Choosing the Right Oil Pump for the GM LS Series (Gen III and IV Small Block) Engine
This guide is intended to aid in the selection of the best oil pump for your GM LS series engine. We cover several factors that must be taken into consideration when selecting an oil pump, as well as the basic functionality and potential side effects of using the wrong pump.
1. Standard Flow vs. High-Flow Pumps
GM offers both standard flow and high-flow versions of OEM oil pumps for various engine applications. Refer to the chart below for detailed specifications.
Key differences include:
- Aluminum Blocks: Engines with aluminum blocks larger than 4.8 liters and equipped with Variable Valve Timing (VVT) or Active Fuel Management (AFM) systems require high-flow pumps. These systems consume more oil when active. This may be because aluminum’s higher coefficient of thermal expansion means it requires more oil flow to maintain proper pressure as the engine heats up.
- Iron Blocks: None of the iron blocks use high-flow pumps, regardless of whether they have AFM or VVT. This may be due to the more stable bearing clearances in iron blocks, which do not require the increased oil flow.
2. Stock Engines vs. Modified Engines
The specifics of your engine build will be the primary factor when selecting an oil pump.
- Stock Engines: For engines with standard bearing clearances and no modifications, the chart below is a reliable reference for choosing between standard and high-flow pumps.
- Modified Engines: Engines with modifications such as looser bearing tolerances, hollow push rods, axle oiling lifters, or piston squirters may require a higher flow pump. In these cases, practical experience and consultation with a skilled engine builder are crucial for selecting the right pump.
3. Oil Pressure Relief Valves
The relief valves play an important role in the function of the oil pump and are an important factor to take into consideration when selecting a pump.
- Primary Relief Valve: Located in the oil pump, this valve manages excess oil flow to prevent over-pressurization.
- Secondary Relief Valve: Found in the oil pan, it relieves extra oil flow when systems like AFM and VVT are active. This valve is necessary because the primary relief valve in the pump might not be sufficient to handle the excess oil flow.
4. Impact of Running a High-Flow Pump When It's Not Needed
Running a high-flow pump on an engine that does not require it can have some negative side effects:
- Increased Oil Pressure: Using a high-flow pump in an engine that does not require it will result in higher-than-normal oil pressure. This can cause both the oil pump’s relief valve and the secondary relief valve to open more frequently. The peak oil pressure might still be too high if these valves cannot manage the excess flow.
- Oil Aeration and Wasted Horsepower: Excessive reliance on relief valves can waste horsepower and lead to oil aeration. Aeration occurs when excess oil recirculated through relief valves becomes foamy, potentially causing intermittent oil pressure drops and additional strain on the oil pump, which can lead to premature failure.
- Decreased Oil Level: High-flow pumps generally do not significantly exceed the engine’s oil consumption because most excess oil is returned to the pan through relief valves. Thus, a high-flow pump doesn’t exactly “suck the pan dry". However, the excess flow through relief valves can lead to increased oil aeration (foaming of oil), which may cause oil starvation. Additionally, high-flow pumps can cause more oil to accumulate in the heads and valve covers. This might result in the oil level in the oil pan being down by an additional quart during high-G cornering, potentially leading to oil starvation, which is one of the reasons GM recommends adding an extra quart of oil when tracking the car.
5. Ideal Oil Pump Operation
- In an ideal scenario, the oil pump would supply only the amount of oil needed to maintain proper pressure, without relying on relief valves. This principle is embodied in variable displacement pumps found in newer LT series (GM Gen VI small block) engines. These pumps feature a solenoid and sliding gear housing that adjust the volume of oil pumped, maintaining consistent pressure around 30 psi at various RPMs. While more complex and potentially less reliable, these pumps offer superior efficiency and oil control.
Setup Recommendations for Oil Coolers
Oil coolers can add a slight additional restriction to the oil circuit. Here are the factors to consider when adding an oil cooler:
- Not required but recommended: Use the high-pressure relief valve spring provided with most aftermarket oil pumps to compensate for the additional restriction and maintain adequate pressure at high RPMs. Otherwise, the standard spring should be sufficient, but it generally won't hurt to run the stiffer spring regardless of your setup.
- An oil thermostat is highly recommended. Oil thermostats will bypass the oil cooler until the engine oil reaches operating temperature. This will accelerate engine warm up times and improve efficiency, since cold oil is more viscous and requires more work to pump through a restrictive oil cooler.
Melling Performance Series Pumps
Melling offers performance series pumps (models 10255, 10296, and 10355) designed to provide more stable oil pressure. These pumps aim to reduce cavitation and oil aeration, particularly at higher RPMs. According to Melling, their pumps perform better than standard factory pumps, though actual performance improvements may vary.
Conclusion
Choosing the right oil pump involves understanding your engine's specific needs, including material, size, and modifications. By selecting the appropriate pump, you ensure efficient lubrication and optimal engine performance. For additional questions or guidance on selecting the right oil pump, please reach out to our team.
