Enhancing oil pressure dynamics in a high-performance racing engine with innovative lubrication system tuning

This work focuses on fine-tuning the oil pressure dynamics of a single-seater formula car, a participant in international engineering competition organized by the Society of Automotive Engineers (SAE). Adhering to competition guidelines, the Honda CBR600RR 05-06® motorcycle engine, renowned for its 600 c.c. displacement and exceptional power-to-weight ratio, emerges as a popular choice. However, as this engine is originally equipped with a wet sump lubrication system (featuring deep wet sumps to prevent oil starvation during turns), this presents challenges when adapted to Formula Society of Automotive Engineers (FSAE) cars. Cornering leads to significant pressure drops, as sloshing exposes the pickup port, causing consequential engine issues. To tackle sloshing-related challenges and pressure loss during lateral and longitudinal g-forces, a dry sump lubrication system was introduced in the Formula car. The dry sump system also lowers the engine’s center of gravity, by reducing sump height. However, transitioning to the dry sump system and integrating it with the existing engine demanded extensive design modifications to various components, including the oil reservoir, lubrication lines, scavenging pump, and oil ports. These adjustments were essential to achieve the targeted elevation in oil pressures at higher engine RPMs. A relationship between the engine oil pressure and the engine RPM was developed as part of the study.


Introduction
Engine lubrication plays a critical role in the smooth operation, longevity and overall efficiency of internal combustion engines.The different engine components move and interact during the continuous operation and hence susceptible to the friction and heat [1][2][3].This can lead to wear, damage, and degraded performance if not properly managed which necessitates an effective engine lubrication system.Lubrication involves the application of a lubricating substance, typically oil, to minimize friction between moving parts, dissipate heat, and provide a protective barrier against wear and corrosion [4][5][6][7][8][9].
Efficient lubrication enhances the engine's efficiency, reduces energy losses, and extends its operational life [10,11].Engine lubrication systems can be broadly classified into two main types: wet sump and dry sump systems [12,13].Each system offers distinct advantages and is tailored to different engine designs and applications.The most traditional and widely used kind of lubricating system is the wet sump system.In this layout, the crankshaft and other moving parts of the engine are immersed in an oil reservoir at the bottom of the engine called the sump [14].The oil is pumped from the sump to various parts of the engine, where it lubricates and cools the moving parts before returning to the sump.Wet sump systems are relatively simple, compact, and cost-effective, making them suitable for most everyday vehicles and applications.The dry sump system is a more advanced and performance-focused lubricating system frequently utilized in racing and high-performance engines [15].The oil is kept in a separate external reservoir as shown in figure 1, unlike the wet sump arrangement located within the engine.In order to increase the oil capacity and improve cooling, a number of pumps scavenge the oil from the engine's parts and send it to the external reservoir.As required, the oil is then injected back into the engine.In situations where high g-forces, quick acceleration, and protracted durations of operation in harsh circumstances are anticipated, dry sump systems are chosen.
