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Bored&Stroked · 03-09-2026, 08:52 AM

Having the correct "squish" clearance above the piston dome is really important. You want .040" to .045" maximum clearance. Also, keep in mind that many Ford cast iron heads have a dome shape for a multi-elliptical piston crown (they are kind of "pointy" in the middle). Back in the day, lots of folks ran Jahn's/J&E pistons on their stroker motors. I'd guess they were available in your build years.

Popping the piston up just a bit and tuning the squish would be a good setup. This is especially true if you have a consistent radius piston crown (like Ross, Jahn's and most others), so you'd re-dome the heads with the correct radius cutter (that matches your piston crown shape). You can also create a 3D model and use a 1/4" ball on a CNC machine and then "polish" it afterwards.

Mockup: You should have the crank ground first, then put together a "mockup" with the crank in the block, with 2 rods (one each side) and 2 wrist pins - one in each rod. Then you can accurately measure and determine what the compression height would be at the deck. This makes it possible to see if you can run a stock stroke piston and understand the pop-up amount, or order exactly the right piston from somebody like Ross. (This is what I do).

Deck Height: By putting two rods in the mockup (one each side), you can also measure the difference between the deck heights for each bank. Usually one is lower than the other. You can then determine how much to clean up the decks on each side - and use those final measurements to determine the final compression height. If you put two rods in the front and two in the back, you can see if the decks are parallel to the crankshaft centerline. When I have blocks decked, I only have it done with a machine that picks up the mains - this ensures the same height and squareness to the crank centerline on both sides.

I always like my head dome shape to match my piston crowns - then tune the squish for exactly .040. If you order pistons from Ross, you can have them put the pin location exactly where you want it (which is what I do).

03-09-2026, 08:52 AM	#12
Bored&Stroked Senior Member Join Date: Jan 2011 Location: Central Ohio Posts: 5,906	Re: Crank stroke before 49 Having the correct "squish" clearance above the piston dome is really important. You want .040" to .045" maximum clearance. Also, keep in mind that many Ford cast iron heads have a dome shape for a multi-elliptical piston crown (they are kind of "pointy" in the middle). Back in the day, lots of folks ran Jahn's/J&E pistons on their stroker motors. I'd guess they were available in your build years. Popping the piston up just a bit and tuning the squish would be a good setup. This is especially true if you have a consistent radius piston crown (like Ross, Jahn's and most others), so you'd re-dome the heads with the correct radius cutter (that matches your piston crown shape). You can also create a 3D model and use a 1/4" ball on a CNC machine and then "polish" it afterwards. Mockup: You should have the crank ground first, then put together a "mockup" with the crank in the block, with 2 rods (one each side) and 2 wrist pins - one in each rod. Then you can accurately measure and determine what the compression height would be at the deck. This makes it possible to see if you can run a stock stroke piston and understand the pop-up amount, or order exactly the right piston from somebody like Ross. (This is what I do). Deck Height: By putting two rods in the mockup (one each side), you can also measure the difference between the deck heights for each bank. Usually one is lower than the other. You can then determine how much to clean up the decks on each side - and use those final measurements to determine the final compression height. If you put two rods in the front and two in the back, you can see if the decks are parallel to the crankshaft centerline. When I have blocks decked, I only have it done with a machine that picks up the mains - this ensures the same height and squareness to the crank centerline on both sides. I always like my head dome shape to match my piston crowns - then tune the squish for exactly .040. If you order pistons from Ross, you can have them put the pin location exactly where you want it (which is what I do). Last edited by Bored&Stroked; 03-09-2026 at 11:54 AM.