Carb and Intake for 5.2 Magnum

Magnum Engine Swaps

  1. Miloburnz

    Miloburnz Member

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    I am doing a custom build with a Magnum 5.2 and 46RH OD trans going into a 1960 Studebaker which i bought with no engine, a rare find here in Spain. I bought a running 93 Cherokee as a parts car that had failed the annual inspection so drove it around on dirt tracks to check the engine before i pulled it out and it ran really good so i have no intention of doing any unnecessary work on it.
    As its in a 60's car i i thought it would look better with a carb as i've already fitted V-belts, what i've found so far is a Speedmaster 1-147-028 intake, Holley 0-80457S 600 CFM and proform 440-426 distributor. What i'm looking for is similar performance to the MPFI i'll be replacing and similar fuel economy as gas is expensive here. Would be interesting to know what combinations people have fitted for a street car.
     
    Last edited: Jan 30, 2021
  2. dano

    dano Evil Handy Man

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    That intake operates from 1500-6500 rpms, so it might be much for your 5.2 but i don't know of a smaller intake for Magnum heads. I think Mopar made one. Never been a fan of the side hung float Holley's. In the 600cfm range the AVS2 650 Edelbrock or625 Street Demon would be my choice and possibly any of the 4150 Holley's in the 600cfm range. For economy, whats wrong with keeping the EFI on there?
     
  3. rumblefish360

    rumblefish360 So close, yet so far away FABO Gold Member

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    Disagree in a big way...

    There is no Dedicated 318/5.2 intake for the Magnum. The ports of the intake are the same (close) to the cylinder head which is the same cylinder head for both engines.
    MoPar did have there standard dual plane available for the Magnum engines. (The early 340 intake modified) They are not made anymore and were not that popular which makes them very expensive IF you find one. Pretty much the same rod there single plane intake for the Magnum.

    @Miloburnz Use the Edelbrock RPM intake manifold. It is worth the price. I like ethers MSD or an Accel distributor.
    With any vacuum secondary Holley carb, you’ll need a throttle arm adapter, secondary spring kit & jets to tune the carb.
     
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    • dano

      dano Evil Handy Man

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      My point wasn't so much the port size, it was it might not work well with the 5.2 cam's RPM range is all. But, options are limited and the Edelbrock RPM doesn't fit Magnum heads unless you mean this one, Which is an Air Gap like the Speedmaster and Crosswind.

      RPM Air-Gap Small Block Chrysler Magnum Intake Manifold
       
      Last edited: Jan 30, 2021
    • Miloburnz

      Miloburnz Member

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      For the intakes the RPM Air Gap is the only one i could find that is advertised as been for Magnums only, the Crosswind states its drilled for both LA and Magnum but not sure with the Speedmaster as it is for LA and later Magnums so not sure what a later Magnum is , the one i have is 93. These are all 1,500 - 6,500 rpm range but i don't know what the standard cam specs are. I am sure any of them would work fine so long as you can fit the vertical bolts, i already have LA headers fitted ,not perfect but line up close enough.
       
    • rumblefish360

      rumblefish360 So close, yet so far away FABO Gold Member

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      The ENGINE PM intake doesn’t RPM fit the 5.9, cam/RPM wise. But it works really well. BTDT
      Port size was a mention of only what the factory offered vs who ever makes an intake.
      Other than Edelbrock’s own RPM for the Magnum headed engines, what else does Edelbrock make for the Magnum intake wise. What else would I be talking about?
      You gotta be kidding me right? Seriously! This is a joke right?
       
    • rbkt65

      rbkt65 FABO Gold Member FABO Gold Member

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      it is in the magnum category so you would think we are talking about a magnum. i agree with rumblefish360. i have 2 of the e-brock knock offs and the only thing i see different is it may take a little effort to make the bypass hose work. knock off have la style bypass hookup and not magnum. i have 3 buddies that use them cause they are tightwads to a point and the just use which ever hose they have in the parts bucket.
       
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      • rbkt65

        rbkt65 FABO Gold Member FABO Gold Member

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        i re-read the post and what another buddy i just got off the phone with, says that he was told when talking about magnum cams with cam companies, you should use a 5.2 cam in a 5.9 as it will make more power and torque than the stock 5.9 cam.
         
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        • rumblefish360

          rumblefish360 So close, yet so far away FABO Gold Member

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          I have read that before. The 5.2 Is actually bigger IIRC.
          I found that fact out odd. But hey! (And) what the heck, if you can swap cams, then an easy gain it will be.
           
