High compression 348 question.

[348NUT]

I was reading that the early 11 to 1 348s did not have the counterbore in the cylinders and had a bigger cutout to compensate. The 61 FH block I have is a stock bore with the counterbore and ordinary cutout. I'm wondering if they changed the way they built the high compression engines or if there is something funny with my block :confused: Does any one know this or had experience with the original high compression blocks. Thanks, NUT

[bubbletop61]

Nut, This is a good question that I hope someone on here can answer. What is the date code on your FH block? This may be a dumb question, but what do you mean by the counterbore?
Thanks
Gar

[348NUT]

Gar, Most Ws had a counter bore in the tops of the cyliders to help with ring installation. It was aprox .055 bigger than the bore. In a 1959 article it is said the high compression blocks didn't have this for whatever reason. My H looks like it was stamped after the rest of the stamping since it is a little crooked. I'm wondering if my block is an actual FH or not. I know this would have had to be done in the early 60s because I know the history of this engine from then on but why would they have been worried about the stamping back then and it has the correct heads wich are date coded within 4 days of the block! Which is I-27-60. I'm hoping someone here can tell me what I have. NUT

[SS425HP]

Those gang stamps they used were not exactly perfect. Think about it, how many blocks did each stamp do before it was thrown out. The numbers and letters are never in perfect alignment. I wouldn't worry about that for a minute.

Fred

[348NUT]

Now if someone tells me they had the counterbore I'll be happy!:D Here's a pic that shows the stamping (It looks better in the photo than in real). It also shows the cutout, counterbore, and even a little ring ridge :p NUT

[SS425HP]

Looks right to me. Stamp does too.

Fred

[Bungy]

Nut, You read that the early 11-1 had no overbore even if this is true, your's would be a late 348. So it would have the overbore. Anyway I have never heard or seen of a w-engine that didn't have the overbore from the factory. Do you remember where you saw this?

[bubbletop61]

Nut;
Is this counterbore done parallel with the cylinder walls, with a step in to the bore, OR is it a taper to let in the rings gradually? I'll have to go out and look at the block we have, but it's -15F in the garage right now....
Gar

[bubbletop61]

Nut;
I was under the impression that the Letter "I" was skipped for date codes to avoid confusion with "1". Is your car a September or November build? Could be L for November? Our 61 is a third week November 60 build, so if you ever want to get rid of this FH Block....LOL The stamping on the deck looks as good as any I have seen, the alignment of the stamping is usually a little askew.
Thanks
Gar

[64ss409]

That looks like 1019 doesn't it? That would be Oct 19.
Ron

[art38]

Not that this means anything, but that picture looks exactly like my 65' 409 truck block.
Art

[348NUT]

"The counterbores were aproximately .055-inch larger in diameter than the cylinders and their lower end was at aright angle to the walls of the cylinders.....Engines that have 11 to 1 pistons as standard equipment don't have this counterbore and the single relief in their cylinder walls is considerably larger to compensate for the reduced chamber capacity resulting from the counterbore's elimination." (Modifying Chevy's BIG V8-1959 -Musclecar & hi-po engines p.20)

The block casting date is I 27 60. Yes I'm sure they did use I (at least most years) The heads are I 23 60 and the build date stamped in the photo above is 10 19 60. So the block was cast September 27th and assembled Oct 19th. (If it was cast 1 for January, it would have been assembled before Oct.) Letters weren't used in the deck stamping date code and the year was not stated.

Gar, a casting date of Sept. 27th and build date of Oct. 19th should be completly acceptable for your November built car. I don't have a 61 but for now I don't know what my plans are for this engine? Look at the ridge in the photo. It is fairly sharp but it is angled to let the rings pass. It's bored at a right angle to the cylinder so you can use a ring compressor with the original bore size or if you have the counterbore enlarged the same amount when boring the cylinders you can still use a compressor. I believe this was the original reason for the counterbore.

Note all 348s had notches(or reliefs) in the cylinder walls. Cars had one like in the photo above and trucks had two much larger ones. 409 car engines had no notches. truck 409s had one. (Sounds like a nursery ryme. LOL) :D All this said, I'm still hoping for someone to say thier FB,FC,FD,FE,FG,FH,FJ stamped 348 block has a counterbore and the normal size notch.:D NUT

[fiftiesbob]

348nut:

I hope the following information will help you.
I have three 348 engines that I know are original with standard bores. They all have the same counterbores, normal notches and are as follows: 1959 348 FA/280HP, FD/305HP, FE/335HP

Fiftiesbob

[SteveD409]

I have a hipo 348 block in the barn, I will also check, if I can just remember to!:D

SteveD

[bubbletop61]

