Should I chance it?

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PanGasket

PanGasket

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We always get a lot of Magnum engines into my job and I was wondering, is it worth a shot to pull a set and put em on my 318 for some more compression and hardened valve seats? They aren't much for a set and we always get magnum engine trucks that have decent engines. Worth a shot or no? I heard these heads have a habit of cracking
 
If they arent cracked, go for it.

the advantage is the closed chamber, but as for flow...they flow in 'stock form' about what 1.88 360 heads flow=215int/145exh cfm

If u port them, the exhaust will flow better with less work...but ultimately they will not 'in ported form' flow more/as much than the older heads.

the exh seats are induction hardened, they tend to crack there and into the water jacket. Induction hardening is not ideal and does not last like a pressed in seat does.

As for how the closed chamber will benefit u...is simply a compression gain from the smaller chamber... for unless u have a piston that comes up high enough to provide quench...u will have none.
 
It'll probably knock like 10ccs off of your combustion chamber size which couldn't hurt.

I have only pulled the heads on 6 or 7 of these motors so far, but so far every single head has been cracked.
 
its $50 for a set at my work, with 30 day warranty. I just have been battling myself back and forth on this one
 
if you are worried about it, then you are second guessing them. if they end up cracking, you will have replace them again. i would just get some head work done on an older set and not have to worry everyday if this will be the day they go south. i have never ran them so i cant tell you to use them .
 
If you're gonna do a budget build with stock pistons that sit in the hole, I would do it.....in fact, I am. I am fixin to build a 318 using stock 4 eyebrow pistons that are .030" over and with the magnum heads I can get 9.5:1 if I wanna go that high, but I'm not. I will probably end up with 9.1 or 9.2 just to be safe since I won't have any quench. Justin is right though about the seats. They're nothing special. Might as well be plain cast iron. Now, if you went to the trouble to have hardned seat inserts installed, then you'd have something.....but whether it's worth all that is debatable. If you find a good uncracked set, I say run them.
 
Another thing to consider is, you will not have the extra exhaust heat that is responsible for cracking them in the first place. A catalytic converter. A good free flowing exhaust will help keep cylinder head temps down.
 
I hear alot of talk about the Magnum heads and cracking. I had a 91 5.2L TBI that had 190,000 miles and no problems. Now I have a 92 5.2L MPI W150 Club Cab that just past 280,000 miles, No problems with cracking and trust me both these trucks where and are run HARD. I blast up and down I95 everyday @ 80 mile an hour. More than a few times with the speedo buried past 100. A couple of times with the OD off it bounced off the factory rev limiter.(no idea what rpms that is). So yea I'd run em.
 
You can usually see the cracks.. but... If you're just bolting them on and not spending on re-doing them... The majority will have cracks present. But they will not go to water, nor will they ever. So if the engine is running well now, the heads are fine to use. Magnafluxing will always show a crack. But not all cracks are anything more than superficial. Pressure testing will show if they are leaking cracks.
 
Just clarify in regards to what moper said...some do crack around the combustion chamber/plug, those 'most of the time' do not become an issue...however, the cracks that more often occur at the exhaust seat DO go into water.

Fact is all factory sb mopar heads have water around the seat/bowls. In some really bad cases of core shift, can possibly leak a lil when taller hardened seats are machined and pressed in, not all heads but possible for some according to some long time machinists ive dealt with. fwiw
I remember a shop way back when made a disclosure that they could not garuntee the heads would not possible weep after a hard seat install. though I have never seen it happen myself.
 
Don't you also get 1.6 rockers?

That'd be like getting the next size cam as well.

For $50, it sounds decent.

=flow

+hardened seats
+smaller chamber/more compression
+1.6 rockers

- might crack
 
YY1 said:
Don't you also get 1.6 rockers?

That'd be like getting the next size cam as well.

For $50, it sounds decent.

=flow

+hardened seats
+smaller chamber/more compression
+1.6 rockers

- might crack
Click to expand...

I agree, when people say they feel a power increase over the old small valve stuff...it's mainly the 1.6 rockers that do it.
 
Run em! You bet man. Magnum's will give you a bit better gas mileage as well as raising the cr. More efficient chamber's designed for today's fuel mean's less timing adv is needed as well.he power increase is coming in a couple form's on the Magnum head. One is the raised cr,the other is the combustion chamber and intake/exhaust runner's with an ootb flow ration right around 75%.
 
I can't believe the 1.6 rocker would be worth very much over the 1.5. A little bit of lift and a microsecond of duration. Back in the day when I was a mustang guy, we'd see about 5-7 rwhp going from stock sled 1.6 to aftermarket roller 1.7.

Fortunately the pistons on the 318s are so far down in the hole you don't have to worry about piston to valve clearance. LOL

If it was me, and you were seriously going to do the work, buy gaskets, intake manifold, etc. I would just buy a set of these:

http://www.hughesengines.com/Index/...HM=&searchmode=partnumber&page=2&partid=25426

Have them drilled (or buy the castings that are already drilled) for LA intakes so you don't *have* to buy an intake, and you especially don't have to buy that POS pro products thing. You get actual hardened seats, more flow, an honest 58cc chamber, stainless valves, and upgraded valve springs (stock Magnum valve springs are crap if you want to run any kind of cam).

