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Technical Pontiac 347 vs 370 heads

Discussion in 'The Hokey Ass Message Board' started by hpBent, Aug 29, 2022.

  1. Joe H
    Joined: Feb 10, 2008
    Posts: 1,874

    Joe H
    Member

  2. hpBent
    Joined: Jul 16, 2019
    Posts: 80

    hpBent
    Member

  3. hpBent
    Joined: Jul 16, 2019
    Posts: 80

    hpBent
    Member

    Out of curiosity, does anyone know which Hilborn pump was used with the 347-P-8 unit?
     
  4. hpBent
    Joined: Jul 16, 2019
    Posts: 80

    hpBent
    Member

    OK, so I am determined to get to the bottom of the mis-aligned bolt hole issue.

    While I realize '56-'60 heads are supposed to be interchangeable, I am wondering if Pontiac could have made small
    changes between years, possibly resulting in my mis-alignment issue, or was this Hilborn's doing?

    Now, my '58 heads have casting number 528511. I see that the '57 heads should have casting number 523298 or in the case of a FI engine 52(****) - last four stamped on O.E. install.

    Does anyone happen to have a 528511 head that they could take a couple of photos of for me so I could compare the positioning of the upper-two intake bolt hole locations to my '58 heads? It would be greatly appreciated!
     
  5. bchctybob
    Joined: Sep 18, 2011
    Posts: 6,037

    bchctybob
    Member

    I’ll bet it was Hilborn moving the hole because utilizing the factory hole would have meant an awkward divot in the port casting (going by your photos)
    It probably came with a PG-150 or 150a pump. But you won’t need one going the direction you are going.
     
  6. wheeltramp brian
    Joined: Jun 11, 2010
    Posts: 3,348

    wheeltramp brian
    Member

    I've got a 1957 motor in my hot rod and a spare 1955 motor and a 20220604_165611.jpg 20220604_165020.jpg couple of sets of extra gaskets so I can get a picture when I get home later today
     
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  7. hpBent
    Joined: Jul 16, 2019
    Posts: 80

    hpBent
    Member

    I agree. I bet they moved it, but how on earth did they expect someone to install it on the engine it was designed for? I wonder if they offered adapter plates? I certainly can't find any references anywhere. Adapter plates OR the correct head is the path I am on now. If all fails, I might play around with mechanical just to frustrate myself even more LOL. I hear it is possible but not easy...
     
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  8. hpBent
    Joined: Jul 16, 2019
    Posts: 80

    hpBent
    Member

    Very nice ride! I will keep an eye out for your photos. Thanks!
     
  9. wheeltramp brian
    Joined: Jun 11, 2010
    Posts: 3,348

    wheeltramp brian
    Member

    Sorry forgot to take the photos I'll try again tonight
     
  10. hpBent
    Joined: Jul 16, 2019
    Posts: 80

    hpBent
    Member

    OK, thank you.
     
  11. hpBent
    Joined: Jul 16, 2019
    Posts: 80

    hpBent
    Member

    Fel-Pro gasket # MS9498SH1

    You can see it covers two holes on the head but matches the intake ports correctly. Using a felt marker, I scribed where the head bolt hole should be on the Hilborn base plate.

    I am not 100% positive I have the correct gasket, although they claim it is supposed to be compatible with the 347 and 370 engines. Still, why would Hilborn drilled the hole where they did, when the unit was supposed to "fit" the head? I have seen two Hilborn 347-P-8 units and the bolt hole locations are the same as mine. There is some piece to this puzzle that is missing...
     

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  12. wheeltramp brian
    Joined: Jun 11, 2010
    Posts: 3,348

    wheeltramp brian
    Member

    Sorry I forgot again going to make a note to remember
     
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  13. wheeltramp brian
    Joined: Jun 11, 2010
    Posts: 3,348

    wheeltramp brian
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    That's basically the same gasket I have just made by best. It fits my 55 Motor and my 57 motor perfect. Perhaps hilborn marked the casting wrongs and it's for a later year 20220909_171034.jpg
     
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  14. wvenfield
    Joined: Nov 23, 2006
    Posts: 5,667

    wvenfield
    Member

    Just a wild thought based upon another remark earlier. The holes all should be the same as others have noted.

    Is it possible the engine came out of a GMC truck and they had a different intake? I've only seen a couple 370 Pontiacs in a GMC truck and I don't recall.
     
  15. wheeltramp brian
    Joined: Jun 11, 2010
    Posts: 3,348

    wheeltramp brian
    Member

    The motor that's in my hot rod now came out of a 57 GMC ramp truck. It started as a 336 cubic inch and all the heads are all the same bolt pattern
     
  16. hpBent
    Joined: Jul 16, 2019
    Posts: 80

    hpBent
    Member

    Thank you very much for taking time to post the photo. I don't think Hilborn stamped the number in error. I have seen a couple of these and the bolt pattern is the same. So puzzling....
     
