Circle Track Crate Engine Technical Manual - Chevrolet Performance

Engine Specifications
This section covers recommended rebuild specifications. All three engines are assembled with brand new
parts. Each engine will be within a tight horsepower range from the factory. Customers typically get 2
seasons of service from each new engine.
GM does not recommend rebuilding engines. We recommend purchasing a new engine and selling the used
engine to the hot-rod, street rod or drag racing community. This will ensure 100% integrity of the
program.
If rebuilds are allowed, It is up to the track owner or sanctioning body to manage
the rebuilders and closely monitor the rebuilt engines.
The key to maintaining close competition between new engines and rebuilt engines is to make sure rebuild
specifications are kept close to factory tolerances. These specifications are only guidelines. If the engine is
rebuilt to these specifications minimal horsepower differences should be noticed. These specifications also
provide a reference point for inspection of suspected modifications to the factory engine.
Valve angles and depths are critical to valve life and horsepower levels. The valve seat width and angle
affects airflow. It’s also a crucial part of removing heat from the valve and extending valve life. The
balance of keeping good air flow in all the lift ranges, as well as getting the heat out of the valve is necessary
to extend the life of the valve and seat. Engine rpm’s also affect the valve and seat life. When the
harmonics of the valvetrain overcomes the valve spring, the valve bounces off the seat and the valvetrain
becomes unstable, this reduces the amount of time the valve contacts the seat and transfers heat. Every
millisecond the valve is bouncing it reduces the seat contact and heat transfer.
RPM recommendations need to be strictly enforced to prolong valve life. These recommendations were
tested and designed to extend the life of the valve train components as well as the complete engine. Do not
exceed the recommended rpm limits.
The following page covers the details of the valve seat area. These are the factory machining specifications.
Anytime the valve seat and valve is “touched up” it may affect the height of the valve in the combustion
chamber. This will have a negative effect on the compression ratio but not enough to make a large
horsepower difference.
Reference the page on valve springs for factory specifications when new. Valve springs lose strength
during the life of an engine. The major factor in reducing valve spring life is heat, therefore no oil
restrictors are installed in the engine. Oil restrictors are not necessary when the rpm’s are kept within
factory recommendations. All three engines have excellent drain back to the oil pan. As long as the
breathers are functioning properly and the engine has minimal ring blow-by, oil drainage to the pan will be
good.
Some engine builders have learned from experience the negative effects that improper valve seat machining
has on the engine. Make sure your engine re-builder follows these specifications.
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