Gen III V-8 Cylinder Head Shootout

Power exists in the cylinder heads you choose for your Gen III V-8 engine. No matter what type of engine you build--normally aspirated (NA), blown, nitrous, big cubic-inch, or otherwise--there is a production cylinder head that will work for your application.

With all the interest in the General Motors Gen III V-8-based LS1 and LS6 engines, there has been a need for a story showing what the best production cylinder heads are for making power with this engine family. This excerpt from the just-released book How to Build Performance Chevy LS1/LS6 V-8s, by Will Handzel, contains key cylinder head information performance enthusiasts need to know when working with the Gen III V-8.

Overview of the Gen III V-8

The General Motors Gen III V-8 engine, what most refer to as the LS1, is an engine family that was initially released as the GM Regular Production Order (RPO) code "LS1" engine in the '97 Corvette. The exact same V-8 architecture went on to be used in other GM products like Camaros/Firebirds ('98-'02), all fullsize trucks and SUVs ('99-present), some midsize SUVs ('04 to present), GTOs ('04), and the special production run of CTS Vs ('04). This means a set of LS6 performance cylinder heads will bolt on to your '00 Suburban, '99 Camaro, or '04 GTO!

Power Heads

The best heads for most performance applications are by far the LS6 cylinder heads built beginning in 2001. They were designed for higher-rpm applications that require increased airflow and higher compression ratios. These cylinder heads will fit any Gen III V-8 engine, but you'll need to mind the details when switching heads such as combustion chamber volume, valve-to-piston clearance, and valvetrain geometry.

The combustion chamber volume does vary across the Gen III V-8 engine family. We've included a chart listing combustion chamber volumes (including gasket volume) and engine compression ratios. On some engines, like the 10.08:1 compression ratio LQ9 345hp 6.0L Escalade Gen III V-8 engine, installing a set of LS6 cylinder heads without changing the head gasket thickness or swapping in dished pistons would result in almost an 11:1 compression ratio. This would force the use of 100-octane fuel to prevent detonation and yet would not net enough power gain for the hassle--not a winning situation for a street vehicle.

If you want to know what cylinder heads you have on your Gen III V-8 engine, look for the last three numbers in the casting part number. The close-up image shows the exact location of the last three numbers of the eight-digit casting part number located next to the rocker cover seal lip at the far right end of the head on the exhaust-port side of the head. For instance, the "243" cast into this head signifies it is an LS6 head cast made between '01-'04.

Here's a secret: If you want the best heads for performance, make sure your heads have these small triangle marks below every spark plug hole. The marks are left by "chills" used during the casting process in GM's semi-permanent mold (SPM) tooling. Of the three casting facilities that make Gen III cylinder heads, two use SPM tooling, the other heads are sand-cast. The SPM tools produce heads with very smooth, consistent ports and chambers which consistently dyno at least 4 to 7 hp better than the sand-cast heads.

If the valve covers are off the heads, you can read the complete casting part number located in the rocker valley of each Gen III head. GM has cylinder head part numbers that are different from the casting and machined number because every step of the manufacturing process requires a part number.

In fact, swapping LS6 heads on the aluminum-head-equipped LQ4 or LQ9 6.0L would only result in higher compression. This is because the LQ heads were derived directly from the LS6 heads. This means the LQ intake and exhaust ports are exact copies of the LS6 heads. The main difference is the LQ cylinder head has a 72cc chamber volume while the LS6 head has a 64cc chamber volume.

The valve-to-piston clearance in swapping LS6 heads on another Gen III engine is also an issue because GM has used multiple piston dome/dish and cylinder head combinations. Going with the small LS6 combustion chamber cylinder heads, a nearly 0.600-inch lift cam, and a flat-top piston will challenge the accepted 0.080-inch clearance between the piston and valve at max lift and piston TDC. This is best accomplished by using modeling clay (not Play-Doh or similar play clay, as it "springs" back giving a false reading) between the valve and piston during the "mock-up" stage of the engine build.

The most recognizable feature of the Gen III V-8 engine is the "cathedral" intake ports. These were used to fit between the four head bolts and pushrod holes while allowing for a symmetrical intake and exhaust port configuration throughout the cylinder head. GM cylinder head and port gurus, brothers Ron and Ken Sperry, led the team that developed these great cylinder heads.	If you are looking at a Gen III V-8 cylinder head sitting on a bench, a quick way to tell if it is an LS6 head is to look at the exhaust ports. If your heads have oval-shaped exhaust ports, they're the LS1-style exhaust port.
If the exhaust ports are "D" shaped, they are LS6 heads.