L Holmes

I have what I thought was a 69 or 70 350 350HP motor disassembled in my garage and I noticed on the inside of the top of the piston there is the letters "TRW". There are a series of numbers on the top of the pistons as well. These are dome type pistons and I was looking for a part number or way to ID these rods & pistons. Did GM ever use TRW pistons in their engines? Anyone have some pictures of 69 to 70 350 350hp or LT1 pistons?

rick1500

Not 100% sure about the pistons, but I have a 1970 350/350 L-46 like you with TRW domed pistons, and the machinist I took it to for inspection said they are replacements. My rods are original "pink" rods though. Yours should have a stripe of pink paint on them, indicating they are the shot-peened ones used in the L-46 and LT-1. As for the rest of the engine, you should have the "double camel hump" heads which give the 11:1 comp. ratio.

L Holmes

Rick: I found this info. on a camaro web page. It lists the pistons as part number 3988051. I know the numbers on top the piston started with 3 but Im at work now and cant check for sure until I get home. I got an email from a friend that said TRW sold GM the forged pistons for these motors nut I was looking for more info. This part number is goping to be the tell I guess. The rods do not have any pink paint on them but I wouldnt expect them to after all the miles this motor probably saw. I was hopeing there was another way to ID the rods?

http://www.nastyz28.com/sbcmenu.html#pistons

HP Hunter

Back in the area of the 1960 and 1970 and even later, the LT-1 and the Z-28 and many of the big block engines all used pistons forged by TRW and made for General Motors.

The LT-1 had a 1/8" dome and centered wrist pin. The L-82 also used TRW forgings but were flat tops but centered pins as well. All the big blocks that came with forged were by TRW. They were all considered to be the top end of the hi-perfomance engines from Chevrolet. These had the centered pins as well.

Harry P. Hunter

rick1500

Maybe I have the original pistons afterall? Here are some pics:

I believe the number stamped on top is 3942545, which does not seem to be listed on the webpage you mentioned (however, that page only lists up to a '69 L46, then it goes to '70 LT1):




Here are all the pistons and rods before install. You can see some of the pink paint on the rods (I couldn't see it before they were cleaned up):



Do these look like yours? I thought my motor hadn't been touched before the machinist told me the pistons were replacements, but maybe he was mistaken and everything's all original. Now I'm curious.

HP Hunter

Those 8 assemblies look like the LT-1 pistons and I'm pretty sure if you examine the rod caps you will see a letter O forged into the bottom.

If that letter is there those are the original pink rods without question and they have the right paint also

The forging numbers on the pistons may not be the part numbers that are used in Chevrolets catalogs. Often the casting or forging numbers are seperate but close.

Harry P. Hunter

rick1500

Harry,

Are these the "O" forgings you're talking about?

L Holmes

Those pistons are the same as the ones I have. Thanks for posting the pic. Mine have allot of black carbon on top but they are the same or very similar. Mine have the number 336744 on top of the piston. Does anyone have pics. of the early L82 pistons?

HP Hunter

Thats on original LT-1 y'all got there. The original pink rods, 4 bolt main, and steel crank! Nice parts!

I hope ya ain't puttin those rings in there though. Good luck!!!!

Harry P. Hunter

rick1500

Thanks Harry. Are you referring to the Hastings iron rings? When I took my block to the engine builder, he said I could get away with lightly honing it and not boring it over, so I chose to do that. But, he said I'll need to use iron rings because the moly rings I was looking at wouldn't seat properly. I figured that since I wasn't planning on racing or even using it as a daily driver that it wouldn't be a problem. Do you think that's a bad idea?

HP Hunter

Most certainly. Moly seats on the stand while you assemble (just about). Guys sell those cast rings because of the markup. The Moly's sell for about 60.00 where the irons sell for about 35.00. Those Hastings are probably even cheaper. No one uses cast rings anymore. Not with todays fuels.

Like I said good luck.

Harry P. Hunter

L Holmes

Anyone have any pics. of early L82 pistons? I have a 73 L82 or so I think. It sure seems to have the good stuff internally as well.

L Holmes

btt

1970 LT-1

So these were factory GM forged L-82 pistons standard bore just to put an end to this post.

Gearhead74

I suspect your engine is an L-46 as opposed to an L-82. L-46 was introduced in 1969 while the L-82 was introduced in 1973. Check the engine block to verify the date of origin.

I believe the post I've copied below is accurate:

Found a old set of TRW sbc pistons #3942545 on the dome and 202-99 on the inside of the dome. Anyone have any idea if its a cast or forged piston? New to the post, have a 73 Nova, and a 75 Camaro.

That is the 350" L46 engine piston, the 350/350 HP engine. It is a forged piston, basically identical to the TRW aftermarket #L2304 F forged piston. Listed as an 11-1 piston(at blueprinted engine spec), has a .100" tall flat topped dome on it. Dome is approximately 4cc

Regardless of the technicalities, you have a set of original forged GM/TRW pistons.

The GM one you have is also forged....made by TRW for GM.

Mooser

Good information and all but this is a 14 year old post...
M