1971 454/425hp LS6 Heads - Uncertain Usage?

[Warren F.]

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

I can tell you for a fact that the '70 LS-6 piston and the '71 LS6 piston are not the same. There is a significant difference in dome height as well as dome configuration between the two. With the Chevelle's application for 11.25 to 1 compression it uses a .395 dome height. For the 9.0 to 1 compression the Corvette's application uses a .095 dome height. The piston part #'s are completely different as well, because of the closed chamber vs open chamber combustion chamber design.

[Clem Z.]

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

the 454 450HP 1970 chevelle had a piston dome volume of 30.6 cc and even installing 118 cc heads the CR would 10.1:1 which would be too high for regular gas that is why the 71 corvette had 13.3 CC piston dome volume with the open chamber aluminum heads

[Joe L.]

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

Joe, I'm not exactly sure I'm understanding what you're saying. I agree that the 71 LS6 used the same head as the SECOND DESIGN '69 L88, which was an open chamber motor as was the '69 ZL1. Obviously throwing the open chamber heads on an engine that was previously closed chamber would lower the compression a couple of points and I thought that's what they did. In other words, all of the '69 big blocks (except the LATE or 2nd design L88 and the ZL1) were closed chamber and of course these two had significantly different dome volumes than the early '69 as well as 68 & 67 L88's. In addition to the '69 stuff, ALL '70 big blocks were closed chamber including the LS6 in the Chevelle............. the point being, I THOUGHT (not sure) that the '70 LS6 engine in the Chevelle and the '71 LS6 in the Corvette carried the same piston part number and the compression was lowered by changing to the open chamber heads on basically the same short block as before.

Admitedly I don't have any experience whatsoever with the '71 LS6 Corvette, BUT do have closed chamber (early) '69 L88 and a couple of '70 LS6's as well as LS7 crate and have been in all of 'em. In addition, I did a good bit of work on the Ontario Orange '69 L88 that was the first L88 ever awarded Survivor at Bloomington and was in that one too. It was the 2nd design or open chamber L88 and since it was showing 8K miles at the time I believe the pistons were original to it and the domes were massive compared to my early closed chamber L88. Also, although I no longer own the car, I bought a '71 LS5 once that was maybe 15 years old and noticed that it had the same piston as the '70 LS5, but of course had the open chamber oval port heads. I stuck a set of closed chamber oval ports I had on the shelf on it and woke it up. I'm not saying that the pistons were original to the engine because the car was multi owner before I bought it so I don't know the history, but this too made me think at the time that all Chevy did in '71 to drop the compression was go to the open chamber heads on both the oval and rectangular port stuff and leave the shortblock alone, at least for the '71 model year.

I'd like to know for sure if the 70 & 71 LS6 pistons were the same part number, AND ALSO if the 70 & 71 LS5's shared pistons also as I've always thought.

What do you think?

Norris------


As Warren and clem have mentioned, the 1970 and 1971 LS-6 pistons were different in terms of dome height as well as part number. The 1970 LS-6 (Chevelle) pistons were GM #3976013 (std). The 1971 LS-6 (Corvette) pistons were GM #3994035 (std). The 1970 LS-5 pistons were GM #3976024 (std); the 1971 LS-5 pistons were GM #3993874 (std).

[Norris W.]

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

Norris------


As Warren and clem have mentioned, the 1970 and 1971 LS-6 pistons were different in terms of dome height as well as part number. The 1970 LS-6 (Chevelle) pistons were GM #3976013 (std). The 1971 LS-6 (Corvette) pistons were GM #3994035 (std). The 1970 LS-5 pistons were GM #3976024 (std); the 1971 LS-5 pistons were GM #3993874 (std).

Thanks for the part numbers. I'll jot them down for future reference. I was talking with my son about the '71 LS5 car that I put the '70 model heads on. He thinks he remembers that it had a CE block in it, so it may very well be that somebody had put a '70 LS5 shortblock in it at some time in it's past. I'd have bet the farm that car had the same pistons as my '70 LS5 does, 'course keep in mind that I can't seem to remember what I had for lunch today.

If the '71 engines did in fact have a different piston I'd be interested in knowing if the dome was shaped like the typical closed chamber dome, with the side toward the sparkplugs squared off OR if it the dome was rounded around the lower edge like the 12:1 LS7 open chamber piston.

I've got one more ole' shortblock in the warehouse with the heads off that's either from a '71 or '72 and now y'all are gonna' make me go look and see what the pistons look like and see if I can read a number.

[Clem Z.]

