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Technical 261 Jobmaster Progress

Discussion in 'The Hokey Ass Message Board' started by Cosmo49, Oct 13, 2020.

  1. Cosmo49
    Joined: Jan 15, 2007
    Posts: 1,551

    Cosmo49
    Member

    Robert J. Palmer and VANDENPLAS like this.
  2. Aeroman
    Joined: Apr 19, 2005
    Posts: 707

    Aeroman
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    Looks and sounds great.

    Sent from my SM-G965U using Tapatalk
     
  3. Cosmo49
    Joined: Jan 15, 2007
    Posts: 1,551

    Cosmo49
    Member

    Feels great. Will have a Clifford four barrel intake with a Holley 390 cfm, the Clifford will mate to an early style integral heat Fenton Header.
     
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  4. Aeroman
    Joined: Apr 19, 2005
    Posts: 707

    Aeroman
    Member

    I'm running a 261 myself. Great engine.

    Sent from my SM-G965U using Tapatalk
     

  5. Ya got a bit of a coolant leak :rolleyes:



    nothing like the sound of a inliner !!!! Love it
     
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  6. What's the difference between the 848 and 913 head?
     
  7. 848 head is the “ good head” for 235’s bumps the compression up by a 1/2 point.

    but any 235 head on a 261 is an improvement. Over stock.

    did you drill the steam holes in the head?
     
  8. Cosmo49
    Joined: Jan 15, 2007
    Posts: 1,551

    Cosmo49
    Member

    Yes, steam holes were drilled on the early head.
     
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  9. Cosmo49
    Joined: Jan 15, 2007
    Posts: 1,551

    Cosmo49
    Member

    Here’s the mock-up of the Clifford intake with Fenton’s. I have a machinist friend who married them together.

    upload_2020-10-14_8-0-37.jpeg
     
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  10. This fentons look snazzy !!!
    Great job !
     
  11. Cosmo49
    Joined: Jan 15, 2007
    Posts: 1,551

    Cosmo49
    Member

    Both the Clifford intake and the Fenton header are the early versions. The Clifford intake changed to a water heat version in the later version. The 235-261 Chevy Fenton headers changed to pipe plugs to access exhaust heat to prevent icing in the carburetor base.

    I can only guess that in both Clifford and Fenton’s reasoning they went to a ‘universal’ application because IMHO, close is not good enough when it comes to exhaust leak.

    My machinist friend made these two now rare pieces ‘gasket perfect tolerance’.

    I now have 115 k miles on a 1956 235 so it will be fun with a 1962 261 with the set up above.
     
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  12. belair
    Joined: Jul 10, 2006
    Posts: 9,013

    belair
    Member

    Jealous. I want one in my 55.
     
  13. Cosmo, I have a spare 848 head, if you're looking for one!
     
  14. Thanks for the pm, Cosmo!

    So is there a benefit to using the 913 (instead of the 848) head on a 261?
     
  15. Cosmo49
    Joined: Jan 15, 2007
    Posts: 1,551

    Cosmo49
    Member

    In my case I bought an engine with a 913 head it was ported and polished which is a science unto itself.
     
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  16. Gotcha!
    I have my dad's 261 with the 848 head that Jiggs Jenkins (before he was known as Grumpy) ported and polished back in the 60's. Unfortunately, it's hosted multiple generations of mice in the head, so I'll have some work to do :rolleyes:
     
  17. grumpy gaby 2
    Joined: Aug 10, 2019
    Posts: 462

    grumpy gaby 2
    Member

    I am tearing a 41/46 truck up and found that it had a 261 block and a 848850 head. I was wondering where the 848 head was origanly used. Looks like 2.02 intakes. I have done several searches but no luck. Any help?
     
  18. 302GMC
    Joined: Dec 15, 2005
    Posts: 7,856

    302GMC
    Member
    from Idaho

    Read the casting # again - it has 7 digits.
    After 1956 on the 848. Intake valves that big would take some pretty serious machine work.
    Then post the pictures of it here ...
     
  19. Gofannon
    Joined: Feb 8, 2007
    Posts: 924

    Gofannon
    Member

    There is no real difference in port or valve size between a 850, 913, or 848. Just the size of the combustion chamber. If you mill them, you lose the relief area from the intake valve into the combustion chamber. Top pic is a 850, bottom a milled 848. I'd rather use the 850 or 913 and use a pop up piston to get higher comp ratio. 850 head has the steam holes which must be drilled when adding an 848 to a 261.
    upload_2020-11-24_11-51-9.png

    upload_2020-11-24_11-51-35.png
     
    Last edited: Nov 23, 2020
  20. Gofannon
    Joined: Feb 8, 2007
    Posts: 924

    Gofannon
    Member

    I think this is a pic of Cosmos 261 pistons?? Nice pop ups.
    upload_2020-11-24_12-3-50.png
     
  21. Dyno Dave
    Joined: Feb 18, 2011
    Posts: 339

    Dyno Dave
    Member

    My 1960 261 is the Canadian Pontiac base line version, and it has the factory installed #848 head on it. Dyno Dave
     
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