For the racing car considered in the study, the Honda CBR600RR 05-06 engine, with a displacement of 600 cc was employed since the engine displacement restrictions were limited to 710 c.c. as per the rules of the competition [16], the engine specifications are shown in table 1. Accordingly, the majority of the teams use motorcycle engines with modified, custom wet sump lubrication system as shown in figure 2, that involves the inclusion of a customized horizontal windage tray and vertical baffles.These engines perform admirably when riding on normal roads but suffer from excessive sloshing, reductions in oil pressure, and starvation under lateral and longitudinal g-forces [17,18].This occurs because the oil pickup port of a motorcycle always has oil on it because the rider leans in while taking a turn.The exposure of the pickup port results in diminished oil pressure at higher engine speeds expressed in Rotations per Minute (RPM).This situation has the potential to severely damage the engine, causing scuffing marks or, in the most extreme cases, even catastrophic engine failure as shown in figure 3. The lateral and longitudinal g-forces on the car are shown in figure 4. Other disadvantages of wet sump systems include power losses at the crankshaft, termed as windage losses, as the oil vapours rotating along with the crankshaft offer inertial resistance.Additionally, larger height of the sump affects the centre of gravity of the car adversely influencing the handling and performance.To avert such a situation, ensuring a continuous supply of oil to the engine's moving parts becomes imperative.This goal can be achieved by embracing alternative approaches beyond the standard wet sump lubrication system.This includes options like integrating an oil accumulator or selecting a dry sump system.The Accusump system employs an oil accumulator, characterized by a pressurized cylinder designed to store oil under pressure.As the oil pressure within the system reduces, the oil accumulator releases stored oil to restore and maintain optimal oil pressure.On the other hand, dry sump systems store oil externally, allowing for a significant reduction in the depth of the sump (pan).This reduction enables the engine to be mounted even lower within the car's chassis/frame, effectively lowering the car's center of gravity.This modification greatly enhances the car's handling capabilities, leading to improved dynamic performance.1.1.Literature review on lubrication systems of racecars Over the past 20 years, Formula SAE race cars have undergone noteworthy improvements in both dry and wet sump systems, driven by a constant quest of greater performance and reliability.Superior lubrication under demanding racing conditions has been made possible in dry sump systems by advancements in oil pump efficiency, the use of lightweight materials, better oil pan designs, and the adoption of multi-stage pumping.Conversely, wet sump systems have witnessed improvements in oil control thanks to more advanced baffles, integrated cooling systems, and more effective pumpsall of which are intended to guarantee dependable and efficient lubrication.Furthermore, the integration of lightweight materials and compact designs in both systems has significantly contributed to the overall weight reduction and enhanced packaging of Formula SAE race cars.Table 2 shows the summary of such modifications carried out in last two decades.
Based on the lubrication issues of the formula car, and the modification routes employed by researchers in Formula SAE cars, the following objectives were framed: • Achieve the desired oil pressure dynamics (oil pressure ∼80 psi) at higher engine RPMs.
• Develop a mathematical relationship between the engine oil pressure and the engine RPM.This necessitated implementing various modifications to the lubrication system of the FSAE car engine, involving innovative alterations to the components of the dry sump lubrication system.Dry sump Turbocharged engine with custom scavenge pump KF-SC07 Improvement in maximum boost pressure and maximum torque ∼11 % May et al [21] Hybrid wetdry sump Accumulator in hydraulic circuit with one-way flow control valve Scavenging eliminated, oil pressure maintained in the system Sethi [14] Wet sump system Custom oil pan designed with baffles and windage tray, strategic baffle slots Use of windage tray reduced oil return rate to the pan, causing starvation Cazon et al [22] Wet sump Suzuki GSRX 600 turbocharged engine, custom additive manufactured oil sump with V-baffles around oil pickup pipe Lesser oil sloshing, lighter sump due to use of carbon fiber Wang et al [23] Wet/ Dry sump Custom turbocharger fitted, 20 mm intake restrictor, led to oil leakage within turbocharger, 7 different lubrication system designs tried Dry sump with PCV check valves minimized the leakage, with the electric scavenging pump as second best lubrication solution Khanna et al [2] Custom dry sump