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

Thanks for the part numbers. I'll jot them down for future reference. I was talking with my son about the '71 LS5 car that I put the '70 model heads on. He thinks he remembers that it had a CE block in it, so it may very well be that somebody had put a '70 LS5 shortblock in it at some time in it's past. I'd have bet the farm that car had the same pistons as my '70 LS5 does, 'course keep in mind that I can't seem to remember what I had for lunch today.

If the '71 engines did in fact have a different piston I'd be interested in knowing if the dome was shaped like the typical closed chamber dome, with the side toward the sparkplugs squared off OR if it the dome was rounded around the lower edge like the 12:1 LS7 open chamber piston.

I've got one more ole' shortblock in the warehouse with the heads off that's either from a '71 or '72 and now y'all are gonna' make me go look and see what the pistons look like and see if I can read a number.

here is a picture of the 1971 corvette piston. http://www.summitracing.com/parts/TRW-L2399F/?rtype=10

[Clem Z.]

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

here is a picture. http://www.summitracing.com/parts/TRW-L2399F/?rtype=10

here is the 1970 chevelle piston. you can see the difference in dome height. http://www.summitracing.com/parts/TRW-L2349F/?rtype=10

[Ray K.]

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

Joe

I believe the #3976024 piston is .020 oversize and is a R. H. cylinder application. The corresponding L.H. is #3976023. Standard pistons are 3976015 L.H. and 3976016 R.H. Also, I think the number for the 1970 LS7 454 piston is 3976014.

[David D.]

1969 Numbers Matching 427/400hp

You guys have done a great job of running this LS6/LS7 issue down to the details and I have a better understanding of my 71 heads/engine.

I have another Novice question. I have confirmed that my 1969 Roadster has a numbers matching 427/400hp Suffix LQ, Tri-power with a Muncie 4 speed. The head casting numbers and dates are also correct for the car. How can I confirm if the transmission and rear end are numbers matching as well.

I bought the car from the 3rd owner and the VIN Registration records show it to have 54,000 original miles on it but the tank sticker was never found so I'm trying to piece this all together.

Thanks,
Dave

[Joe L.]

Re: 1969 Numbers Matching 427/400hp

You guys have done a great job of running this LS6/LS7 issue down to the details and I have a better understanding of my 71 heads/engine.

I have another Novice question. I have confirmed that my 1969 Roadster has a numbers matching 427/400hp Suffix LQ, Tri-power with a Muncie 4 speed. The head casting numbers and dates are also correct for the car. How can I confirm if the transmission and rear end are numbers matching as well.

I bought the car from the 3rd owner and the VIN Registration records show it to have 54,000 original miles on it but the tank sticker was never found so I'm trying to piece this all together.

Thanks,
Dave

Dave------


The transmission should have a VIN derivative stamping on it if it's original to the car. This stamping will be found on the rear vertical surface of the main case on the passenger side. There will be two stampings. One which begins with a "P" is the transmission production code which includes the date it was assembled. The other stamping, usually of slightly smaller font size, is the VIN derivative. This should match the last portion of the car's VIN.

There is no VIN derivative stamping on the differential, so there's no way to be absolutely sure that it's original to the car. However, the date code on the carrier housing casting and cover should be correct for the car. Also, the code stamped into the bottom of the carrier housing should be correct for the car, including date.

[Norris W.]

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

Norris------
As Warren and clem have mentioned, the 1970 and 1971 LS-6 pistons were different in terms of dome height as well as part number. The 1970 LS-6 (Chevelle) pistons were GM #3976013 (std). The 1971 LS-6 (Corvette) pistons were GM #3994035 (std). The 1970 LS-5 pistons were GM #3976024 (std); the 1971 LS-5 pistons were GM #3993874 (std).

Here's another fly in the punchbowl. One of my '70 LS6 cars with THE original engine has piston # 3963550.

I've owned this one (an El Camino actually) since the mid '80s. When I bought it the third owner here had removed the original engine at approximately 20K miles according to him, and had replaced it with a smallblock and used it as a worktruck until it reached about 100K. Owner #1 from parts unknown sold the 'Camino with supposedly 6K miles when it was less than 1 year old and it came here to a used car lot. Owner #2 used it as an extra car/toy and said he never had the engine out, but did hate the 4:10 gears and changed the whole rear to a 3:31. Owner #3 fought the big block for a while, hated it and had the smallblock installed. Owner 5 is a local birddog that loves to hunt old hot cars from back in the day. (He also found my L88 which was a local car when new and the ZL1 Camaro, also local when new or within 35 miles that just sold in the Milton Robson collection.) Birddog never did anything with the Camino except pull and dispose of the smallblock and retrieve the original motor from wherever it was stored. I'm number 5. The point of all this history is, I'd find it hard to believe that sometime early on these pistons were changed out, although obviously I don't know anything about the first year of it's life. It is still standard bore and is being freshened as std with these pistons going back in. Without my Vernier Caliper tonight, just using a crude measuring method I'd guess the domes are about 1/32 more than .250, or somewhere in the .280 range, give or take.

