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Technical 1956 DeSoto hemi engine rebuild.

Discussion in 'Traditional Customs' started by 40 DeSoto Hemi Coupe, Jan 16, 2017.

  1. Hi , all Hemi lovers. Norway calling. I Have two 1940 DeSoto cps. One found behind a barn in 1977 and given to me by the old Nice folks at the farm. I still have it. My other cpe was purchased on Ebay in 2008. Ment to be my user car. It looked very Nice, but was a technical wreck. So i had to rebuild everything. Suspension, brakes, frame, floor. It came With a 350/350. Unacceptable for a MOPAR head. MOPAR in MOPAR for me ! Installed a 360/904 combo. It Works fine.
    Now I`m in the process of rebuilding a 56 4bbl 341 DeSoto Hemi for the second 1940 DeSoto Cpe. Purcased in a basket. Bought a Complete rebuild kit from Kanter auto products. A friend who has a engine shop is doing the machine work. Here is my question : The engine came With a brand "New" set of Jahns racing pistons , 11:1 compression. I want to use it, but friends says it`s not a good choise for street use.
    Any ideas ? Not too many to ask up here in the North...
    Thanks ! Any comment will be appreciated.
    Sorry for the poor English.. :-(
    Best regards! :))
    36 ROKIT and Bruce Fischer like this.
  2. jvpolvere1
    Joined: Aug 19, 2016
    Posts: 176


    Lars, your English is fine.
    My machinist believes an engine for street use should not exceed a 10 to 1 compression ratio in order to run on pump gas.

    Sent from my SM-T377V using The H.A.M.B. mobile app
  3. RRichFox
    Joined: Nov 15, 2016
    Posts: 63


    I am not sure that you couldn't get by with 11 to 1 pistons. You should check your combustion chamber size before you believe what's on the box. If you confirm the 11 to 1 CR. You can always face a little off the dome to get 10 or so. High compression is not easy to get in a hemi chamber.
    40 DeSoto Hemi Coupe and 'Mo like this.
  4. Lars. Do you have a picture of the old girl? Thanks Bruce.
    40 DeSoto Hemi Coupe likes this.

  5. 'Mo
    Joined: Sep 26, 2007
    Posts: 7,432


    Guys used to run thin copper gaskets for a compression boost. How about double gaskets?
    Do the math. Run the pistons. Mill the tops if you have to.
  6. Thanks Bruce. I`ll check With my engine Builder. There is some more pics if you klick om my profile Picture to left side.
  7. Lars, O.K.Thanks Bruce.
  8. Arominus
    Joined: Feb 2, 2011
    Posts: 394


    You can take some off the pistons as suggested or get a thicker head gasket. You should check your CC's as suggested, I bet you come in closer to 10.5... I think you would be ok on the highest octane available so long as you don't take the timing too far. I've been reading everywhere that 30 degrees of total advance is the max number you should run in these.

    cam choice will also play a role here, what cam would you be running?
  9. CJ 56 hemi
    Joined: Oct 25, 2011
    Posts: 107

    CJ 56 hemi
    from NJ

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