Magnum Head Cracks

-
72dart_swinger

72dart_swinger

Well-Known Member
Joined
Oct 2, 2009
Messages
435
Reaction score
4
I have heard that magnum heads are prone to cracking, and I was wondering If anyone could show a pic of where they crack at. I was toying with getting a set from a junkyard and slapping them on a stock 360 bottom end w/ a cam. And Question number 2, Would it even be worth doing this to a stock 360.
 
Not sure on question 1, but I did the exact same thing as what you propose in question 2. I put 5.2 Magnum heads on a '74 360. I think it is a worthwhile swap because you get the better exhaust ports along with the closed combustion chambers, which raises static compression.

Remember to get the associated hardware for the Magnum head swap. There is a ton of info available on the swap on this forum and all over the web. I know oil-thru pushrods are needed, but I can't remember what else.
 
wish4hemi said:
Remember to get the associated hardware for the Magnum head swap. There is a ton of info available on the swap on this forum and all over the web. I know oil-thru pushrods are needed, but I can't remember what else.
Click to expand...

Are the factory magnum pushrods the right length to use in a la motor
 
hydraulic lifter that support pushrod oiling....which almost all the new lifter do..

cracks...look between valves..but you probably have to have a machine shop check them oout
 
It's a good swap and I have done it. I have heard that magnum heads can support up to 400 hp in stock form. The biggest thing to look out for are cracks between the valves. If you can find a set with fairly low miles then I would go for it. Longer pushrods are needed. Mancini sells them for magnum heads. AMC style lifters will be needed. You need a magnum intake also. The cross wind actually work great and they are cheap, but the Eddy air gap has both patterns also. Magnum heads also came with 1.6 ratio rockers.
 
I believe the magnum head cracking issue is very much over stated. My son was the service manager for the local Dodge dealer until they lost the franchise in the Chrysler melt down. He doesn't recall ever having to replace a set of heads because of cracks.

I have magnum heads on my LA360 block and I am very happy with the results. Can't talk to a power difference since I built the engine with those heads. But, the closed chamber heads and close quench is allowing me to have a measured 10.6:1 compression ratio (195 +/- 5 psi cranking pressure) and run 89 octane and 87 in a pinch. The engine is also making approximately 370 HP based on 1/4 mile trap speeds with a relatively small Comp XE268H cam.

I found the Mopar Performance conversion push rods are a little short (7.625"), resulting in a noisy valve train. I wound up with 7.650" long push rods. I would recommend you mock the engine up with a checking push rod and determine the length you need. Also, virtually any aftermarket lifter you can find will have the hole in the cup to provide the push rod oiling needed for the magnum rockers.

I have the Crosswind intake on my engine and it has worked very well, the ports are a little smaller than the Ar-Gap. The reason I went with the Crosswind is it has both LA and magnum bolting provisions where as Edelbrock has two different manifolds for the head types.
 
dgc333 good call on the air gap. My bad. With the magnums you could also run certain chevy bee hive springs and retainers like I did for a fairly mild cam. Here is a thread about it at moparts http://board.moparts.org/ubbthreads/showflat.php?Cat=0&Number=3134434&page=1&fpart=1&vc=1

You can also run cheap chevy roller rockers, comp cam pedestals and guide plates and hardened pushrods. Just to piss off the locals. I have 3K miles on mine with zero issues and I am running a comp XE256 cam.
 

Attachments

  • Rockers.jpg
    149.7 KB · Views: 390
dgc333 said:
I found the Mopar Performance conversion push rods are a little short (7.625"), resulting in a noisy valve train. I wound up with 7.650" long push rods. I would recommend you mock the engine up with a checking push rod and determine the length you need.
Click to expand...

Just FYI, the conversion pushrods are disco'ed. Maybe not a big deal if they end up too short, though. Guess I will see when I get mine together in a week or two.
 
Anybody built their own throttle cable bracket?

I know you can buy one, but it's another $45 out of the limited funds I have available.

Just curious.
 
