340 Engine Power Boosts

Discussion in 'First Generation Challenger Forum' started by SRT-Tom, Apr 5, 2020.

  1. SRT-Tom

    SRT-Tom Well-Known Member Staff Member Super Moderator Article Writer

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    Hot Rod took a 1970 340 engine, conservatively rated by the factory at 275 hp. and got an amazing 391.6 hp. with bolt-ons.

    Here were the stages of the performance boosts, based on dyno tests:

    Base

    281.3 hp. and 328.5 lb./ft.

    1st Stage- Edelbrock 800 AFB Carburetor

    316.9 hp. and 351.3 lb./ft.

    2nd Stage- Hooker Competition Headers

    330.4hp. and 369.1 lb./ft.

    3rd Stage- Two-Plane RPM Air Gap Manifold

    354.5 hp. and 384.5 hp.

    4th Stage- SSI Valve Springs

    355.9 hp. and 383.6 lb./ft.

    5th Stage- Competition Cam Xtreme Energy 268 Cam

    391.6 hp. and 412 lb./ft.


    https://www.hotrod.com/articles/mopp-0102-1970-340-high-performance-mill-dyno/
     
  2. IntimidatorRT

    IntimidatorRT Well-Known Member Staff Member Super Moderator

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    Major boost right there with the carb.


    Sent from my iPad using Tapatalk
     
  3. SRT-Tom

    SRT-Tom Well-Known Member Staff Member Super Moderator Article Writer

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    The 1970 340 engine only had a 600 CFM carb. In 1971, it got the 750 CFM Carter Thermo-Quad.
     
  4. Katshot

    Katshot Full Access Member

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    #1.. The Thermo-quad was garbage!
    #2.. Although the data doesn't lie, if you read the article you'd know that they admitted the carb used for the baseline pull was junk so I'm sure that's what led to the exaggerated improvement provided by the newer, larger carb.
     
  5. Climber

    Climber Full Access Member

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    In Sep. '71 I purchased my '70 340 4 speed Challenger. I was told by the dealer that the car would dyno at 348 rwhp. I have no idea if this claim from the dealer was true or not. He could have blowing smoke at my barely 21 year old self. If memory serves and upon visual inspection of the engine bay, the car looked bone stock but as we all know and have seen at times, looks can deceive. I had several of my Mopar/Chevy speed addicted friends look at the car and as I remember nothing jumped out at them other than just a bad-ass Mopar small block.

    We do know that the stock 340 put out a good bit more than the factory claim of 275 hp. The NHRA set the real numbers in the 325-330 hp range by just doing an average of several ETs on the quarter mile drag strip. Such as....how much energy does it take to propel this much weight this much distance in this much time? Some not so simple algebra will give the answer. I do know that back in the day there were many Mopar brands sporting the 340. The Dart, Duster, '71 Demon, Challenger and probably others. If memory serves, the Challenger was the heavy one of the aforementioned models. Many of the Darts and Dusters came with a three speed manual transmission and saw fit to shut down its Ford or Chevy counterparts in street racing or a NHRA sponsored event. The 340 had the reputation of being a "giant killer" with its ability to shut down many a big block in the give or take quarter mile street race or a local drag strip. Some engines were of course off limits unless a 340 owner wanted to get his or her ass kicked in public.....The 425 HP 396 Corvette, the 327/365 HP Corvette, the Z/28 302 or Z/28 350 just to name a few were not worth picking a fight with. Hell, I was there as many of you were. I was lucky to live through it, I do believe.

    I was watching an episode of "Nick's Garage" and he had a stock '70 340 on the dyno and got out about 90 or so HP over the factory claim. So, I guess the arguement will go on for a while longer.
     
  6. SRT-Tom

    SRT-Tom Well-Known Member Staff Member Super Moderator Article Writer

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    The larger carb in the test was rated at 800 CFM- 200 CFM more than the OEM carb found in the 1970 340. The carb used in the 1971 engine, the Carter Thermo-Quad, was almost the same size at 750 CFM.
     
  7. Katshot

    Katshot Full Access Member

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    You forgot the Barracuda! I had a '70 'Cuda with a 340. Torque-flight with a shift kit, headers, dual Thrush glass packs and a 390 rear made it quite the giant-killer!
    That being said, the car really was crap. Broke down constantly. I had a motorcycle at the time and it was a challenge keeping them both running. Vehicles are far more reliable these days.
     
  8. Katshot

    Katshot Full Access Member

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    Not sure what your point is.
     
  9. SRT-Tom

    SRT-Tom Well-Known Member Staff Member Super Moderator Article Writer

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    My point is that the 750 CFM Carter Thermo-Quad (installed on 1971 340 engines) was not "garbage." It was not on the 1970 engine tested. That 340 had a low flowing 600 CFM Carter AVS. The carb that Hot Rod installed was a 800 CFM Edelbrock that flowed 200 CFM more.

    Per Hot Rod, "Those old enough will remember that it was popular to swap out the original small AVS (about 600 cfm) for the larger bore version (about 750 cfm) from the 440 Magnum. It was no secret back then that the 340 responded favorably to the increased carb capacity, suggesting that a larger carb would add to the horsepower bottom line."
     
  10. Katshot

    Katshot Full Access Member

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    My comment about the Thermo-Quad being "garbage" had nothing to do with the article. I was merely making the comment in response to your mentioning that it was what was used on the '71 cars. I am old enough to remember those days and I can tell you that most guys I new didn't use Thermo-Quads. If we were replacing a carb on a Dodge or Plymouth, it was a Thermo-Quad we were removing and Holley we were replacing it with! The scrap pile behind our shop had plenty of Thermo-Quads in it! Like I said, they were garbage.