The Ford Barn

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.

Bluebell · 09-04-2016, 04:36 PM

I have C7RA ali heads. I had them faced, one needed more than the other.
I have Ross pistons. Without gaskets they lifted the heads when I turned the motor over.
I mentioned it on this forum. Another kiwi on here told me to measure the lift with a dial gauge on each cylinder, which I did. I wrote each measurement in each chamber and sent my heads to Brian. Brian had previously built a jig and made a tool to cut the heads to suit the Ross domes. I am lucky and grateful for his help. One head needed on average about 0.040" thou out, and the other about 0.022" out. The heads are on, but as yet the engine is not yet finished.
I have used Best composite gaskets which I am told settle out at about 0.055".

09-04-2016, 03:15 PM	#1
Bored&Stroked Senior Member Join Date: Jan 2011 Location: Central Ohio Posts: 5,723	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.

09-04-2016, 04:36 PM	#2
Bluebell Senior Member Join Date: Nov 2012 Location: Tauranga, New Zealand Posts: 726	Re: "Squish" problems I have C7RA ali heads. I had them faced, one needed more than the other. I have Ross pistons. Without gaskets they lifted the heads when I turned the motor over. I mentioned it on this forum. Another kiwi on here told me to measure the lift with a dial gauge on each cylinder, which I did. I wrote each measurement in each chamber and sent my heads to Brian. Brian had previously built a jig and made a tool to cut the heads to suit the Ross domes. I am lucky and grateful for his help. One head needed on average about 0.040" thou out, and the other about 0.022" out. The heads are on, but as yet the engine is not yet finished. I have used Best composite gaskets which I am told settle out at about 0.055".