Turbo charged and gasoline direct injection (T-GDI) engines have been the craze of the automotive industry. Most cars coming off the assembly line utilize at least one if not both of these systems. Why has turbo charging or gasoline direct injection become the norm? The answer to that question has to do with the federal government.
In the 1970s, the US federal government created what are called CAFE requirements. CAFE stands for Corporate Average Fuel Economy. This was created in the 1970s and the federal government has mandated that all automobile manufacturers produce vehicles that can deliver a minimum average fuel economy or face penalties. Over the years, CAFE minimum allowable fuel mileage economy has risen and by 2026, automaker vehicle fleets must meet 40 mpg. To meet these requirements, OEMs have been utilizing any advanced technology they feel will help meet these requirements, which includes turbos and direct injection.
How Turbos Improve Fuel Economy
A turbo charger basically is an air compressor that is powered by exhaust gasses. These exhaust gasses then spin a turbine that pulls air through the intake and then forces it into the combustion chamber. This process enhances combustion because of the increased oxygen, which then translates to improved horsepower and fuel economy.
Turbo chargers seem like the perfect technology to increase fuel economy and power, but there’s a downside.
Turbos Create Too Much Heat
A turbo charger spins upwards of 300,000 rpm. Stop and think about that tremendous speed. To gain a perspective on those high rpms, understand that the average engine today redlines at about 6,000 rpms. What this means is that a turbocharger will spin up to 50 times faster than your engine can run. The gases that cause a turbine to spin at such high rpms can exceed 1,000 degrees F, so the blistering heat along with the extreme spinning action together can cause deposit buildup, which is known as turbo-coking. If left unchecked, this turbo-coking can cause catastrophic failure of the turbocharger.
Conventional or Synthetic Oil for Turbo Cars?
Turbochargers rely on engine oils to cool and lubricate them, so the logical strategy is to find the best possible engine oil for your turbocharged car or truck.
When choosing the best oil for turbo cars, it is critical that the base stock oils used in the manufacturing of the oil be thermally stable and be able to withstand tremendous heat and still maintain its viscosity through a wide temperature range. Conventional base oils come from the ground and are refined from this crude oil. Mineral based oils or conventional lubricants contain unwanted byproducts, such as sulfur, nitrogen, oxygen, etc.
Also, when the processing of crude oil is finished, the molecular structure of a conventional oil contains molecules that are dissimilar in structure. With its unwanted byproducts and uneven molecular structure, mineral oils are not the best choice for turbo charged engines. Over time, they will start to oxidize when exposed to high heat and this oxidation leads to deposits. These deposits are quite detrimental to the turbocharger.
Also, a mineral based oil will not retain its viscosity when exposed to heat. It will start to fail to reach its required viscosity grade. Conversely, synthetic base stock oils are man made and chemically engineered to create pure base stock oils. These synthetic base stock oils have no unwanted byproducts, plus the molecules are of uniform size and structure. Synthetic base stock oils can withstand tremendous temperatures, making them thermally stable and when exposed to heat, they are able to maintain their viscosity. They offer better friction reduction, tough film strength, and extreme temperature performance.
Their superior capabilities in these areas make them the ideal choice when creating the best oil for turbo cars. An example of a high performance synthetic oil for turbo cars would AMSOIL’s Signature Series Synthetic Motor Oil. Signature Series will reduce deposit buildup on turbo spindles and will help maintain performance.
During independent testing of Signature Series 5W30 in the GM Turbo Coking Test, AMSOIL’s oil was able to control heat and it minimized any deposits from forming on the turbo bearing and shaft surfaces. The conclusion from the test showed that Signature Series protects turbochargers 72% better than is required by the GM Dexos1 Gen 2 specification. In other words, Signature Series circulates through the turbocharger and will cool the turbo properly and help to reduce any formation of deposits that could rob the turbocharger of performance.
A good idea to help lengthen the life of your vehicle’s turbocharger is to let your turbo car idle for 1 or 2 minutes after driving.
Gasoline Direct Injection
Another popular technology that car makers have designed into engines along with turbos is the gasoline direct injection (GDI). In the past, fuel injectors were located in the intake manifold, but GDI engines locate the fuel injectors directly in the combustion chamber. By locating the fuel injectors inside the combustion chamber, car maker engineers can now very accurately control fuel injection timing and in many cases can perform multiple injections during the same piston stroke.
Traditional port injected engines have an air/fuel ratio that operates around 14.7:1. On the other hand, GDI systems are so precise that the computers are able to adjust air/fuel ratios to be as lean as 50:1, depending on the conditions. This type of advanced precision translates into superior fuel mileage economy.
Modern Fuel Pumps
Traditional port fuel injected engines have fuel pumps that generate fuel pressure of about 40 psi. In comparison, today’s GDI engines come with fuel pumps that generate high pressures of up to 2,000 psi. By having fuel pumps that generate such high fuel pressures, this goes a long way toward helping keep cylinders cool and also to atomize the fuel better for a more complete and efficient burn.
GDI Engines and Fuel Dilution
Yes, GDI engines offer many benefit, but like all things, there is no perfection and in the case of GDI engines there are a few negative issues that can occur. By locating the fuel injectors in the combustion chamber, the potential for over-spray to hit the far cylinder wall is a real possibility. If over-spray occurs and the fuel finds a way past the piston rings, this fuel can end up in the oil sump and unfortunately can contaminate the engine oil.
