340 HP's vs headers

Mopar Exhaust Systems

  1. RustyRatRod

    RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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    Beautiful little motor. You do nice work.

     
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    • Johnny Dart

      Johnny Dart Well-Known Member

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      Thanks Stroker,thats a nice compliment...:thumbrig:
       
    • PAR/T

      PAR/T Active Member

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      I speak from years of experiance when I say this, especially when dealing with A-bodies...Headers are not worth the trouble for that level of performance. For 300 hp you'll be much happier with the 340 manifolds. If in the future your shooting for 375-400 hp, I would consider swapping in the headers.
       
    • Saetun

      Saetun Sinister Swinger

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      These are great threads & the 2nd one has several folks indicating that the large tubes (1 5/8") & collectors (3") would actual hurt torque in a setup like mine which will probably make just short of 300hp. Am I reading that correctly? That ideally a mild setup like the one I'm building would only properly benefit from 1 1/2" tubes & 2 1/4" collector? Even the Hedman shorty headers referenced above still have a 2 1/2" collector & still use 1 5/8" tubes. Folks from that thread compare the shorty headers to the 340 manifolds would any of you guys see things the same way as described there & if so, is that telling me to either have custom headers built (which Im sure is not in my budget) or go shorty or manifold? I dont want to make a poor decision based upon my modest goals.

      What are your thoughts on the shorties as they seem to run just a little cheaper? Similar pro's & cons to the 340's in your opinion?
       
    • 340sFastback

      340sFastback Well-Known Member

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      Lets not forget about the automatic trans lines that have to be re-routed when running headers...
       
    • RustyRatRod

      RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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      Only if you run a wussified automatic.
       
    • 1970Duster

      1970Duster Well-Known Member

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      More Autos win races then sticks do. Besides I like my 200R4 (which is waiting for my adaptor).
       
    • dustoff440

      dustoff440 Well-Known Member

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      As I understand it large tube headers can hurt bottom end torque on a milder "STReet" ENgine by reducing back pressure too much.A friend of mine years ago had put the largest diameter headers he could find on his 273/235 NHRA stock automatic car and realized minimal gains, He swapped them for a set of Stahl 1 1/2 tube headers and picked up 2/10, Down load camquest6 at compcams.com and and plug in your motors values and then see what the difference would be between large tube and small headers.
       
    • MopaR&D

      MopaR&D Nerd Member

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      I am running these headers on my '70 Duster with power steering and mini starter; the factory one fits but only with some grinding of the collector flanges. They fit fine although the head pipes were tough to make and I have scraped them pretty badly; find the best exhaust shop in your area to do it and make them like jerry6's car. Also make sure you buy 2 1/4" collectors to bolt on instead of the puny <2" ones that come with the headers.
       
    • DartSport340

      DartSport340 Well-Known Member

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      not really...why...because their HYPE is for the most part just that..unless your doing some kind of racing(like that FAST racing) your not really gonna notice the MAYBE 5-10 MAX(if that) HP advantage that the 340 hi-pos have over other manifolds like say the stock log style SB manifolds from say 73/74 just pull up that old mopar muscle test they did a few years back..i think on a crate 300 hp motor there was a 2-3 hp difference between the 340 hi-pos and 73 340 log manivolds and ONLY like 5-7 between the hi-pos and 318 manifolds...in otherwords save your $.
       
    • DartSport340

      DartSport340 Well-Known Member

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      true but these days thats more because of BRACKET racing and the consistency than anything else.
       
    • MRL Performance

      MRL Performance Well-Known Member

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      The 340 I built for the 2010 Mopar Muscle Mag engine challenge made 39HP more going from a set of Hooker 1 5/8 headers to a 1 5/8- 1 3/4 header. And it was not all on the top end either, it made more power everywhere on the dyno pull from 3000-7500rpm. If you want power, ditch the stock manifolds and go with a header.
       
    • moparmat2000

      moparmat2000 FABO Gold Member FABO Gold Member

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      I know this may be a nutty question on this topic but here goes. I got a set of 68 hi po exhaust manifolds. My machinest and i discussed a 408 stroker, 6,000 rpm limit. Mostly low to midrange grunt, with a 4 speed O/D and 3.73 combo, eventual upgrade to a Passon 5 speed. I want it to be a sleeper looking like a stone stock 273 4 barrel. He is talking 9.5 to 1 CR for pump gas, and about 450-500 HP. He looked at me like i was nuts for wanting to extrude hone the 340 manifolds and use them. He told me choking it like that i'd be lucky to get 350HP out of it. I really dont want headers. I hate them actually. Will i really lost that much HP out of a stroker like that with 340 exhaust manifolds on it? If i lose 40-50 hp with that bottleneck, but its still grunting out a tick over 400-425 i'm ok with that. Whst he's describing is a 100hp loss. Any thoughts? Real world experience? I eould be nice to get a high figure doing a dyno pull and then say slap these 340s on and see what the drop really is. I bet these flow better than chivvy rams horns.
       
