While enthusiasts can comprehend the fact that the camshaft is responsible for opening and closing the intake and exhaust valves on an LS motor, relating these events to crank position, engine displacement, or even operating speed is somewhat more difficult. The difficulty is only compounded when you add things like forced induction to the mix. From an anatomical standpoint, the camshaft can be likened to the brain, as the cam profile determines how effectively (when and where) breathing takes place. Camshafts are one of the major determining components of the effective operating range of the motor. Of course, the cam timing must be combined with the proper intake manifold, head flow, and primary length on the exhaust for optimum operation over a given rpm range, but the right cam all but determines the character, or personality, of the motor. Stock or ultra-mild aftermarket cams will provide a dead-smooth idle while more radical grinds can transform that mild-mannered motor into one seriously radical ride. Unfortunately, that radical ride route often includes ill-tempered, cantankerous behavior until the motor comes on the cam, but such is the price for all that high-rpm heaven. As luck would have it, modern cam technology has come a long way since the introduction of the original small-block Chevy. Technology has provided not only a much more efficient small-block in the form of the new LS family, but it has also allowed us to produce impressive power, driveabiliy, and even fuel mileage all in one package.
Many LS1/LS2 and LS3 enthusiasts at least understand the basics of cam timing. They realize that so-called "Saturday-Night Special" grinds are much wilder and potentially more powerful than the production cam profiles. The problem arises when deciding to choose between these two extremes, especially for a daily driver. The temptation is certainly there to go "BIG" on the cam profile, after all, isn't bigger always better? The problem with going big is twofold. The first problem is that the cam profile must be selected not just for bragging rights at the drive-in (or coffee house), but rather to work with your existing components. Adding the right cam to your otherwise stock motor can result in impressive power gains. Adding wild cam timing to your otherwise stock motor will likely result in a drop in power throughout most of the rev range and can actually decrease peak power since the cam was designed to run effectively at 7,500 rpm and the rest of your stock components (intake runner length, head, and stock valvesprings) sign off at just 6,000 rpm (or less). As a general rule, the closer to stock the remainder of the components, the milder the cam profiles that should be chosen. This means leave those weekend-warrior cams to the drag racers and stick with mild but effective profiles that will offer power gains not just at high rpm, but through the entire rev range. After all, what good is it to add 25 hp at the power peak only to loose 35 lb-ft down at 3,000 rpm? Think for a moment about where (what rpm) you spend most of your time driving and choose a cam accordingly!
Enthusiasts often make the same mistakes with camshafts as they do with carburetors, cylinder heads, or even boost pressure on turbo or supercharged combinations. It is sometimes hard to convince performance enthusiasts that more power is not always better. As with any good thing in life, there is always a downside to the additional power. In the case of cylinder heads, a larger port will offer more airflow potential (assuming proper shape), but the air speed will be dramatically reduced at lower engine speeds and throttle angles just like with a carb. As for boost, more boost will make more power but so too will it increase the likelihood of harmful detonation. Like carbs, heads, and boost pressure, there are potential drawbacks to excessive cam timing as well. Wilder cam timing (meaning more lift and duration) can yield additional power, but this usually comes at elevated engine speeds. While it is possible to improve the power output of a motor throughout the rev range by replacing the stock cam with a more aggressive (street) profile, at some point, trade-offs become necessary. The usual scenario is that wilder cam timing will improve the power output at the top of the rev range, but the trade-off will be a loss of power at lower rpm. While additional high-rpm power can be desirable on a race motor, this reduction in torque is obviously not desirable on a street application. For most street motors, the abundance of torque is put to use much more than any gain in high-rpm horsepower. This test on a 408 stroker illustrated the trade offs that are inherent when you install a wild solid roller cam in place of a milder (though still powerful) hydraulic roller cam.
The test motor started out life as a 6.0L iron truck block. The standard-bore block was equipped with a Lunati 4.0-inch stroker kit. The Lunati reciprocating assembly included the forged steel crank, forged rods, and forged pistons. The dished pistons were employed to keep the static compression ratio at a street-friendly 10.0:1. This motor was previously used as the foundation for a turbo build up that exceeded 1,000 hp, so it was a stout combination. The 408 short-block was topped off with a set of AFR 205 Mongoose heads. The CNC-ported AFR heads offered nearly 300 cfm on the intake side and 230 cfm on the exhaust side. In anticipation of the higher engine speed with the roller cam, the heads received a valvespring upgrade (p/n 8019). We also took the liberty of installing the AFR-recommended Crane billet lifters. Crane also supplied a set of their Gold roller rockers. Pushrods for both the hydraulic and solid roller cams came from Comp Cams. The finishing touches on the test motor included a FAST LSX intake, a 78mm throttle body, and FAST XFI/XIM management system that allowed us to dial in the air/fuel and ignition timing curves on our stroker combination. Spent gases were exhaled through Hooker long-tube Super Comp headers and 18-inch collector extensions.
Initially, the test was to be a comparison between a pair of cams, a healthy hydraulic roller and an equally healthy solid roller. Since our test motor was already up and running and equipped with a slightly milder Comp RPM-series hydraulic roller cam, we decided to run it as is before performing the first cam swap. Cam swaps are quite easy on the LS-series, though switching to the solid roller required removal of the cam and lifters. The first cam in our test was the XR277HR from Comp Cams. The XFI RPM series cam offered a .534/.537-inch lift split, a 224/228 duration split, and a 112-degree lobe separation angle. Equipped with this cam, the 408 produced peak power numbers of 551 hp and 523 lb-ft of torque. Torque production exceeded 500 lb-ft from 4,300 rpm to 5,700 rpm, but horsepower production started to fall off at 6,400 rpm. Next up was the larger XE-R-series profile. The XER281HR offered a .595/.598 lift split, a 232/234 duration split, and a 12-degree lobe separation angle. This wilder hydraulic roller cam increased the peak numbers to 574 hp and 520 lb-ft of torque. The larger XE-R cam lost out to the smaller RPM version up to 5,300 rpm, but pulled away thereafter.
After backup runs verified the power numbers, it was time to swap out the hydraulic roller valvetrain for the solid components. This required removal of the AFR 205 heads and replacing the hydraulic roller lifters with the solid version. This also necessitated a change in pushrod length. After the heads were torqued back in place, we reinstalled the Crane Gold rockers and set the valve lash at .014-.015. The solid roller from Comp Cams offered just a tick over .600-inch lift (both intake and exhaust) and a 240/244 duration split (with a slightly wider 114 lobe separation angle). Not only did the solid roller allow more usable engine speed (up to 7,000 rpm), but the profile offered more peak power. Equipped with the custom roller cam, the 408 produced 609 hp and 523 lb-ft of torque. Note that the peak torque was right near 520 lb-ft with all of the cam combinations, the wilder cams simply shifted the torque curve to increase high-rpm power production. Torque production exceeded 500 lb-ft from 4,500 rpm to 5,900 rpm with the XR281HR cam, but the spread was from 4,700 rpm to 6,300 rpm with the solid roller. Not surprisingly, there was a loss in power below 5,500 rpm with the solid roller, so in the end, it all comes down to where you want your power production.