#21  
Old 02-27-2023, 11:25 AM
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I have a 4 bolt block that came in a 1969 Grand Prix I once had. The block casting number on the back of the block was partially ground off and restamped. I seem to remember an article in the past talking about blocks that had this treatment referred to "H'ot Wiping" done to the cast #. Can anyone here provide any information about this? How and Why was it done?

  #22  
Old 02-27-2023, 04:02 PM
Tellyshavilli Tellyshavilli is offline
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Quote:
Originally Posted by wase View Post
I have a 4 bolt block that came in a 1969 Grand Prix I once had. The block casting number on the back of the block was partially ground off and restamped. I seem to remember an article in the past talking about blocks that had this treatment referred to "H'ot Wiping" done to the cast #. Can anyone here provide any information about this? How and Why was it done?
Are you talking about a 400 block and can you let me know the number that was cast and stamped also the date would also help

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  #23  
Old 03-02-2023, 04:03 PM
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Yes I believe it's a 400 block,. XH code. Stamped # looks like 9790071. Date CO39. It came in a 1969 Grand Prix.
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Last edited by wase; 03-02-2023 at 04:11 PM.
  #24  
Old 03-03-2023, 12:56 AM
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From what I recall reading, prior to the end of the 1970 model year, the casting number was either partially, or fully removed for the ‘915, or SR for earlier castings.
It seems as though after the end of the 19670 model year, the block casting number was left as-is, and the block was just finished as required.

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1970 Formula 400
Carousel Red paint on Black standard interior
A no-engine, no-transmission, no-wheel option car.
Quite likely one of few '70 Muncie three speed Formula 400's left.


1991 Grand Am: 14.4 @ 93.7mph (DA corrected) (retired DD, stock appearing)
2009 Cobalt SS: 13.9 @ 103mph (current DD; makes something north of 300hp & 350ft/lbs)
  #25  
Old 03-03-2023, 04:26 PM
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I looked at Wallace Racing and the casting # for 1969 GP XH 400 was listed there as 7029268.
I did some more research and found this site; https://wowmusclecars.com/pontiac-engine-codes-specs/
There I found "1969 400 XH 9790071 4 Bar Carb 350HP Grand Prix" . just what is stamped on my blpck.
I can't tell what was ground off, but a 4 bolt main 400 that came in a 1969 Grand Prix . OK

  #26  
Old 03-03-2023, 04:36 PM
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The 7029268 is the carburetor number.

The 9790071 would be the 1969 block code, possibly they had a 9799914 which were starting to be used in 1969 Firebirds mainly because of the extended year for them. They probably 'wiped' it and stamped the 9790071 into it.

Does the block have 2 engine mount holes or 5?


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  #27  
Old 03-03-2023, 05:35 PM
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The block has two engine mount holes per side.

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Old 03-03-2023, 06:15 PM
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I just noticed a tiny, but huge typo, that makes my post almost seem gibberish with just one extra charecter...

Quote:
Originally Posted by unruhjonny View Post
From what I recall reading, prior to the end of the 1970 model year, the casting number was either partially, or fully removed for the ‘915, or SR for earlier castings.
It seems as though after the end of the 1970 model year, the block casting number was left as-is, and the block was just finished as required.
Fixed.

I would be incline to agree with John's post;
I have observed that regardless of casting number, the date code is generally present, and can be used as an indicator of when that block was made (eg: which block casting was being used at the time).

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1970 Formula 400
Carousel Red paint on Black standard interior
A no-engine, no-transmission, no-wheel option car.
Quite likely one of few '70 Muncie three speed Formula 400's left.


1991 Grand Am: 14.4 @ 93.7mph (DA corrected) (retired DD, stock appearing)
2009 Cobalt SS: 13.9 @ 103mph (current DD; makes something north of 300hp & 350ft/lbs)
  #29  
Old 03-04-2023, 12:35 PM
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So as it was cast March 1969, the 4 bolt block casting for that time would have been 9792506 for RA III or RA IV stick or A/T application.
So could this have been a service replacement upgrade done at a dealer? Or a substitution done at the factory?

  #30  
Old 03-04-2023, 04:05 PM
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With the engine unit number and engine code, it would be done at the factory. Possibly the original was messed up and they set it off line for another engine to put in?



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  #31  
Old 03-04-2023, 07:55 PM
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I had thought that prior to 1970, service replacement blocks were cast and prepped (along with being renumbered) for their intended application;
eg: a car with an original 9790071 cast block, would receive a replacement block with the same number.

