way to tell if pistons are forged?

[Grandnat]

I purchased a set of speedpro/TRW pistons. They look real nice but underneath the piston, and on the sides where the pin goes through, the surface it looks like cast to me.

Is there a rule of thumb to tell if a piston is forged?

I have seen forged pistons before and I remember the surface being really smooth. although the machined surfaces are shinny The bottom looks rough, almost like the texture of my T-type rims.

 

[gofstbuick]

It just so happens I have a forged TRW 11:1 SBC ashtray in my office. I don't see any casting flash like you described in that piston. Also, TRW and Speedpro puts the part number on the face of the piston. Is it still visable? It may be possible that you have a Hypereutectic piston.

 

[S10xGN]

Put em in and set your boost for 30 PSI! (just kidding!)

 

[SteveRacer]

The forgeings are shot peened or glass beaded and that is what gives them the "cast" appearence. This probably actually increases the pistons strength. I'm assuming the pistons you bought were suposed to be forged. The TRW-L2481F30 has that "cast" look.

 

[bruce]

Originally posted by Grandnat
I purchased a set of speedpro/TRW pistons. They look real nice but underneath the piston, and on the sides where the pin goes through, the surface it looks like cast to me.

Are you sure they're a forged set?.

A Forged piston, is generated by an AL slug being crushed with a set of dies. So that means there's there's no *undercutting*, so there will be no recess, above the pin area, ie between the pin area, and piston dome. The interior sides of a forged piston, have to allow for the die to be removed. A cast piston, can have all sorts of undercutting since they typically use 3 peices to form the interior of the piston.


Part of the high price for forged pistons is that they're often heat treated several times during the machining process. Once after the intial rough machining, and then just prior to the barrel cutting.