Use stock 2.3 HSC pistons, and longer 6"2.5 HSC rods for your next 250 rebuild, fellas.
A little while back, Jack Collins gave us some good info on those HSC ohv 2.3 and 2.5 engines used in the American sub-compact Topaz/Tempos. The engines are 'just' cut-down sixes, with a medium or tall deck block.
Ford used the same piston blank for many engines. The 3.68" bore 250, 200, 221, 188 I6's, 2.3 and 2.5 HSC four, and 255 V8 used almost exactly the same piston design. Even the 3.5" diameter 144/170 pistons saw duty in the 221 V8.
These HSC engines are great sources of longer rods to replace that rather too short 250 Ford rods. Good thing is, they are likely to be much stronger than stock rods, and longer. The compression gets a rise, and the rod ratio improves from 1.505:1 to a better 1.535:1.
As for the HSC rods, the 2.3 ones are 5.45" long, and the 2.5 HSC ones are 6.00", perfect for a 250. The original 2.5 pistons are a little too tall at about 1.579", but the 2.3 HSC pistons are almost perfect at around 1.530" tall or so from the wrist pin to the top. You may need to use a thicker composite gasket, not the thinner steel one, but it should fit.
The original US 250 had rods with a centre spacing of less than 5.88", 1.955" throw crank (3.91" stroke) and shallow 1.53" pistons all in a 9.469" deck, leaving the piston over 100 thou down in the bore at top dead centre.
With 6 inch rods, 1.955" throw and 1.53" pistons, thats 16 thou popping out of the deck. With a nice thick gasket or some closed and ground rods or decked pistons, you'd just fit them in without taking the head off. That improves the rod ratio a little, and gives you more modern components which allow a 6000 rpm rev range to be explored.
A little while back, Jack Collins gave us some good info on those HSC ohv 2.3 and 2.5 engines used in the American sub-compact Topaz/Tempos. The engines are 'just' cut-down sixes, with a medium or tall deck block.
Ford used the same piston blank for many engines. The 3.68" bore 250, 200, 221, 188 I6's, 2.3 and 2.5 HSC four, and 255 V8 used almost exactly the same piston design. Even the 3.5" diameter 144/170 pistons saw duty in the 221 V8.
These HSC engines are great sources of longer rods to replace that rather too short 250 Ford rods. Good thing is, they are likely to be much stronger than stock rods, and longer. The compression gets a rise, and the rod ratio improves from 1.505:1 to a better 1.535:1.
As for the HSC rods, the 2.3 ones are 5.45" long, and the 2.5 HSC ones are 6.00", perfect for a 250. The original 2.5 pistons are a little too tall at about 1.579", but the 2.3 HSC pistons are almost perfect at around 1.530" tall or so from the wrist pin to the top. You may need to use a thicker composite gasket, not the thinner steel one, but it should fit.
The original US 250 had rods with a centre spacing of less than 5.88", 1.955" throw crank (3.91" stroke) and shallow 1.53" pistons all in a 9.469" deck, leaving the piston over 100 thou down in the bore at top dead centre.
With 6 inch rods, 1.955" throw and 1.53" pistons, thats 16 thou popping out of the deck. With a nice thick gasket or some closed and ground rods or decked pistons, you'd just fit them in without taking the head off. That improves the rod ratio a little, and gives you more modern components which allow a 6000 rpm rev range to be explored.
