340 actual horsepower

Mopar General Discussions

  1. pagilman

    pagilman Well-Known Member

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    Does anyone know if an early stock 340 was independently tested on a dyno for actual horsepower? We all know that @275 hp was under rated. I remember when my buddies dad bought him a new 68 gts 4 gear for gradualtion!! He picked me up and that car would actually cause neck damage from the factory, they had high compression I think 10.5 to 1(i got drafted he went to australia). Everything i read today states that a cam upgrade with comp springs and -0- decking, air gap and you have 400 horses?

    Just thought you guys would have your educated opinion for the world to see!!!!!!!! Walt :coffee2:
     
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    • mikedevore

      mikedevore Well-Known Member

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      My Dads cousin bought a new 1969 Swinger 340, 4-speed, & 3:91 Sure Grip. He ran it in the pure stock class at Lions Drag Strip. He said it ran a best of 13.80! At an est. 3300 LBS. this comes to an est. rear wheel horsepower of 249, with a flywheel reading at 300 horsepower. I think an NHRA rates these at 315 horsepower.
       
    • 71DusterStruck

      71DusterStruck Well-Known Member

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      Yes there is a bit of confusion with power ratings because as far as mopar engines are concerned, the power figures given were actually the net power of the engine and not the power measured on the flywheel. From what I read this was some kind of trick to fool insurance companies... anyway the flywheel power of the 340 is somewhere around the 300bhp, as mikedevore said, the 360 is around 330bhp and the 426hemi is above 500bhp!!!
       
    • pagilman

      pagilman Well-Known Member

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      you brought up lions drag strip, man i used to go there in the late 60's and got to see all the greats run there. I used to take a bus from the navy base to the strip every chance I got. I heard it is shut down and gone now.:sad1:
       
    • C130 Chief

      C130 Chief Mechanical Genius

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      I doubt these factors are still current, as not too many people currently run 340's in NHRA Stock Eliminator classes, but here's a few factors from back in the day:
      1970 340-6 Bbl. 325 hp E Stock
      1971 340-4 Bbl. 320 hp D,E,F,G Stock (w/Thermoquad)
      1968-70 340-4 Bbl. 295 hp F,G Stock (w/AVS)
      1972-73 340-4 Bbl. 275 hp G,H,I,J Stock

      In most cases (except the 440-6 cars for some reason), the NHRA factored Mopar engines at a higher output than their advertised output. Horsepower numbers before 1972 were pretty much advertising propaganda, and seldom reflected actual output. Beginning in 1972 the SAE "net" ratings were mandated for all cars sold in the US, which were supposed to reflect output "as installed".
       
    • dgc333

      dgc333 Well-Known Member

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      Mopar did and still does rate horsepower at the flywheel. Around 72 all the manufacturers were required to rate them with an SAE net system which still measure the power at the flywheel but included all the accessories (water pump, alternator, p/s, etc), intake and stock exhaust. Prior to 72 they did what ever they wanted, headers, no accessories, non stock air cleaners, what ever gave the number the marketing boys wanted.
       
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      • chasb

        chasb Well-Known Member

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        I remmebr 315 to 325 as the estimated flywheel horsepower as well.

        My 69 318 stock was 230 rated and dynoed at 271

        My 72 Demon 340 was rated at 240 (8:5 to 1 compression) and dynoed at 275
         
      • 71DusterStruck

        71DusterStruck Well-Known Member

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        Yes prior to 72 it was called SAE gross horsepower. Thanks for making that clear :thumbup:
         
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        • IndianaDodge

          IndianaDodge Well-Known Member

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          I was reading a article once in a Mopar Mag about the 340, they started stock and begin adding bolt on performance parts. toping out some where close to 400!

          Does anyone recall this MAG article?

          Jason
          1971 Dart
           
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          • Ace

            Ace Guest

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            Bolt on's like carbs, headers, etc. + a little tuning really amplifies when you have a solid platform to start with.
             
          • IndianaDodge

            IndianaDodge Well-Known Member

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            Bump
             
          • rumblefish360

            rumblefish360 Getting closer FABO Gold Member

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            Yes indeed. I have it clipped out.
             
          • tom340

            tom340 Well-Known Member

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            YES, and the heads were not even ported. Just basic bolt-ons. Updated 4bbl, dual plane intake manifold, mild street perf. camshaft/lifter kit and exhaust headers. Nothing fancy, stock compression if my memory serves me correctly. They peaked at 396 HP.

            Not related to this post: but to clarify NO 360 motor ever put out more HP than any 340 motor. ALL 340 MoPar smallblocks were HP, and the 360 was always a low compression engine. Someone stated something about the 360 making more power (hahaha) believe me, that NEVER happened from Chrysler.
             
          • rumblefish360

            rumblefish360 Getting closer FABO Gold Member

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            In a stock form, correct. Aftermarket parts, well, it'll have a torque advantage and be real close in HP a few RPM's sooner.
             
