Crate Questions
Technical problems and questions are inevitable with any performance engine. With that in mind, the folks at GMPP answered some frequently asked questions regarding crate engines. As you'll see, most solutions can be traced back to common oversights that occur when installing a new engine.
Frequently Asked Questions
Q. Why doesn't my carbureted crate engine make the power advertised by GM?A. Any GMPP crate engine shipped with a carburetor is jetted rich. This is done to ensure that no matter where the engine is shipped and no matter what the climate or altitude, there is little chance that the engine will run too lean, which can damage pistons. GMPP suggests that you re-jet the carburetor to tune the engine for your specific climate, altitude, exhaust system, air cleaner, and other variables. Engines typically require one- to three-size smaller jets. And each GMPP crate engine will make its advertised power or more when properly tuned and broken in.
Q. Why doesn't my crate engine make power? I set the timing at 10 degrees.A.Ignition timing is critical to the performance of your crate engine, and when set improperly can result in a significant power reduction. Most GM crate engines have ignition timing specified as "total timing" at some rpm level, for example, 36 degrees of total timing at 3,000 rpm. Many crate engine owners set their timing based on initial timing, using 8, 10, or 12 degrees advance at idle. Then, depending on the distributor used, total timing can be off by as much as 10 degrees or more. It is vital that timing be set at the specified rpm level, and that it be set with any mechanical and/or vacuum advance device in operation.
For good street driveability, your distributor's vacuum advance should be connected to "ported vacuum," which is drawn from a source in the carburetor above the throttle plates. This results in increasing vacuum as the throttle is applied. The function of vacuum advance is to provide timing advance in low-rpm acceleration conditions for smoothness and improved driveability. The alternative, manifold vacuum, is taken from a source below the throttle plates, resulting in decreasing vacuum as the throttle is applied. If your distributor is connected to manifold vacuum, full vacuum advance may be applied at idle. Then, as the throttle is applied, vacuum decreases and timing advance is decreased, causing poor engine performance and acceleration at low speeds.
Think about ignition timing: If your engine starts, your initial timing is fine. Ported vacuum gives the best performance around town. Mechanical advance brings you up to desired total timing for midrange and top-end performance.
Q. My crate engine runs hot. What's wrong?A. Most of the time the cooling system-not the engine-causes a hot-running crate engine. Let's dispel some myths.
Myth: Without a thermostat my engine will run cooler.
Truth: Without a thermostat the coolant moves too quickly through the radiator and doesn't pass the heat into the radiator's cooling fins, possibly overheating the engine.
Myth: Electric fans will cool my street engine; after all, they cool race engines.
Truth: Drag cars only run for minutes at a time, and racers try to heat the engine quickly so it will make good power on the pass. A properly selected and installed electric fan must cover the majority of the radiator and be capable of moving enough air for street use. An improperly selected electric fan with inadequate fan speed can actually block airflow at higher speeds.
Myth: If my mechanical fan is close enough to the radiator, I don't need a shroud.
Truth: There are two reasons why we suggest using a fan shroud with a mechanical fan. First, without a proper shroud, your fan's ability to move air is decreased by half. Secondly, without a shroud your fan will not draw air over the entire surface of the radiator. A proper fan shroud should cover the entire cooling surface of the radiator in order to create a low-pressure area on the entire backside of the radiator. This ensures that air will move across all the cooling fins, maximizing the radiator's efficiency. Additionally, a proper shroud should be no further than an inch away from the tips of the blades, and the fan should sit half-in and half-out of the shroud.