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Bored&Stroked · 09-04-2016, 03:15 PM

Whose pistons are in the engine? The reason I ask is that there are different crown/dome profiles - and the profiles on the heads need to match (if you're going for a tight squish).

On many OEM Ford type pistons (cast), the dome is not a consistent radius - it is a combination of three tangent arcs. A good example is an early 4-ring cast Jahns piston - completely different dome than the 3-ring racing Jahns.

The forged Ross pistons have a consistent radius profile - typically .1875 deep. Most modern head manufacturers use a dome pocket profile that is very close to the Ross profile (though not compatible with some of the cast pistons). I recently had to have the domes on a new set of Edelbrock heads CNC profiled to match the early 4-ring Jahns pistons on a given engine.

Due to the above, I have two different 3D CAD models for the domes - such that I can get the CNC work done to "tune" the squish to match the specific pistons, gaskets and compression height of a specific engine.

09-04-2016, 03:15 PM	#5
Bored&Stroked Senior Member Join Date: Jan 2011 Location: Central Ohio Posts: 5,079	Re: "Squish" problems Whose pistons are in the engine? The reason I ask is that there are different crown/dome profiles - and the profiles on the heads need to match (if you're going for a tight squish). On many OEM Ford type pistons (cast), the dome is not a consistent radius - it is a combination of three tangent arcs. A good example is an early 4-ring cast Jahns piston - completely different dome than the 3-ring racing Jahns. The forged Ross pistons have a consistent radius profile - typically .1875 deep. Most modern head manufacturers use a dome pocket profile that is very close to the Ross profile (though not compatible with some of the cast pistons). I recently had to have the domes on a new set of Edelbrock heads CNC profiled to match the early 4-ring Jahns pistons on a given engine. Due to the above, I have two different 3D CAD models for the domes - such that I can get the CNC work done to "tune" the squish to match the specific pistons, gaskets and compression height of a specific engine.