Magnum Heads

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DARTLARRY

DARTLARRY

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What Are The Advantages Of Using Late Model Magnum Engine Heads On An La Block. And What Do I Have To Do Exactly To Use Them. Ive Heard That You Have To Change Intakes, Or Drill New Holes In Them To Bolt Them On. I May Want To Up My Compresssion And Heard That This May Help Without Any Major Machine Work. Kind Of New To This, All I Have To Go Off Of Is Advice From Experienced People Like The Guys On This Site. (very Helpful People) Any Help Would Be Appreciated.
 
I Have A Set Of J Heads. My Question Is Should I Keep Them Or Go To The Trouble Of Running Magnum Heads.
 
It depends on what you are looking for. The magnum heads are much more friendly quench wise because of thier closed chamber. They are better in the air flow department as well. Most engines would work well with the smaller intake valves as they increase the velocity in the intake runners as compared to the 2.02 valves.

Jack
 
Magnum heads are great, you just have to have:

the magnum specific intake
magnum head bolts
lifters with oil holes in the center of them
hollow 7.650" pushrods
magnum rocker arms

You will need to put the R/T springs on and also the Mopar retainers. If you plan on running a cam bigger than .500 lift with the 1.6:1 rockers you may have issues.

Also, i have to take the heads back off of my engine to grind the casting flash off for pushrod clearance.

They are worth it though!
 
I have done this on my 340 block. I have had a lot of problems that I have run accross. If it were me I would go with the J heads. Bob
 
I built a 360 with magnum heads and installed in my 68 Barracuda in July of 05. I have almost 15,000 miles on it now and the engine runs great.

The only issue is I am running a very agressive hydraulic flat tappet cam that is plain just noisier than you would expect of a hydraulic cam. I also, get a fair amoutn of lifter noise when I first start the engine after sitting over night but it goes away within a few seconds.

The engine has 10.6:1 compression with zero decked pistons and runs on 89 octane fuel. It makes approximately 370HP based on a 102 mph 1/4 trap speed and has run a best of 13.7 with really bad 60' time of 2.2 seconds, so there is a lot more potential in it if I take the time to sort out the traction issues.

The combination of relatively high compression with a decent head design with an ideal quench clearance has the added benefit of providing 17-18 mpg around town and 21-22 mpg on the hiway.

It's truely a bolt on upgrade but I would recomend that you actually measure what you need for push rods and not just through the MP conversion push rods in the engine. I have 0.020" machined off my block which should increase the lifter preload but mine is right a 0.027" so it seems depending on the cam's base circle size and other varibles you could easily have a situation where the MP push rods are two short.
 
I had a very hard time finding magnum heads that weren't cracked. I had one good head out of eight that were pressure checked. The stock heads are junk and should not be used, the chambers measure 67cc's and need to be milled a lot to get the compression up, further weakaning the head. I bought the heavy duty magnum heads bare and reused some magnum valves. Had to have the spring seat cut to fit the 1.5" valve springs and the retainers are hard to find. I used Hughes springs and they have the retainers to fit the 8mm valves. Bolted on the heads and the rocker arm nearly rolled off the edge of the valve. Installed lash caps and the geometry is a lot better. I used the Crane chevy roller rockers and they fit like crap. Had to grind a wider slot to clear the stud.
Not much of a choice of intake manifolds either, you should use the angled I would just call Hughes Engines and order there heavybypass hose intake. I found a Mopar M1 dual plane that I'm using.
The magnum accesory holes are a little bit different causing alignment issues.
I havn't even started the kickdown and throttle cable yet.
A lot of the problems are due to me trying to save some money.If I had to do it all over again I would just call Hughes Engines and order there heads and rockers and studs, guideplates. Bob
 
Yes I was aware of the cracking issues.It seems to be worse in the pre 99 heads.

I got lucky and found a pair with no cracks right away.

My stock heads chambers measure right around 63 cc.Is there that big a diff in castings?

Sounds like your app is far from stock,judging from the mods.

I thought chevy locks would work??Seem to remember something about LS6 locks being 8mm..
 
I don't know if there's a big differance in castings. I used the 466 casting. I was told magnum heads are the thinnest and weakest of any Mopar casting ever made. Just because your's are ok now does not mean they won't crack in the future.
Then what do you do, try and find a used head to match your good one and have it remachined. Then maybe the other one will crack. You''ll have a lot of money in a set of junkyard heads. More than a new set will cost you. That's the conclusion I came to. I see other members have had good luck with used heads and I'm glad, I just didn't want to take that chance.
You can get a nice set of J heads for a lot less money invested, and the engines there bolted on run well. Just my 2 cents.
 
