396 vs 427 Why?
 

How can the 3855961 casing number be the same for a 396 nd a 427 ci motor. There is no way a 396 can be bored out to a 427. Confused.
I can not find anyone who can explain why GM used the same casting number for two different cubic inch blocks.
Help me solve this puzzle.
Thanks George :cheers:

Well when Zora Duntov was asked how come a 425 HP 427 Corvette was so much quicker than a 425 HP 396 Corvette, he is quoted as saying: "Well we bored it out 30cubic inches. Just check how much 30 cubic inches of cast iron weighs".

Yes, there are in fact some 396 castings that can go all the way to 427 bore.

Not true, the early engines can handle it. Later engines would probably hit the water jacket at that level of overbore.

The 1965 396 "962" block (all 4 bolt mains) is a THICK wall casting, in most cases, unless there was significant core shift during the casting process, they can be bored out the additional 1/8" to 4.250" (427 spec).

The 1965-66 396 "961" block (2 bolt & 4 bolt mains) is a THIN wall casting. Regardless of core shift, boring one out to 4.250" (427) will result in either breaking through a water jacket, or dangerously thin cylinder walls that will cause the engine to run hot and be impossible to keep cool without boiling over on the street. Of course you'll always hear somone claiming how they bored a 396 "961" block out to 4.250 inches "back in the day" and raced it, but I doubt they got further than a 1/4 mile before it was puking antifreeze.

..and to answer the next question that usually follows, NO - there were no documented 1966 427 Corvettes ever produced with the 961 block ...even if GM did slip a few onto the assembly line early in Aug/Sept 1965, they would've rolled off the showrooms with 396 cid.

It's not the first time GM used the same block for two different engine displacements. I have first-hand knowledge of two others and there may be more:

1. In 1957, some passenger cars came with 265 engines. The 265 block has the same casting number as the 283 block and differs only in the bore.

2. In 1961, 409s were made from 348 blocks. The 348 casting number was ground off and a different "casting number" was stamped in its place.

Jim

:iagree: The engine that was in my 62 when I first got it, was a 57-issue 265. Sold it to a drag racer 'cause he thought it had a beefier cylinder wall for better boring.

Well, there was at least enough cylinder wall thickness to bore it .125" to be a 283. :)

Jim

Jim,
As to the '61 409, most 348 blocks will not survive the 3/16" overbore. The 011 348 core casting was modified to provide thicker cylinder walls. There were also some changes at the main webs due to the new crank. The '61 409 was indeed a new casting rather than just a bored and stroked 348.
As you say, the new casting number was obviously overlooked on some early blocks, but corrected later.

http://i83.photobucket.com/albums/j3...61409623sm.jpg

http://i83.photobucket.com/albums/j3...kcastingno.jpg

Thanks for the clarification. I was mistaken about the 409 block I saw and I appreciate knowing the real story.

It's been 25 years so my memory is hazy. What I think I recall is larger numbers on the "casting number" stamping than those shown in your photo (3/8" or maybe 1/2" tall) and a slightly different font, one with (for lack of a better description) more "style" to it. I do remember the casting date was sometime in October of '60.

And apologies for hijacking this thread which was really about 396/427 engines.

Jim

...and here's some useful info on overboring early SBC's for anyone interested;

http://books.google.com/books?id=g46...3OLojcd705wfcg

One of my racing friends had one of these five 4-bolt main cap 396's out of a 65 Chevelle that we ran in a 68' Camaro. When a rod scored a cylinder wall in the block we looked to add a thin wall sleeve. Our machinist ran the block through a sonic test and came back to tell us it could be bored an 1/8th over, to a 427 bore, to clean up the cylinder. The set of 427 pistons cost a little bit, but worth the expense. One of our rivals who ran a SS legal 375hp/396 67' Camaro heard a rumor of what we did and claimed it could not be done safely, so we had our pin-striper paint "396 ? - 427 ?" on the sides of the hood scoop (just to keep him guessing). The guessing lasted about two drag race meets, before the track times improved to answer the question.

We ran this over-bored block for a year of racing with L72 pistons, with no failures. We then tore it down and swapped in L88 pistons (12.5:1 CR), and at the second or third weekend outing at the strip with the much faster configuration we blew a hole in the #5 or #7 cylinder wall. We added a sleeve and continued to run the block for the balance of the race season, and the entire next year.

