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360 LA with Magnum heads
I bought an '86 D-150 with a stock 318. i did away with the emissions when i bought it and put on a weiand stealth intake and holley 600 carb, new stock dist, cap, rotor, 8mm wires, and headers. the timing is set with vacuum adv unhooked at 12 btc like the placard on the hood says. when i put it into gear and accelerate, it begins to hesitate and misfire like the timing is way off. there is a black box in my left front fender well with two harnesses hooked to it and an opening for direct hook up to the stock aircleaner (which is no longer on the engine). did i offset something in this box causing the misfire prob and drag under acceleration? i have considered a recurve kit but will this even help? i also heard that this intake doesnt compat well with the 2bbl heads. ALSO one more thing..>>
im building a 360 to swap in. its bored 0.030 over, a "magnum" Crane Cam, double roller timing chain, mallory mechanical adv dist, unilite coil, stock setup on the magnum heads and hedman hedders. is there anything i need to consider as far as ignition timing when i go in with this engine? whats a good range to set timing at? id like to run a stand alone ignition system and maybe bypass that black box in my fenderwell(whatever that may be..). are the stock valve springs going to be good enough for the cam im using? i hate to put in a fully rebuilt engine and have the same problem back at square one again. Any help is really appreciated on this. im pretty much learning as i go. so thanks again! |
#2
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Because of the more effcient chamber design Magnum heads do not need as much total timing as open chamber LA heads. I am running 33 degrees total on my magnum headed 360. The Comp XE268H cam I am using likes 15 degrees of initial timing. Initial timing is increases as duration of the cam increases. Not sure what the specs are of the cam you are using but you find what the cam wants for initial by tuning (increasing or decreasing initial from your baseline) for maximum manifold vacuum.
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#3
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Dave and I have very similar engines. I run a Comp Cams Magnum280H in mine. My timing is 16 initial and 34 total. As far as a stand alone ignition, I run a MSD 6AL box, blaster 2 coil and an MSD billitt dizzy (8534)? I think. I have no problems at all and I can run mid-grade gas with 10.58:1 compression. As far as your valve springs are concerned, the stock springs probably won't handle much more than about .475 total lift. I would talk to the cam manufacturer to make sure your springs will work. I have the better MP springs in my setup.
Jack |
#4
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ok here are the specs for the cam.. im using the 1.6 roller rockers for the magnum heads as required.. which UPS my lift of course.. im going to be at 0.498/0.527(exhaust), duration is 0.50 at 222/234 with a lobe seperation of 114 degrees. i talked to a tech at Mancini today and ordered better springs, capable of 0.600 lift.
did yall have to gasket match port the runners on the heads at all? also.. these are closed chamber heads, with my 0.030 pistons, what thickness head gasket would yall recommend in order to keep my compression under 10:1. Im building this engine for the street, of course.. gas isnt an issue, for it will be to cruise to the local hot spots and enjoy. |
#5
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Is it possible that maybe you have a vacuum leak causing the off-idle stumble/missfire? Was this problem there before the intake swap & timing adjustment?
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#6
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Better check the retainer to valve guide clearance on those heads before you get to far into your build. You start to run into clearance issues at 5.25 lift on magnum heads. Easy enough to have the guides cut down but much easier before you put the engine together.
Also, if the springs Mancini sold you are Mopar Performance springs you will need new retainers too. 2.2/2.5 mopar 4cyl work good with those springs. You can get them for free or real cheap at the local pick-n-pull. |
#7
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If you're re-using the stock (86) distributor in the 318, it doesn't have any mech. or vac. advance in it, that's all handled by the black box. So if you took the box out of the picture or even took some of the signals it needs (engine vacuum, ambient air temps, etc) away, it ain't gonna do it's job. If you want the 'teen to run right, either convert it back to a pre-leanburn/e.s.c. system, the aftermarket setup you are planning, or get the black box reconnected. BTW, you should be able to swap any ignition conversion over to the planned 360 Magnum
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#8
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I'd recommend you at least smooth out the edges in the chambers of the Magnum heads when you build the 360. There are a lot of sharp edges in there that could be potential hot spots, causing detonation. If you really wanted to you could go as far as radiusing the edges, this would improve flame travel even more and allow you to run more compression with the same gas/timing.
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