Bill

A quick question that should be right up your alley. Can all 396 blocks be sucessfully bored to stasndard 427 bore size? Just to be sure the question is clear...can a good (no core shift) 396 block accept an over size bore to make a 427.

Asked a little differently: If no core shift existed in any 396 blocks ever cast by the factory is it true that only SOME specific 396 casting numbers can make it to 427 bore size but not others?

Some of the Corvette guys are running around saying that only 1 specific 396 casting will take the overbore to 427 size and still have sufficient wall thickness. Of course if that casting is right for their year Vette the price they are willing to pay for this "super tough" 396 casting is astronomical. I just find it hard to believe GM cast different wall thicknesses in varous 396 block castings. If they were gonna make one with thick walls why bother with a thin wall variation...weight saying (NOT!) cost saving due to elimination of the extra iron when making the thin wall blocks (NOT!). In fact switching care sizes in and out for various casting runs in the foundry would seem to ADD cost.

What do you think about this? Seems like urban legend to me

Went and looked at casting numbers for big blocks at Mortec (http://www.mortec.com/bbc.htm) and found that GM did not use one casting number for both 396 and 427. But thats not to say some blocks are not thick enough, just that the general didn't cast a one size fits all block.

3855961....396.......65-66...2 or 4 bolt
3855961....427.......66......2-bolt

I see that the "961" appears to be the only casting used to make both 396 and 427 BY THE FACTORY. Just such fast analysis easily leads to conclusions like "Well it must be the ONLY 396 that can be bored to 427 bore"! Considering the level of anal investigation the Corvette guys do into part numbers and casting IDs any conclusion could be reached.

It seems to me that ya just fired up the boring bar, reamed out your 396 cyl walls to 427 dimensions and ordered new pistons. PRESTO 427. The only guys who will know are guys like Bill K. who run the boring bars.

Wonder what he will say.

Oman,
Personally, I think the correct answer to the question is that you HAVE to sonic check the block. I am certain that you will find some that will go out to 4.250 without having the walls become too thin. And, you will probably find just as many that will not work. Thats the only way to know for sure.

Originally posted by oman:
Considering the level of anal investigation the Corvette guys do :eek:

Thats it. Never going to attend anything Vette related again. I feel dirty now.....

With all the 454 blocks laying around that are already the correct bore why would you want to?

Oman,

There was a thread in the Engine forum that discussed this issue also. See
http://www.chevelles.com/forum/ultimatebb.php?ubb=get_topic;f=9;t=013644#000000

My increadibly uneducated guess is this; '65 was the 1st year for the 396 and 66 was the 1st year for 427's. Perhaps Chevy was rushing to get the 427 into production and couldn't swing a dedicated casting for 427 so ended up just making bigger holes in the already available 396 castings. They probably deisgned the 961 blocks knowing the 427's would be coming and simply cast the blocks with thick walls - thus cutting out some R&D work/time, from an already streched engine development program, to do the new castings.

But then again, maybe not.

In the end - until we hear from the dude who designed the 961's, it's as Bill said; a sonic check is the only way to know for certain.

Beaux, your mind works in mysterious, rather frightening, ways.

Steve, everyone has their reasons - intelligent or not so much. I have a keen interest in the topic.

I believe you can bore the 65-66 and possibly 1967 4 bolt main 396 blocks to 4.251

I do know a guy who bored his #'s matching 69 Nova SS 396/375 to 4.251 and ruined it. :eek:

I like the 961 block theory. I have one of those ! A 66 at .030 and fresh smile.gif

In response to "why not use a 454 block ?"
Maybe because you already have the 396 :rolleyes: DOH


Nate

Well I gotta go with Bill on this. As I read the other post refecenced and as I read some responses here my conclusions are confirmed. The only way to know is to sonic check the block. All this "I heard" ..."I read"..."Chevy did it all cause they were ....." is not worth more than the electronic bits used to type the info.

