From the combustion chamber to the cylinder, a piston works inside the core of the engine assembly where the energy of the explosion is converted into rotational movement. The piston suffers the most abuse out off all the components inside an engine, withstanding such factors as the force from constant amounts of massive energy and severe fluctuation in temperatures.
FORGED PISTON
Since the piston is one of the most important components in an engine assembly, transferring combusted energy to mechanical movement, it must have enough strength to withstand severe temperature fluctuations and high pressures. Stock OEM manufactured pistons are typically made from cast metal and is ideal for mass production, however they cannot sustain the stress when used in highly modified engines that produce over 100 horsepower per cylinder. By using forged metal made from aluminum alloy to construct our pistons, the metal can then endure severe circumstances beyond the stock level. These forged pistons can withstand combustion pressures of 200 kgf and 11 tons of force with the combusted gas temperatures up to 2,500 degrees Celsius. Tomei pistons that are used in highly tuned RB26 and SR20 engines are the same type of pistons used in Group C and F1 racing.
3 DIMENSION PROFILE
The metal expansion rate in each piston will differ according to the material of the piston and driving conditions. In order to develop the perfect piston for each and every engine types, we have studied the characteristics of heat expansion in aluminum with many prototypes and countless hours on the engine bench dynamometer. The resulting product is a 3 dimensional profile of the oval and barrel design. We have succeeded to produce a piston in 1/1000 mm of accuracy that applies to the appropriate piston to wall clearance.
Too big of a clearance results in power loss due to escaping gases between the cylinder wall and piston rings (blow-by), with decreased combusted energy transferred to mechanical movement. Another factor that causes blow-by is when the clearance is too large; the piston begins to rock at its pin axis inside the cylinder, causing the piston to scuff the cylinder walls at times. Perfectly circled pistons are unable to wholly expand into the diameter of the cylinder, especially because of the difference in thermal expansion between the top land and piston skirt areas. This is why in some engines, the contact occurs at the vertical position of the perfectly circled piston because of the uneven expansion.
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THINNER RINGS
We selected high performance thinner piston ring for less friction loss and to prevent fluttering. This can also prevent having a floating piston ring by reducing its inertia to help cut down the blowby. In addition to it, there will be more open area for designing between the piston head and piston pin; it is possible to set the size and shape of the piston topland freely. Designed in an ideal spec the pistons strength has been dramatically increased.
APPLICATION SPECIFIC ESPECIALLY FORGED CORES
By using especially selected forged metal alloys on each part of our products, we succeed to giving our products an extraordinary extraordinary strength while greatly reducing the pistons overall weight. For this reason it is impossible to make all pistons on the same metal core as it may not be beneficial for another engines application.
EXTREME TESTING
TOMEI forged piston has been through extensive extreme testing on the engine dyno and in real life applications both on the street and as you can see here in actual drag racing (photo os of the TOMEI BNR34 Drag Machine). In our drag racing GTR we installed TOMEI forged pistons in the RB26DETT engine which made over 1000 HP on 3.3kg/E of boost and after a season of racing it passed successfully.
"DUMMY HEAD" BORING
RB26 engine block with dummy head
Piston is installed after boring and horning
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It is impossible for the car manufacturers to mass produce pistons with high gas sealing properties when considering the cost, productivity and the difficulty of all year round climate conditions as well as possible lack of maintenance and high mileage use etc. The cylinder block which is manufactured in the production line of car manufacturers has a given quality and cylinder accuracy by itself, yet this is not enough to keep equal quality and accuracy when it is assembled with a mass produced cylinder head. Therefore to give cylinder a high gas sealing characteristics that is highly accurate, even after the head is attached the use of the oversized pistons with proper profile and then accurate boring of the cylinder block with the "dummy-head" attached is necessary.
