Note: Added ring gas port making a total of 6 rather than 4 and piston diameter is 83mm for an overbore or rebuild application where as the original piston was 82.465mm in diameter. Pistons are not round, they are slightly oval shaped to compensate for thermal expansion of material on axis of the wrist pin. This is a ROUND piston ie: no compensation of dimension along pin axis for thermal expansion!
Original Audi pistons have a pin offset of 2mm from center. This is to reduce piston slap and noise. All my files and the JE pistons that are being used have no pin offset. This makes for more noise but more power and cylinder bore wear.
Click to Download: Original Piston File
Click to Download: Piston for JE Rings
Here is the final finished piston machined by JE pistons:
"Pistons that are made from 4032 wrought aluminum alloy are designed for street/strip applications utilizing compression ratios that are compatible with pump gas. These pistons also provide a quieter engine on cold start-up.
Physical Properties of 4032
Nominal Density 2.68 g/CC. 097 lb/in3
Mechanical Properties of 4032
Tensile Strength, Ultimate 380 MPa 55, 000 psi
Tensile Strength, Yield 315 MPa 46, 000 psi
Modulus of Elasticity 79 GPa 11, 400 psi
Fatigue Endurance Limit 110 MPa 16, 000 psi
2618 forged piston blank
Pistons made from 2618 wrought aluminum
Alloy are designed for higher performance
Applications such as FlyWeight or domed highcompression
Pistons. These environments necessitate
The higher tensile strength 2618 aluminum alloy.
Physical Properties of 2618
Nominal Density 2.81 g/CC. 100 lb/in3
Mechanical Properties of 2618
Tensile Strength, Ultimate 440 MPa 64, 000 psi
Tensile Strength, Yield 370 MPa 54, 000 psi
Modulus of Elasticity 74 GPa 10, 400 psi
Fatigue Endurance Limit 125 MPa 18, 000 psi
Coefficient of Thermal Expansion
2618 aluminum expands approximately 15% more than 4032 aluminum, thus the 2618's initial piston-to-wall clearance has to be 15% greater. This difference is most noticeable during a cold engine start. When cold, the 2618 piston can rock back and forth producing a slight noise (sometimes referred to as piston slap)
Until the aluminum expands. Both types of aluminum have approximately the same clearances once the pistons have expanded and the engine is running at operating temperatures. Temperature Range Average Coefficient C F μm/m K μin/in F 20 to 200 68 to 392 23.2 12.9
Coefficient of Thermal Expansion for 2618 BOLD = NEEDS EDITING
Temperature Range Average Coefficient
C F μm/m K μin/inF
20 to 200 68 to 392 20.2 11.2
EXAMPLE: When measured at room temperature, a 4 inch diameter piston made from 4032 measures 4.000". If the same piston weremeasured at 375, the piston would measure 4.0034".
Coefficient of Thermal Expansion for 4032
Temperature Range Average Coefficient
C F μm/m K μin/inF
20 to 200 68 to 392 20.2 11.2
EXAMPLE: When measured at room temperature, a 4 inch diameter piston made from 4032 measures 4.000". If the same piston were measured at 375, the piston would measure 4.0034"."
More on the thermal expansion of pistons and cylinder walls here: Click
A whole paper on thermal expansion of pistons: Click
Physical Properties of 4032
Nominal Density 2.68 g/CC. 097 lb/in3
Mechanical Properties of 4032
Tensile Strength, Ultimate 380 MPa 55, 000 psi
Tensile Strength, Yield 315 MPa 46, 000 psi
Modulus of Elasticity 79 GPa 11, 400 psi
Fatigue Endurance Limit 110 MPa 16, 000 psi
2618 forged piston blank
Pistons made from 2618 wrought aluminum
Alloy are designed for higher performance
Applications such as FlyWeight or domed highcompression
Pistons. These environments necessitate
The higher tensile strength 2618 aluminum alloy.
Physical Properties of 2618
Nominal Density 2.81 g/CC. 100 lb/in3
Mechanical Properties of 2618
Tensile Strength, Ultimate 440 MPa 64, 000 psi
Tensile Strength, Yield 370 MPa 54, 000 psi
Modulus of Elasticity 74 GPa 10, 400 psi
Fatigue Endurance Limit 125 MPa 18, 000 psi
Coefficient of Thermal Expansion
2618 aluminum expands approximately 15% more than 4032 aluminum, thus the 2618's initial piston-to-wall clearance has to be 15% greater. This difference is most noticeable during a cold engine start. When cold, the 2618 piston can rock back and forth producing a slight noise (sometimes referred to as piston slap)
Until the aluminum expands. Both types of aluminum have approximately the same clearances once the pistons have expanded and the engine is running at operating temperatures. Temperature Range Average Coefficient C F μm/m K μin/in F 20 to 200 68 to 392 23.2 12.9
Coefficient of Thermal Expansion for 2618 BOLD = NEEDS EDITING
Temperature Range Average Coefficient
C F μm/m K μin/inF
20 to 200 68 to 392 20.2 11.2
EXAMPLE: When measured at room temperature, a 4 inch diameter piston made from 4032 measures 4.000". If the same piston weremeasured at 375, the piston would measure 4.0034".
Coefficient of Thermal Expansion for 4032
Temperature Range Average Coefficient
C F μm/m K μin/inF
20 to 200 68 to 392 20.2 11.2
EXAMPLE: When measured at room temperature, a 4 inch diameter piston made from 4032 measures 4.000". If the same piston were measured at 375, the piston would measure 4.0034"."
More on the thermal expansion of pistons and cylinder walls here: Click
A whole paper on thermal expansion of pistons: Click
