Magnum Heads

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Orionsax7

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How many of you use, or know someone that used, magnum heads on their 360 a engine blocks? I've been reading about this and am interested to learn more as far as street engines.

Do they flow well enough in stock form to support 400hp? They need different head bolts right? The come with 1.6 non adjustable roller rockers? Magnum intake required(obviously) Is there a difference between the 5.2 heads and the 5.9 heads? Chamber size? Valve size? Know where I can find flow numbers?

I still haven't decided on the heads I will use on my zero deck 360 build for the street and am now considering this...(450hp target).

-Alex
 
Alex, The heads are the same from the 5.2 and the 5.9. The problem with the heads is that they are very prone to cracking between the valves, as there isn't enough material casted in them between the seats. This was a way for the manufactures to make lighter weight parts and keep the industry going. The heads come with 1.92 /1.62 valves. If you can get a good set that isn't cracked they will support 400 hp but not much more.


BJR Racing
 
I am using magnum heads on my 360. The stock rockers are not rollers, they are stamped sheet metal similar to a chevy. The magnum engine has a roller cam. The stock heads are around 64cc's.

I disagree with BJR Racing in that they barely support 400HP. The crate 360/380HP typically dynos at 420ish and the crate 408/435HP will dyno around 460HP. The magnum head is the best flowing sb head mopar has ever delivered from the factory and the same porting tips that work on an LA will work on the magnum head.

You can re-drill the heads so any LA intake will fit but mopar sells a single plane & a dual plane, Edelbrock has their Air-Gap set up for the magnum heads and Professional Products has an intake similar to the air-gap that has mounting provisions for either magnum or LA heads.

I keep hearing about cracks in these heads. FWIW, My son over the past 5 yrs has been a tech at a Dodge and a Jeep dealership. They never had any real warranty issues with magnum heads according to him. The belly plate gasket on the intake manifold is the only significant issue with the magnums which won't be if you are not using a stock EFI intake. The two sets of heads that I have had didn't have any signs of cracking between the valves.

All the head bolts under the valve cover are the same length and the ones outside are longer than LA bolts so you do need Magnum head bolts.

The valve springs won't support much more than stock lift so new springs and retainers are required. You are limited on what you can use without addtional machining (LA springs are larger in diameter). The only available spring that doesn't require head machining is the MP R/T spring (good for .525 lift but remeber LA cams will have higher than advertsied lift because of the 1.6 rockers). These are straight wound springs with a damper (vs the stock beehive spring) and will require new retainers. Because the valve stems are 8mm on the magnum LA retainers won't work. Either use 2.2/2.5 mopar 4cyl retainers or get the MP ones.

You will need hollow push rods because oiling is through the push rod, MP sells them just for this conversion. After market lifters are set up for this but to be sure just order ones for an AMC 304/343/360/390/401.

If you use a magnum intake you will need magnum specific intake manifold gaskets, LA head gaskets work fine. The magnum head has 10 bolts for the valve covers, but 5 are in the same palce as LA valve covers. mI am using cast LA MP valve covers and they don't leak a drop.

If you are going to have more than .5" of lift check for clearance between the push rod and head, they some times touch. If they do just clearance with a die grinder.

I built my 360 for strickly street use with no intention of winding the rpm's much past 6000. I am using the Professional Products CrossWind dual plane manifold, a Comp XE268H cam and have the block zero decked for 10.5:1 compression. Everything is optimized for 1500-6000 rpm and the engine absolutely rocks in that rpm range.
 
Wow great info already, thanks.

dgc333, your setup is very similar to what I am planning:
360 zero-decked, kb pistons, xe274, air gap intake

I was first thinking about using RPM heads but then started leaning towards some form of stock heads with some work done. Now I'm learning more about the magnum heads and might go that way. The fact that they are much cheaper is a major plus. I definately want to get in the 400-450 power range.

Have you dyno-ed your combo?

BJR, in what situations are the heads prone to cracking? When used for racing and such? This will be a 90% street car with some passes down the 1/4 mile for fun once in a while.

-Alex
 
I plan to get my car to a chassis dyno in the spring (first snow has arrived and the roads have been salted so car is away for the winter) and get an optimal tune on it.
 
Alex, Most all of the heads that I've checked have been cracked, but keep in mind that they are the 92-00 heads. I guess that they are just getting to the mileage that they need service, some just for valve jobs and some for engine rebuilds. They go for 100.00 - 150.00 $ for cores around here if you can get good ones. The new heads have more material in them to help stop this problem. Some of the problems with them cracking was caused by detonation in the cylinders from the computers running them so lean, other problems was just plain bad gas. I've built a few magnum engines 3.9/5.2/5.9 and they have all had cracked heads or been repaired. Chrysler knew that they had a problem in the heads after being in service for awhile and, made some changes, as this is what the tech engineers had told me a few years ago.
As for the crate engines making this much HP this is true but that isn't to the ground this is from the engine, most chassis are in the 15-20% efficent range so when you take 15-20 % off, even the 480 hp engine your under 400 hp.


BJR Racing
 
Hi BJR,
I just bought a pair of Magnum heads for $90. out of a burned up P/U truck. I have no idea what year it was, because it was burned so badly. According to the Mopar Performance Magnum Engine Manuel, these heads should have foundry initials, CF = 360. These initials are not on these heads. A friend of mine says they must be the newer castings. Do you know any #'s that would identify the year? The ports don't look any different than the 318's (NH) that I have seen. And I have been told that the later 360 castings are the same as the 318's.
Are the cracks visual? Do they need to be repaired? I read where the 2.2 L heads had cracks between the valves that never cause any problems. Thanks.

Dave,
Mopar Performance sells porting templates (P/N 4876413) if you should care to try porting your own heads.
 
Dave, Thats cheap for those heads and yes the heads are the same as the 318s. The cracks are visiable on most but the middle cylinders have to be magnafluxed. The end cylinders are the ones that crack the easiest as the coolant flow isn't as good there. Yes the heads have to be repaired as the water jackets are very close to the seats, what we do is interlock the seats so this doesn't happen again, then recut the valve seats.
I'll have to check on the casting #s for you next week as the only time that I can get with the engineers is on mondays when they'er not teaching classes,(techs) on new car services. Then if they'er not in Detroit or somewhere else. The only 2 guy's that I talk to is Chris and Ed.



BJR Racing
 
Dave, Give me the casting #s that you have on the heads. E-mail them or IM me and I'll see what we can do for you.

BJR Racing
 
dgc333, you mention redrilling the heads to take LA manifolds - do you just set the manifold on the heads to mark them and then drill or what?

how much better are magnums compared to 308s?
 
I would say that you can't do it that way. The vertical holes have clearance chamfers and a drill would walk making for an innaccurate hole. I believe it's the moparstyle forum where some one made a drill jig that they lend out so you can do it youeself or it will need to be done at a machine shop.

Don't knwo anything about 308's, I was always under the belief that all 360's up to the magnum introduction had open chamber heads that essentinally had the same port design as every other 340/360 head.
 
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