C3: L46 350/350 - TRW Pistons?

[Dan Pepper]

Did GM use TRW pistons in all it's engines? Just curious as I noticed that my stock L46 has TRW cast into the pistons.

[J M.]

Re: C3: L46 350/350 - TRW Pistons?

Do they look like this?

[Duke W.]

No, just forged pistons for SHP/FI

The L-46/LT-1 version is still available AFAIK from Speed Pro since Federal Mogul bought most of TRW's automotive operations 15 years ago.

L2104R-xx std. size and .030",.060" oversize

Forged with .100" dome, 2.4cc net dome volume, 1.560" compression height,nominal 579 grams (with pins) for standard size, 585 for -30 oversize, 604 for -60 oversize. Fit all to .004" nominal skirt clearance.

Calculated CR for .030" overbore with nominal .025" deck clearance and .026" OE shim gasket and 64 cc heads is 11.05:1; with 76cc chamber 9.62; with 64cc head and .039" composition gasket 10.68; with a .015" shim gasket and 76 cc heads 9.87.

The maximum CR I recommend for detonation free operation on premium unleaded fuel with either the L-46 or LT-1 cam is about 10.5. This should be achievable with a little chamber grinding and a .039" gasket, plus deck clearance is usually a few thou high, which helps keep things in check. And there is also the option of cutting down the domes a few cc if necessary; plus or minus one cc from the head chamber or dome is about 0.13 CR change.

Duke

[Joe L.]

Re: No, just forged pistons for SHP/FI

Dan-----

Usually, GM forged pistons will have a GM forging number seen on the bottom. They may or may not have an easily discernable manufacturer's ID (i.e. like TRW). TRW (and, possibly, other manufacturers) supplied the forged slugs to GM. However, I believe that the slugs were finish-machined at the GM engine plants. However, not all GM forged pistons do have the forging number.

As far as I know, GM never had any in-house aluminum forging capability. So, any forged aluminum parts (like forged pistons) had to have been supplied by an outside supplier. However, the GM engine plants of the day usually machined the pistons in-house, whether they were castings (which probably comprised about 99% of the pistons used in PRODUCTION and which were usually supplied by the GM Bedford, IN aluminum foundry) or forgings, supplied by outside suppliers like TRW. I think that TRW was the major source for the aluminum forgings, but I don't know if they were the exclusive source.

[Dan Pepper]

Thanks to all for the information! *NM*