SR20 FORGED PISTON KIT Tomei

Forming a combustion room inside the cylinder, piston is working as a core of the engine where the energy of the explosion translated into the moving moment. Accordingly, they suffer from the hugest amount of energy, the most severe fluctuation of temperature and the highest pressure from the movement among all the engine parts.

Since piston is one of the most important parts in the engine exchanging combustion energy into the moving moment, the material of the piston must have enough strength against severe fluctuation of temperature and extremely high pressure from the movement. Cast metal, which is used for the stock piston, is suitable for mass production but cannot maintain enough strength when used in those tuned engines that produces over 100hp per cylinder. Instead, forged metal made from alloy aluminium, must be used as the material for those parts that will be used under the severe circumstances beyond stock level. Atmospheric pressure from combustion; 200kgf/・. Total amount of concerned energy is 11tons. Temperature of exploding gas; 2500℃.
You have to focus on the truth that todayﾕs highly tuned engines now have reached equal level with the racing engines of former group C and Formula 1.

The expansion rate of running piston body will be various according to the structure and its condition of drive. To comprehend the subtle changing of the expansion accurately, we gave countless testing on the bench and it resulted in this oval-barrel shaped piston that is designed in 3dimentions. Considering both pistonﾕs temperature distribution that is affected vastly from its shape and driven circumstances, and wide expansion rate character of the aluminium, it is necessary to understand the exact temperature and expansion rate of every parts of the piston body in order to give it a appropriate clearance from cylinder. We succeeded to calculate out this oval-barrel shaped piston in 1/1000 mm level accuracy under the highest pressure to correct the distortion.

Too much clearance between cylinder and piston will results not only in incomplete combustion and power down of the engine, but also cause the piston to rock inside the cylinder and oil to blowby. Blowby would tear the oil sealing between cylinder and piston ring, or mixed into the engine oil and spoil the oil. It is not rare that blowby cause the blown crank metal or worn out metal. Moreover, on such places where the expansion rate is high and clearance is narrow, piston rings would blow or the cylinder gets scuffed. Especially in the case of the perfect-circled piston, it is impossible to correct the heat expansion from top land to piston-pin-boss direction where the temperature gets highest, and this is why the "hit" tend to occur at vertical direction of the piston in some tuned engine that installed perfect-circled piston.

Cooling channel is the most efficient way of keeping temperature of the piston body down that is not only used in the racing engine but also adopted in high performance-mass produced engines. It takes so huge advantages in cooling the temperature of the piston body, resulting torque, boost, max RPM and durability are extremely superior that it is almost meaningless to compare to the ones without channel.
To get the desired performance from the engine, it is necessary to reduce the temperature of the combusting gas from 2500℃ to 300℃ at most at the top of the piston. If the temperature of the combusting gas exceeds 300℃, piston no longer be able to keep the enough strength to stand the enormous exploding power. Basically, total amount of thermal energy is "the larger the better", however, there is a certain limit of temperature where you cannot exceed it. Understanding and taking control of the subtle adjustment of temperature of engine parts enables you to get the most power out of your engine. Cooling channel can reduce the temperature of piston head about 50 to 60℃, and this cooling performance gives you great advantages on boost torque, maximum RPM, load, duration time, and so on to gain greater combusting energy.