I see your point but...

From what I have learned Magnums were cracking due more to the engine running either a very lean mix or poor fuel.This would not be the situation in a hi perf application.

And as I said,they sorted the problem out in later years.

I wouldnt totally panic with regards to cracks either .They are repairable rather cheaply with something called pinning.I've never had it done,but it involves no welding.Other brands of heads were prone to cracking in that era as well.It's not a mopar/magnum only thing.
 
So does this include standard 5.2L magnum heads, or only the 5.9L R/T magnum heads? Is there a significant difference in performance between these when bolting them onto an LA engine? At some point in the future (like when I get a new truck someyear) I was going to take off my heads from my '95 5.2L Dakota and put them on a rebuilt LA 318 for my Scamp. Right now the Dakota has 203k miles on it, so those heads are well used. I'm assuming they should be okay with a rebuild on them. The truck still runs great, so I'm also assuming the heads are in fine shape.

Sound like a good idea? I've heard this setup makes great power....
 
The 5.2L and 5.9L heads are the same.

The production Dakota/Durango R/T heads are yet again the same.

The Mopar Performance R/T heads are the way to go!!! Magnum style head with much more flow and will not crack.
I have a set and they are awesome in my opinion.

I read on one of the mopar boards where a guy with a flowbench tested the J 2.02 heads (~185 cfm) famed X 2.02 heads (~215 cfm) and stock magnum heads (~215 cfm ) and MP R/T heads (~245 cfm).
A stock Magnum head will flow about what a ported J 2.02 head will flow.

The magnum heads are a direct bolt on for the later 1987+ 318 / 1988+ 360 roller cam engines.
 
bobscuda67 said:
I had a very hard time finding magnum heads that weren't cracked. I had one good head out of eight that were pressure checked. The stock heads are junk and should not be used, the chambers measure 67cc's and need to be milled a lot to get the compression up, further weakaning the head. I bought the heavy duty magnum heads bare and reused some magnum valves. Had to have the spring seat cut to fit the 1.5" valve springs and the retainers are hard to find. I used Hughes springs and they have the retainers to fit the 8mm valves. Bolted on the heads and the rocker arm nearly rolled off the edge of the valve. Installed lash caps and the geometry is a lot better. I used the Crane chevy roller rockers and they fit like crap. Had to grind a wider slot to clear the stud.
Not much of a choice of intake manifolds either, you should use the angled I would just call Hughes Engines and order there heavybypass hose intake. I found a Mopar M1 dual plane that I'm using.
The magnum accesory holes are a little bit different causing alignment issues.
I havn't even started the kickdown and throttle cable yet.
A lot of the problems are due to me trying to save some money.If I had to do it all over again I would just call Hughes Engines and order there heads and rockers and studs, guideplates. Bob
Click to expand...

More often than not the cracks that folks see in these heads are a cosmetic issue and have no detrimental effect on the operation. Engines run for 100,000's of miles with cracks. For sure you need to make sure that they aren't compromising the water jack or the ports but a small crack on th surface is not a reason to discard a set of heads.

There are quite few spring options that do not require cutting the seats. MP has two springs, one good for .525" lift and another for .600" lift, a little pricy compared to other springs but not if you factor in cutting the seats. Retainers for these springs are dirt cheap and in most cases can be had for zip. Just harvest them from any 2.2 or 2.5 mopar 4cyl. Comp now has a drop in beehive spring for magnum heads but I do not know if the stock retainers work. the GM3800 v6 spring is a drop in and the retainers are for 8mm valves, these are dirt cheap also but are only good for cams in the .480" lift range.

If you want to use Chevy roller rockers you will need to get longer pushrods. The chevy 7.8" push rod worked well for my motor but unless you are planning on reving past 6000 rpm all the time the stock stamped rockers are more than adequate.

Granted there is not a lot of choices in manifolds but really how many do you need? MP has a single plane and a dual plane. Edelbrock has their Air-Gap in a magnum bolting and the Professional Products CrossWind will bolt to either LA or Magnum heads. Wouldn't be surprised to see the new Weiand Air-Strike in a mopar version soon either.