Sump design, scavenge pump and oil pump optimization
Sloshing analysis of sump pan conducted, pick-up points highlighted

Methodology
This section entails the methods taken up to carry out the study of the oil pressure variation with engine RPM with the introduction of the dry sump lubrication system.

Dry sump system design
To design the dry sump system, the dimensional specifications of the previous wet sump lubrication system were taken as the reference.Notably, a slanted base was integrated to minimize the delay in oil reaching the ports, particularly from the rear of the engine.This design element also served to impede any reverse oil flow.In the lateral aspect (Y-axis) of the sump, two scavenging ports were strategically positioned.To enhance performance under lateral g-forces and guided by insights from past car data, lateral cavities were introduced (Y-axis direction).The engine oil used for the current study was Motul 300V 10W-40 ® Racing Synthetic motor oil.Moreover, a sloped base and a lateral front cavity were integrated.These components interconnect the two scavenging ports and the pressure relief valve, facilitating the oil flow toward the two lateral ports, to effectively counter longitudinal g-forces (X-axis).Figure 5 shows the dry sump system initially designed for the car with a sloped base, and the ports 1 and 2 as shown.To maintain effective scavenging and keep the oil pan consistently dry, it is crucial for the scavenge pump to possess a higher flow rate compared to the oil feed pump.For this purpose, the 04-99-2220 scavenge pump from Dailey Engineering ® was acquired.Notably, this pump boasts a scavenge rate of 1.57 kg/s that is twice the rate of the oil pump feed (0.713 kg/s at 12 000 RPM), ensuring efficient oil management.In order to assess the arrangement and confirm the design's effectiveness, the MoTeC M400 Electronic Control Unit (ECU) was employed to log data concerning oil pressure, g-forces, and engine RPM.Table 3 shows the specifications of the ECU, These recorded parameters were then visualized using the MoTeC i2 ® software.Given that the oil pump operates in tandem with the crankshaft, higher engine RPM results in an elevation of oil pressure; this implies a direct proportionality between oil pressure and engine RPM.Consequently, the oil pressure-to-RPM curve should ideally exhibit linearity up to a specific threshold.Beyond  this point, the pressure release valve initiates its opening, causing the curve to gradually level off.This adjustment occurs due to the marginal nature of pressure increase in comparison to the more significant rise in engine RPM.However, the engine RPM after the fitment of the dry sump lubrication system was staying low < 30 psi even at engine RPM > 6000, as shown in figure 6.The trend line fitted to the curve is represented by equation (1), with 'P oil ' indicating oil pressure and 'N' is the engine RPM.The regression coefficient, R 2 ∼ 0.362.This extremely low slope is disastrous for the engine operation as oil starvation is inevitable at higher RPMs.
Hence, the dry sump system requires several modifications to improve the oil pressure characteristics.The causes of low oil pressure can be attributed to different causes as shown in figure 7.

Modification in lubrication lines
Initially, a hose with a size of 6-AN was employed to convey engine oil from the oil reservoir to the pick-up port.However, when the engine was running at 6000 rpm, the maximum oil pressure recorded was only 26 psi, which was notably below the required 78 psi specified in the service manual.The restricted flow caused by the small inner diameter of the 6-AN hose, running from the reservoir outlet to the engine pressure pick-up port, led to the loss of oil pressure at high engine speeds, ultimately resulting in engine failure.Subsequently, the hose size was changed from 6-AN to 12-AN, and the system underwent testing.6-AN hoses have a smaller diameter compared to 12-AN hoses, which result in higher oil-flow (velocities) at higher engine speeds, causing an increase in the frictional losses, and in turn a drop in oil pressure.Whereas 12-AN hoses with a larger crosssectional area, reduce the frictional losses, maintaining oil pressure, even at higher engine speeds.High-  temperature polymer braided hoses supplied by M/s BMRS, with an operational temperature range spanning from −54 °C to 200 °C, were utilized for the lubrication routing.

Modification in Oil Reservoir design and baffles
Modifications were made to the design and placement of the oil reservoir.The previous flat-base reservoir with a tangential outlet and vertical baffles (figure 8) was found to result in oil starvation during cornering, as the oil tended to shift to the opposite end.The flat base reservoir was substituted with a conical base reservoir featuring a spiral structure at the top and a frustum baffle in its lower half.The conical base reservoir design is shown in figure 9.The inlet remained tangential, positioned just above the spiral, and the outlet was located at the base of the conical reservoir to ensure a constant oil supply.Due to its taller conical design compared to the previous flat-bottomed reservoir, it couldn't be accommodated behind the driver's seat.Instead, it was mounted between the rear left A-arms.This new placement brought it closer to both the sump and the reservoir, reducing the length of the plumbing and enhancing the efficiency of oil supply and scavenging.A decrease in oil pressure values was seen to be caused by the oil sloshing within the reservoir.To address this issue, a flat, horizontal baffle was incorporated between the conical base and the frustum baffle, effectively preventing oil starvation at the outlet port of the oil reservoir.During acceleration and cornering, the conical base design helps to direct oil towards the pickup point.By maintaining a steady flow to the oil pump and preventing oil from collecting in corners, this lowers the possibility of oil starvation during lateral acceleration.The reservoir's spiral construction improves oil swirling, which facilitates effective de-aeration and eliminates air pockets that can interfere with oil flow.The frustum baffle controls oil movement, reducing sloshing and preserving a constant oil level near the pickup point.These characteristics are enhanced by the horizontal baffle, which stabilizes the oil in the reservoir even more.It lessens the possibility of oil depletion during abrupt changes in vehicle direction by preventing excessive side-to-side movement.

