One of the things we are on the alert for in this forum is PISTON COMPRESSION HEIGHT, the measured distance from the centerline of the wrist pin to the crown of the piston just above the top ring land. PISTON DECK HEIGHT, the measurement from the crown of the piston to the flat part of the block deck where the heads bolt on, added to the head gasket compressed thickness, describes the SQUISH/QUENCH thickness. Ideally, the motor will like a SQUISH/QUENCH dimension somewhere between 0.035" and 0.045". It must be thin enough to create a good squish of the air fuel mixture across the chamber, but not so thin as to allow the piston crown to crash into the underside of the cylinder head. There is a little flex in the crankshaft and a little stretch in the rods and pistons that close up the safety margin of 0.035" to 0.045" when the motor is at speed. Again, SQUISH/QUENCH is the PISTON DECK HEIGHT (measurement from the crown of the piston to the top of the cylinder bore with the piston at top dead center) added to the compressed thickness of the head gasket. Experience teaches us that the motor will be maximum detonation-resistant if we squeeze the fuel/air mixture between the piston crown and the underside of the cylinder head and blow it into the chamber area (and past the spark plug) as the piston rises in the bore, to break up large clumps of fuel and homogenize the mixture into a totally flammable mass instead of a hit and miss mass with large droplets interspersed in the mix.
Now, in determining the viability of the engine that we have to work with, we will begin with the block. A 289 Ford, from the parting line of the main bearing bore to the deck of the block where the heads bolt on measures 8.206". This is the BLOCK DECK HEIGHT, not to be confused with the PISTON DECK HEIGHT.
The parts that go into the block to make up the reciprocating assembly are the crankshaft, the connecting rods and the pistons. To make up our STACK of parts to fill the block, we will use the RADIUS of the crankshaft (1/2 the 2.870" stroke of a 289 crankshaft = 1.435"). To the 1.435" CRANK RADIUS, we will add the rod center to center length of 5.155" and the PISTON COMPRESSION HEIGHT, not to be confused with PISTON DECK HEIGHT, of 1.605"...…..so 1.435" + 5.155" + 1.605" = 8.195" STACK HEIGHT.
Now, if we are to fit the 8.195" STACK of parts into the 8.206" BLOCK DECK HEIGHT, we find that it will fit with 0.011" of space (PISTON DECK HEIGHT) left above the piston with the piston at top dead center. This 0.011" PISTON DECK HEIGHT added to the COMPRESSED GASKET THICKNESS is what describes the SQUISH/QUENCH thickness into which the air/fuel mixture is compressed with the piston at top dead center. In this particular example, if we used a gasket that would compress to 0.030" and added the 0.011" PISTON DECK HEIGHT to that, we would find a SQUISH/QUENCH figure for that combination at 0.041", solidly in the middle of the suggested 0.035" to 0.045" figures that are suggested by experience.
Now, in looking at the parts used in your build, we find that whoever chose parts for the STACK in your motor chose a piston with a reduced PISTON COMPRESSION HEIGHT of 1.585".
https://www.summitracing.com/parts/slp-273ap30
This makes the piston 0.020" shorter than a stock piston. Normally, but not always, this is done so that the machine shop can take a 0.020" cut on the block decks to flatten them or cut off some damaged part of the block deck(s) and keep the same SQUISH/QUENCH. Sometimes though, these "rebuilder" pistons will be chosen on price only and the person choosing them will have no idea that there is any such thing as SQUISH/QUENCH to be considered in an engine build. When this is the case, and the block is not cut on the decks to restore the correct margin, SQUISH/QUENCH is out the window and the motor finds itself much more succeptible to detonation. In some cases however, even though the PISTON DECK HEIGHT is increased, the builder can use a thinner head gasket to restore the same SQUISH/QUENCH that the motor had before the piston change. It matters little how you arrive at the correct SQUISH/QUENCH, as long as you arrive.
With iron heads, any kind of gasket can be used, including steel shim gaskets. With aluminum heads, a more forgiving type of composition gasket must be used to prevent fretting, the wearing away of the aluminum material due to the difference of the growth characteristics between iron and aluminum. You are free to use any kind and any thickness of head gaskets due to using iron heads, but I don't know how you're going to determine the PISTON DECK HEIGHT or the SQUISH/QUENCH if the motor is assembled.
Don't expect too much from this motor, the heads are awful. I know, I've built a few of them. Normally you would know the static compression ratio before you would choose a cam, so that you could figure the dynamic compression ratio. The whole mess balances on the closing point of the intake valve.
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