3916321 67-68 427 block

[Charles A.]

Every book I have seen list casting number 3916321 as a 427 block used in late 67 and 68 corvettes and 68 passenger cars. I have a 3916321 block with a T besides the numbers when would indicate to me it was a truck block. Is this block acceptable for judging on a 68 corvette or does it have to have a P besides the numbers?

[Terry M.]

Re: 3916321 67-68 427 block

Every book I have seen list casting number 3916321 as a 427 block used in late 67 and 68 corvettes and 68 passenger cars. I have a 3916321 block with a T besides the numbers when would indicate to me it was a truck block. Is this block acceptable for judging on a 68 corvette or does it have to have a P besides the numbers?

That T has nothing to do with truck. It signifies that the cylinder case was cast at Tonawanda New York, but then we somehow knew that without the help of the T.

Edit add: The folks pouring the metal into the molds had no clue the ultimate destination of the casting they were making, and couldn't care. It could wind up in a passenger car, and irrigation pump, or a boat -- and probably a few other options I can't think of. There is no such thing as a truck block or a passenger car block -- at least not until some other parts are added to the cylinder case.

[Joe L.]

Re: 3916321 67-68 427 block

That T has nothing to do with truck. It signifies that the cylinder case was cast at Tonawanda New York, but then we somehow knew that without the help of the T.

Edit add: The folks pouring the metal into the molds had no clue the ultimate destination of the casting they were making, and couldn't care. It could wind up in a passenger car, and irrigation pump, or a boat -- and probably a few other options I can't think of. There is no such thing as a truck block or a passenger car block -- at least not until some other parts are added to the cylinder case.

Terry-----


Yes, all Mark IV blocks originally used in Corvettes were cast at Tonawanda, NY whether, or not, there is a "T" found on the casting. All big blocks from 1958 to 2009 were assembled there, too. However, not all big blocks were cast at Tonawanda. The foundry there shut down permanently in 1984. After that time, big blocks were cast at Defiance, OH.

Also, while there was no difference between Mark IV big blocks used for passenger cars and LIGHT trucks, there was a difference between these blocks and those used for HD trucks. The passenger car/light truck blocks had a 9.8" deck height; those used for HD trucks had a 10.2" deck height. The latter blocks are also used for some "monster motors".

[Wayne M.]

Re: 3916321 67-68 427 block

.....Also, while there was no difference between Mark IV big blocks used for passenger cars and LIGHT trucks, .....

Agree -- but on my 961 block (May '65) under the timing chain cover there's PASS and HI PERF, and on the back of the block, under the bellhousing, close to the top on the passenger side, is cast HI - PERF and TRUCK and PASS.

Am wondering if all pass/light truck big blocks had these letters cast in those positions ?

[Terry M.]

Re: 3916321 67-68 427 block

Terry-----


Yes, all Mark IV blocks originally used in Corvettes were cast at Tonawanda, NY whether, or not, there is a "T" found on the casting. All big blocks from 1958 to 2009 were assembled there, too. However, not all big blocks were cast at Tonawanda. The foundry there shut down permanently in 1984. After that time, big blocks were cast at Defiance, OH.

Also, while there was no difference between Mark IV big blocks used for passenger cars and LIGHT trucks, there was a difference between these blocks and those used for HD trucks. The passenger car/light truck blocks had a 9.8" deck height; those used for HD trucks had a 10.2" deck height. The latter blocks are also used for some "monster motors".

Of course Joe you are right about the tall-deck medium and heavy duty truck cases, but I wasn't considering what happened more recently than 1974 -- when the last Mark IV engine went into a Corvette. I guess I should have bounded my broad-brush statement a little bit.

[Robert G.]

Re: 3916321 67-68 427 block

Wayne, 1965 may be different since it was the first year for the big block for the vette, but I've never heard or seen of both PASS and TRUCK cast into the area near the bellhousing. Maybe a judge will weigh in, or someonne with a judging guide.

[Wayne M.]

Re: 3916321 67-68 427 block

Wayne, 1965 may be different since it was the first year for the big block for the vette, but I've never heard or seen of both PASS and TRUCK cast into the area near the bellhousing. .

Here's some pics to ensure we're all on the same wavelength as to location.

Big photo is the front; thumbnail below it is of the back of the block, which is covered by the bellhousing, so engine rebuilders, rather than judges, would be more familiar with this feature.

[Joe L.]

Re: 3916321 67-68 427 block

Here's some pics to ensure we're all on the same wavelength as to location.

Big photo is the front; thumbnail below it is of the back of the block, which is covered by the bellhousing, so engine rebuilders, rather than judges, would be more familiar with this feature.

Wayne-----


I've never noticed this, but it's possible it's common. However, I believe that the term "PASS" refers to the 9.8" deck height blocks used for both passenger cars and light trucks whereas the "TRUCK" refers to the 10.2" deck height blocks used for MD/HD trucks. There would be no reason to make a distinction between the blocks used for passenger cars and light trucks since hey were the same.

If what I describe above is the way it is, obviously no block could be both "PASS" and "TRUCK". However, it is possible that some of the pattern elements used for casting the blocks were the same. The pattern element for the bulkhead area might be one of those.

[Charles A.]

Re: 3916321 67-68 427 block

The deck height difference is correct and you can tell the difference in blocks by looking at the water pump inlets at the front of the block. My questions is if there is a T as opposed to a P besides the casting number where the casting number is located looking down on the back of the block below the distributor. I know on my 67 351 block there is a P and on the 321 block there is a T. This is not where the plant i.d is located it is on the data boss.I want to sell the block to someone who needs an early 68 block but I want to make sure it is OK for judging.

[Wayne M.]

Re: 3916321 67-68 427 block

Charles -- are your casting #'s and the "HI-Per" upside down from the normal, like these ? Shots I took of a friend's '68 SS427.

[Charles A.]

Re: 3916321 67-68 427 block

I will check tonight and let you know.

[Rich P.]

Re: 3916321 67-68 427 block

Wayne,

I have seen the High perf pass truck on many 65-69 BB.

Rich

[Charles A.]

Re: 3916321 67-68 427 block

Wayne mine are not upside down and I am to dumb to attach pictures. Send me an email address and I will send them to you and maybe you can post them so all can see what I am talking about.

[Wayne M.]

Re: 3916321 67-68 427 block

Wayne mine are not upside down and I am to dumb to attach pictures. Send me an email address and I will send them to you and maybe you can post them so all can see what I am talking about.

Here they are, Chuck -- tried to lighten the middle pic with a photo editor, but it wouldn't "take" as there was a padlock symbol on all three desktop thumbnails, which I'd never seen before. It didn't affect the uploading to the NCRS site, though.

[Charles A.]

Re: 3916321 67-68 427 block

Thanks Wayne hope someone can solve the mystery of whether this block is suitable for an early 68.