With that being said, according to my Pete McCarthy “bible”, the 9790071 block was a 1968/1969 two bolt main block casting number, so my initial thoughts were that the block being renumbered meant that it was an SR block intended for 1968/1969 application;
Again according to the “bible”, XH was a 1968 & 1969 full sized/G.P. 400/4bbl-350hp motor.

I think that it might be prudent to take pause and question weather the Pontiac foundry swapped over to the 1970 castings by March 1969 - the block being drilled and tapped for four bolt mains might seem to suggest this.
OR(!)
maybe the early motor mount bosses would suggest this was cast prior to the 1970 change over.
I am thinking now that this block was originally created as a 9792506 casting, but supply demanded that it be renumbered and used as a non-RA engine…

Does the block code ect. look legit?
Does the block have the G.P.’s partial vin on it?

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1970 Formula 400
Carousel Red paint on Black standard interior
A no-engine, no-transmission, no-wheel option car.
Quite likely one of few '70 Muncie three speed Formula 400's left.


1991 Grand Am: 14.4 @ 93.7mph (DA corrected) (retired DD, stock appearing)
2009 Cobalt SS: 13.9 @ 103mph (current DD; makes something north of 300hp & 350ft/lbs)
  #32  
Old 03-04-2023, 09:24 PM
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The stampings; EUN, engine code, and partial VIN all look like legit Pontiac font and size stamps. The hot wipe of the cast block part number, and subsequent re-stamp makes this block's origin the mystery.

Dealer replacement with upgrade to 4 bolt mains ?

I almost want to get the PHS for the car it was in, to check if the EUN on the block matches the " as built with" EUN on the billing history.

If they are the same, then it would have been a factory substitution

If non matching EUN, then a dealer SR block.

Assuming every block was assigned it's own EUN, whether going into a car on the line, or going into inventory as stock for OTC or SR sales. with the other identifying stamps to be done by the installer.

So OTC blocks may have no code or VIN stamp, but dealer installed would get legit Pontiac font re-stamp? And maybe a hot wipe and a block # re-stamp.
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  #33  
Old 03-05-2023, 01:49 AM
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If the stampings look legit, I’d really be curious to hear the thoughts from someone authoritative on this.

An XH block used in either the 1968 or 1969 model year should be a 9790071 block.

If I have this straight, the 1967-1968 RAI block used a 2-bolt engine with cast slugs just like everything else made before the introduction of the ‘2506 block with the RAII;
That is to say that all 1968, and 1969 D-port 400’s would have used the 9790071 short block assembly.

Only the 1968.5 RAII & 1969 RAIV used the 9792506 casting, which was finished with four bolt mains, and assembled with forged (TRW) slugs.

With a change in how PMD was dealing with substitution or SR short blocks starting around 1970, it would not seem to be a stretch to think that a ‘2506 casting could have been put in service as a ‘0071 block…

The difference between 1969 & 1970 was that for 1969 only ‘2506 blocks were drilled and tapped for four bolt mains - while for 1970, the few 400’s NOT drilled and tapped are the oddities.

Could PMD have started substituting blocks assemblies before 1970?

I think it’s quite feasible.

If PMD did substitute, would the casting number have been wiped?

I think that everything I have learned of PMD’s practices would suggest that prior to 1970 the number of the block was of upmost importance..

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1970 Formula 400
Carousel Red paint on Black standard interior
A no-engine, no-transmission, no-wheel option car.
Quite likely one of few '70 Muncie three speed Formula 400's left.


1991 Grand Am: 14.4 @ 93.7mph (DA corrected) (retired DD, stock appearing)
2009 Cobalt SS: 13.9 @ 103mph (current DD; makes something north of 300hp & 350ft/lbs)
  #34  
Old 03-05-2023, 01:52 AM
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unruhjonny unruhjonny is offline
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I believe the EUN was used for warranty purposes, and would not have ever been stamped on an OTC sale….
but I am a little muddy on precisely when or where the EUN was stamped.

It would be great if someone documented this kind of stuff for people like me who were born too late

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1970 Formula 400
Carousel Red paint on Black standard interior
A no-engine, no-transmission, no-wheel option car.
Quite likely one of few '70 Muncie three speed Formula 400's left.


1991 Grand Am: 14.4 @ 93.7mph (DA corrected) (retired DD, stock appearing)
2009 Cobalt SS: 13.9 @ 103mph (current DD; makes something north of 300hp & 350ft/lbs)
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