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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.
     
  8. wayne

    wayne Well-Known Member

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    I will guess 420 hp Either way should be a great street motor
     
  9. MerlinsMopars

    MerlinsMopars Well-Known Member

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    Just built a 340 and broke it in on a dyno because i didnt want to ruin my ceramic headers but my motor is comparable. Bored .030 forged pistons10.2 compression total , scat rods, heads are pocket ported j heads with 2.02 valves and shaved to 62cc. racer brown cam ssh-44 536" lift, 292 duration hydraulic, comp roller rockers 1.5 which gave me that lift, 510with stock rockers, ld340 intake and a 750 holley brawler. Dyno'd at 363 hp at the crank and 378 torque. Doesnt seem alot with all the work done but they only had 275 stock so almost 100hp more with the work that was done.
     
  10. fasjac

    fasjac Well-Known Member

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    Just from what I see, I’m guessing 392hp with a steady climb to 6000rpm.
    It will be a great motor for sure.