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60s/70s era SBC OEM pistons are pretty identifiable by piston top shape. Here is an original 1970 LT-1 pop up piston. Maybe 1/4" high dome with a flat edge and a slot for the valve reliefs .Combined with the 64cc heads you got 11:1 C.R. I had these in my blue-printed '70 Z28, and after we decked the block some we got a true 11:1 CR. From the factory, with an un-decked block, they were about 10.7 CR. It seems Chevy's CR numbers were always .2 to .3 optimistic back then. That may be the setup what you have, with 64cc heads.
The 1971LT-1s lost the dome and became a flat top. Still forged. Had one long valve relief slot. Not eyebrows. Same forged piston used on all L82s. This lack of dome, combined with the 71+ up 76cc head chambers, gave about 9:1 CR with the big 76cc chamber heads. Upgrading these to the 64cc small chamber heads works extremely well and gives 10:1 CR.
The1969-70 L48 pistons were cast, not forged, flat-tops, and had either 2 or 4 valve reliefs. 10:1 CR.
The 1971 and up L48s had a deep d-dish depression in the piston top. And very low 8.0:1 CR. Their deep dish and lack of quench, gave detonation problems, even with the low CR. These pistons do not generally like being "upgraded" to small chamber iron heads, even tho the CR jumps to 9:1. They then like to detonate due to very little quench.
Last edited by leigh1322; Jun 18, 2025 at 01:15 PM.
This rebuilder/replacement piston (enginetech P/N P1505) is much more representative of the dished piston as found in '71-up low-compression L48/ZQ3 sbc.
It has 4 Valve Reliefs and its dish located in center of crown w/ very narrow quench band with a steep-wide chamfer; not D-Dish aka reverse dome.
FWIW, pistons' crowns in '96-up L31 Vortec truck motors are also similar to this pic's crown.
My money is on it being an over the counter "CE" "Chevrolet Engine" replacement '70 LT-1. Intake / carb dates tell the rest of the story. C/R would be close to 11:1, but you would need to pour everything to nail it down 100%. Great place to start.
My boroscope skills are crap, (I can't seem to get the other side of the piston!) but from what I can see, they look like the first ones you pictured.
Originally Posted by leigh1322
60s/70s era SBC OEM pistons are pretty identifiable by piston top shape. Here is an original 1970 LT-1 pop up piston. Maybe 1/4" high dome with a flat edge and a slot for the valve reliefs .Combined with the 64cc heads you got 11:1 C.R. I had these in my blue-printed '70 Z28, and after we decked the block some we got a true 11:1 CR. From the factory, with an un-decked block, they were about 10.7 CR. It seems Chevy's CR numbers were always .2 to .3 optimistic back then. That may be the setup what you have, with 64cc heads.
492 heads I believe were over the counter not factory but still 64cc heads which are the best original performance heads available back then.1.94 or 2.02 intake valves came in them ,as well could be had in angle plug.
Date code on the carb would be easy to see and decode.
Depending on the source of one's info source, carb looks to be made in 69, maybe for Vette ("70 LT-1, manual transmission 49 state LIST 4555")
or the LT Camaros to come?
Depending on the source of one's info source, carb looks to be made in 69, maybe for Vette ("70 LT-1, manual transmission 49 state LIST 4555")
or the LT Camaros to come?
That decodes to 1969, November, 1st week..
But interestingly Camaro and vette 1970 models did not start til January.
OEM factory production line carb due to 3 digit date and drilled hidden screw hole in front of choke horn.
Depending on the source of one's info source, carb looks to be made in 69, maybe for Vette ("70 LT-1, manual transmission 49 state LIST 4555")
or the LT Camaros to come?
That decodes to 1969, November, 1st week..
But interestingly Camaro and vette 1970 models did not start til January. Strike.
OEM factory production line carb due to 3 digit date and drilled hidden screw hole in front of choke horn.
Last edited by leigh1322; Nov 9, 2025 at 10:40 AM.
The 3972121 is the correct Holley carb for a 70 LT-1. Production of the 70 Corvette didn't begin until January 1970, but production of parts from both GM and their outside suppliers started months ahead of time.
I believe the date is the first week of December 69, not November. Holley dating ran 1-0 for January through October, then "A" for November and "B" for December. Either way, a Holley carb made in late 69 would be correct for an engine installed in a car built anytime in the first few months of 1970.
[/Quote]What is the block casting number and date? (Located on the top of the block's transmission mounting flange - cast # on driver's side, date, I believe passenger side.)
I realize this is a lot of questions, but when you're trying to answer another you've got to look at all the clues.[/QUOTE]
Here you go. Tough to read =Drivers side, clear = pass side.
The "010" (last three digits) block is a very common block used for 350's from 1969-1979, and in just about every Chevrolet model. The date is July (G) 26, 1971. A block cast at the end of July in 71 would have gone into a 1972 Chevrolet, as most 71 models had completed "build out" by then (the last 71 Corvette was built on July 16, 1971).
Darn! Rebelyell beat me in with the answer. I have to learn to type quicker! LOL
Since you have pics of the crank, can you get a pic of the main caps to see whether 2 or 4 bolts? An LT-1 block should have 4 bolts.
You could also stick a borescope thru the oil plug to see.
You might not be able to see the casting number of the crank, but I would bet you could see the LT-1 windage tray, and the casting part line on the crankshaft.
A thin part line means a cast crank.
A wide part line, that has been ground down, and looks like 1/2-3/4" wide, that signifies a forged steel crank, which an LT-1 should have.
A forged crank should also have an 8.0" diameter crank balancer on the front. That one is easy with a tape measure.
You might not be able to see the casting number of the crank, but I would bet you could see the LT-1 windage tray, and the casting part line on the crankshaft.
As mentioned in the first post, it a 4 bolt main block. It has the LT partial windage tray as it has the later, smaller LT oil pan which will not fit a full windage tray. (Though it did have full windage tray main cap stand offs which were incorrect for the pan as well deforming it!) Crank weights look cast by your pix but parting line (and paint marks?) sure looks forged.
thx for all detective work.
Sure looks like a forged crank to me. Ground down parting line. Cast ones are really thin., so sharp they can cut.
As well as rounded off crank throws. Cast ones have will-cut-you sharp edges.
Windage trays could also have easily varied slightly between Camaro and Corvette LT-1s, because the oil pan varied.
And there were 2 different LT-1 vette oil pans anyway, the early 6 qt and the later 5 qt, with different length sumps.
That is why the early 70 C3 LT-1s could not be had with PS it would not fit, until after the pan change.
So 3 different configurations on oil pans alone. Just in 70. with the hi-compression.
A GM replacement hi compression block would have to allow for all 3. Likely be the reason for the unused long cap studs you found.
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