Lets talk Magnum heads

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AdamR

AdamR

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Im trying to put together a list of parts that work on these heads.

Valvesprings, Rocker,valve covers, valves. Anything that will interchange from other makes and models. My reason for this is because Im going to be swapping a set on my 340 soon. Im running a CompCams XE274H and Im having a real hard time finding valve springs.

Mopar sells the R/T spring. however this spring is right at its limits with my cam and may have coil bind and/or valve float problems. If I was running a XE268H They would work. However you need to swap to 2.2/2.5L retainers with these springs.

the Mopar "6062" spring also works with magnum heads but is to stiff for my cam. It also requires machining of the seat and a differant retainer. Anyone know what retainer to use with this spring ?

Another valve spring choice is to machine the seats to run LA valve springs. this would seem like the thing to do but again what retainers to use? You can't use LA retainers becuase the valve stems are 8mm

Ive heard that you can use CompCam beehive springs #26918 with retainer #772. Still looking to find out if the seats need to be cut to run them.

Rocker Arms

The Magnum arms Ive checked have the same part# as chevy arms. So you have plenty of choices there. You'll need 3/8" screw in studs and guide plates. I'll add part numbers later.

What about Stud girdles ? Anyone try running a set on magnum heads ? When I get my heads I'll measure the stud spacing. If its the same as the Chevy spacing they should work assuming the fit under the valve covers.

Pushrods.
Mopar sells a set of of push rods for converting LA to Magnum heads

Ive also read that Boss 302 push rods work. I'll look in to that some more also.

Valve covers.
You can use production Magnum or Mopar Performance covers.
Ive seen LA covers used also and this is what Im going to do.
Again Chevy cover work with alittle bit of filing the bolt holes.

Intakes. A few choices here.
Shell out almost $300 for a Mopar Perf. M1 single or Dual Plane or an Edelbrock AirGap.
Professional Products AirGap for around $175
Redrill your heads and use any LA intake.

So thats what I know about Magnum heads at the moment. Anyone have anything to add or comments ?
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Here's what I have learned in my quest to put magnum heads on an LA engine. Start with the exterior stuff first;

1. LA valve covers have 5 fastners, magnums 10. the 5 on the LA's line up with 5 of the magnum holes and nothing appears to be uncovered that will cause a leak.

2. The accessory holes on the ends of the heads are not in exactly the same place on the two styles of heads. They are close and it looks like a minimal amount of fiddling and fabrication to mount you LA accessories.

3. The intake situation. I was told you could redrill LA manifolds to work. At least with Weiand I have that's not posssible, not enough metal. Likely could weld on bosses and drill but unless you can do that yourself likely would cost more than purchasing a proper manifold. I have been told you can also redrill the heads, again need to way the cost of this against the purchase proce of a proper intake. I wound up puchasing a Professional Products Cross Wind off eBay for $140.

4. Unless you are sticking with a cam that is close to stock you will need new valve springs. There is only two magnum specific springs and they are from mopar performance that I have found. The R/T spring has a .525 lift capacity and will fit the machined seat area of the head, the "hi-lift race" spring is larger in diameter and won't fit with out the seat being machined. Both these springs are straight where the stock spring is beehive shaped so new retainers are required. Mopar performance has retainers for both no one else that I am aware of specifically list a retainer. A less expensive alternative for the R/T retainer is mopar 2.2 retainers but you will need to use the magnum locks. LA springs are all larger in diameter and will require maching of the seats on the heads. Also the magnum retainers are all to small. LA retainers won't work because they are designed for 3/8" valve stems. No one specifically advertises that I have found an LA compatable retainer that works with the 8mm valve stem of the magnum head.

5. Rocker arms. Magnum rockers are a 1.6 ratio so any LA cam rated at a 1.5 ratio will give you more lift. Rockers from a Viper V10 are 1.7 ratio and are a inexpensive drop on. There are 1.6 and 1.7 roller rockers available.

