Last month, we brought you the bottom-end assembly article for the 5.7-liter iron-block LS engine which will power Off Road Xtreme’s Project Resurrection through its off-road exploits and hijinks. With the solid bottom-end in place, now we can move on to the top-end, where we have a number of goals.
First, we want a top-end for this project that is durable and reliable, to match the bottom-end of this engine. Since the engine will be force-fed by a ProCharger system, the design parameters were slightly different, with robust, affordable parts taking priority. This is something that CBM Motorsports has experience with, since the off-road world is all about substance over flash.
Next, we want parts that will complement each other, and the supercharger which will feed the combination. When air is under pressure, the requirements of the system are a little different. Again, thanks to CBM’s experience in the arena, and the fact that the LS platform is so incredibly supported by the aftermarket, this shouldn’t be an issue in the slightest.
With the input of CBM’s owner, Bruce McKillop, and several of the biggest names in the aftermarket, we put together a top-end combination that is a combination of badass and budget, that makes for affordable, reliable performance without breaking the bank.
Enforcing Budget Performance
When it comes to LS cylinder heads, there usually isn’t an “in-between” option. Either you are using stock castings as they came off the assembly line — which really isn’t a drawback in most cases, since the stock LS cathedral port heads, in general, are solid performers, and can be sent off to a cylinder head porter to really improve their flow characteristics.
The next option would be to use a set of aftermarket heads, that either come pre-ported with massive ports and flow numbers (and a matching price tag) or a set of new castings which have an improved port shape and design cast directly into the head, right out of the mold. While the factory 706 head castings were perfectly serviceable, there was another option on the table, which come in at about the same price as having the 706s worked over: AFR’s LS1 Enforcer heads.
We covered the Enforcer lineup when they were first released, but this has been our first chance to actually use them on a project. The Enforcer LS1 cylinder head is a perfect fit for our short-block, as we turned the 5.3-liter LM7 bottom end into what is essentially an iron-block LS1. The Enforcers are cast from industry-standard A356 aluminum and the runners are “as-cast” which means that AFR’s permanent molds already have an optimized intake and exhaust runner shape and size.
The provided flow sheet shows that the 210cc intake runner (10cc more than the OEM 706) flows 268 cfm at .600 inch of lift, and the 82cc exhaust runners (12cc more than the 706) flow a stout 207cfm at .600 lift. The combustion chamber is slightly larger than the 706’s at 64cc, but that was accounted for when choosing pistons and head gaskets.
To attach the cylinder heads to the short-block, we went with the gold standard when it comes to cylinder head fasteners — an ARP Pro-Series head stud kit. Made from the upgraded ARP2000 steel for increased strength under the boost this engine will see. To seal the heads to the block, we went with a set of Cometic MLS head gaskets with a 3.930-inch bore and .072-inch compressed thickness, to bring the compression down a little bit.
Performance Valvetrains Don’t Have to Cost a Fortune
While the Enforcer line is considered a budget option, the only place where money is saved is the lack of CNC porting. All of the included valvetrain and cylinder head components are the same parts as you’d find on any of AFR’s non-budget cylinder heads. The 2.02-inch steel intake valves are .130 inch larger than the original 1.89 intake valves and the 1.600-inch steel exhaust valves are .050-inch larger than stock — both with three-angle valve jobs and 8mm stems.
Controlling those valves are a set of dual PAC valvesprings from AFR, which produce 140 pounds of seat pressure and are designed to handle 6,500 rpm, which should pair perfectly with the camshaft we used. AFR also supplies 7-degree chromoly locks and retainers as well as a hardened spring locator and all-new Viton valve seals right out of the box.
Speaking of the camshaft used, the team chose Comp Cams’ LSR Centrifugal Blower 227/243 camshaft for this engine. It specs out at .614 inch of lift on the intake side, and .624 inch on the exhaust, with a duration split of 227 degrees at .050 inch on the intake and 243 degrees on the exhaust, with a 114-degree lobe separation angle. “This grind should make power from around 2,500 rpm on up,” says McKillop of the blower-specific camshaft grind.
For the hard parts of the valvetrain, we turned to the name that first pops into our collective heads when you talk about bulletproof LS valvetrains, and that’s Comp Cams. “Reliability is the main goal here, and that’s why we went with these parts,” McKillop says. “The Comp pieces are just quality parts.”
First, to keep the camshaft in sync, Comp’s Hi-Tech Roller Race timing set was used. The kit uses a cast iron cam gear and an induction-hardened steel crank gear for durability, with nine timing options, allowing for up to 8 degrees of maximum adjustment in either direction. The single roller chain is an upgrade from the stock chain and has been pre-stretched and heat-treated to prevent any unintentional timing changes.
Comp recommended a set of its short-travel Retro-Fit Link Bar hydraulic roller lifters for this application. The short travel design combines the benefits of a light preload on a standard travel lifter as well as reducing the oil volume in the lifter, which increases the lifter’s stability at elevated RPM. Additionally, the link bar eliminates the factory plastic lifter guide tray, which can prove to be problematic when getting into the mid-.600-inch lift range.
Riding atop those lifters are a set of Comp’s Hi-Tech 5/16-inch diameter pushrods. Built from one-piece of .080-inch wall-thickness seamless chromoly, the 7.400-inch pushrods are heat-treated and have reinforced ends, making for a stout, lightweight pushrod that will handle everything this project will throw at it.
Then, possibly one of the coolest components in the valvetrain, Comp supplied us with one of their Max-Lift BSR shaft-rocker arm systems. Possibly the definition of bang for the buck, the BSR system uses new stock-pattern rocker arms, which are a proven design, along with a built-in bushing upgrade. But, on top of that, it ties all of the rocker arms together on a single shaft, which immensely increases the stiffness of the system.
That additional rocker arm stiffness deflects less, which has the effect of acting like a larger camshaft as well as being more durable and better able to handle aggressive valvetrain loads. Even though the camshaft we’re using is designed with Comp’s low-shock design philosophy, the BSR’s benefits still improve the system as a whole.
Big Flow To Feed the Beast
When it comes to intake manifolds, a really well-built long-block combination needs the right intake manifold to really support its mission. The wrong manifold can neuter the combo, while the right one can really let the combination shine. Since this project isn’t one that really has the engine in tight confines, Comp suggested the FAST LSXRT truck intake manifold.
Designed specifically for the truck variants of the Gen-III engine — and cathedral-port LS1, LS2, and LS6 race applications with plenty of hood clearance, the LSXRT uses an easily disassembled runner design to allow for easy porting and modification, if that is a road you choose to go down. In the stock configuration, the manifold offers plenty of airflow and should place our powerband in our desired RPM range.
Built with a 102mm inlet, we paired the manifold with one of FAST’s 102mm Big Mouth cable-actuated throttle bodies. With both an idle air control valve and throttle position sensor, the Big Mouth is made from aluminum for durability and anodized black for sleek good looks. The 40-percent-larger-than-OEM throttle blade has a beefed-up design to help prevent any deflection in our boosted application and has an offset blade pivot design to improve throttle response, while maintaining solid driving manners.
The combination of the LSXRT intake and 102mm Big Mouth throttle body, should not only allow for plenty of airflow from the ProCharger kit and produce power in a solid, usable RPM range, but should also have decent on-road manners as well. Remember, the operating range of an off-road vehicle is vastly different from that of a drag car or even a street truck. With the top-end of Project Resurrection’s 5.7L engine complete, now, all that’s left is to install the supercharger kit and fuel system, and it’ll be ready to turn gasoline into horsepower.