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Horsepower Guess on my 340

Performance Upgrades

  1. jjklongisland

    jjklongisland Well-Known Member

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    So I am almost ready to fire up the motor once I finish the wiring. Definitely want to Dyno it and see how much power I am making once its broken in. I am curious what you guys are thinking how much power I should be making based on the following upgrades.

    Its a 1969 340, bored 30 over with the following upgrades:
    Speedmaster Cast Aluminum Cylinder Heads with Hydraulic Roller Cam 65 cc / 170 cc
    Comp Cams Mutha Thumpr Hydraulic Roller Camshaft 522/509 lift, 291/311 duration
    Comp Cams Ultra Pro Magnum Shaft Mount Rocker Arms
    Edelbrock Air Gap Intake
    ARP Head Studs
    Holley Sniper Fuel Injection
    TTI Headers with 3" Exhaust with X pipe
     
  2. Adam

    Adam Well-Known Member

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    If you look around on the web you can find a “desktop dyno” hp calculator.. they will be close but not exact. You will probably need compression ratio, and to account for parasitic losses.
    The 340 has the same stroke as a 318 (3.31) so it revs well, but not the best for low end torque. You got to get the revs up there... but looking at your specs I think you have a beast of a motor.
     
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  3. jjklongisland

    jjklongisland Well-Known Member

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    Thanks, I will definitely look up the hp calculator. I am hoping for at least 450 hp.
     
  4. Steve340

    Steve340 Well-Known Member

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    Ok my guess is 430HP at the crank and 450 ft/lbs torque.
    Let us know what the final dyno result was.
     
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  5. gzig5

    gzig5 Well-Known Member

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    Unless the heads are the CNC version or have been ported, I think you are going to see about 380. My guess. There's a thread on the SM heads on FABO and data on a recent build using those heads on a 360 with less compression and smaller cam was 330hp. If you are at 10:1 that will help and your cam is bigger, but I would be surprised if you are over 400hp. That should take some good breathing heads that will spin to 6500+rpm making power.

    "
    The “reference” point for the ootb heads(since I haven’t seen any other dyno results)......
    360+.030, about 8.5cr, std performer, Ede 750 carb, xe268 cam, PRW 1.5 rockers, 1-3/4” headers.......
    367tq@4600/331hp@5200."
     
  6. jjklongisland

    jjklongisland Well-Known Member

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    I think I will be at 10.5:1 compression and its a pretty aggressive cam. She should be a quick revving motor. I also put in a 3000 stall speed converter. I was going to open up the heads a little more and gasket port them but figured once I break something I will do it next time. Found a cool 340 build article. I had the X-heads but figured if I am going to a roller cam from a flat tappet I might as well go with something newer and flashy.

    https://www.hotrod.com/articles/mopp-0211-340-x-head-buildup/
     
  7. gzig5

    gzig5 Well-Known Member

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    Hey, I hope you make the 450! I've got a set of ProMaxx heads that are supposed to flow a little better than the SM that I need to get on. Ive seen that article before. They make some pretty impressive numbers on that motor.