Small Block and Big Block Chevrolet engines have become legendary since they were introduced over 50 years ago. The people at COMP Cams®, along with a lot of top engine builders, have spent many years improving these and other Chevrolet powerplants. We know the basics, and the basics are important. We have also learned a few tricks along the way.

If you’re rebuilding an engine, it will be worth your while beforehand to either read our books or watch our videos on the subject. If you need more help or have any questions, call our CAM HELP® line at 1-800-999-0853.

Engine Types

V6 90º -uses “18”, “09” and “56” Prefixes
The 4.3L V6 90º engines produced since 1985 are equipped with two types of camshafts and three types of cam drive systems. Early 1985 and 1986 engines (Prefix “18”) were produced with flat tappet cams. Hydraulic roller cams were first introduced in 1987 (Prefix “09”). These two cam types require different timing chain sets, because the hydraulic roller cams have a stepped nose like the LT1 engine as described later in this section. In 1992, a balance shaft was incorporated in this engine, which necessitated a third timing chain setup to drive both the cam and the balance shaft. The cam (Prefix “56”) in this balance shaft engine is also shorter than the earlier model and does not have a fuel pump lobe.

Small Block V8
There are several varieties of small block engines currently in use in the aftermarket. Although they mostly use the same block, the cylinder heads are very different and require totally different camshafts. The valve arrangement in the heads is different, and therefore the lobe placement on the camshafts must coincide with the head you are using. The “54” is the first cam to completely stray from the original design. It is .300” larger in diameter.

The nose of the standard early model cam “12” is very different from the later model hydraulic roller “08”. The nose of the hydraulic roller “08” is necked down to accommodate the cam retention plate. The “07” is an LT1/LT4 shaft which has a longer dowel pin and a center hole for the distributor. Be sure to check the diameter and depth of the hole in the front, as well as the length of the dowel pin.

Standard Small Block Chevy -uses “12” Prefix
This is the basic engine configuration found on all small blocks from 1955 until 1987, when Chevrolet introduced the roller cam.  It’s important to note that the 1955-1957 versions require an oiling groove to be machined into the rear cam journal, but the camshafts are interchangeable.

OE Hydraulic Roller Small Block  -uses “08” Prefix
Beginning in 1987 small block V8 engines were equipped with hydraulic roller cams. There are differences in the block to accommodate a cam retention thrust plate and antirotation mechanism for the lifters. These blocks are identifiable by bolt holes for a cam retention plate behind the upper timing sprocket, as well as bosses and tapped holes in the lifter valley.

The camshafts on these engines have a step nose and smaller bolt pattern on the front of the cam. An earlier model camshaft may be used in these blocks by using the appropriate timing chain set and adding a thrust button when using a roller cam.

LT1 and LT4 Engine -uses “07” Prefix
These engines are, as far as the camshaft is concerned, essentially the same as the hydraulic roller engines, with one exception. The distributor is driven from the front of the cam, requiring some changes in the cam core. There is a deeper pilot hole in the front of the cam, as well as a longer dowel pin to locate this drive. These engines require a special timing chain set, and they utilize a self-aligning rocker arm. COMP Cams® LT1 and LT4 Magnum rocker arms can be found on page 268.

Buick Head, Splayed Valve GM and Dart Buick
Small Block, -uses “19” Prefix
Buick made a small block cylinder head in the early 1980's which fits a small block. This head was made by Dart and is still very common in drag racing and some oval track racing. The camshaft is different because of the different valve arrangement in the head. The valve arrangement of Splayed Valve GM and Dart Buick heads are identical to the Buick, so the camshaft is the same.

SB2 -uses “03” & “04” Prefixes
One of the latest versions of true race engines from GM is the SB2. It uses a totally different valve arrangement, and therefore a different core. One major item that changed is that there is a special SB2 block. The lifter bore spacing and lifter angle are different, specifically to work with a flat tappet for cup applications. When using a standard block and SB2 head, use prefix “03”. When using the SB2 block and the SB2 head, use prefix “04”.