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.
This is the cam kit we’ll be using; a custom-grind based on a COMP Cams core, selected, spec’d and ground by Mr. Brian Tooley of BTR himself. The valvesprings were sourced through COMP Cams directly.
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!
Swapping cams in a truck is easier than most LS equipped cars because of the truck’s spacious engine compartment. First thing to be done was removing the radiator, cooling fan, and air intake elbow.
Next the spark plug wires are disconnected along with the harness for the coils, then the ignition coil assembly is unbolted from the valvecovers so they can be removed.
Next up the water pump comes off. If your pump has a lot of miles on it, now is the time to consider replacing it with a fresh one.
All 1999-2013 4.8 and 5.3 truck engines use the same 1.7 ratio rocker arms as the LS1, LS2, and LS6. The valvetrain is a net-lash design, meaning it is non-adjustable from the factory.
Even though the timing cover on an LS motor can be removed without dropping the oil pan, the harmonic balancer does need to come off. You’ll need a three-jaw puller for this one.
With the timing cover off we can unbolt the cam and timing chain. All the early truck engines used a three-bolt cam gear, and that’s what most aftermarket cams are machined to accept. If you have a 2007 or later truck, you need to pick up a three-bolt cam gear from your local Chevy dealership parts department, or from Summit Racing, part number 12586481. If your engine has variable valve timing, you need to call the cam company to discuss your options, and possibly deleting the VVT system. Depending on the mileage of your motor, or if it’s a 99-04 with the thinner factory chain links, you might consider replacing the whole timing set.
Along with the cam, we also installed new valvesprings. The factory spring (right) is too weak to take the lift and profile of our new cam, so in the trash they went. In their place we installed a set of factory-spec LS6 valvesprings, part number 12499224. They feature a rate of 375 pounds per inch, a seat/open pressure of 90 pounds at 1.800-inch installed height, and open pressure of 295 pounds at 1.250-inch height. They have a max lift rating of .570-inch, a coil bind height of 1.085-inch, and will work with the stock retainers and valvestem seals.
Thanks to the net-lash design, the factory rockers can all be removed at once on the rocker stand once all of the rocker arm bolts have been unbolted from the head. Once the rockers are out, remove the pushrods.
Our Brian Tooley designed cam featured a lobe separation angle of 114-degrees, with net lift of .552/.552, and duration at .050” of 218/224. The increased lift combined with increased duration meant the cylinders could be packed with more air/fuel charge on the intake stroke, and more exhaust gasses would be scavenged from the cylinders on the exhaust stroke, both leading to more power. It also meant that when the nitrous button was pushed, more nitrous could get into the cylinders for an increased power boost. Here, the trucks’s owner, Billy M., models with the killer BTR bumpstick.
A great thing about the LS series is not having to remove the intake or lifters for a cam swap. Once the rockers and pushrods are removed, all you need to do is rotate the cam a few times to lock the lifters in place inside the plastic lifter guides/retainers in the block. Once that’s done, you can remove the cam. Then the new one can be slid in place. The lifters will slide back down onto the lobes once the pushrods and rocker arms are reinstalled.
To reinstall the timing cover, you’ll need a special alignment tool like this one. If you don’t use the alignment tool and just try to “eyeball” it, there’s a 99-percent chance you’ll have an oil leak. These covers were designed to be precisely in place against the crank snout, block, and oil pan, with almost no margin for error in reinstallation. This is also one of the reasons why you seldom see an LS motor with oil leaks.
After the truck was put back together (everything reinstalled in the reverse order it was removed) we strapped the truck to the dyno and Greg Lovell did the necessary computer tuning to get everything with the cam dialed in just right. Once that was done we dropped the hammer to see what we’d got.
We started the day with 267 peak horsepower and 310 pound-feet of torque, and ended it with a peak horsepower of 318, and peak torque of 311 pound-feet. While peak torque stayed the same, it increased in the upper RPM range drastically, with only a slight loss on the bottom end. For horsepower we’d picked up 51 horsepower at peak, along with an enormous gain above 5,000 RPM, where the factory cam wouldn’t even rev to without stumbling and falling on its face.
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