Modification in pump feed line port
Alterations were made to the original OEM Pump Feed Line Port design.In the previous design of the oil delivery system, a significant issue was identified in the feed line where a sudden expansion occurred after a 12-AN adapter, which was welded to a strainer port cavity in the 2016 sump.This abrupt transition from a circularshaped 12-AN feed line to a rectangular cavity machined in the sump billet, followed by a circular strainer port connecting to the OEM Oil Pump Port, led to an undesirable pressure drop along the feed line from the oil reservoir to the OEM oil pump port.To address this concern and enhance oil pressure values, the design was   effectiveness of this design change in optimizing the flow characteristics of the oil delivery system.The design modification is shown in figure 10.To ensure effective oil scavenging and maintain a consistently dry oil pan, it was essential for the scavenge pump to have a higher flow rate compared to the oil feed pump.The 04-99-2220 ® scavenge pump from Dailey Engineering was acquired, which had a scavenging rate twice that of the oil pump feed rate.
The adjustment in lubrication routing was primarily necessitated by the original positioning of the oil reservoir, which was situated immediately behind the driver's seat.This placement led to a longer overall length of the lubrication routing system, and consequently, a larger volume of oil was retained within the hoses.Such an arrangement introduced potential challenges related to oil distribution, flow efficiency, and responsiveness in the lubrication system.The positioning of the oil reservoir behind the driver's seat resulted in issues such as oil sloshing and pooling, causing inconsistent lubrication and limited space for heat dissipation, ultimately leading to elevated oil temperatures.Furthermore, the placement of the oil reservoir in this location posed a safety concern, as any oil leakage or spillage could go unnoticed by the driver.By reducing the volume of oil with the modified lubrication routing, the inertial effects during rapid changes in vehicle direction were minimized.In response to these concerns, the newer design was implemented as shown in figure 11.
One of the key changes involved a deliberate reduction in the total volume of oil contained within the lubrication hoses.Specifically, this volume was decreased from 0.5303 L to 0.366 L (∼30.9 % reduction).This decrease in oil volume is not only an outcome of optimizing the routing but also serves to enhance the overall performance of the lubrication system.Firstly, by reducing the volume of oil within the hoses, the lubrication system becomes more responsive, ensuring that oil delivery is quicker and more precise.Secondly, this reduction in volume also contributes to a more efficient distribution of oil, particularly in situations where rapid changes in engine speed or vehicle dynamics occur.This reduction in oil volume not only helps maintain the reliability and effectiveness of the lubrication system but also aligns with safety and performance considerations, ultimately enhancing the overall performance and longevity of the engine.

Results and discussion
The influence of the various modifications taken up in the dry sump lubrication system for the FSAE engine are summarized in this section.

Effect of lubrication line modification on oil pressure
The lubrication line modifications and the engine oil volumes in the piping have been computed in table 4. A total of 0.366 L of engine oil at any point would be held within the lubrication lines.As a result of increasing the hose size from 6-AN to 12-AN, there was an increase in the oil pressure during the mid-range of the engine RPM.The oil pressure variation with the engine RPM is shown in figure 12.The trend line fitted to the curve is represented by equation (2), with a negative slop mainly due to the drop in pressure at engine RPM > 10 000.The regression coefficient showed a very low value, R Larger passages result in reduced flow resistance, allowing more oil to flow through the system at the same RPM.This increased flow rate can lead to higher oil pressure, as more oil is available to maintain pressure in the  system.Additionally, larger hoses can help dissipate heat more efficiently.Oil passing through larger hoses may have more contact with the hoses' surfaces, which can help cool the oil slightly.Cooler oil can have a higher viscosity, potentially leading to higher oil pressure.But, at engine RPM > 10 000, the oil pressure drop to 20 psi was observed.Higher RPMs increase the demand for oil circulation and lubrication.High RPMs mean that the engine's components are moving at very high speeds generating greater friction and heat.Therefore, at speeds exceeding 10,000 RPM, a greater oil flow is necessary to ensure optimal lubrication and cooling.Hence, in addition to upgrading the lubrication lines to the 12-AN hose, the modification in the oil reservoir design was taken up.The drop in engine oil pressure beyond 10 000 RPM is clear from the timeline history shown in figure 13.

