Twisted Steel Performance
Anything worth doing is worth overdoing.
While the TBC (Thermal Barrier Coating) function on a Piston top coating is important it is different than a normal TBC, when used in an internal combustion chamber engine. Typically, with a TBC we are looking for the maximum reduction in thermal transfer possible and the thicker and denser a coating is the more heat transfer is reduced. However, this is not the case with an internal combustion chamber engine.
An engine is a cyclical environment and while the temperature of combustion can reach above 1100C/2000F this is just a momentary event. Even with EGT’s (Exhaust Gas Temperatures) reaching over 820C/1500F the piston does not normally reach a temperature over 205C/400F. If it did the alloy would begin to rapidly fail leading to engine damage. A few alloys even soften below that temperature.
Why is this the case? The piston experiences 4 strokes (The general principles will also apply to a 2 stroke or even a Rotary engine); a power stroke where the heat is generated, the exhaust stroke where the majority of the heat generated by combustions is driven out the exhaust port, an intake stroke where a much cooler air fuel mix is drawn in and a compression stroke where some heat is generated prior to ignition by the compressive action. The actual time the piston sees the very high temperatures before being cooled is extremely minimal.
If a typical V8 engine was turning 2000 RPM, each piston is firing 1000 times or about 66 times per second. There is a very short period of time for the piston to absorb the heat of combustion. Consequently, the totality of TBC function, while important, is just one of the critical functions of a TBC.
When we consider it is normal to hold engine oil temperatures to between 230F to 260F and the oil is the primary coolant for the piston, it does not take a large drop in temperature before the oil would stabilize the piston temperature. If a TBC actually took the temperature of the piston below the oil temperature, the oil would heat the piston. It is true that a good TBC will also reduce the oil temperature and in testing our coatings have shown a drop-in oil temperature of about 8C/47F.
Tech Line has been producing TBC’s for 30 years and originally started working with Top Fuel Dragster Engines. In initial testing, we dropped the piston temperature over 25%. This would mean a piston running at about 380F uncoated, would now be running at about 295F. The total drop in temperature at this point is not significantly of importance. Why not?
Once below the temperature that a piston alloy can begin to degrade there are other areas of greater concern than the heat of the piston during the power stroke. Once the power stroke and exhaust stroke are completed the next critical event is the intake stroke when the cool air fuel mix impacts the piston. The critical event at this point is how much eat is retained by the TBC. That heat will now transfer to the air fuel mix and begin to heat that up. As compression heat is added the total heat in the air fuel mix it can lead to pre-ignition or detonation/pinging. This leads to power loss and potential damage to the piston.
While the piston temperature can impact the clearances set, and tighter clearances can be set, there is also a limit to the benefit here. Some clearance is needed for the rings to function properly. The alloy of the piston will also impact the clearances desired when considering the expansion rate of the TBC treated piston.
In addition the actual shape, total area, sharp surfaces such as the edge of a valve relief on the piston and the existence of any tight compression areas in the compression chamber, can also impact the fuel burn. These issues need to be addressed by a good TBC as well.
This is why we specialize in thin film coatings. The total thickness of the TBC is not critical to the actual need for a TBC. Once the temperature of the piston has dropped by the 25% we have experienced, its first function has been fulfilled. The next functions also do not require a thick coating. This is the ability of the coating to do the following:
The thin coating simply cannot retain much heat, nothing even close to a much thicker coating. In addition, the natural TBC function will reduce or even eliminate any reversion of heat from the piston back to the surface of the TBC. This means less total heat can be transferred to the incoming air fuel mix, moving the engine away from pre-ignition issues. This also means the amount of timing can be reduced as the issue of pre-ignition is reduced and less initial timing improves mid range power and results in better fuel mileage.
