LSA Piston Oil Squirters
When GM designed the OEM supercharged variants of the LS platform, the LSA and LS9, they made a number of changes to manage the increase in output and thermal loads. In this article we take a closer look at the piston engine oil squirters as a unique feature fitted to both engines.
A disassembled OEM piston engine oil squirter. Note the banjo type fitting, o-ring gland, and oil passage through the thread/shank. Each squirter has an internal check valve set at ~40 psi to prevent oil pressure drop at low rpm.
The oil squirters are tapped into the hydraulic valve lifter oil galleries that run the length of the block, directing a stream of pressurised engine oil underneath the crown of the reciprocating piston in each cylinder. They are sealed by an o-ring which sits in a machined pocket in the block (see below). The purpose of the design is to cool the piston, increasing performance and reliability. Depending on conditions, the piston crown can reach temperatures of 500 degrees C, where as engine oil temperature is around 120-130 degrees C, giving a large differential and potential for cooling.
An LSA block with the oil squirters removed. The squirters are tapped into the lifter oil galleries on each side of the block.
Supplementary systems are used to support the changes in oil supply and thermal requirements:
As the heat is transferred from the piston crown to the engine oil, the LSA and LS9 equipped vehicles have a supplementary water/oil heat exchanger. This system takes the heat from the oil and passes it water based cooling system.
A higher volume oil pump is fitted to meet the additional oil flow demands when the squirters check valves are open.
A limitation of the OEM system is that most aftermarket pistons will foul on the squirter nozzles. The squirters can be deleted entirely or aftermarket squirters fitted.