Lets talk Magnum heads

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.