Magnum heads on a 74' 318 LA

Magnum Engine Swaps

  1. dusterman79

    dusterman79 Active Member

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    Hey guys I've heard and read about putting the 302 series heads on a 318 and getting super performance when done right. I have also heard about putting Magnum heads on one and having better results with less machine work. Are any of you aware of this mod? If so, any suggestions or article or post links? I have a very strong 318 LA in my 74' Duster, but I want to do this head conversion along with a good cam set-up. Any suggestions please let me know. I'm not putting a 360 or Hemi in it. It seems that's all any one says to do. That's not my cup of tea. I want to do this on a tight budget.
     
  2. 71beater

    71beater Well-Known Member

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    You need to talk to RustyRatRod, he's built one...
    I have the engine, but haven't gotten around to putting in my car yet.

    Magnum heads oil through the pushrods, so you will need the appropriate lifters and pushrods. They also have 1.6 to 1 rocker arm ratio. I think they typically out flow all of the older heads, save for ones that have the 2.02 intake valves. Bigger intake valve than all but the earlier 340 heads (1.92" vs 1.88" for later 340 and all 360, 1.78" stock 318).Valves should be lighter, too as they run 8mm stems, .315" vs .375". Drawback... Don't have shaft mounted rockers...

    There was a thread on here of the build, though I couldn't find it last time I looked. Maybe he can give you the link.

    The engine he built was to be low budget, but make good power.
    Basically a totally fresh, blueprinted .030" over 318 bottom end, magnum heads shaved to give a true 9.2 to 1 compression running a Lunati 60403 cam, appropriate lifters/pushrods and valve springs. Edelbrock RPM Air-Gap intake.
    He ran numbers on his dyno program for 650cfm carb and 1-5/8" headers and showed something like 330HP around 6000RPM, 350Lb torque.

    I just haven't had the money lately to purchase a proper torque converter so I can get this thing done...

    Oh, and WHY can I not type 3 1 8 without spaces and NOT get that damn emoticon... Yes my 3 1 8's make me smile smile but WTF?
     
  3. Robbie2734

    Robbie2734 Lambcharger

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    I have magnum heads on my 360LA, it's just a few things you should do. I tapped and plugged the oil passages in the block, used lifters that oil through the push rods (AMC type) and then measure for the correct pushrod length and use magnum style pushrods (hollow). One more thing, make sure the magnum heads you get are drilled for a LA type intake. My motor is sitting on the engine stand waiting for warmer weather, it's cold out there!
     
  4. rumblefish360

    rumblefish360 So close, yet so far away FABO Gold Member

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    The 302 head is OK. It shines when you put work into it. It is pricey by compare. What needs to be done on a 302 to really see them work we'll is install the 1.88/1.60 - 360 valves and open up the port windows to match your intake.

    The Magnum head conversion is a nice set up but also has it's price tag. While you can use them as is, the following mod is a good one IF you plan to run a cam with some decent lift. I forget at what lift the Magnum head can go to before issue, but if I remember correctly, it's just passed .500 lift.
    So;

    Have the machinist modify the head for the amount of big lift you plan on running if need be. Add matching springs to the cam at this time.

    Above, it is noted that you "Make sure the head is drilled for "LA" intakes." This is not needed but a good idea for a wider verity of intakes that will cost less. I can only think of two heads out there right now that are dual drilled and they may not fit your intended purpose or budget.
    The Magnum intakes are prices higher since there is less demand. Though there are basically 3 intakes for the Magnum head. They are as followed;

    MoPar's dual plane - idle to 5500
    Edelbrock's RPM - 1500-6500
    MoPar's M1 single plane the book lists this intakes rpm incorrectly IMO since it is an upgraded copy of the Holley Strip dominator. It has a 3000 - 7000 RPM band and is a good race intake.
    A note though, Hughesebgines has there FI. Version of Edelbrocks RPM Intake. While it is cast by Edelrock and made for Huges, it is an excellent intake that has the FI bosses cast in and ready to go.

    But the intakes are the only pricey cave eat of this kind of build. So, IMHO, getting a head that is dual drilled for either intake is not needed.

    As said above, use AMC lifters, remeasure your pushrod for the new length and order them hollow for oiling.

    As far as cams go, what is the rest of your set up? Trans, gear ratio, tire size, car weight, the intended purpose of the car?

    Also remember that any "LA" cam you get, divide the cams lift by 1.5, then multiply that by 1.6 Magnum rocker ratio for the new lift.
     
  5. Abodybomber

    Abodybomber Breaking street machines , since 1983.....:) Legendary Member

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    All good info... If you can buy the whole top end as a assembly,will save you major dinero. Pushrods/springs,will need to be replaced, the whole assembly is cheaper,than piece by piece.
     
  6. Tinbasher

    Tinbasher Well-Known Member

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    Have 302 heads on a 318 in a 75 Scamp
    Valve pockets cleaned up,188/160 valves, intake ports matched to an Edelbrock performer
    KB flat tops and a Lunati Voodoo 401 cam.
    Approx 10 to 1 compression 165 lbs cylinder pressure
    Engine works like gangbusters even with a 2.76 rear
    302,s are cheap if you can find them, Larger valves really wake them up.
     
  7. Hersbird

    Hersbird Well-Known Member

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    The crosswind intake is less then an airgap but the same design and drilled for both style heads out of the box, it also has the bosses for injectors if you wanted to go that route. If just looking for simple and low cost just keep the heads stock, heck you can find low mile used ones that will be great. A mild cam, the lifters and pushrods, the crosswind and headers and you will be pretty happy with the motor. Should be as good as a stock 340.
     
  8. rumblefish360

    rumblefish360 So close, yet so far away FABO Gold Member

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    Ouch!!! I forgot about that intake. Good lookin out!
     
  9. 65RoadRacer

    65RoadRacer Member

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    Still running that LA with magnum heads? I've had a shop build a 73 360LA with Edelbrock magnum heads, and I have all kinds of problems with the lifters. Curious about the work you had done to the block ... can you be more specific?
    Thanks - tried to send a private message, mailbox was full.
     
  10. Robbie2734

    Robbie2734 Lambcharger

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    Yes, I just had the car out today. Sorry about the mail box, my wife passed away a while ago and I haven't been on here much. Question, what was the problem you had with the lifters??? I used a roller cam from Bullet and it works fine for me. I did go to adjustable roller rockers to get the correct lash. I used a dual plane magnum I got here, the combo works good. Next step is FI!
     
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