There are very few engine upgrade packages that provide more real “bang for the buck” performance on the Gen III V-8 than the addition of CNC-ported cylinder heads, an intake, a camshaft, a pair of long-tube exhaust headers, and a modified engine control calibration. In this chapter, we’ll show you how to bolt on these pieces, offered by SLP in New Jersey, to add 100 hp to the power production of a stock 340-hp LS1 V-8 engine (the power numbers are higher than this on the dyno because there are no accessories, and a set of headers was used in place of the stock manifolds).
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For simplicity, this chapter will focus on the disassembly process once the engine is out of a vehicle. For details on how to remove from a vehicle, see Chapter 4. The reassembly is not fully detailed, as most of it is just the reverse of the process detailed here. The few different steps in the reassembly process are detailed towards the end of the chapter.
All of the pre-’01 LS1 Gen III V-8s will respond with power to the addition of GM ’01 and later LS6-type components, so SLP includes the dropped floor LS6- style intake manifold with their CNCported LS6 cylinder heads, customground hydraulic roller camshaft, and assorted other performance-adding components. The LS6 made 405 hp in the ’02 Z06 Corvette, so picking up a few ponies is where the CNC-ported heads and matching cam make the difference.
The part that makes the addition of these parts so attractive is they require no modifications to the LS1 short block. Also, SLP offers a revised engine calibration to take advantage of the additional performance components. This new calibration can be added to your factory controller by filling out an information card and sending SLP the controller from your vehicle in the mail.
This power package makes real power in a very unspectacular way. There isn’t a supercharger hanging off the top of the engine or some other wild looking external clue that the power is going to increase 100 hp over the entire powerband. The heads obviously flow more air, but increased flow volumes in the port and chamber combination do not always equate to power. As the saying goes, “we don’t race flow benches.” For this reason, the combination of the CNC-ported cylinder heads, camshaft, valvesprings, intake, cold-air box, and calibration all add up to the performance improvement.
The engine work performed here was done with the engine out of the vehicle, which we recommend. For detailed information on how to remove a Gen III V-8 engine from a production vehicle, refer to Chapter 4. These changes could be made with the engine in the vehicle, but the tight confines of the engine bay make a simple job very difficult. As you’ll notice in Chapter 4, a four-point (not a drive on) vehicle lift is required to raise the vehicle up over the engine/suspension cradle assembly to access the engine. Obviously, not everyone has one of these lifts in their garage, so you’ll have to determine a solution to this to get to the engine. Believe us — removing the engine is worth the effort vs. doing the swap with the engine still in the vehicle.
There are very few special tools required to do the installation of these performance components. In Chapter 4, we showed you how to remove a Gen III V-8 without buying many special tools. Simple hand tools like a radiator hook tool, wrenches, pliers, and screwdrivers were used in inventive ways to get many of the special connectors and linkages apart.
Engine reassembly does require a special tool: a bolt-stretch angle socket. This tool clips on to a 1/2-inch breaker bar and is used to read how much the bolt is turned. The tool has a “zero” bar that is rested against something solid, then the dial is rotated to read zero on the pointer. The engine assembler then uses the breaker bar to turn the fastener a specific angle, like until the dial pointer is aimed at 76 degrees, to add 76 degrees of stretch to the bolt — which results in more clamping force on the components that are bolted together. Adding “angle” to the clamping fastener is more accurate than torquing, which is why it is used. There are many companies offering these tools. The most common we have seen is from Snap-On, PN TA-360.
In the case of the Gen III V-8 aluminum cylinder heads, the fastening process looks like this. The 10 head bolts per head are first torqued to 22 ft-lbs. Then, most engine builders use a Sharpie pen to mark each bolt head with a vertical line — this is done so if the builder gets mixed up in the midst of the torquing procedure, the lines will help them remember where they are in the process. From there, all the head bolts receive 76 degrees of stretch in the GM-specified sequence. Then, the eight long head bolts get 76 degrees more stretch, following the radial torquing sequence recommended by GM. As a final step, the two shorty bolts at the ends of the head receive only an additional 34 degrees of stretch. This is for an aluminum engine block; the head bolts for iron-block engines receive 90 degrees at first, then 90 degrees on the long bolts and 50 degrees on the shorties.