[Clem Z.]

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

Here's another fly in the punchbowl. One of my '70 LS6 cars with THE original engine has piston # 3963550.

I've owned this one (an El Camino actually) since the mid '80s. When I bought it the third owner here had removed the original engine at approximately 20K miles according to him, and had replaced it with a smallblock and used it as a worktruck until it reached about 100K. Owner #1 from parts unknown sold the 'Camino with supposedly 6K miles when it was less than 1 year old and it came here to a used car lot. Owner #2 used it as an extra car/toy and said he never had the engine out, but did hate the 4:10 gears and changed the whole rear to a 3:31. Owner #3 fought the big block for a while, hated it and had the smallblock installed. Owner 5 is a local birddog that loves to hunt old hot cars from back in the day. (He also found my L88 which was a local car when new and the ZL1 Camaro, also local when new or within 35 miles that just sold in the Milton Robson collection.) Birddog never did anything with the Camino except pull and dispose of the smallblock and retrieve the original motor from wherever it was stored. I'm number 5. The point of all this history is, I'd find it hard to believe that sometime early on these pistons were changed out, although obviously I don't know anything about the first year of it's life. It is still standard bore and is being freshened as std with these pistons going back in. Without my Vernier Caliper tonight, just using a crude measuring method I'd guess the domes are about 1/32 more than .250, or somewhere in the .280 range, give or take.

the 550 piston is listed as the 11.25 70 454 chevelle piston.

[Joe L.]

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

Here's another fly in the punchbowl. One of my '70 LS6 cars with THE original engine has piston # 3963550.

I've owned this one (an El Camino actually) since the mid '80s. When I bought it the third owner here had removed the original engine at approximately 20K miles according to him, and had replaced it with a smallblock and used it as a worktruck until it reached about 100K. Owner #1 from parts unknown sold the 'Camino with supposedly 6K miles when it was less than 1 year old and it came here to a used car lot. Owner #2 used it as an extra car/toy and said he never had the engine out, but did hate the 4:10 gears and changed the whole rear to a 3:31. Owner #3 fought the big block for a while, hated it and had the smallblock installed. Owner 5 is a local birddog that loves to hunt old hot cars from back in the day. (He also found my L88 which was a local car when new and the ZL1 Camaro, also local when new or within 35 miles that just sold in the Milton Robson collection.) Birddog never did anything with the Camino except pull and dispose of the smallblock and retrieve the original motor from wherever it was stored. I'm number 5. The point of all this history is, I'd find it hard to believe that sometime early on these pistons were changed out, although obviously I don't know anything about the first year of it's life. It is still standard bore and is being freshened as std with these pistons going back in. Without my Vernier Caliper tonight, just using a crude measuring method I'd guess the domes are about 1/32 more than .250, or somewhere in the .280 range, give or take.

Norris------


I don't know what a GM #3963550 is. If this is the number found under the piston, it is a forging number and not a finished part number for the piston.

[Norris W.]

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

Norris------


I don't know what a GM #3963550 is. If this is the number found under the piston, it is a forging number and not a finished part number for the piston.

Joe, it's stamped on the dome. I'm not near them now, but I'm pretty sure they were stamped GM either before or after the part number.

I love these kinds of discussions 'cause I almost always learn something.

[Norris W.]

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

the 550 piston is listed as the 11.25 70 454 chevelle piston.

Obviously that's what a 70 LS6 is, so what's the deal with this part number and the #3976013 listed above showing the same application?

I've also got a std GM set of '70 LS7 pistons that came out of one of my crate motors when I went .030. If I get a chance tomorrow I'll compare the number on them to the LS7 number listed above.

[Joe L.]

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

Joe, it's stamped on the dome. I'm not near them now, but I'm pretty sure they were stamped GM either before or after the part number.

I love these kinds of discussions 'cause I almost always learn something.

Norris------


Generally, when the part number is stamped on the top of the piston, it does represent a finished part number. However, I can find no record, at all, of the 3963550 part number as a finished part number. It's possible, I suppose, that it was the part number of the machined piston exclusive of the pin. Of course, pistons were never available without pins, so if that's what the stamped number represents, it would never have been available in SERVICE under that part number.