This photo is from a month or so before we scored the 396 block (we suffered a drunk hitting the front end of the car the weekend before this photo, and we were forced to run with no hood).

http://members.aol.com/Stvns/cars/DonsCamaro1982.jpg

:cheers:

Sorry for the dumb question, but is a 396 considered to be a true BB? I always thought that the 427 was the BB and a 396 was a short block. :rolleyes:

396, 402, 427, 454 are all big blocks

265, 283, 302, 307, 327, 350, 400 are all small blocks

any motor with crank, pistons and no heads is a short block

AHHH, 400 came either way. There was the 400 small block and the 400 big block (a .030 overbore 396, actually 402 ci).

Rich:cheers:

Forget the old greasy cars. Who is the chick with the pink top?:D

You too? Thats what I saw, :lol:

the hell with the Camaro

LOL!!! Me too. :willy:

:cheers: :thumbs:

sweet smoke
 

nice rack !!!

NASCAR allowed the Chevy to run as a 427 in 1965 to compete with the 427 Ford and 426 Hemi.

I have not seen it in writing, but would not be surprised if this is at least one reason why the early 396 block would take the 427 bore size.

They all wanted to win in NASCAR including Chevy even though Chevy was not supposed be involved in racing.

It's funny how the 1965 396 could be run as a 427 as only 2 years before management stopped the 1963 427 NASCAR engine program.

by the way, very cool Camaro picture

Happened in 8yrs earlier in 57 also.
The 548 block could be either a 265 or a 283.

The 307 and 327 have the same stroke. A FEW 307s have been known to be bored to 327 (although it would scare me to bore one that much!).

I remember some guys punching the 283 out .125 to create 301's. A lot of those blocks were really thin and caused problems. Some held together with no problem. It was just a matter of how thick the walls were in the original castings.

Steve

How About 4X4`s from 283 V8`s
 

A few 283`s in the earlie 60`s were made into 4X4`s using Buick rods, special pistons, crank and a overbore. They didn`t perform as well as was expected either supercharged or normally asperated.

How did this get to SB`s...:lol:

Thread creep...

Let's try to stay on topic.:D



http://members.aol.com/Stvns/cars/DonsCamaro1982.jpg

Yep, almost forgot about her. thanks for refreshing my memory.....:lol:

The 1965-66 396 "961" block (2 bolt & 4 bolt mains) is a THIN wall casting. Regardless of core shift, boring one out to 4.250" (427) will result in either breaking through a water jacket, or dangerously thin cylinder walls that will cause the engine to run hot and be impossible to keep cool without boiling over on the street. [/QUOTE]

So how do you rebuild a 396 that needs to have the bores cleaned up?

So how do you rebuild a 396 that needs to have the bores cleaned up?[/QUOTE]

Commonly refred to as .030 over. :thumbs:

Left a couple out Donny.:thumbs:
262, 267 small blocks
366, 400 big blocks

Boring out a 396 30 over would not make it a 427 :nono:

OK, So does this answer my question? R U saying a 396 can be bored out to a 427? Still confused. I have a 396 dated July 65, cast 961. Could this be a 427 mistakenly by the seller?
George

30 cubic inches........... not .030 over

The answer is some early 396 blocks have been successfully bored out to the 427 bore. This is what we did, with a 396 block that had four bolt caps for all five main bearings (another indicator, in addition to the 1965 casting & 961' casting number).

The real answer to this question with any individual block is to have the bores sonic tested to see if there is enough material to bore out the specific block you are considering. If you fail to have the blocked checked, you run the risk of breaking into a water jacket or suffering from a weak (thin) cylinder wall.

Could the 65' block you have commented on be a 427? Verify all the qualifiers (date, main caps, casting number). Have them check the bore diameter with a bore gage. If it's 4.125", or close, it's a 396. If it's 4.250", or close, it's a 427. If you are considering the block to purchase, consider the cost of a sonic test of the cylinder walls as insurance.

The other question, the girl? She was the Camaro owner's girlfriend (then wife, then ex-wife). She could have doubled for Natalie Wood with similar good looks, with ample additional qualifications (perfect for a distraction during late night heads-up racing).

:cheers:

Someone really needs to analyze the structural integrity of the brassier she is wearing! Is it a thin wall in jeopardy of causing overheating amongst spectators? It looks bullet proof.

:yesnod:

\Thanks

:iagree: with everything but the bore on the 396. The standard 396 bore was 4.096" up until 1970 then they were bored 4.126" to 402".