          Last edited: Jan 31, 2021
        • DionR

          DionR Well-Known Member

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          I could be wrong, but I think that info is based on wrong documentation put out by the factory. The 5.9 Magnum was released in ‘93, the year after the 5.2 Magnum. So, the factory documentation for ‘92 still had the old LA 360 info along side the updated 5.2 Magnum info and when the 5.9 Magnum came out the following year, I think the factory forgot to update it and carried forward the old broomstick cam info.

          To further demonstrate this, I had a cam reground by Bullet Cams and asked them to send me the original specs first. The info they sent showed a cam larger than the 5.2 specs I have found. I have posted my info before, but don’t have it handy right now.

          Not saying I am certain, but just makes no sense that the cam in a 5.9 would be smaller. And based on the above, I thinking it is a wife’s tail that it is.

          But still just my opinion.
           
        • DionR

          DionR Well-Known Member

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          Here's a thread where I posted the info I have on the 5.9 cam.

          Further down that thread YY1 posted an alternate theory where maybe the factory forgot that the lift at the valve was with a 1.6 rocker ratio and published numbers using the old LA rocker ratio of 1.5. Seems like a valid theory as well.
           
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          • AJ/FormS

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

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            I also found oddball specs that advanced the chit out of that cam in a 5.9. It had a lot of exhaust duration on it,, so they could get away with that, but according to the specs I found, the overlap period was all crossed up. I found a lot of internet hoopla about these Mopar factory Magnum cams, but no one would commit to hard numbers so I gave up looking.

            When I backed that 5.9M cam up on paper, it looked suspiciously like the 5.2M cam. Again, I found nothing but whispers on the wind.

            IMO, what ever cam was in my 92 5.2MDakota, that thing did pretty good on gas. When I replaced the timing gears I just slammed it in dot to dot. I wasn't thinking that many years later, it might be valuable information, lol.
            My old MP catalog lists two cams for electric fuel-pump engines;
            P5249549 at 260/264/109 and lifts of .458/.467 lifts, no .050 numbers; and
            P5007551 at 272/278/119 and lifts of .467/.482 >050s of 208/216
            Yes that 119LSA looks real, cuz it shows up in the mechanical pump engines as well.If it is, it will be horrible on gas.
            But the smaller cam should do well on fuel. In at 109 the Ica would be 59* for lots of trapping, and the powerstroke comes to 119* for lots of extraction. The overlap is 44* and well-centered so reving to 5500 should not be a problem.
            The only unknown is the .050s, which judging from the other cams in the catalog that do have .050s, the Mopar cams have really really long accelleration ramps; read tiny, .050s for their advertised, I would suspect that small cam has less than 196* intake duration at .050. I wouldn't buy it.

            The catalog also lists 4 cams for mechanical pump engines

            IDK if any are still available
             
            Last edited: Jan 31, 2021
          • Miloburnz

            Miloburnz Member

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            Amazing how quickly this thread went off topic although interesting talking about cams it is seemingly an endless subject and irrelevant as i am not seeking info on camshafts.

            So back to my original post i have a 5.2 Magnum and i have no intention of changing cams or heads all i want to do is change the MPFI for a carb set up.

            All i would be interested to know is what manifold and carb people who have actually done this used. :)
             
            Last edited: Jan 31, 2021
          • AJ/FormS

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

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            sorry

            but if you intend to operate this Stude at widely varying altitudes, keep in mind that each 1000 ft will change your cylinder pressure by about 5 psi. This is about the same pressure difference as one cam size.
            Since you mentioned fuel economy, I jumped in with the cam-talk. A loss of cylinder-pressure directly leads to a loss in fuel economy.
            Whereas, in steady-state use, the intake, any common intake you chose, will make very little difference.
            And NO intake you can install,without other engine changes, can touch the EFI-keg, for low-rpm torque and fuel economy. That Keg is like a folded long-ram. Look on this graph and see how that Keg, at low-rpm (say 3200 and down), makes the 5.2 engine feel and act like a much bigger engine than it is. On this graph you can see nearly 300ftlbs available at 3200 rpm. That is a pretty big number for an engine of it's size. And you can see the oddball kink in the power curve that the torque is generating. But take a look further down! The available torque at 1200 is ridiculously high.
            When you swap that keg intake off, you will lose a sizeable chunk off that, also losing some of the fuel economy it was helping to generate.

