2 or 4 bolt main?

[justin4260]

is there a way to tell if i have a 2 or 4 bolt main 400 small block without droping the pan? casting number 3851511 and if anybody could give me some more info on this that would be great

[ho70]

CHECKED ONLINE AND 4 BOLT IF THREE FREEZE PLUGS AND 2 IF TWO FREEZE PLUGS
http://outintheshop.com/faq/casting/castings2.html

[MARKDTN]

Originally Posted by ho70

CHECKED ONLINE AND 4 BOLT IF THREE FREEZE PLUGS AND 2 IF TWO FREEZE PLUGS
http://outintheshop.com/faq/casting/castings2.html

What he said. I think that is almost always true.

[LT4XTREME]

I believe all 400s have three freeze plugs or at least the boss for the third one. I don't think you can tell without dropping the pan. Jason

[cdowns]

no big difference one way or the other

way overrated

[65standard]

1970 was the only year for 4-bolt mains 400 SBC.

[Swar]

Justin, is that the number on the back of the block? I used silly putty to press into it to get an imprint of the number?
It's located on the driver's side down by the bell housing. That's on a 350 though, not sure about the 400.

[hugger6933]

I'm pretty sure that all 400's were three freeze plug motors. Dropping the pan is the only way I think. I didn't know that the 400 was made as early as 70 though. I do remember when GM sent out a statement to all dealers saying they were discontinuing the parts replacement short blocks and they had a limited number of them the price I could have bought a short block for was about $400 to $450. That was late in the 80's. Jim

[justin4260]

thats the number on the driver side back of the block infront of the bell housing. the date number is D 3 72.
pic 1: block casting number 3951511
pic 2: block date number D 3 72
pic 3: ID number on the right. its located on the passenger side inform of the head number T04L9CKB.
pic 4: id number on the left of the number from pic 3 number 12Y140503.
i talked to a guy who had a 68 stepside he has a book with casting number ids and such. he told me it was a 4 bolt main and that 70-72 was 4 bolt 73 was only 2 bolt.

EDIT: if you look to the right of picture 2 it looks as if the block casting number is on the other side as well but upside down. I'm not home at the moment so i can't wire brush it to find out.

[65standard]

I just checked with my old engine builder about our days building 400s. He corrected me and said the 4-bolt main blocks are 1970-1972 only. 1973-1980 were all 2-bolts. The 1970 was the only year with any compression. After that, they were all 8:1 motors.

[hamjet]

Originally Posted by 65standard

i just checked with my old engine builder about our days building 400s. He corrected me and said the 4-bolt main blocks are 1970-1972 only. 1973-1980 were all 2-bolts. The 1970 was the only year with any compression. After that, they were all 8:1 motors.

x2

[bruceman1968]

3951511= 400cid, Car & Truck, 2 & 4-Bolt main, 3-freeze plugs
D 3 72 Block casting code
D=April
3=3rd
72=1972
T04L9CKB Engine id stamp=plant/assembly date/application code
T=Towanda
04=April
L9=19=19th
CKB=Chevelle/Impala 350cid, 165hp, 350trans, 2bbl BUT
CKP=Impala, 400cid, 170hp, 400trans, 2bbl Rochester
Check the last digit again. I think that's a P not a B
12Y140503
1=Chevrolet
2=1972
Y= Wilmington assembly plant
140503=Build sequence number

Your engine is a 1972, 400 out of a Impala.
EDIT: 1970 to 1972 400s were all 4 bolt mains as 65standard stated in post 10. Your block is a 4 bolt main..

[GRX]

Like cdowns said. Factory 4-bolt is way over-rated so don't fret it too much. In fact, some racers actually prefer the two bolt blocks. Far as freeze plugs go. I have seen sb 400's with three plugs per side, two plugs per side with center cast bosses not drilled for plugs, and some which had no center cast bosses at all. Those are usually early '70 blocks and said to be the strongest.

[Canuckvetter]

I had 2-400sbc 3951511 blocks with 72 cast dates. Both sold as 4 bolt, both had 3 frost plugs, dropped the pan both 2 bolt. http://67-72chevytrucks.com/vboard/a...1&d=1430283047

I had the engine builder machine the block for Eagle splayed main caps.

[justin4260]

Originally Posted by bruceman1968

3951511= 400cid, Car & Truck, 2 & 4-Bolt main, 3-freeze plugs
D 3 72 Block casting code
D=April
3=3rd
72=1972
T04L9CKB Engine id stamp=plant/assembly date/application code
T=Towanda
04=April
L9=19=19th
CKB=Chevelle/Impala 350cid, 165hp, 350trans, 2bbl BUT
CKP=Impala, 400cid, 170hp, 400trans, 2bbl Rochester
Check the last digit again. I think that's a P not a B
12Y140503
1=Chevrolet
2=1972
Y= Wilmington assembly plant
140503=Build sequence number

Your engine is a 1972, 400 out of a Impala.
EDIT: 1970 to 1972 400s were all 4 bolt mains as 65standard stated in post 10. Your block is a 4 bolt main..

yes that is definitely a P not a B. typo. thanks for the info some guys were telling me i would never know what it came out of.
thanks everybody for the help, i really didn't want to lift the engine to drop the pan just to see if it has 2 or 4 bolts lol

[GRX]

Dropping the pan is the only way to be 100% certain. Why does it matter? Selling the engine?

[justin4260]

Originally Posted by GRX

Dropping the pan is the only way to be 100% certain. Why does it matter? Selling the engine?

wanted to make sure the bottom end can handle boost before i start investing in new headers and heads and superchargers or turbos. if it is a 2 bolt main i might sell it but most likely i will just put good heads on it and not boost it and then get a different truck or car to do boost on.

[bruceman1968]

Justin you may still have to drop the pan. If the 2 engines that canuckvetter is talking about in post 14 were built in the first half of 72, then you'll have to drop the pan to be sure. But if they were cast later in the year then stick with 4 bolt. Need to find out the month codes of his 2 engines. Real life always trumps the book. Here is a pic of the table I used to answer your question.

[justin4260]

Originally Posted by Canuckvetter

I had 2-400sbc 3951511 blocks with 72 cast dates. Both sold as 4 bolt, both had 3 frost plugs, dropped the pan both 2 bolt. http://67-72chevytrucks.com/vboard/a...1&d=1430283047

I had the engine builder machine the block for Eagle splayed main caps.

do you know what month they were casted in?

[GRX]

Originally Posted by justin4260

wanted to make sure the bottom end can handle boost before i start investing in new headers and heads and superchargers or turbos. if it is a 2 bolt main i might sell it but most likely i will just put good heads on it and not boost it and then get a different truck or car to do boost on.

Many performance builders prefer the 2 bolt blocks. Do a web search and see for yourself. Far as personal experience goes. I have magnafluxed more than a couple 4 bolt 400 that had cracks emanating from the outer bolt holes.

[justin4260]

what is the significance to the 4 bolt vs the 2 bolt and vise versa?

[4X4GMC1972]

The two bolt main caps are stronger

[Hubscrub]

I agree, overrated. My dad always said he wouldn't turn around for the difference. He ran two bolt engines in his dirt track cars didn't worry about It, he said the rods would probably go first.

[justin4260]

ok some guys are saying 2 bolts stronger some guys say 4 bolts stronger some say it don't matter. i think its personal preference and application then.