I went back to check Chevy by the numbers this morning. "I" was definitely used on Blocks and heads in the date codes. My confusion had come from what Colvin had said about "I" being used in the engine code in place of "1" for stamping clarity.
Nut;
What is the casting number of your block? I don't know if this would cofirm an FH vs an F that has been restamped. I am with you on the idea that no one would have restamped the block back in the sixties, when they were plentiful, and probably very few people knew this level of detail about the cars. It is possible that the factory put a second strike on the number,if the H did not come out clearly on the first stasmping strike. In Colvin's book, he says that the digits were set up in a holder, locked with a set screw, and struck with a dead blow hammer prior to the heads being put on. With the H being at the end of the sequence it may not have been clear enough and the guy on the line could have just restamped the H....??? Please check your PMs
Thanks
Gar

[348NUT]

That's just what I wanted to hear. You've put my mind at ease. Unless I hear some more on this, I'll assume my block is a true FH. Thanks again guys. NUT

[Phil Reed]

HOLY CRAPOLY!!! After 20 years of looking at these parts....I've learned something today!!!

I have a factory T716FB shortblock assy.....late 58 production....and it doesn't have the counter bore.!!! I never would have thought that. WHY would Tonawanda make a different block for H/Perf????? That doesn't make econmical sense...cents!! Why not have all blocks the same and just increase the piston height and compression ratio to compensate!!??

GOT ME:confused: :confused: :confused:

Learn somethin' every day...I can go home now!!!!

[fiftiesbob]

To: 348nut and Phil Read

I have also seen two original 1958 FB H/P engines that a friend has and they also have no counterbores. whereby, it is my understanding that this was 58 H/P only which had 11 to 1 compression. However, in 1959 to 61 the H/P engines went to 11.25 to 1 compression with the standard counterbore, notches
and a much different piston. Also late in 1960 the H/P pistons were changed again for the new H/P heads but the compression remained the same.
I also have an original 1962 409/409 with the counterbore with no notches.

I hope this information will help all of you on this site. Whereby, I have certainly been impressed by the willingness you all have to share information and help each other.

This is a great site.

Fiftiesbob

[SteveD409]

I have a T502FB short block and it has no counterbore. I was also looking at some of my other 348 blocks and found one that is J--57 dated "H" block and it has no casting number. Where casting number usually is, it is cast only with the "GM1". Anyone know about this?

SteveD

[348NUT]

SteveD, I've never heard of a block with no casting # :confused: I'm wondering what the casting date is on your FB block. I see it was assembled May 2nd. Wondering if it's a 58 or 59 engine?
If it's too hard to get at that's O.K. Thanks NUT

p.s. If anyone has a digital camera and could take a photo of one of these cylinders with no counterbores, I'd like to see it and I'm sure Bob would like these for our reference page.:)

[Bungy]

SteveD, You didn't happen to buy that no casting number block at a Wisconsin swap a couple of years ago did ya? I sold a disassembled 348 at the Jefferson swap meet a couple of years ago that had no casting number. It was dated J3157 (Halloween) The heads, intake, and exhaust manifolds were all dated K757 and had casting numbers. The block was stamped TIIIIH :confused:

[bubbletop61]

I went and had a look at Alan Colvin's book "CBTN". He says that "in some cases , during a production changeover, blocks had the original casting number ground off and a new casting number hand stamped into the block" This is one possibility, so you might have a look for this, which I guess woould have been done on the
bellhousing mounting flange of the block. Stamping might be harder to see after 45 years than the cast digits.

For the Casting date, Colvin wrote , "Some blocks have the casting date on the long side of the block, near the freeze plug."

Maybe this helps????

[SteveD409]

Bungy: I remembered the build date because it was so strange-TIIIIH, but I didn't remember the date of cast, so I went and checked--sure enough it's J3157, but here comes the kicker--I've had this stuck solid short block for at least 8 years. Got it and two others along with a 57 2 door sedan.

348NUT: The FB block was cast late Feb, like B2758. I remember that because it was a full two months before it was assembled!

bubbletop61: there is no sign of grinding and no hand stamped number in the normal position or any sign of anything on either side of the block.




SteveD

[SteveD409]

So, Bungy, did they just forget to put casting numbers on all the W blocks cast on Holloween day 1957?:)

SteveD

[348NUT]

Sounds Spooky to me! :D
Are you guys talking about two different blocks that were cast the same day (on Halloween) and then assembled the same day (on November 11th) !? and neither had a casting # and they were both H codes! That's just plain weird. :) NUT

[SteveD409]

Looks like that what we be sayin'! He sold his a couple of years ago and I've had mine for at least 8.

SteveD

[Bungy]

Yes, two different engines. That is kinda weird. The casting numbers are permenately in the mold correct? Not like dates that are screwed on. I always wondered why it didn't have a casting date. At least I know there is more then one out there. Anyone know why there would be no casting number? Fran?