That crown design was 3rd on the best top we tested.
15.8:1cr and almost zero angles. Gain 6% more hp than traditional domed flat high cr piston crowns with angles. This is direct after dynorun of 990hp using VPimport and 15psi boost.
The shape of the piston bowl controls the movement of air and fuel as the piston comes up for the compression stroke (before the mix is ignited and the piston is pushed downward.) The air and fuel swirl into a vortex inside the piston bowl before combustion (or compression) takes place, creating a better mixture. By affecting the air/fuel mixture, you can achieve better and more efficient combustion, which leads to more power.
Of the types of motion popularly being studied, swirl and tumble are foremost. Motion that tends to be directed along the plane of inlet flow generally describes swirl. This can be movement in the same direction as this flow, or in an opposite direction. Positive swirl is motion in the same direction as incoming flow. Negative swirl is in an opposite direction but still in the plane of the inlet flow. Tumble is motion akin to rolling a ball down a flight of stairsessentially end-over-end flow in a plane roughly perpendicular to the swirl plane or axis of the crankshaft.
The shape of a pistons crown can affect both swirl and tumble. In its simplest form, a flat-top piston can influence swirl more than tumble. This is because protrusions above the pistons deck surface are minimized, leaving a broad surface upon which features can be built for swirl enhancement. These include tapered ramps and/or strategically placed texturing or dimples, all intended to modify the quality of swirl, improve quench, and aid combustion efficiency.
Where engine-building rules permit higher mechanical compression ratios, the effectiveness of piston-crown protrusions in the combustion chamber should be carefully considered. Protrusions, or shapes built into the cylinder head, can encourage flame migration toward the exhaust valve, but at the same time they increase compression ratio. This opens the possibility that such protrusions can cause an impediment to flame movement and a disruption of the air/fuel mixture during the burn. The potential result is lost power and possible detonation from excessively lean blends in affected areas.
When considering the advantages of manipulating the shape and texture of the piston crown to enhance in-cylinder mixture motion, remember that there are advantages and disadvantages to swirl and tumble. Even though swirl tends to increase flame rate and help deliver a more uniform rate of combustion, used improperly it can lead to increased spark timing and reduced volumetric efficiency. Excessive swirl can also cause heavier fuel droplets to be centrifuged from the airstream, which disrupts the in-cylinder air/fuel mixture ratios. Tumble also has advantages and disadvantages. Much like swirl, it can aid combustion rate and uniformity. It can also reduce net volumetric efficiency, leading to losses in net torque. But implemented correctly, either by itself or in conjunction with swirl, tumble can produce increased power.
That crown design was 3rd on the best top we tested.
15.8:1cr and almost zero angles. Gain 6% more hp than traditional domed flat high cr piston crowns with angles. This is direct after dynorun of 990hp using VPimport and 15psi boost.
The shape of the piston bowl controls the movement of air and fuel as the piston comes up for the compression stroke (before the mix is ignited and the piston is pushed downward.) The air and fuel swirl into a vortex inside the piston bowl before combustion (or compression) takes place, creating a better mixture. By affecting the air/fuel mixture, you can achieve better and more efficient combustion, which leads to more power.
Of the types of motion popularly being studied, swirl and tumble are foremost. Motion that tends to be directed along the plane of inlet flow generally describes swirl. This can be movement in the same direction as this flow, or in an opposite direction. Positive swirl is motion in the same direction as incoming flow. Negative swirl is in an opposite direction but still in the plane of the inlet flow. Tumble is motion akin to rolling a ball down a flight of stairsessentially end-over-end flow in a plane roughly perpendicular to the swirl plane or axis of the crankshaft.
The shape of a pistons crown can affect both swirl and tumble. In its simplest form, a flat-top piston can influence swirl more than tumble. This is because protrusions above the pistons deck surface are minimized, leaving a broad surface upon which features can be built for swirl enhancement. These include tapered ramps and/or strategically placed texturing or dimples, all intended to modify the quality of swirl, improve quench, and aid combustion efficiency.
Where engine-building rules permit higher mechanical compression ratios, the effectiveness of piston-crown protrusions in the combustion chamber should be carefully considered. Protrusions, or shapes built into the cylinder head, can encourage flame migration toward the exhaust valve, but at the same time they increase compression ratio. This opens the possibility that such protrusions can cause an impediment to flame movement and a disruption of the air/fuel mixture during the burn. The potential result is lost power and possible detonation from excessively lean blends in affected areas.
When considering the advantages of manipulating the shape and texture of the piston crown to enhance in-cylinder mixture motion, remember that there are advantages and disadvantages to swirl and tumble. Even though swirl tends to increase flame rate and help deliver a more uniform rate of combustion, used improperly it can lead to increased spark timing and reduced volumetric efficiency. Excessive swirl can also cause heavier fuel droplets to be centrifuged from the airstream, which disrupts the in-cylinder air/fuel mixture ratios. Tumble also has advantages and disadvantages. Much like swirl, it can aid combustion rate and uniformity. It can also reduce net volumetric efficiency, leading to losses in net torque. But implemented correctly, either by itself or in conjunction with swirl, tumble can produce increased power.
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