Alternative Piston For 250 Other than the 255 V8
- Thread starter rocklord
- Start date
The stroke of the 2.3 HSC is 3.3", the 200 has a 3.126" Stroke. The 2.5 HSC has a stroke of 3.58", the 250 has a 3.91" stroke
The 200 and the 250 use the same piston. The oem Ford small six piston is a slotted piston with ~64mm long slots and weighs ~600 grams with the pin.
The Silvolite 2.5 HSC piston is a slotted piston with ~54mm long slots and weighs ~580 grams with the pin.
The skirts on the stock piston are ~11mm longer than the skirts on the 2.5 HSC piston. The 250 has a 1.5 R/S ratio, the 200's is 1.51. The 2.5 HSC engine is better @ 1.67 with a 5.99" rod, the 2.3 is 1.65
The design base of the HSC engine was the 200 block with 2 pistons lopped off.
I would submit that if you rev either of these pistons, stock or hsc, 2000 rpm above redline, or even above 5500-6000, for any length of time they or their rods/bolts will fail esp in a 250. Don't do that :nono:
If you're building a race car or high performance engine and put in some crazy high lift cam with an aluminum head and 4 barrel carb, get forged pistons, forged rods, arp fasteners and balance the rotating assembly.
I hope my piston tops don't find themselves fleeing their bodies anytime soon on my mild 250. The van will be on the road soon. I'll let you know if/when the pistons come apart
The 200 and the 250 use the same piston. The oem Ford small six piston is a slotted piston with ~64mm long slots and weighs ~600 grams with the pin.
The Silvolite 2.5 HSC piston is a slotted piston with ~54mm long slots and weighs ~580 grams with the pin.
The skirts on the stock piston are ~11mm longer than the skirts on the 2.5 HSC piston. The 250 has a 1.5 R/S ratio, the 200's is 1.51. The 2.5 HSC engine is better @ 1.67 with a 5.99" rod, the 2.3 is 1.65
The design base of the HSC engine was the 200 block with 2 pistons lopped off.
I would submit that if you rev either of these pistons, stock or hsc, 2000 rpm above redline, or even above 5500-6000, for any length of time they or their rods/bolts will fail esp in a 250. Don't do that :nono:
If you're building a race car or high performance engine and put in some crazy high lift cam with an aluminum head and 4 barrel carb, get forged pistons, forged rods, arp fasteners and balance the rotating assembly.
I hope my piston tops don't find themselves fleeing their bodies anytime soon on my mild 250. The van will be on the road soon. I'll let you know if/when the pistons come apart
Lots of apples and oranges here. 
The 2.3 flattop HSC pistons work fine in the US 200. The flattop bumps the CR by a bit and there aren't any differences in piston pin geometry from the stock 200 pisitons. If you're really are intent on revving your engine to 7000 rpm, a cast piston is the wrong piston no matter what the pin offset may be. The 2.5 HSC pistons will not work on a 200 because the Compression Distance is too high and the pistons may end up sticking out of the hole by .020 or more.
I never tried HSC flattops in a US 250. There's no point, even with the taller CD 2.5 HSC pistons. The problem with the US 250 is the negative .140" deck height and that's where the 255 piston with its 1.585" CD helped. I was able to deck the block by .045" or so and actually get a quench distance that works, and still have a reasonable CR. Putting HSC flattops in a 250 increases the compression, but the piston is still so far below the deck that there is effectively no quench happening and the engine becomes more sensitive to ignition timing and pinging.
Deano, good stuff, but keep in mind that Aussie engines are different deck height dimensions than the US equivalents. My comment on the dish size you mentioned was in relationship to the X-flow engine. The X-flow 250s typically have smaller chambers and don't have that whopping big deck height issue so they use a big-dish piston. I used US 250 pistons, not 255 in the crossflow. The 255 pistons would have been too tall for that application and the piston would have exceeded the block by a good bit. But without that big 12-16cc dish the CR gets pretty high with US 250 pistons and I had a helluva time managing the nearly 11:1 CR that I ended up with. I got away with it in the end because I was using a mapped ignition and the alloy cylinder head was a little more tolerant of CR than iron would be. I also kept the revs down to 6000. No need to rev the engine to death when torque is the objective.
The Jeep pistons make for an good alternative but the price of resizing rods for the larger pin may make the economics a little harder to deal with.
But all those observations were made over 15 years ago. These days I think I would simply go for a longer, lighter rod to make up the CD delta and use a stock style piston.
The 2.3 flattop HSC pistons work fine in the US 200. The flattop bumps the CR by a bit and there aren't any differences in piston pin geometry from the stock 200 pisitons. If you're really are intent on revving your engine to 7000 rpm, a cast piston is the wrong piston no matter what the pin offset may be. The 2.5 HSC pistons will not work on a 200 because the Compression Distance is too high and the pistons may end up sticking out of the hole by .020 or more.
I never tried HSC flattops in a US 250. There's no point, even with the taller CD 2.5 HSC pistons. The problem with the US 250 is the negative .140" deck height and that's where the 255 piston with its 1.585" CD helped. I was able to deck the block by .045" or so and actually get a quench distance that works, and still have a reasonable CR. Putting HSC flattops in a 250 increases the compression, but the piston is still so far below the deck that there is effectively no quench happening and the engine becomes more sensitive to ignition timing and pinging.
Deano, good stuff, but keep in mind that Aussie engines are different deck height dimensions than the US equivalents. My comment on the dish size you mentioned was in relationship to the X-flow engine. The X-flow 250s typically have smaller chambers and don't have that whopping big deck height issue so they use a big-dish piston. I used US 250 pistons, not 255 in the crossflow. The 255 pistons would have been too tall for that application and the piston would have exceeded the block by a good bit. But without that big 12-16cc dish the CR gets pretty high with US 250 pistons and I had a helluva time managing the nearly 11:1 CR that I ended up with. I got away with it in the end because I was using a mapped ignition and the alloy cylinder head was a little more tolerant of CR than iron would be. I also kept the revs down to 6000. No need to rev the engine to death when torque is the objective.
The Jeep pistons make for an good alternative but the price of resizing rods for the larger pin may make the economics a little harder to deal with.
But all those observations were made over 15 years ago. These days I think I would simply go for a longer, lighter rod to make up the CD delta and use a stock style piston.
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