  17. wheeltramp brian
    Joined: Jun 11, 2010
    Posts: 3,348

    wheeltramp brian
    Member

    Very weird. I've had every intake for these early Pontiacs besides a dual quad cross ram in my possession and they are 16628266178108929120550571641749.jpg 16628266477326604551289532050976.jpg 16628266898534431807855046583658.jpg all the same bolt pattern. The 6x2 that I have has the coolant Port so it'll fit early and late heads. And apparently I'm missing two air cleaners somewhere in the move
     
  18. hpBent
    Joined: Jul 16, 2019
    Posts: 80

    hpBent
    Member

    Thank you for the photos! The attached image is comparing your 6x2 manifold to my Hilborn. We can see that where I scribed the black circle from the gasket, is in the same location as is on your manifold and correct for the heads. Notice how high up on the flange the hole is on the Hilborn, yet all other holes and ports match - it's just the two uppers. Did the later heads have this patten? I don't have any to compare.

    Cool 6x2 by the way! I hope you find those air cleaners.
     

    Attached Files:

  19. wheeltramp brian
    Joined: Jun 11, 2010
    Posts: 3,348

    wheeltramp brian
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    I don't have any later stuff to compare it to. It doesn't look like the water Port would line up either
     
  20. Rocky
    Joined: Mar 3, 2001
    Posts: 17,626

    Rocky
    Classified Editor

    34intakedualquad.jpg Only thing I can figure is maybe the F.I. heads had a different bolt pattern than the carbureted heads. Nothing else makes sense to me. I have a late [64 and newer] intake I can take a photo of. Here it is........
     
    Last edited: Sep 10, 2022
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  21. hpBent
    Joined: Jul 16, 2019
    Posts: 80

    hpBent
    Member

    You could be onto something. I see there was also a T395A option in addition to the FI for the 370 in 1958. I bet the Hilborn unit was intended for those heads and the bolt pattern, etc. may have been slightly different. What are the chances of finding a set of heads off of one of those? Slim to none, I am thinking.
     
  22. Fordors
    Joined: Sep 22, 2016
    Posts: 6,520

    Fordors
    Member

    The Tempest 395A designation was for over the counter parts. Pontiac offered high perf exhaust manifolds, a few different camshafts, valve springs and lightweight retainers. The hottest cam along with the other parts bumped the 310
    horse FI engine to 338. There were no unique ‘58 heads.
     
  23. hpBent
    Joined: Jul 16, 2019
    Posts: 80

    hpBent
    Member

    Thank you for the information - much appreciated.

    And, supposedly, the '57 heads should be identical to the '58 heads - correct?
     
  24. Mr.Racer
    Joined: Jul 8, 2018
    Posts: 26

    Mr.Racer
    Member
    from Ohio

    Do you have an early Olds intake gasket or head laying around?
     
  25. flamedabone
    Joined: Aug 3, 2001
    Posts: 5,759

    flamedabone
    ALLIANCE MEMBER

    I am not holding the parts in my hand, so I may not have a complete grasp of this issue, but it looks to me that if you use all the existing bolt holes in the intake, you would have to drill the two that don't exist on the head. Does the head have enough material to make new holes where you need them? If so, drilling and tapping the head is a fairly simple task.

    Also, if you can drill holes in the head, does the intake water port seal the head port enough so it won't leak? If so, the mis-alignment in the port shapes is not anything to worry about. You can do some mild porting to blend a bit, but in the end, water will find a way. Particularly if this is not a "driver".

    By the way, I have a garage full of Pontiac engines and they are all stupid. Just different enough to be a pain in the ***.

    -Abone.
     
  26. hpBent
    Joined: Jul 16, 2019
    Posts: 80

    hpBent
    Member

    Unfortunately, I do not have any lying around.
     
  27. hpBent
    Joined: Jul 16, 2019
    Posts: 80

    hpBent
    Member

    I see why Hilborn placed the upper two holes on their flange where they did. They couldn't place it to line up with the upper holes on the heads, because the bolt head and shoulder would have been jammed against the outer throttle bores.
    I wonder if Hilborn informed their customers that the upper bolt holes on the heads would have to be relocated? Unfortunately, I can't find anyone from that era that knows.
    Yes, there appears to be enough material to drill and tap to match the upper holes on the Hilborn unit - like they planned it that way...
     
    Mr.Racer likes this.
  28. curt e
    Joined: Apr 10, 2008
    Posts: 15

    curt e
    Member

    The upper bolt holes on your picture of the Hilborn unit look to be smaller than the other bolt holes . . . or is it just my old eyes?
     
  29. hpBent
    Joined: Jul 16, 2019
    Posts: 80

    hpBent
    Member

    They are all the same diameter. It was probably just the camera angle.
     
  30. 34 5W Paul
    Joined: Mar 27, 2020
    Posts: 435

    34 5W Paul
    Member
    from Fresno CA

    What he said.
    Those pictures are worth a thousand words. Glad you posted them. Unless those heads are unobtanium, I'd carefully drill and tap them using a drill alignment tool or block and call it a day.
     
    hpBent likes this.

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