It was said earlier in the book a few times but needs to be reinforced here — the factory head bolts are single-use only. Do not reuse them, because the clamping load they provide the second time they are stretched is not the same as the first time.
Tips for Success
Upgrading just the top end of a Gen III LS1 V-8 is a good way to start off modifying these engines. The top end of the Gen III engine is very straightforward and making changes here provides a dramatic change in the power output of the engine. Some tips to maximize your pleasure include the following:
- Make sure you drain the coolant out of the top end of the engine by removing the two drain plugs at each side of the engine block (one is above the starter). This will keep coolant from drooling into the cylinders and blindtapped head bolt holes. This is critical, as any fluid in the blind holes increases the risk of cracking the block when the head bolts are reinstalled and torqued.
- Perform the top end work in a clean area.
- Blow out the blind tapped head bolt holes with pressurized air before reinstalling the head bolts and torquing them in place. If you don’t and there’s oil, coolant, or other incompressible liquid in those holes, you could crack the block — which would force you to replace it.
Why CNC Porting?
Up until the late 1980s, any ported cylinder head was done by hand. The skilled artisans that did the grinding to create high-flowing cylinder head intake and exhaust ports were sought out for the feel and control they displayed in creating shapes that made power. The only problem with this situation was that getting a ported head was very expensive and each one was a little different. Then came the CNC-machining center, and everything has changed.
The term “CNC” stands for computer numerical control. It describes a machining center that is run by a computer. In days past, a mill or a lathe needed to be operated by a skilled tradesman to perform its duties. While skilled tradesmen still set up the CNC machining centers, the computers run the machines during the actual operations. This allows the employee to do more valued work while the CNC machine whirs along.
Early CNC machines operated in just three axis: what many would call the X, Y, and Z axis. These machines were good at making simple components in large lots.
Then, four-axis CNC machines started to become available and more intricate machining could be performed. Intricate components and areas, like combustion chambers, could be machined to very tight tolerances. The extra axis came from splitting the normal axes at a 45-degree angle, which gave the machining center and computer another angle to approach a component from.
The big leap came when five- and six-axis CNC machining centers became available. Now, a CNC machining center could articulate a spinning cutting tool and the object being machined, like you’d do with human hands. Complex, hard-to-reach shapes, like the port of a cylinder head, could be machined to within thousandths of an inch.
When CNC machines first appeared, many head porters feared their profession was going to be eliminated. Instead, CNC machines have made great head port creators like rock stars. Their port jobs are digitized and copied in CNC machines onto an untold amount of cylinder heads for performance enthusiasts all over the world to enjoy.
Vehicles That Respond
This SLP component package will work on any Camaro or Firebird built between 1999 and 2003 with a V-8 engine called out by the GM regular production order (RPO) code LS1. The LS1 engine in the F-body cars was initially rated at 305 hp and 335 ft-lb of torque (SAE corrected), and the SLP package should bump that number into 440 hp and up (standard corrected).
The SLP cylinder heads are fully CNC-ported, which means the intake, exhaust, and combustion chambers have been machined. Beyond the cool look of the heads, the valve sizes have been increased to 2.020 /1.575 inches and the factory valves are replaced with Manley stainless-steel units. The valvetrain is also upgraded with SLP titanium valvespring retainers and performance valvesprings.
In the chart to the right, the engine on the left is a relatively stock 2001 SS 5.7- liter LS1 with only a set of headers, and the engine on the right has been modified with the complete SLP Stage III kit, including the heads, cam, intake, and headers.
Written by Will Handzel and Posted with Permission of CarTechBooks
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