GM Gen III/LS1/LS2/LS6 -uses “54” Prefix
This engine is the first real departure from GM's original small block design. Almost none of the parts carry over from previous engines. The camshaft is a steel roller cam, approximately 4” shorter and .300” larger in diameter, so there should be no problem with misapplications.

Big Block  -uses “11” Prefix, Gen VI Big Block -uses “01” Prefix, 8.1L Big Block -uses “46” Prefix
This engine was introduced in 1965 and with the exception of some of the very early 1965-1966 models, which had an oiling groove in the rear journal, the camshafts are interchangeable. This includes all of the big blocks, including the Mark V, with just about any style cylinder head until the 454-502 Gen VI was introduced in 1996. This engine is similar to the earlier standard big block. The heads are interchangeable, but there is nonadjustable valve train. It is equipped with a hydraulic roller camshaft. There is a positive camshaft retaining plate on the front, and the nose of the cam is stepped down to accept this plate. The lifter bosses are taller to accommodate the lifter anti-rotation plates. This engine will require a special timing chain set.

Older Engines
The very first 1955-1957 265 c.i. small blocks had a unique oiling system. The same holds true for the first 1965 and 1966 396/427 big blocks. When one of these blocks is used, it is necessary to machine a small groove in the rear journal of the cam to allow oil flow to the top of the engine. COMP Cams® camshafts come without this groove, so it is important to check the vintage of your block prior to camshaft installation. COMP Cams® can perform this operation or supply the specs to you for local machining.

This chart shows the valve arrangement of typical Chevrolet cylinder heads. You can see each of these will require a different camshaft.

General Tips

Springs
By far, the most common problem encountered when installing a new high performance camshaft is the incompatibility of the existing valve springs to the new cam. Factory valve springs are designed to work with stock, low lift camshafts, and since most aftermarket cams have higher lift, the springs must be replaced with compatible components. It is highly recommended and a requirement of the warranty that the suggested springs be installed along with any COMP Cams® cam. Most big block engines come stock with a double spring consisting of small diameter wire and many coils. Some people think that because it has double springs it is already high performance. However, nothing could be farther from the truth. This particular spring is one of the worst for accepting extra lift. Almost all big block engines will require a spring change along with the cam. Whenever installing a Hi-Tech™ racing cam in any small or big block engine, the cylinder heads must be equipped with the correct valve springs, screw-in studs, guide plates and hardened pushrods. The increased loads and ultra high speeds of the racing engines make this a necessity for valve train stability.

Small Block Spring Pockets
When machining a small block head for larger diameter valve springs, be aware that the area around the spring pockets in the head is very thin, especially the end or outboard exhaust. Care must be taken not to machine through the head when increasing the diameter of the spring pocket. You can round the edge of the cutter used to machine the pocket to resemble the diameter of the wire in the valve spring. Another way is to insert a .030” standard 1.250” diameter spring shim in the pocket prior to machining and cut only down to that point. The safest way is to seek professional help before ruining the heads.

Studs
When you are using a high performance camshaft and have problems with the valves not staying properly adjusted, one of the first things to check is the rocker arm studs. Most early model small block heads utilize pressed in studs. When high spring loads and high engine speeds are used with these stock type studs, they tend to pull out of the heads. You can check for this by laying a straight edge across the top of the studs to see if any of the studs are too high and out of alignment. If so, the heads should be removed and machined for screw in studs.

Factory small blocks were equipped with 3/8” studs and rocker arms. One of the most common practices on these engines is to replace these with larger 7/16” versions similar to those found on the big block engines. This is a simple conversion but requires a roller trunion rocker arm. See page 269.