1970 3963512 Block Strange One

[3macs1]

Just when you think you have a grip on the GM numbers bang you get hit with this. Probally 20 years ago I pulled an original 454 engine complete out of a 70 impala. I knew the entire history of the car since it was purchased in the family new until the day I sent it to the junk yard.
About a month ago someone finally convinced me to sell the 454 since it would make his 70 chevelle closer to original. We agreed on a price and off he went.
This motor was never apart. He called today to ask me if I knew this was a 3963512 4 bolt main block with a steel crank.Of course now he is looking for ls-6 heads, etc.
Has anyone ever heard of GM doing this. This engine was 100% oval port, 3963512 2 bolt 70 Impala as far as I was concerned.
Last motor I leave the pan on before sale that is for sure. Boy did he get a deal. I never even looked at the side for oil filler plugs, etc.

[BARRY]

HI WHEN GM BOUGHT OUT THE 454 WITH THE LONGER STROKE THE FIRST BATCH ALL HAD 4 BOLT MAINS??? I HAVE SEEN THIS BLOCK BOTH WAYS

[3macs1]

Never knew that Barry. Wish I did. Been around these big blocks since my first chevelle in 76 and worked on dozens of them when I worked in the service station. Never before did I see a 4 bolt block on a factory oval port other than the tall 366 and 427 truck blocks.There probally was not that many in the initial run of 70 454's.
Any idea Rick or Mr.70 how many oval port 512's may have been sold with 4 bolt mains and steel cranks. Rods and pistons were oval port gear.

[370454s]

The one I have in my 70 Chevelle is a 4 Bolt Steel Crank 390 HP,454. Motor came out of a 70 Caprice that was sold new in Oct 69.

[Hotrodpaul]

Probably a supply or engineering decision based on the new large displacement engine. GM may have done it for warranty prevention reasons. I presume the steel crank was non Tufftrided and non Crossdrilled.

Paul

[nuch_ss396]

Joe,

The use of a 4-bolt block in place of a 2-bolt block is
one thing. However, I'd like to know if this engine in
question had a '6223 crank, dimpled rods, etc.. Also, of
particular interest would be the piston domes. Rectangular
port heads have larger combustion chamber volumes than
those of the oval port heads ( 107cc's vs. 101cc's ).
SHP piston domes are considerably higher, so I suspect they
wouldn't fit in the oval port heads properly. Can you find
out more about the rods & pistons? I'd like to know
more.

Knowing what we know today, I'm not at all surprised at a
finding like this. If they needed a block to make production
and a 2-bolt version wasn't available, they took what they
could find.

[nuch_ss396]

Come to think of it, I remember seeing something in the past
about the 1966 big blocks. I believe some 360hp 396 engines
used 4-bolt blocks in some cases and GM sent a service bulletin
to dealers alerting them to the fact that the piston domes
were different and that care should be taken when replacing
the short block assemblies as the SHP pistons would interfere
with the oval port top ends.

Anybody remember this? It may have been in Colvin's books.

[69L72RS]

What date range was the first batch of engines (454 CID) made.
I have a 454 2-bolt block coded T0806CGV.
Just curious.
Eric

[Mr70]

The CGV was a 345HP engine.
I've not seen any 345HP's w/4 bolts yet,so far only 2-bolt mains.
The only EARLY casted 1970 non LS-6 coded 512 4-bolt blocks I've seen so far were 390HP engines slated for Impala-Police & Taxi useage.

[olredalert]

------A couple of years ago I pulled two oval-port 351 67 dated complete engines out of a completely dry-rotted Pacemaker boat. They were both 4-bolt main along with the oval-port, but one was reverse rotation. Both were very low hour, beautiful standard-bore pieces, and, although low compression had the good rods and crank. Both the blocks are sitting in restored 67 Corvettes today........Bill S