Effect of modification of oil reservoir design on oil pressure
After modifying the base of the oil reservoir to conical shape from the initial flat one, there was a notable increase in oil pressure with engine RPM as seen in figure 14 The conical shape can help direct oil towards the oil pump intake more effectively, especially during high-G maneuvers or when the car is subjected to significant lateral forces.This improvement likely contributed to an increase in oil pressure at lower and moderate RPMs, ensuring better lubrication and cooling.However, lower oil pressures were noticed in some cases for higher RPMs.To overcome this, the vertical baffle design inside the oil reservoir was improvised with the inclusion of a horizontal flat baffle, spiral baffle and the frustum baffle.The oil pressure variation with engine RPM after this design alteration is shown in figure 16.The time-histories of the engine RPM and oil pressure are shown in figure 17.The sudden drop in oil pressure when engine RPM approached 12 000, was noticed which had to be overcome by modifying the baffle designs.The trend line fitted The design modification in the baffles was instrumental in achieving higher pressures at higher RPMs which was extremely vital to the operation of the car in racing events.The spiral baffle construction enhanced oil swirling, promoting efficient de-aeration and eliminating disruptive air pockets that may hinder oil flow.Simultaneously, the frustum baffle plays a crucial role in controlling oil movement, minimizing sloshing, and maintaining a consistent oil level in proximity to the pickup point.These attributes are further reinforced by the  presence of a horizontal baffle, which prevents excessive side-to-side movement of the oil in the reservoir, reducing the likelihood of oil starvation during rapid changes in vehicle direction.Consistent oil pressure is vital for proper lubrication, and these modifications collectively work to mitigate the effects of lateral forces and rapid directional changes.

Effect of modification of pump feed line port design
After modifying the pump feed line port, with the side-taper in the cavity, there was a notable increase in oil pressure with engine RPM, as seen in figure 18 and the timeline of engine RPM and oil pressure is indicated in figure 19.The trend line fitted to the curve is represented by equation (5) with a high slope of 0.0092.Thus, improving the feed port design was beneficial to the oil pressure increase at higher engine RPMs.The high slope of the trend line (0.0092) indicates a strong positive correlation between engine RPM and oil pressure.This suggests that the modification resulted in a steeper increase in oil pressure as RPM increased, indicating a more responsive and effective lubrication system.The modification may have resulted in a more direct and efficient path for oil to reach the port, reducing flow resistance and improving flow rates as RPM increased.Reduced restrictions lead to smoother oil flow, preventing pressure drops that may occur when oil encounters obstacles or narrow passages.Efficient oil flow ensures that the engine receives an adequate supply of oil for lubrication and cooling.The regression coefficient was the highest after this modification, R 2 ∼ 0.8342.This high coefficient suggests that the modification had a significant and consistent impact on oil pressure, making it a reliable and predictable improvement.The oil pressure increase with the engine RPM was evident at N ∼12 000 RPM. Hence the design modifications carried out in the dry sump lubrication system resulted in optimum oil pressure-engine RPM characteristics.

5 oil
In summary, the design modifications made to the pump feed line port in the dry sump lubrication system resulted in a substantial increase in oil pressure with rising engine RPM.These modifications likely enhanced oil flow, reduced flow restrictions, optimized pump performance, and improved the pressure-flow relationship.The high correlation coefficient suggests that these changes had a consistent and beneficial impact on the engine's oil pressure characteristics, especially at high RPMs, leading to an overall optimized lubrication system performance.The modified lubrication system on the car is shown in figure 20.

