Originally Posted by geo1rem

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

Originally Posted by 66BlkBB

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

Originally Posted by Ironcross

How did this get to SB`s...

Originally Posted by MikeM

Let's try to stay on topic.

Originally Posted by woodsdesign

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.

Originally Posted by Donny Brass

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

Originally Posted by 63Corvette

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".

Originally Posted by 63 340HP

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).

Originally Posted by geo1rem

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

Originally Posted by geo1rem

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

Originally Posted by 70GHH

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.

Originally Posted by 63 340HP

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).

Originally Posted by 63 340HP

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).