These are the heads I put on my car. The motor that in there now is the first Magnum engine I bought. The #1 cylinder was leaking down 90% because of a crack between the valves with the stock heads.

My stock Magnum pistons are .050 in the hole and I am running these heads on 93 Octane, with lots of timing and the skinny Mopar head gaskets. No issues with quench or anything else.

Yes its a helluva lot more money than stock heads. They're faster than stock heads, and you don't have to worry about cracks.

My .02
 
Mike, if you wanna bring them to me, I will show you how to tear them down and check them for cracks. I use dye penetrant because it checks ferrous and non ferrous metals. If they are nasty, we'll need to clean um up first.
 
If the actual lobe on a cam is .270...a 1.5 rocker yeilds a valve lift of .405 (close to stock 318 ).
A 1.6 rocker yeilds a valve lift of .432.

There are formulas for duration, but it's not very much different at .1 increase, and much more complex to figure, IIRC.

Anyway, that's close to 2 times larger in the cam catalog.

Isn't 8 RWHP about equal to about 22 crank HP?
 
if it was me after i found a set that wasnt cracked, i'd find the best deal in town to get them cleaned and hardened seats pressed in. might only cost you parts & a sixpack of beer & a couple hundred bucks. i would probably keep all the valves that come in and you will end up with a nice set of valves too after you clean them up.
 
I think the stock magnum head is limited to about .520 of lift,anything more requires the valve guide to be cut down.
 
Remember also that if you install them on a LA block you will need different lifters and oil through pushrods along with a Magnum intake manifold. tmm
 
needsaresto said:
I think the stock magnum head is limited to about .520 of lift,anything more requires the valve guide to be cut down.
Click to expand...

Since the stock port flow is limited to about a .500 lift cam, that works out pretty good.
 
Yes exactly Rob. I have a cam that I bought off ebay for my magnum heads/360 in my old cop car. It's a single pattern crane cam ,which suit's a magnum's 75% flow balance well,and has about .470 lift. I figured it was bang on for 9.5:1 as well.


Style: Hydraulic flat tappet
Basic Operating RPM Range: 2,800-6,000
Intake Duration at 050 inch Lift: 222
Exhaust Duration at 050 inch Lift: 222
Duration at 050 inch Lift: 222 int./222 exh.
Advertised Intake Duration: 294
Advertised Exhaust Duration: 294
Advertised Duration: 294 int./294 exh.
Intake Valve Lift with Factory Rocker Arm Ratio: 0.480 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio: 0.480 in.
Valve Lift with Factory Rocker Arm Ratio: 0.480 int./0.480 exh. lift
Lobe Separation (degrees): 106
Intake Valve Lash: 0.000 in.
Exhaust Valve Lash: 0.000 in.
Computer Controlled Compatible: No
Grind Number: H-222/3200-6


Crane Racing Camshaft part #CRN-690141 and lifters part #CRN-99278-16. Items are used but in great shape all lifters numbered to match cam lobes they were mated to. Camshaft retails for $259.69 new, and lifters for $89.99. Specs for cam are as follows:
Part Number: 690141 Grind Number: H-222/3200-6
Engine Identification:
Start Yr. End Yr. Make Cyl Description
1964 Up PLYMOUTH-DODGE-CHRYSLER 8 ROUGH IDLE, MODERATE PERFORMANCE USAGE, GOOD MID-RANGE HP, LIMITED OVAL TRACK, MILD BRACKET RACING, AUTO TRANS W/3000+ CONVERTER, 9.5 TO 11.0 COMPRESSION RATIO ADVISED. BASIC RPM 2800-6000
Engine Size Configuration
273-360 C.I. V

Valve Setting: Intake .000 Exhaust .000 HOT

Lift: Intake @Cam 320 @Valve 480 All Lifts are based
on zero lash and theoretical rocker arm ratios.
Exhaust @ Cam 320 @Valve 480
Rocker Arm Ratio 1.50

Cam Timing: TAPPET @.004
Lift: Opens Closes ADV Duration
Intake 40.0 BTDC 74.0 ABDC 294.0 °
Exhaust 72.0 BBDC 42.0 ATDC 294.0 °

Spring Requirements: Triple Dual Outer Inner
Part Number 99838
Loads Closed 112 LBS @ 1.650 or 1 21/32
Open 296 LBS @ 1.190
Recommended RPM range with matching components
Minimum RPM 2200
Maximum RPM 5600
Valve Float 6200

Cam Timing: TAPPET @.050
Lift: Opens Closes Max Lift Duration
Intake 9.0 BTDC 33.0 ABDC 102 222.0 °
Exhaust 41.0 BBDC 1.0 ATDC 110 222.0 °

Remarks
 
For $50, I doubt the OP is interested in a .500 cam or installing seats in a head that is already unleaded friendly. The oiling issue and intake bolt angle are real issues, however.
 
The issues are easy to solve however. Oh and one more thing. Magnum uses a different length head bolt,so your LA head bolt's wont work. Another hidden cost. But the pushrods are cheap enough. Boss 302 pushrod's will work,and mopar used to sell a pushrod specifically for this app. The intake bolt angle is easy to solve too,just have the LA pattern drilled and tapped into the head. Used to be there was a jig for drilling LA pattern on magnum's on mopart's that got passed around and used up. It would be simple enough to do it your self,the plan's are still available to build the jig.
 
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