The ability to transfer some heat over the surface is also important as it means a reduction in any hot spots, which can cause pre-ignition, more even heat both during the power stroke (More even piston temperature also means lower temperature overall) and intake stroke, which leads to better oxidation of the fuel and potentially better flame travel. This leads to more efficient combustion of the fuel and the ability to reduce the fuel air mix as more of the fuel will be burned in the same amount of air. Reducing the fuel in the air, leaning, without any detonation issues will improve fuel mileage and potentially emissions.
In testing and in actual use in Race Engines as well as Street Engines, timing has been reduced from 2 to 5 degrees and the air fuel ration has been significantly reduce (leaned). In carbureted engines a 4 to 5 size reduction in jets is common, and a similar change in fuel injected engines. IN certain instances the timing was not changed significantly and the benefits were still seen. Each engine and its design is different.
In addition, due to the thin film of the TBC the likelihood of any film delamination is minimal and of it does occur, a condition known as Frangibility exists (meaning the particles will be extremely small and can cause no damage).
Thicker coatings will not reduce any further significant amount of heat in the piston, will not hold significantly more heat in the chamber than a Thin Film TBC during the Power stroke, and will hold more heat in the coating due to the total mass leading to a greater transfer of heat to the incoming air fuel mix and will have minimal impact on the surface temperature variations on a piston top. These are of concern, but the greatest issue is delamination.
If we see a thick coating experiencing 2000F at the surface and 290F at the piston top, then the vast difference in temperature the coating is experiencing will lead to dramatic expansion and contraction. This is especially critical on very thick or hard coatings. The rigidity can cause even faster failure. When micro cracking occurs and ultimately delamination, the particle size is now of great concern as well, especially if these particles end up around the rings or even in the exhaust flow on a Turbo Charged engine.
The thin film TBC’s do not experience these significant heat variations and are also formulated to mirror the actual rate of expansion and contraction of the piston, making delamination a non issue.
In testing in real world applications as well as on Dynamometers, coated pistons in a typical V8 engine usually show an increase of about 10HP and totally coated pistons and combustion chamber surfaces have shown 25 HP gains.
On pistons (and Combustion Chamber surfaces) actual testing and use for over a 30-year period, have demonstrated the superiority of Thin Film TBC’s.
An engine is a cyclical environment and while the temperature of combustion can reach above 1100C/2000F this is just a momentary event. Even with EGT’s (Exhaust Gas Temperatures) reaching over 820C/1500F the piston does not normally reach a temperature over 205C/400F. If it did the alloy would begin to rapidly fail leading to engine damage. A few alloys even soften below that temperature.
Why is this the case? The piston experiences 4 strokes (The general principles will also apply to a 2 stroke or even a Rotary engine); a power stroke where the heat is generated, the exhaust stroke where the majority of the heat generated by combustions is driven out the exhaust port, an intake stroke where a much cooler air fuel mix is drawn in and a compression stroke where some heat is generated prior to ignition by the compressive action. The actual time the piston sees the very high temperatures before being cooled is extremely minimal.
If a typical V8 engine was turning 2000 RPM, each piston is firing 1000 times or about 66 times per second. There is a very short period of time for the piston to absorb the heat of combustion. Consequently, the totality of TBC function, while important, is just one of the critical functions of a TBC.
When we consider it is normal to hold engine oil temperatures to between 230F to 260F and the oil is the primary coolant for the piston, it does not take a large drop in temperature before the oil would stabilize the piston temperature. If a TBC actually took the temperature of the piston below the oil temperature, the oil would heat the piston. It is true that a good TBC will also reduce the oil temperature and in testing our coatings have shown a drop-in oil temperature of about 8C/47F.
Tech Line has been producing TBC’s for 30 years and originally started working with Top Fuel Dragster Engines. In initial testing, we dropped the piston temperature over 25%. This would mean a piston running at about 380F uncoated, would now be running at about 295F. The total drop in temperature at this point is not significantly of importance. Why not?
