alternative 250 pistons

I used the 255 pistons in my 250 many years ago and they worked well with some decking, but the flat top pushed the CR too high for iron heads and now they are getting harder to find.

Let me toss out one more piston option that may be viable, available, and cost effective.

The piston that may work out is the 1979-1990, 258 Jeep, KB Silvolite pn 2227. It has a 1.63" height, a 3.75" bore (.070" overbore), and a 21cc dish. The pin is larger, though, so you'll have to open up the small end of the rod from .912" to .931".

Depending on your chamber size you can get a zero deck height with only minor machining, end up with a manageable 8.5 to 9.5 CR, and still retain some quench area.

The downside is that this is probably the last overbore you'll be able to do on your engine unless you were willing to risk a .090" overbore.

Oversize pistons for 250 are listed in NAPA catalog out to .080 - !

http://www.napaonline.com/Catalog/Catal ... 0306926461

Ford 250: bore = 3.68 / comp distance = 1.5 / dish volume = 13cc
AMC 258: bore = 3.75 / comp distance = 1.633 / D-Sump = 21cc's (TRW's)

This puts the bore @ .070 over and raises piston toward the deck .133 . Spec pin diameter of the ford is .9122 and the AMC's at .9310 which the rod can accomodate .

The cc volume of the recess is 21ccs. With the .070" overbore the bore is 3.75", stroke of 3.91, with typical composite head gasket at @.050", a zero deck height, chamber volume of 60ccs and a piston recess of 21 ccs, gives a static compression ratio of @ 8.8:1 to start with ...

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Over five years reliable - on street and strip

Ford C8DE 250 Six; Bored .070 over with TRW AMC 258 Pistons, Clifford Shot Peened Rods, Clifford 272H Cam, Cloyes timing set, Melling blueprinted HP oil pump, Fisher Dampener, Offenhauser Tri-Power 3X1 aluminum intake manifold adapter w/log Hi-Rise Plenum - Holley 4412 500CFM performance carb, GM HEI ignition trigger, Champion racing spark plugs., SFI 157 neutral balance-lightened racing flywheel spinning Centerforce Stage II Clutch, T5-Z Cobra 5speed tranny, Pinned engine mounts, Short throw Hurst Indy shifter, 8” 3.80:1 TracLoc Posi rear, Cal-type Traction Control devices and Shelby sway bar, Mustang front strut bars, Scarebird Disc front brake mod, Fabricated subframe connectors, tranny crossmember and rear spring mounts, 8 Point Roll bar, 5 point Safety Belts, Mustang 5.0 alum. racing radiator, Perma-Cool electric pusher fan, Holley fuel pump/pressure regulator, Hooker 6602 dual out longtube headers, Matte black/alum. 6=8 Clifford valve cover.Smithy silencers, Original tube radio, vacuum wipers and front fender Gunsights…

You know, I had forgotten that you had used these pistons already! Thanks for the reminder, Powerband.

8.8:1 is not a bad start. That's actually in the sweet spot where you could easily run regular fuel. But I was thinking that most heads would require at least a light skim to get them straight again and most might need .010 to .020 leaving them several cc's smaller and in the mid 9's on CR. Still safe with that big dish.

I think Hesco makes a forged version of this piston and I did find some .010" oversize pistons which would bring you out to the .080 overbore. That should give you right at 260 cubic inches as well.

I'm quickly getting hooked on these small sixes. My question is how much life can you reasonably expect from an overbore like this? I'm thinking strictly street, not hammering the gas (except when you wanna show up that Camaro butthead) and generally taking good care of it.
Opening up the small end of the rods is another concern for me. Sending one thru the side of the block ain't much fun.

vntgtrk":2ueip0um said:

I'm quickly getting hooked on these small sixes. My question is how much life can you reasonably expect from an overbore like this? I'm thinking strictly street, not hammering the gas (except when you wanna show up that Camaro butthead) and generally taking good care of it.
Opening up the small end of the rods is another concern for me. Sending one thru the side of the block ain't much fun.

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as with any engine, it all depends on usage, and maintenance, but it is not unreasonable to expect 100,000 miles from such a build given the parameters you outlined. as for opening up the small end, you are not opening it up that much, so it is not a concern. remember that there is a safety factor built in, and a fairly large one at that.

Yeah, the material removal isn't an issue since your only removing less than .010" from the inside wall of the rod, and it's only just a honing operation. Opening up the rod for bushings would be another matter, where a greater amount of metal is removed and the pin hole in the rod will need to be centered as much as possible and not offset.

How thin are the cylinder walls at 0.070 overbore, let alone 0.080?

I know you should sonic test the block when doing a large overbore, but how much wall thickness is safe?

rocklord":z2ukyvxi said:

How thin are the cylinder walls at 0.070 overbore, let alone 0.080?

I know you should sonic test the block when doing a large overbore, but how much wall thickness is safe?

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i generally recommend no more than .060" overbore unless the cylinder walls have been sonic checked for core shift.