1971 454/425hp LS6 Heads - Uncertain Usage?

[Norris W.]

Re: 1971 454/425hp LS6 Heads - Uncertain Usage?

Joe, now I'm more confused than ever. Warren lists the dome height on a '70 LS6 piston as .390. Mine measure approx. .280. Again, my measuring was crude, but it's less than 1/16 more than .250, and appears to be about 1/32 more, which would be .250 plus .030.

I also just glanced at my LS7 pistons. They are stamped on the dome GM (above the part number instead of inline like I thought) 3963551. I said above that they came from a '70 LS7 crate, but actually I don't know what crate they came from, only that it was a factory LS7 long block, and they are open chamber design domes and are the taller ones, and the camshaft is the part number used in ZL1, 2nd design L88 & LS7...... 3959180 if I remember right (which is doubtful these days)

What would be the source of Clem's post above saying the 550 piston shows as 11.25:1 70 Chevelle if that isn't a valid number for that application?

[Joe L.]

Re: 1971 454/425hp LS6 Heads - Uncertain Usage?

Joe, now I'm more confused than ever. Warren lists the dome height on a '70 LS6 piston as .390. Mine measure approx. .280. Again, my measuring was crude, but it's less than 1/16 more than .250, and appears to be about 1/32 more, which would be .250 plus .030.

I also just glanced at my LS7 pistons. They are stamped on the dome GM (above the part number instead of inline like I thought) 3963551. I said above that they came from a '70 LS7 crate, but actually I don't know what crate they came from, only that it was a factory LS7 long block, and they are open chamber design domes and are the taller ones, and the camshaft is the part number used in ZL1, 2nd design L88 & LS7...... 3959180 if I remember right (which is doubtful these days)

What would be the source of Clem's post above saying the 550 piston shows as 11.25:1 70 Chevelle if that isn't a valid number for that application?

Norris-----



My guess would be that clem's information is derived from NHRA or NASCAR tech inspection documents. These sort of documents usually list IDENTIFICATION NUMBERS that can be used to confirm stock configuration for classes requiring that stock parts be used. Piston casting or forging numbers are one form of an identification number that could be used for such purposes. Such numbers usually are not GM part numbers for a finished part.

[Clem Z.]

Re: 1971 454/425hp LS6 Heads - Uncertain Usage?

Norris-----



My guess would be that clem's information is derived from NHRA or NASCAR tech inspection documents. These sort of documents usually list IDENTIFICATION NUMBERS that can be used to confirm stock configuration for classes requiring that stock parts be used. Piston casting or forging numbers are one form of an identification number that could be used for such purposes. Such numbers usually are not GM part numbers for a finished part.

you got it joe. the numbers on the pistons are not GM part numbers just like some cylinder heads casting numbers are not the GM part number.

[Norris W.]

Re: 1971 454/425hp LS6 Heads - Uncertain Usage?

So to be sure I'm understanding, the number stamped on the dome of the piston with GM above it is NOT a part number for a finished piston?

I looked at 7 different pistons last night from old engines that I've had over a 30+ year period, many of them from 425/435 427's and some from 11:25 454's and then open and closed L88 plus LS7 and I'm not seeing anything with .390 dome. One thing that surprised me a little is that I found a set of new .030 Speed Pros that I ordered as LS7 replacement a long time ago and the dome on them is more pointy and higher than the GM LS7 take out piston that has the GM 3963551 part number stamped on top. Another thing I was unaware of was that the SHP closed chamber 427 & 454 have exactly the same dome height with the only noticable difference being the wristpin location. I'd have thought the 454 would have been slightly lower to maintain the same C/R given the longer stroke.

I think I've got some closed chamber HP pistons, which I guess would've been in the range of 10:1 from both 427 & 454 in another spot. I'm going to try and measure domes on them today and see if the part numbers jive with the info y'all have.

All this lookin' around has uncovered a pretty good stash of parts that've been accumulated over the years and forgotten that I think are going to show up on E bay now to maybe make some shelf room.

[Joe L.]

Re: 1971 454/425hp LS6 Heads - Uncertain Usage?

So to be sure I'm understanding, the number stamped on the dome of the piston with GM above it is NOT a part number for a finished piston?

Norris------


Let's put it this way: I can find no record of that part number ever having been available as a SERVICE part. That strongly implies that it was never a part number for a finished part. Could it be the part number of a finished part that was used only as part of an engine assembly and not otherwise available in SERVICE? Yes, it could but such parts are EXTREMELY rare.