I have read this stuff about the ONLY 396 casting that will....." and it just makes no sense to me. I was thinking Bills answer would be along the sonic check lines as indeed it was. The Vette guys are so obsessed with part numbers and casting dates and (I think) with parting with their money buying rare exotic dated parts that I think they invent some of this stuff. I bet there are samples of that magic casting that won't make it to 4.250 and I bet there are other samples of the non magic castings that will make it to 4.250.

My reason for checking is just rooted in frustration with hearing things like ..."That is the only casting......so I want $4000.00 (or whatever) for it"! If some of those guys just said "No way ....too much money" I think the hobby would be more accessible to the average stiff and generally more fun.

Believe it or not there was a discussion of ...are you sittin down.....DATE CODED DIODES IN ALTERNATORS the other day on a Vette forum. The discussion rambeled along going into the "correct COLOR" ink for stamping the diodes and the "correct FONT" for the numbers that are stamped on the diodes using the CORRECT color ink. It is all just so silly. Particularly when you consider they are talking about correct fonts and correct colors being stamped on recently manufactured diodes going into rebuilt alternators.

Might be time to get outta that side of the car hobby...my sides hurt too much from laughing at them and my head hurts too much for reading junk about correct ink and correct fonts on dated diodes. Now if i can just find a few of those precious magic casting blocks that are the only ones that will.....I can retire.

Just remember, not all Corvette guys are like that................

Originally posted by oman:
3855961....396.......65-66...2 or 4 bolt
3855961....427.......66......2-bolt

I see that the "961" appears to be the only casting used to make both 396 and 427 BY THE FACTORY. Just such fast analysis easily leads to conclusions like "Well it must be the ONLY 396 that can be bored to 427 bore"! Considering the level of anal investigation the Corvette guys do into part numbers and casting IDs any conclusion could be reached.

It seems to me that ya just fired up the boring bar, reamed out your 396 cyl walls to 427 dimensions and ordered new pistons. PRESTO 427. The only guys who will know are guys like Bill K. who run the boring bars.

Wonder what he will say. Guess it is time for new glasses, getting old sucks graemlins/clonk.gif

No big deal. I know what ya mean about the glasses though. I can not read ANYTHING below the headlines without them. Cool thing is now I can read the monitor while my legs are stretched out on the desk. The chair is reclined, keyboard on my lap and I use my glasses to read the keyboard letters.

A funny thing about that mentioned block which I am sure has not occurred to a lot of the "analysts". Perhaps it can be used to make a 427...granted it can. On the other hand it might be all finished after the 427 standard bore is worn to the point that it needs a rebore. Bet nobody considered that! The thought process they use might be "This block is so thick, so strong (so desireable, so rare so VALUABLE) cause it can be a 396 or a 427. Everyone knows a 427 can be bored say 60 over so this block must have super thick walls because it can go from a standard 396 all the way to a 60 over 427". Might be it can do that. Might be it is paper thin at say 10 over 427. Ah the birth of road legends and urban legends.

As for the Dated Diode Dopes. That level of nut case restoration is a logical extension of the quest for the perfect car. I guess I understand going the "extra mile" but crimony man lets think about this for a second. Dated parts INSIDE other components? WTF next? Don't just blow by this as a radical lunatic fringe group. The fact that people make their livings doing the work I outlined is testimony to the fact that enough people are "infected" with the "virus".

Yeah I know that not all the Vette people are like that but an awful lot are. They just can not see beyond the folly. A few deep breaths of fresh air are required!!!!!!!

Hey oman..there are probably more "non numbers" vette guys than you think. When my 65 hits the road in a couple years, the "numbers matching" block will be in a bag, underneath the bench in the garage. I'll let a future owner of my car have all the "fun" of finding those correctly stamped diodes, and paying for the correct vintage oil fumes. Me, I understand that the factory leaves a lot of room for improvement, especially in the drive train department.

I think BillK's advice on sonic checking is right on. The corvette guys should be smart enough to know there are too many variables and inconsistencies in other areas of the cars for there to be an "absolute" that the block can take the increased bore. I would not be surprised to find that a majority of the newer blocks could not be safely overbored, as GM was working to save weight by making thinner castings, and as technology improved to allow tigher tolerences.