Ron78Z&66Vette

Is it just a matter of looking for casting marks inside the bottom part of the piston? Is it that simple, or should I be looking for something else?

The pistons are flat-top, 4 valve relief (if it matters), and all have a light "bullseye" (for lack of a better term) machined or pressed on the top of the piston perfectly centered. I'm thinking this might tell me something too??

AZDoug

Casting marks are an excellent clue, but if they are flat top, they are 99.9% positive to be cast, unless machined out of billet, which is sort of the same thing as forged, but not exactly, but I can't imagine anybody machining billet flat top pistons

Doug

Vipermike

Look at the underside of the pistons. The unmachined areas of a cast piston will be somewhat rough looking (not as rough as an aluminum intake manifold but simliar) where a forged piston will be smooth.

BADBIRDCAGE

Nay Nay big fella. Gotta disagree on this one. Lots of forged flat top pistons with four eyebrows out there.

Thompson Ramco Whitledge (TRW) produced (and probably still does produce) these pistons for years. Many were used by drag racers running in stock and pure stock classes in the 60's & 70's as a replacement piston that could take the high rpm on a consistent basis without snatching the wrist pin down and jettisoning something through the side of a small block at the 70 foot mark on the track.

Lots of street strokes also used forged pistons in rebuilds just because they were readily available, not too expensive and were a bragging right. There was nothing like saying "I have FORGED pistons in my motor". Not that three quarters of the people knew what a forged piston was in comparison to a cast piston. (that comment about not being too expensive has changed in the last 25 - 30 years, EVERYTHING costs a lot more now)

Cast pistons were used in most applications from the manufacturers as they were less expensive. Cast pistons were also used by most rebuilders and, if you are not going to exceed 5800 rpm on a regular basis, should work fine in almost anything you are going to run today.

And, " I have FORGED pistons in my motor". I am not going to punish this thing on a regular basis but when I purchased the complete internal package they were already there. (see, I'm bragging)

Rich

Sky65

Rich
Any idea how to tell a forged TRW piston? When I had the pan down on the 65 I noticed the bottom of the pistons said "TRW". Is there some additional identifier for cast or forged? The crank has an engraving on it saying was ballanced in 1969 so I guess that was the "built" in that time frame.

Thanks
Tom

AZDoug

Thanks for the clarification. I guess I should think outside the box of what originally came in a factory motor.

Doug

BADBIRDCAGE

Tom: On a forged piston looking up from the bottom usually the wrist pin bosses are very smooth as is the inside of the piston, whereas on a cast piston it may be a little rough in texture and you will probably observe an actual casting line or two (tiny little suckers) inside heading vertically from the wrist pin boss to the top of the piston. You don't always have this casting line but it is a teltale. AND, certain manufacturers made raised dome pistons in a cast format.

Doug: As I recall factory 350 HP and up SB motors had forged pistons in them from the factory. 300 HP motors may have had them from the factory, depended on the supplier's inventory at the time they were delivered to the assembly plants.

Rich

MikeM

All solid lifter 327's and the L-79 engine used domed forged pistons. All hydraulic lifter 327 engines with the exception of the L-79 engine used flat top cast pistons.

Cast pistons are fit with around 1.5 thousandths clearance while forged are installed about 5.0

Forged pistons are usually extremely noisy on cold engine startup until the pistons expand and then they quiet down somewhat.

BADBIRDCAGE

Thanks Mike: I have been out of the internal engine business since 1982 and am working from memory on most of it. Don't have total CRS yet but am working on it.

Rich

MikeM

I know the feeling. I can't tell you what I had for supper last night.

AZDoug

That is why loud mufflers were invented. I can't hear any psiton slap on my L-79 block with turbo mufflers and turndown dumps just fore of the rear axle.

Doug