Conclusions
The oil pressure characteristics with respect to the engine RPM have significantly improved as a result of the modifications made to the pump feed line port and other components of the dry sump lubrication system.Particularly in high-performance or racing settings, these findings have significant ramifications for the engine's overall performance and dependability.Based on the observations and revisions, the following are some important conclusions: • The high slope of ∼0.1 and R 2 coefficient ∼0.83 indicate a strong and consistent correlation between engine RPM and oil pressure.This suggests that the modifications have made the oil pressure characteristics more responsive and predictable as the engine operates at various speeds.
• The most notable improvements in oil pressure were observed at high engine RPMs, particularly around 12 000 RPM.This is a critical range for high-performance engines, and the modifications have ensured that the engine receives adequate lubrication and cooling even under extreme operating conditions and high g-forces.
• The modifications in the lubrication lines, the oil reservoir base and baffle alterations, the introduction of a 90-degree bend in the feed line and the subsequent modification of the pump feed line port have all resulted in enhanced oil flow dynamics.These changes have effectively reduced flow restrictions and improved the overall efficiency of the lubrication system.
• Overall, the design modifications have optimized the dry sump lubrication system with improved oil pressure characteristics, ensuring that the engine's vital components receive a consistent and sufficient supply of oil at all ranges on the engine RPM.This can lead to greater engine longevity and peak performance.
• In racing events where engine stress and demands, like cornering at high speeds, tackling longitudinal and lateral g-forces are at their highest, the enhanced lubrication system reliability reduces the risk of engine damage, leading to increased confidence in the engine's durability and performance during competitive events.
The study presents notable advancements in oil pressure characteristics through modifications to the pump feed line port and other components of the dry sump lubrication system, particularly in high-performance and racing contexts.The observed strong correlation between engine RPM and oil pressure, coupled with significant improvements at critical high RPM ranges, underscores the effectiveness of the design alterations.The design optimization is achieved, that should result in longer engine life and optimal performance.The improved lubrication system reliability acts as a vital protective measure against any damage during racing events where engine stress is at its highest, giving drivers more faith in the engine's endurance and performance in competitive situations.To sum up, the results not only enhance the current case study but also prompt a more comprehensive philosophical analysis of the relationship between design, performance, and reliability in highperformance engineering.This further advances our comprehension of the best possible solutions within this field.This study was limited to the oil pressure characterization with engine speed.The study could be extended to the effects of oil temperatures under harsh performance conditions like sudden acceleration and deceleration, abrupt change in directions during cornering or overtaking, and operation on uneven, rugged terrains.

Figure 1 .
Figure 1.Schematic of an open sump lubrication system.

Figure 2 .
Figure 2. Schematic of the custom wet sump lubrication system used for the FSAE car.

Figure 3 .
Figure 3. Engine failures due to low oil pressures and consequent oil starvation.

Figure 4 .
Figure 4.The lateral and longitudinal g-forces acting on the car during a test run.

Figure 5 .
Figure 5. Dry sump design with ports and sloped base for the FSAE engine (a) Front (b) Rear.

Figure 7 .
Figure 7. Fish bone diagram for low oil pressure in combustion engines [24].

Figure 8 .
Figure 8. Flat base oil reservoir of the dry sump system with vertical perforated baffles.

Figure 9 .
Figure 9. Conical base oil reservoir of the dry sump system with flat horizontal baffle, frustum and spiral baffles.

Figure 10 .
Figure 10.90 °oil feedline elbow welded to the dry sump casing.

Figure 11 .
Figure 11.Complete assembly of the lubrication system with modified routing of the lube lines.

Figure 12 .
Figure 12.Variation of oil pressures with engine RPM after modifying the lubrication lines.

Figure 13 .
Figure 13.Time variation of Engine RPM and Oil pressure after modification of lubrication lines.

Figure 14 .
Figure 14.Variation of oil pressures with engine RPM after modifying the oil reservoir design.

Figure 15 .
Figure 15.Time variation of Engine RPM and Oil pressure after modification of oil reservoir design.

Figure 16 .
Figure 16.Variation of oil pressures with engine RPM after modifying the oil reservoir baffles.
. The trend line fitted to the curve is represented by equation (3), the regression coefficient, R 2 ∼ 0.304.The positive slope with a value >0 indicates that the oil pressure increases with engine RPM to compensate for increased oil demand.The timeline of engine RPM and the oil pressure for this modification is shown in figure 15.The oil pressure showed constant fluctuations in the operating range of the engine RPM, indicative of the widespread dispersion in the oil pressure scatter.

Figure 17 .
Figure 17.Time variation of Engine RPM and Oil pressure after modification of oil reservoir and baffles.

Figure 18 .
Figure 18.Variation of oil pressures with engine RPM after modifying the pump feed line port with 90 °elbow.

Figure 19 .
Figure 19.Time variation of Engine RPM and Oil pressure after modification of pump feed line port.

Figure 20 .
Figure 20.Formula SAE car with the modified lubrication system.

Table 1 .
Specifications for the Honda CBR600RR Engine.

Table 2 .
Review of literature on lubrication system of Formula Student Cars.

Table 4 .
Oil volumes in the Lubrication lines.