photos by: the author
We give Blue Magic a shot of adrenaline with a Brian Tooley camshaft upgrade!
The beautiful thing about the 4.8/5.3/6.0 series of truck engines Chevrolet used from 1999-2013 is their positive response to performance upgrades. Cams, intakes, exhaust, headers, throttle bodies, computer tuning – all the usual late-model performance mods give positive results when installed on these engines.
In our first story on “Blue Magic,” our nitrous-equipped 2004 Silverado test mule, we upgraded the exhaust, installed new ignition wires, and threw a fresh tune on the computer, resulting in 267 peak horsepower and 310 pound-feet of torque, over our baseline of 248 horsepower and 293 pound-feet of torque.
Any future mods for the truck would be very limited because of the weak factory cam. Not that the factory designed a bad cam profile, just that it’s a design meant to generate low RPM torque and horsepower for moving a truck (and its load) around. These cams typically run out of power between 4500-5000 RPM, and that’s where things are just getting started in a performance engine, especially in one running nitrous.
Over the years a number of grinds have been designed for the cathedral port head truck engines, ranging from mild performance RV cams to high-winding profiles that make the truck engines act like their F-Body and Corvette brothers. While the peak power numbers see healthy increases, the largest gains are had on the top end, well passed where the factory cam would fall on its face.
After doing some research and looking at the different options available, we decided to call Brian Tooley Racing in Bardstown, Kentucky. Brian has been in the performance business for over 20 years, and has taken his extensive experience of flow-testing and designing cylinder heads to create cam profiles that make the most of the head/engine combo you have. In particular to 1999-2013 truck engines, we asked Brian about his philosophy when it comes to cams for the truck engines.
“Truck LS engines have lower compression than the engines installed in cars. Often people mistakenly want the same cam as their LS1/LS2/LS6. It will sound good and make good high-rpm power, BUT the weight of the vehicle, the deficit of cubic inches, and the lack of compression will make the truck’s acceleration rather lackluster. It will make less peak horsepower, but will be faster due to the under peak broad range of power applied.” -Brian Tooley
Brian explained that a common mistake with LS cam profiles is a ramp rate that is too aggressive and/or too much lift, particularly on the exhaust side. If you’re unfamiliar, the ramp rate of a cam is how fast it opens and closes the valves. When too aggressive a ramp rate is used, it tends to launch the lifter, or loft, off of the cam lobe. Lofting is a trick used in racing where class rules specify a maximum lobe lift, and the lofting of the lifter makes the cam seem larger than it really is.
The downside to lofting is the wear, tear, and abuse it wreaks on the valvetrain. Aside from pounding on the face of the cam lobe, it also puts stress on the pushrods that can cause them to flex and bend, the rocker arm body, and it puts extra harmonic and mechanical stress on the valvesprings and lifters that can lead to premature failure. Many lifter failures can be directly traced back to a valvetrain that is out of control. In a race engine this practice can be tolerated because of the finite number of laps/passes a race engine makes before it will be torn down for a refresh. But in a street engine that is typically run hard until it breaks, this can create a ticking time-bomb situation.
Brian believes in making power with less aggressive rates, and on the exhaust side with less lift as well, instead looking towards proper intake and exhaust valve open and close events to make power in the various LS engines. In back-to-back dyno testing with no other changes, Brian has seen upwards of 10 lb-ft. more torque everywhere using .030″ LESS exhaust lift. He has also seen more power everywhere by running slower ramp rates on the intake lobes. Faster ramp rates and more lift is not the magic answer to making more power as many may think.
Another issue with running excessive lift with stock LS 15-degree rocker arms is that shortly after .600″ lift you run off the end of the rocker scroll, and are opening the valve with the tip end of the rocker arm, something it wasn’t designed to do.
Running too much lift (.640″+) combined with too much open pressure (420 lbs+) can led to damage to the valve tips over the long term. The GM 12-degree rockers are still on the scroll at .660″ lift, so they’re less likely to have valve tip issues.
The profile Brian selected for us was custom ground by Comp Cams, with a lobe separation angle of 114-degrees, net lift of .552/.552, and duration at .050” of 218/224. Compare this to the factory LM7 cam, ground on a 114-degree lobe sep angle, net lift of .466/.457, and duration at .050” of 190/191.
“Truck LS engines have lower compression than the engines installed in cars. Often people mistakenly want the same cam as their LS1/LS2/LS6. It will sound good and make good high rpm power, BUT the weight of the vehicle, the deficit of cubic inches, and the lack of compression will make the truck’s acceleration rather lackluster. It will make less peak horsepower, but will be faster due to the under peak broad range of power applied.”
With cam and parts in hand, we pulled into AntiVenom Performance to do our cam swap and see how the 5.3 responded. Owner Greg Lovell has extensive experience with performance mods on the truck engines, and is well acquainted with how well they respond to cam swaps.
Let’s see what we got!
Patrick Hill has grown up around the automotive aftermarket, and carries a lifelong passion for performance, racing and automotive nostalgia that spans from the Tri-Five era to the current modern performance market.