Once below the temperature that a piston alloy can begin to degrade there are other areas of greater concern than the heat of the piston during the power stroke. Once the power stroke and exhaust stroke are completed the next critical event is the intake stroke when the cool air fuel mix impacts the piston. The critical event at this point is how much eat is retained by the TBC. That heat will now transfer to the air fuel mix and begin to heat that up. As compression heat is added the total heat in the air fuel mix it can lead to pre-ignition or detonation/pinging. This leads to power loss and potential damage to the piston.
While the piston temperature can impact the clearances set, and tighter clearances can be set, there is also a limit to the benefit here. Some clearance is needed for the rings to function properly. The alloy of the piston will also impact the clearances desired when considering the expansion rate of the TBC treated piston.
In addition the actual shape, total area, sharp surfaces such as the edge of a valve relief on the piston and the existence of any tight compression areas in the compression chamber, can also impact the fuel burn. These issues need to be addressed by a good TBC as well.
This is why we specialize in thin film coatings. The total thickness of the TBC is not critical to the actual need for a TBC. Once the temperature of the piston has dropped by the 25% we have experienced, its first function has been fulfilled. The next functions also do not require a thick coating. This is the ability of the coating to do the following:
- Retain minimal heat
- Transfer heat over the surface of the coating
- Transfer minimal heat to the incoming air fuel mix.
- Aid combustion
- Increase power output
The thin coating simply cannot retain much heat, nothing even close to a much thicker coating. In addition, the natural TBC function will reduce or even eliminate any reversion of heat from the piston back to the surface of the TBC. This means less total heat can be transferred to the incoming air fuel mix, moving the engine away from pre-ignition issues. This also means the amount of timing can be reduced as the issue of pre-ignition is reduced and less initial timing improves mid range power and results in better fuel mileage.
The ability to transfer some heat over the surface is also important as it means a reduction in any hot spots, which can cause pre-ignition, more even heat both during the power stroke (More even piston temperature also means lower temperature overall) and intake stroke, which leads to better oxidation of the fuel and potentially better flame travel. This leads to more efficient combustion of the fuel and the ability to reduce the fuel air mix as more of the fuel will be burned in the same amount of air. Reducing the fuel in the air, leaning, without any detonation issues will improve fuel mileage and potentially emissions.
In testing and in actual use in Race Engines as well as Street Engines, timing has been reduced from 2 to 5 degrees and the air fuel ration has been significantly reduce (leaned). In carbureted engines a 4 to 5 size reduction in jets is common, and a similar change in fuel injected engines. IN certain instances the timing was not changed significantly and the benefits were still seen. Each engine and its design is different.
In addition, due to the thin film of the TBC the likelihood of any film delamination is minimal and of it does occur, a condition known as Frangibility exists (meaning the particles will be extremely small and can cause no damage).
Thicker coatings will not reduce any further significant amount of heat in the piston, will not hold significantly more heat in the chamber than a Thin Film TBC during the Power stroke, and will hold more heat in the coating due to the total mass leading to a greater transfer of heat to the incoming air fuel mix and will have minimal impact on the surface temperature variations on a piston top. These are of concern, but the greatest issue is delamination.
If we see a thick coating experiencing 2000F at the surface and 290F at the piston top, then the vast difference in temperature the coating is experiencing will lead to dramatic expansion and contraction. This is especially critical on very thick or hard coatings. The rigidity can cause even faster failure. When micro cracking occurs and ultimately delamination, the particle size is now of great concern as well, especially if these particles end up around the rings or even in the exhaust flow on a Turbo Charged engine.
The thin film TBC’s do not experience these significant heat variations and are also formulated to mirror the actual rate of expansion and contraction of the piston, making delamination a non issue.
In testing in real world applications as well as on Dynamometers, coated pistons in a typical V8 engine usually show an increase of about 10HP and totally coated pistons and combustion chamber surfaces have shown 25 HP gains.
On pistons (and Combustion Chamber surfaces) actual testing and use for over a 30-year period, have demonstrated the superiority of Thin Film TBC’s.