I don't know why folks keep saying the accessory holes on the heads do not line up. I have been involved now with my LA/magnum hybred, a 380HP crate moter into an A-body and a 300HP crate motor into a B-body and there were no issues at all with the alignment of accessories. Everything just bolted on and lined up.
 
bobscuda67 said:
I had a very hard time finding magnum heads that weren't cracked. I had one good head out of eight that were pressure checked. The stock heads are junk and should not be used, the chambers measure 67cc's and need to be milled a lot to get the compression up, further weakaning the head. I bought the heavy duty magnum heads bare and reused some magnum valves. Had to have the spring seat cut to fit the 1.5" valve springs and the retainers are hard to find. I used Hughes springs and they have the retainers to fit the 8mm valves. Bolted on the heads and the rocker arm nearly rolled off the edge of the valve. Installed lash caps and the geometry is a lot better. I used the Crane chevy roller rockers and they fit like crap. Had to grind a wider slot to clear the stud.
Not much of a choice of intake manifolds either, you should use the angled I would just call Hughes Engines and order there heavybypass hose intake. I found a Mopar M1 dual plane that I'm using.
The magnum accesory holes are a little bit different causing alignment issues.
I havn't even started the kickdown and throttle cable yet.
A lot of the problems are due to me trying to save some money.If I had to do it all over again I would just call Hughes Engines and order there heads and rockers and studs, guideplates. Bob
Click to expand...

More often than not the cracks that folks see in these heads are a cosmetic issue and have no detrimental effect on the operation. Engines run for 100,000's of miles with cracks. For sure you need to make sure that they aren't compromising the water jack or the ports but a small crack on th surface is not a reason to discard a set of heads.

There are quite few spring options that do not require cutting the seats. MP has two springs, one good for .525" lift and another for .600" lift, a little pricy compared to other springs but not if you factor in cutting the seats. Retainers for these springs are dirt cheap and in most cases can be had for zip. Just harvest them from any 2.2 or 2.5 mopar 4cyl. Comp now has a drop in beehive spring for magnum heads but I do not know if the stock retainers work. the GM3800 v6 spring is a drop in and the retainers are for 8mm valves, these are dirt cheap also but are only good for cams in the .480" lift range.

If you want to use Chevy roller rockers you will need to get longer pushrods. The chevy 7.8" push rod worked well for my motor but unless you are planning on reving past 6000 rpm all the time the stock stamped rockers are more than adequate.

Granted there is not a lot of choices in manifolds but really how many do you need? MP has a single plane and a dual plane. Edelbrock has their Air-Gap in a magnum bolting and the Professional Products CrossWind will bolt to either LA or Magnum heads. Wouldn't be surprised to see the new Weiand Air-Strike in a mopar version soon either.

I don't know why folks keep saying the accessory holes on the heads do not line up. I have been involved now with my LA/magnum hybred, a 380HP crate moter into an A-body and a 300HP crate motor into a B-body and there were no issues at all with the alignment of accessories. Everything just bolted on and lined up.
 
I have one of those heads that have a cosmetic crack and was going to use it. It is cracked through tthe exhaust seat but holds pressure, but was talked out of it by my machinest. Cracks keep going. He told me that he once pined a magnum head and cut out the seat and pressed in a new one, it only lasted about a month. Also he told me to cut one of my cracked ones and see for myself how thin they are between the exhaust and intake valves.

Part of the problem I have with the rockers is I'm using a small base circle cam and I had the heads milled to 57cc's so the pushrods need to be shorter, about 7.375 inches long.

I am using a Hughes valve springs and there retainers fit the od as well as the id of the spring

The replacement heads are made with thicker decks, more material between the valves, fiow better than a magnum RT head, and are made with a high nickel content, all for $475 a pair bare.
I have $100 in pressure checking junkyard heads.
 
daniel_depetro said:
The 5.2L and 5.9L heads are the same.

The production Dakota/Durango R/T heads are yet again the same.

The Mopar Performance R/T heads are the way to go!!! Magnum style head with much more flow and will not crack.
I have a set and they are awesome in my opinion.

I read on one of the mopar boards where a guy with a flowbench tested the J 2.02 heads (~185 cfm) famed X 2.02 heads (~215 cfm) and stock magnum heads (~215 cfm ) and MP R/T heads (~245 cfm).
A stock Magnum head will flow about what a ported J 2.02 head will flow.

The magnum heads are a direct bolt on for the later 1987+ 318 / 1988+ 360 roller cam engines.
Click to expand...

Yes the magnum r/t is really quite good.In fact a guy on moparts compares them to the commando and W2.They are in the same territory imho.
 
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