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Marc Haibeck · 02-12-2012

Road racers should be aware that water pump cavitation occurs at 6100 rpm. Engine speed over 6100 rpm for more than a few seconds can overheat the engine. I know of two LT5’s that have pushed back head gaskets at VIR.

The common scenario is the driver is busy driving and the check engine light goes on because the coolant has reached the 250 degrees F. high temperature limit. The driver becomes aware of the situation when the engine control system disables the secondary port throttles.

If the driver up shifts and runs the engine at less than 5500 rpm, the engine temperature will drop rapidly as the coolant circulation resumes. The engine temperature will usually return to a normal 210 degrees or so in about half of a lap.

The failure mechanism is that the aluminum liners expand much more than the steel head bolts. The gasket gets crushed and then fits loose after the engine cools. Normal driving eventually pushes the loose fitting gasket off the liner at the exhaust coolant passage.

Reducing the pump speed can raise the cavitation speed. A ZR-1 Products under drive water pump pulley will raise the cavitation speed to 6400 rpm. If an under drive water pump pulley is used with an ATI under drive crankshaft pulley the cavitation speed will increase to 7500 rpm. Use of the two pulleys may cause the engine to run hotter at idle with the AC on.

02-12-2012	#5
Marc Haibeck Join Date: May 2007 Location: Addison IL Posts: 254	Re: Dyno Pull yesterday (OBX Headers) Road racers should be aware that water pump cavitation occurs at 6100 rpm. Engine speed over 6100 rpm for more than a few seconds can overheat the engine. I know of two LT5’s that have pushed back head gaskets at VIR. The common scenario is the driver is busy driving and the check engine light goes on because the coolant has reached the 250 degrees F. high temperature limit. The driver becomes aware of the situation when the engine control system disables the secondary port throttles. If the driver up shifts and runs the engine at less than 5500 rpm, the engine temperature will drop rapidly as the coolant circulation resumes. The engine temperature will usually return to a normal 210 degrees or so in about half of a lap. The failure mechanism is that the aluminum liners expand much more than the steel head bolts. The gasket gets crushed and then fits loose after the engine cools. Normal driving eventually pushes the loose fitting gasket off the liner at the exhaust coolant passage. Reducing the pump speed can raise the cavitation speed. A ZR-1 Products under drive water pump pulley will raise the cavitation speed to 6400 rpm. If an under drive water pump pulley is used with an ATI under drive crankshaft pulley the cavitation speed will increase to 7500 rpm. Use of the two pulleys may cause the engine to run hotter at idle with the AC on.