Raceday Variables – Page 2

Effects of Heat

You must keep the fuel and fuel lines as cool as possible in the engine compartment. Gasoline boils at 150 degrees F., which is easily obtained in the summertime. Isolate the lines with insulation. Between runs, lift or remove the hood to allow the rising hot air to escape instead of providing heat to your fuel line and carburetor. If the carb float bowl reaches 190 degrees, the fuel will vaporize. Hot fuel can cause erratic problems throughout the staging lanes and on the track.

What causes high under-hood temperatures? Usually, high-compression engines run at higher rpm, lean-jetted engines, and engines run over- advanced (ignition timing) create higher temperature problems. In addition, headers increase under-hood temperatures due to extra surface area of the exhaust system. I tried header insulating wrap to reduce heat in the engine compartment. The wrap may have done its job, but the results were undetectable in my car.

A well-worn cam can also cause overheating. If the exhaust lobe does not efficiently vent the hot gases, the gases get trapped in the cylinder. This causes an increase in residual head temperature that is hard to identify and leads to burned valves, pistons, and rings. How can we detect a worn lobe? Unfortunately, a compression check doesn’t indicate the condition of the exhaust lobes at cranking speed. It tests the sealing abilities of the valves and rings. However, a dial indicator placed on the valve retainer while rotating the engine by hand can show us the valve lift. Worn lobes show up as reduced valve lifts.

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