Engineers are constantly trying to find new piston designs so that this fuel can be trapped in the combustion chamber and not find a way past the rings. By trapping the fuel within the combustion chamber, you obviously improve efficiency and then minimize the potential for fuel dilution.
GDI Engines and Intake Valve Deposits
Another potential issue that can occur with GDI engines is the potential for deposits to form on intake valves. In the past, traditional port fuel injected engines were designed in such a way so that the detergent-rich fuel washed over the intake valves, which kept deposits from forming, and thus kept the intake valves clean. Unfortunate, modern GDI engines are designed in a way where fuel no longer comes in contact with the backside of the valves, causing the real potential for deposit buildup on the intake valves.
If this deposit buildup is not taken care of and dealt with, then over a period of time these deposits can stop the valves from seeding properly. If this happens, then there will be a drop in engine performance along with a drop in fuel mileage economy.
Maintaining Your Turbo, Direct Injected Car
If you keep your vehicle on a strict maintenance program, which includes the use of a high performance engine oil such as one manufactured by AMSOIL and couple that with a superior oil filter, then you won’t have to deal with problems that could arise with your turbocharger or fuel injectors. Utilizing the best oil for turbo cars, such as AMSOIL Signature Series Motor Oil, will keep your turbocharger and engine protected regardless of the temperature or the environment it is running in.
Beyond using a quality synthetic motor oil, it also makes sense to keep your fuel injectors clean and performing efficiently by utilizing a powerful fuel additive such as AMSOIL’s PI Fuel Additive. AMSOIL PI Performance Improver Gasoline Additive will remove tough deposits that may have formed. In fact, independent test results show that PI was able to restore GDI fuel injectors to a 100% flow rate after just one tank full of fuel.
PI helps to keep valves clean, it will restore performance and power, it minimizes any need for more expensive higher octane fuel, it will reduce noise from pre-ignition and carbon wrap, and it helps control pre-ignition knock. On average, PI will improve fuel mileage economy anywhere from 2.3% up to 5%. Also, it offers environmental benefits by helping to reduce harmful emissions.
Another way to maintain the benefits that have been reaped through the use of a effective fuel additive such as PI is to also add to your maintenance program an upped cylinder lubricant such as the one formulated by AMSOIL. By consistently utilizing AMSOIL’s Upper Cylinder Lubricant, you will have replenished the helpful lubricity that is required in the fuel system, which unfortunately was refined out of the gasoline. By adding back lubricity to the fuel, you’re able to maximize and preserve performance and horsepower and maintain the gains in fuel mileage economy.
Beware of Low Speed Pre-Ignition (LSPI)
Automotive engineers have definitely been able to deliver fuel economy and meet the tough CAFE requirements through the use of turbochargers and GDI engines. Unfortunately, there is a potentially catastrophic downside when these two advanced technologies are used together. One must be extremely wary of an abnormal combustion event known as low speed pre-ignition.
Turbocharged gasoline direct injection engines, because of their higher power density, can be susceptible to the phenomenon known as low speed pre-ignition (LSPI). When the fuel-air mixture ignites before it is intended, this causes excessive pressure inside the cylinders of an engine, thus the phenomenon known as low speed pre-ignition.
At the bare minimum, LSPI can create an audible knocking noise that can be notice by the driver. If the engine repeatedly is exposed to this knocking, then the potential for certain engine failures such as cracked pistons and cracked spark plugs can occur.
There are various theories on why LSPI occurs. One theory is that an oil droplet could enter the combustion chamber by finding a way past the piston ring and cylinder wall. This oil droplet then mixes with fuel and then auto-ignites. Another theory is that deposits that have formed ignite and cause premature ignition. Again, another source for LSPI.
LSPI has created an incredibly difficult environment for lubricant manufacturers and more and more engine oil manufacturers are being called on to help in trying to minimize the occurrence of low speed pre-ignition. One company that has been successful at protecting engines against LSPI has been AMSOIL.
Independent tests have proven that AMSOIL’s Signature Series 100% Synthetic Motor Oil can provide 100% protection against LSPI. The test that was utilized in proving AMSOIL synthetic motor oil’s capabilities in protecting against LSPI was the GM Dexos1 Gen 2 specification test.
The chemists are now playing a huge role in combating LSPI and, of course, how a chemist formulates an engine oil can go a long way in either reducing LSPI or making it worse. There are engine oil ingredients that add to low speed pre-ignition while other ingredients help to minimize this phenomenon. It is a lubrication engineering balancing act that lubricant manufacturers must deal with.
It is a huge ask to formulate an engine oil that can provide superior wear protection, handle the tremendous heat that is generated by turbocharged engines, be able to reduce and eliminate deposits, and now be asked to fight against LSPI. The ultimate objective is to create the proper engine oil formulation, choose the correct ingredients so that the motor oil can do all the myriad of tasks it must perform, all the while being able to protect critical engine components.
We must embrace the magical capabilities of today’s modern engines and appreciate and enjoy their amazing performance capabilities and useful fuel economy capabilities. If one decides to protect your engine and vehicle with AMSOIL Synthetic Lubricants, then after enjoying your vehicle for the day, you can sleep soundly at night with the knowledge that AMSOIL provides your vehicle with the absolute finest protection there is, which allows you to enjoy all the benefits and joys that your vehicle gives you.