            Is it a big deal?
            Yeah I think it is. I might be willing to bet that the combination of Keg and SEFI might easily be worth 20% fuel economy, in steady state. And we haven't even talked about the ignition timing problems you will have, trying to achieve advance with the overdrive trans, at the low-cruise rpm it offers. The lack of cruise-timing could easily cost you another 10% in steady-state use. When you add those two together. it comes to 90% of 80% so a left over of maybe 72%, So now you are back to 318LA type economy.
            Could I be wrong?
            Sure, but my experience is this; for steady state fuel economy, your engine needs to be in a sweetspot that you create with pressure, valve-events, rpm, and ignition timing. In the case of the engine in question, that sweetspot was created for you by the factory, using the Keg, the SEFI, and the computer controlled timing. Once those are gone, then so is the cruise fuel economy that the Magnum is known for.
            Furthermore, the Sequential Port EFI is able, to some degree, to compensate for changes in elevation, whereas without the computer, the carb/dizzy is hopelessly over whelmed, especially a vacuum-secondary carb, which for fuel-economy, is the better choice.
            I'm just trying to help.
            BTW, other tips
            you don't have to use the factory ECU, there are programmable stand-alone systems out there. But if possible I would install a scanner on the current combo, and get a feel for what the factory ECU is doing, before pitching it,........... cuz you won't believe what the factory timing is doing.
            At one time, you could buy a tool to "redrill" LA intakes to fit Magnum heads. Then weld on some small spacers to get the angle right, under the bolt heads. That opens up your intake choices drastically.
            Today, you can buy heads with Magnum ports and LA intake bolt angles, which totally solves the problem.
            power-318-gif.gif
             
            Last edited: Jan 31, 2021
          • Miloburnz

            Miloburnz Member

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            I mentioned fuel economy to try stay away from discussions about 750 cfm carbs, cams , head swaps ect.. I totally understand the benefits of the MPFI and would chose it over a carb set up any day but i have good reason for changing to a carb setup.
            The Stude was last on the road in 1973 so i need to create a new technical document for it and to do this i have to take it for an inspection where they measure it, check what equipment it has ect.. so basically creating a spec sheet, then they do the road worthy test. If they pop the hood and see an old looking engine with a carb all they'll ask is what cc it is as none of them will know the difference between a Stude, Chevy or Mopar V8 however if they see a fuel injection system then they will assume i have fitted a modern engine which will open up a whole new can of worms which could cost me up to €2,000 and take 2 years to get the car on the road. Spain is the hardest country in Europe to modify your car, just to fit a performance exhaust you need a homologation certificate and engineers inspection. So the plan is dress the engine up to look like it was made in the 60's then after i have all the documents i'll put the MPFI back on it.
            I have a LA 318 with 904 trans that i am thinking of fitting in another car i have, they need a total rebuild but the carb is broken and distributor is missing so i thought i could use the parts i buy for the Magnum on the next project after i refit the MPFI, for this reason i was interested in the Crosswind manifold as it has bolt holes for Magnum and LA, the Speedmaster also states it is for both engines but can only find a basic description.
            I would have mentioned all this in my first post but i was trying to keep it simple and to the point. So basically just looking for a temp carb set up for my Magnum that i can later transfer on to the LA which i will be changing cams on so i could match the cams to the manifold.
             
          • AJ/FormS

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

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            lol, you don't know us bozoz very well, especially me, lol.

            But now I get where you're coming from.
            And in that case, the lo-buck approach is to just install the LA 2bbl on it, by modifying the holes and bolt-seats. I haven't done it, but I read about it being done (on a 4bbl intake mind you) in a magazine..... a long time ago.
            Or what the heck, just bolt the 318LA heads on it too, and solve all your problems. I mean, I have reused FelPro 1008s several times. Just make sure the rocker arms get oiling.
             
            Last edited: Jan 31, 2021
          • Ceedawg

            Ceedawg Well-Known Member

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            Re
            the magnum head will not except early LA intakes unless you drill the heads for them (magnum bolts go straight down)
             
          • rumblefish360

            rumblefish360 So close, yet so far away FABO Gold Member

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            AJ, sometimes your super helpful, but this is not one of them.
             
          • goldduster318

            goldduster318 Overzealous Car Modifier

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            My friend has a 71 Demon with a 318 Magnum. We did upgrade the cam a little but otherwise it has an A904 with a stock converter, a 3.23:1 axle.

            It has the Edelbrock Air Gap for the magnum engine and a 600 Holley Vaccum secondary like the one you are describing. I think its the same one just in Zinc Dichromate instead of shiny finish. It has an electronic distributor that is a stock design one.

            The carburetor is stock except for having a 10.5 power valve and a slightly lighter secondary spring. The distributor was re-curved by shortening the slots to get 15 BTDC up front and 35 total, and only the light spring with one link removed. This works well. The fuel mileage is something I don't know so much but I would say its in the 14 mpg range, so I guess 16.5 l/100km or something like that. Not sure you can ever expect too much better.
             
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