          • mikedevore

            mikedevore Well-Known Member

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            Ever here of the 1972 & 1973 low comp. 340? I owned a 1972 340 duster, best ET was 15.70. I also owned a 1974 360 Duster, best ET was a 15.30. I not sure about this but, I think the low comp. 340's HP was 240 & the 360's were 245 horse power. I had seen a 360 Duster in a 1974 Car Craft mag road test, it had ran 14.30's. There is no doubt the early 340's were giant killers, I think some of this was the optional gearing (3.91). The 360 a-bodys only had an optional 3.55 gear. When the 72-73 340's lost the big valves & comp. they lost some of their bite.
             
          • Longgone

            Longgone John/68 Barracuda & Dart

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            I read that same article regarding the 383. I haven`t seen one about the 340. I did read an article (and I think it was in Mopar Muscle) where the 340, 383, 440, and Hemi were all rebuilt to stock spec`s and then dyno`ed. The gist of the article was that they were all very close to what the factory had rated them. The early 340`s were snappy little engines that came with 10.5-1 comp., a double roller timing chain, dual point distributors, and a nice set of heads. It didn`t take much to make these little engines scream. The exhaust manifolds are probably the biggest detriment to making power, but with a good carb, intake, and a set of headers the 68-71 340 will make over 300 hp without trouble and they`ve proven to be a quite durable engine.
             
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            • inertia

              inertia Well-Known Member

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              I bought my 340 Swinger new, and with it, the Mopar "Hustle Catalog", which recommended hi-po stuff for all the engines.

              For the 340, the immediate recommendation was Holley 3310/780, Edelbrock LD 340 dual plane manifold, and Hooker under chassis headers.

              I did it all including 12.5 pistons, got it down to 13.29, back then... lol
               
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              • AJ/FormS

                AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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                I have seen these numbers posted in numerous places including Mopar literature.The NHRA factored the 360s pretty high. I found this in the Direct Connection Race Bulletin # 42, p6
                In stock classes;
                360s were factored,from the get-go at 290hp, to about 76
                From about 77 the 360 got down rated to 265, in Aspen/Volares
                ------------------------------------------------
                TQ and 6bbl 340s were factored 325hp

                AVS 340s up to 70/71 were factored at 300
                AVS 340s from 72 on were factored at 280
                No 2bbls here.
                 
              • AJ/FormS

                AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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                I bought a nearly new 70 Swinger 340-4spd,3.55s in fall of 1970. The following summer I tracked it pure stock. They shoved me into F/S at 300 hp. She went 14.4@98 and change,still in third, Spinning those Polyglass E/70-14s, for what seemed like forever.
                Got me a trophy that day! It was my first track day, and the last one for over 30 years.
                 
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                • SoulSurvivor

                  SoulSurvivor Well-Known Member

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                  This is the article you probably saw. 1970 340 High Performance Mill Dyno - Mopar Muscle Magazine

                  It originally showed up in Mopar Muscle Magazine. I followed the build almost exactly.My 340 was a '69 date coded 340 for 1970. And it had J heads. Same as the X heads. My dyno results ended up being 410hp/412tQ. But I used Comp Cams Super Roller Rocker assembly, TTI headers and MSD's Billet all in one distributor.
                   
                • mderoy340

                  mderoy340 Well-Known Member

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                  Some folks don't realize all those ETs in the old magazines were off the showroom with some cars getting a performance tune. Most all ran with bias ply E-70 tires. Modern tire technology would propably knock .5 off.
                   
                • crackedback

                  crackedback FABO Gold Member FABO Gold Member

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                  Don't your heads have bowl and clean up port work done to them?
                   
                • SoulSurvivor

                  SoulSurvivor Well-Known Member

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                  oops. left that one out. yes. It's been a while since I have been on this site and it was 5? years ago when I built the motor which is still running strong.
                   
                • crackedback

                  crackedback FABO Gold Member FABO Gold Member

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                  That makes a HUGE difference in power output on a 340 with that camshaft. 1.6 rockers don't seem to hurt either.

                  That article is a pet peeve of mine because it sets unrealistic expectations for the build. Been around at least 6-8 of those same stock headed builds and none made more than 350hp with a xe268H. Once you start porting the heads, they wake up quite a bit.

                  Your car is still one of my favorites on this site!
                   
                • SoulSurvivor

                  SoulSurvivor Well-Known Member

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                  So have I. I knew the article was a little older so that's why I 'added' to the build a bit. I will say that the 800CFM carburetor comes in handy at the top end of the 1/4 mile. My 340 is gobbling all the fuel she'll take and the end of the track. And the TQ Converter makes a world of difference when launching the car which I'm getting better at. Dyno sheets are nice but they don't tell the whole story and its hit and miss with the operator. The only good thing about dyno'ing an engine is that you catch something potentially bad before you put it in the car and you are breaking in the engine at the same time. Thank you for the compliment.
                   
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