      Last edited: Oct 11, 2017
    • 273

      273 Well-Known Member

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      I wouldn't waste my money on 340 manifolds. If you don't want headers you could dig up 360 manifolds for free or near it gain a couple hp. 340 manifolds are only a couple of hp over 360 manifolds but cost about the same as headers.

      Headers are a good addition to any engine but don't start becoming mandatory until around 350 hp. Especially cause of cam over lap needs free flowing exhaust.
       
    • moparmat2000

      moparmat2000 FABO Gold Member FABO Gold Member

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      I mentioned the 340 manifolds because i already have them. Lucked onto em for $150. About 4 years ago.

      If i have to go headers i am not thinking long tube type. I was thinking more like hedman tight toob block huggers.

      Screenshot_20171011-212036.png
       
      Last edited: Oct 11, 2017
    • H22A4

      H22A4 Does anyone read this?

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      I think you answered your own question... if you want to go for that stock look, manifolds are the only way to go.

      The fact you get them for $150 is unbelievable! Nice score.
       
    • moparmat2000

      moparmat2000 FABO Gold Member FABO Gold Member

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      Well that and with some slight hogging out i can get 2.50" opening at the ass end. Damper is missing, going to drill n tap and plug those holes. My performer rpm doesnt have a heat riser that would tak advantage of a heat riser flap anyways. My question is am i gonna lose a lot of power with these over a set of headers on my stroker. I can live with a 40-50hp loss if i'm still in a low 400 hp range with the manifolds.
       
    • 273

      273 Well-Known Member

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      Your probably be at a 50 hp loss over long tube headers maybe only 25 hp over shorties. Porting the manifolds is probably only gonna offer a small improvement.

      I'd have a custom cam made to work with manifolds.
       
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      • moparmat2000

        moparmat2000 FABO Gold Member FABO Gold Member

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        If thats it, i can live with a 50hp loss over having to deal with long tube headers.the shorties dont look bad , and i may still concider them, and put the 340 manifolds on the 318 for my kids car.
         
      • abodyjoe

        abodyjoe Well-Known Member

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        waste of time and money, if you want manifolds then bolt them on and go. years ago i was talking with some of those F.A.S.T guys.. they said they saw no improvement after extrude honing their manifolds.

        what do ya hate about them so much? i ran tti on my small block for years. never had a blown gasket, didn't have to ding them at all, way better plug access and wire clearance then manifolds or cheap headers, hell the tti header were an easier install then the 340 manifolds i put on jamis dart... the entire time i was installing those stupid manifolds i was kicking myself for not just sticking the tti headers i had sitting there on.. my stupid ass went with manifolds just because it was the look i wanted at the time..

        DSC_0013.JPG
         
        Last edited: Oct 12, 2017
      • moparmat2000

        moparmat2000 FABO Gold Member FABO Gold Member

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        I like the stock look, trying to keep it "looking" stock. I wanted a 408 that looks like a stock 273 4 barrel. I always had problems w headers in the past, thats prob what soured me on em now. I am starting to wrap my mind around the hedman tight tube block huggers, and maybe keeping those stock 340s for my sons mild 318 future project. I can prob sand blast em and use the high heat cast iron paint to camouflage em a little bit.
         
      • moparmat2000

        moparmat2000 FABO Gold Member FABO Gold Member

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        Do those hedman block huggers have a decent flange? Can they be run without an oil filter adaptor?

        Also planning on power steering w stock chuck. How tight are they to that, and to the center link? I will be using C body idler and pitman arms to speed up the ratio, it will move the crnterlink back about 1.50"-2.00"
         
        Last edited: Oct 12, 2017
      • MopaR&D

        MopaR&D Nerd Member

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        I have the Hedman Tight Tubes for my Duster, they install easy enough but good luck getting the exhaust hooked up; I had to fab my own downpipes that snaked down off the flanges, up over the steering linkage, then back down to the rest of the exhaust. Very time consuming, and in the end it still looks like you have headers in your car lol.

        Manifolds suck because the exhaust pulses from each cylinder smack into the adjacent ones, on stock engines it doesn't matter because the cam overlap is too short for it to make a difference but put any kind of performance cam in it and the engine is basically working against itself trying to push the exhaust out, instead of it being scavenged out by individual header tubes.
         
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        • 318willrun

          318willrun Utube channel 318willrun

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          Didn't read through the thread. IF your 318 manifolds are the 1 5/8, you'd gain by going either 340 manifolds or headers. Even the later 340 manifolds are 1 7/8. Pro's/Con's, I'm sure would be listed in everybody else's post
           
        • moparmat2000

          moparmat2000 FABO Gold Member FABO Gold Member

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          I know the manifolds hurt performance a bit, however i cannot imagine rhe hi po ones killing a strokers power 100-150HP like my machinest says they will. He's prob used to SBC manifolds doing that, and admits he doesnt know too much about mopar factory hot rod parts especially the 340 hi po mannys. I plan on using a mini denso starter, and using longer C body idler and pitman arms to speed up the ratio. This will move the center link back a bit, maybe that will give me enough room as a work around with shorty headers, if i go the tight tube route, i will prob mock it up as well before blowing the car back apart for paint.
           
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