide a comfortable ride and the same 30.5-inch diameter as the stock 245/75-16s. If you choose a non-stock tire diameter, HP Tuners' VCM software easily corrects speedometer calibration. The Kuhmo tires provided impressive road holding capability, but do add a noticeable bit of noise at highway speeds.
OEM 4x4 shocks were just too...        read full caption OEM 4x4 shocks were just too soft to deal with the reduction in suspension travel. As I was looking for ride quality and handling improvements I chose a set of Bilsteins (P/N BE5-6081-H0 and BE5-6082-H0). After a straightforward installation, the maddening bobbing up and down on the highway was eliminated and the truck felt more composed under braking and acceleration. Although body roll was still a problem it was more predictable. The base 4x4 shocks are so bad I should have upgraded to Bilsteins or Edelbrocks as my first mod. Notice the factory lift block is no longer stuffed between the axle and leaf spring.	With the ride, handling and...        read full caption With the ride, handling and stance squared away I turned my attention to the underachieving 5.3. Torque management was the primary culprit, and I would have to delve into the Vehicle Control Module to fix this. I chose HP Tuners version 1.5 VCM software for its integrated approach to flash, edit, scan, and wideband O2 capability. The HP Tuners cable connects right below the headlight switch to the OBD-II port. HP Tuners software is incredibly powerful, feature rich, and somewhat cryptic at times. As I had never edited a VCM or PCM before, I found HP Tuners somewhat frustrating until I took the time to educate myself using the help menus, accessed using the F1 key, and the forums at Hptuners.com.	While you can use a desktop...        read full caption While you can use a desktop computer, a laptop is best as it allows real time data logging on the road using the HP Tuners Scanner. If your laptop does not have a serial port, PC card to serial port adapters are available. Avoid USB to serial port adapters as they have latency issues, which can result in a disabled vehicle due to a corrupted upload.