Here is where they crack, between seats. Tough to see but its there. Both of my heads were cracked on my pickup. Cylinder 2 and 8, 1 and 7.... both heads outermost cylinders :dontknow:. It has been my truck since day one, never overheated well maintained. The guy who magnafluxed them said most mag heads that come in are cracked. He would buy em up from from the salvage yards and be lucky to get a pair out of 5 engines.
 

Attachments

  • mag head crack.jpg
    149.4 KB · Views: 411
DionR said:
Anybody built their own throttle cable bracket?

I know you can buy one, but it's another $45 out of the limited funds I have available.

Just curious.
Click to expand...


take a look at the one that is being sold...

flat steel stock bend or cut to mount to intake bolts...and piece welded up right..

should not be that hard..
 
70aarcuda said:
take a look at the one that is being sold...

flat steel stock bend or cut to mount to intake bolts...and piece welded up right..

should not be that hard..
Click to expand...

I have, and I agree it shouldn't be hard. Just wondered if anyone else had done it.
 
DionR said:
Anybody built their own throttle cable bracket?

I know you can buy one, but it's another $45 out of the limited funds I have available.

Just curious.
Click to expand...

I used a stock LA bracket with a spacer under each bolt. You will need to long bolts to go with the spacers.
 
Wow, I'm impressed. I was expecting a couple of people to post "magnum heads are junk or boat anchors". Then a fight will break out because someone gets their feelings hurt and the thread will be deleted and the OP will not learn anything. Good Job. :thumleft:
 
dgc333 said:
I used a stock LA bracket with a spacer under each bolt. You will need to long bolts to go with the spacers.
Click to expand...

Did you use the vertical mounting bolts? I was pretty sure from what I had read about your build, you didn't re-drill the heads.

I have an M1 dual plane with the vertical bolts for my build.

Badart said:
I just bent a stock bracket I believe.
Click to expand...

Any pictures from either of you? I know there is one in this thread, but maybe one from the other side?

Thanks!
 
DionR said:
Did you use the vertical mounting bolts? I was pretty sure from what I had read about your build, you didn't re-drill the heads.

I have an M1 dual plane with the vertical bolts for my build.



Any pictures from either of you? I know there is one in this thread, but maybe one from the other side?

Thanks!
Click to expand...

Here you go. I had to bend the linkage on my kick down a little to.
 

Attachments

  • Throttle bracket.jpg
    133.2 KB · Views: 355
I'm in the process of rebuilding my 5.9L for my 2000 W1500 Ram and can attest to trying to find two non cracked magnum heads. The machine shop said not to bother buying used ones..they are all cracked....and burn antifeeze. I bought a set of reman heads with new castings.
Really gave me a bad taste about magnum heads...
(I had Four heads..all cracked between the valves)
 
I was going to swap magnum heads on my 360. I pulled 3 pairs of heads, only took one pair home. Other 4 heads I could see the cracks after roughing them up with sandpaper. Only 1 head was good as the other keeper failed magnaflux. You need to do some research about getting the closest piston to head clearance possible (quench) and still have clearance for your valves. All while making it have the c/r you need. You may need pistons.
 
DionR said:
Did you use the vertical mounting bolts? I was pretty sure from what I had read about your build, you didn't re-drill the heads.

I have an M1 dual plane with the vertical bolts for my build.



Any pictures from either of you? I know there is one in this thread, but maybe one from the other side?

Thanks!
Click to expand...

I bent the ears on the stock bracket so I could bolt the bracket on using the vertical mounting holes. I initially used a stack of washers to space the bracket up so it was in the right position to get a straight pull on the throttle, then made a spacer out of a piece of Alumnium.
 
72dart_swinger said:
I have heard that magnum heads are prone to cracking, and I was wondering If anyone could show a pic of where they crack at. I was toying with getting a set from a junkyard and slapping them on a stock 360 bottom end w/ a cam. And Question number 2, Would it even be worth doing this to a stock 360.
Click to expand...


Just mill your heads... mag junk isn't worth it
 
You must log in or register to reply here.
-

Back
Top