6. Mopar Performance makes push rods specifically for this swap. They are available from Mancini for $39. Not much reason to go custom or fiddle with anything else unless you have plans for ultra high rpms or have a huge cam with mega springs.

7. Because the magnum heads oil through the push rod the lifters have to be of that type. Virtually all after market ones are. The easiest thing to do is just order lifters for a 360/390/401 AMC v8 and you are sure to get the right ones. I am using Melling lifters I ordered for the AMC but the same number is listed for the mopar LA.

I was lead to believe this was a simple swap. It's not hard but there are a lot more things to consider that lifters and push rods that most people mention. Also, anything that is magnum specific is considerable more expensive than LA stuff.

I have got it done now and will be assembling the motor soon.
 
Im getting there too. Its just the springs that have me in a "bind" LOL.

Also if you buy a cam and lifter kit the CompCams 822 lifters will work. they are the same part# as the AMC version.

I also emailed KRC Performance about the the springs. All they do is late model magnums and 4.7L's Hopefully they will get back to me.

I think Im going to run the heads on my 340 till it needs a rebuild then pick up a Magnum short block.
 
Hey Adam...Let me know what KRC says...I'm going to send my block out next week so I'll be gathering stuff to assemble soon. I'm either going to call Comp and get a hydr flat tappet equivelent to the mopar 300/360, or call Crane and fork out the dough for the retro-fit hyd roller lifter/cam.
I think the company I bought the remaned magnum heads from put LA springs on them, the pics I have of Magnum springs have, like a damper sping, inside them!? THanks
 
some comments on what you plan to do:

1) If you redrill the heads as I did use 5/16" (magnum size) bolts. You can get away with just redrilling the heads and tapping. You will have to build a jig for this purpose. If you try to go to 3/8 bolts (LA size you will be very short of material to get enough threads on. Use a quality tap and make sure it is a starter type (tapered)

2) LA valve covers fit, but (on stock steel VC's) the flange will have to be tweaked a little to ensue it fits down on to the gasket surface.

3) I have used both of the MP magunum valve springs and they both fit the head. You can either buy the MP retainers (the springs are straight, whereas the stock magnum ones are beehive) or go to the wrecker and find a 2.2L or 2.5L engine and rob the retainers. They are the same as the MP ones in size shape and material.

All the above things I have tried and am currently running in my circle track car. Below are things I am working on and haven't run yet.

4) KRC performance offers beehive type springs for magnum R/t heads but they wont share the comp cams part number, but I will figure it out soon, as I plan to order a couple of com cams beehive springs and do some testing/mockup. hopefully can use the stock magnum retainer (very light)

5) I mocked up some chev crane roller rockers onto a set of magnum heads (I was building a bowtie engine for a friend, which is why I had some bowtie parts in my garage!) and what I figure out was the rockers will work (ratio 1.5-1.6, not sure about 1.7's), but you will have to put in studs and guide plates. Also MUST get the correct pushrod length (custom) to get the geometry correct - VERY important. If I do this I will use the comp cams 1.6 magnum rollers (for SBC). They are steel. The valve spacing is wider (can remeber how much but something like 0.070") on the magnum so the chev guide plates will have to be modified as well.

One other thing - get the MP porting template kit it is very good, I spent about 18 hours porting a set using the kit, but the power gain was very very noticeable.

Oh yeah as far as cams go I would highly recommend Hughes, they have been good for me (I have the tropheys to prove it).
 
Thanks for the info.

Marty at KRC told me to give him a call. When I did he wasnt in the shop.
I'll try again later.
 
That is where I got some of my info from , but they won't say which of the beehive springs they are using or which retainer.
 
the Edelbrock magnum heads have springs that are good for .600 lift cams. That should clear most cams, unless your going really radical.
 
i have a 2.2 out on the car port, in a car.. the motor runs really shitty, i think the head has had it. 22x,*** miles on the car. who want the retainers :)
show me exactly what you want, and i can get you enough for one head ;) if you really want them.
 
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