Packard Forum Index » V-8 (1955-56)

I have a 374 up on the stand now ready for assembly. I can drop the eggs in one and jahns in two and do some comparison mearuments on skirt to counterweight clearances etc. I am really courious to see the differences in deck height with the pop top. I'll post the finding when I get a chance to do it.

The 55-56 Packard service manual states some aspects of the OEM piston.

SEE page 14 of the Service Manual. Lower right corner titled "Pistons".
Paraphrasing it states: "Al. ALLOY, slipper type, CAM GROUND, STEEL STRUTED and tin plated...".

Do ANY of the REPRODUCTION pistons MEET that criteria or exceed it???

If not, then the piston is inferior to EOM.

Pay close attention to the STEEL STRUTED feature of the OEm piston.

Quote:
Quote:

Life and design requires frequent tradeoffs. The OEM steel strut is designed to control expansion and allows the pistons to be fitted tighter in the bores. (.0005 - .0015") This is quieter when cold and will help keep the rings perpendicular against the cylinder wall. So, yes, for luxury car use, they'd be preferable. The repop pistons without steel struts need more bore clearance (.002"-.003") or they'll scuff and overheat.

But then, it's also a known fact the OEM pistons are weak in that area where the curved slipper skirt turns into the area of the steel strut. If run hard they often crack there and eventually fail. I've never seen an aftermarket piston crack there. For a Studebaker Golden Hawk or other performance build, one wouldn't choose OEM pistons.

jack vines

In a perfect world, I would love to cut from a billet 2618-T61.

Main reason with cracking is the silica content while making more "slippery" so to speak, it makes them very brittle. Once a crack starts it does not stop until failure.

2618-T61 if it were to crack, the crack will stop once the stress is relieved and less likely to hand grenade.

2618-T61 is used for NASCAR and Top Fuel Pistons. I tad bit overkill for night on the town with the Patrician but solid characteristics.

If a replacement piston does not meet the criteria that Packard V8 has quoted from a factory manual that does NOT mean it is inferior.

Different can mean worse, equal to or better. OEM V8 pistons are cast, forged pistons are different and BETTER. Much stronger, forged pistons are used in most racing and hi perf engines.

To add more to the discussion, here is a forged JE Piston. Kind of a modified cross brtween barrel and slipper skirting

Attach file:

---

  (673.19 KB)

quote from post 45 above:
" In aperfect world, I would love to cut from a
billet 2618-T61."

Got CNC equipment??? Then CNC a set of pistons from T61.

Yes we do :)

I just checked Egge's online page and they had a listing for 374 pistons in 020 030 040 060 for $449.82 . Maybe they realized they would not sell any rebuild kits if they didn't offer the pistons.