Pablo Software Solutions
                     Here's the poop for you Magnum guys...

                           ....because I'm tired of typing it on Moparts all the time....

NOTE: The basis of this is Partick Grossman’s (patrick) write-up from “The Best of Moparts”. I added additional information to it to maybe answer some of the routine questions I am asked about this conversion.

                                                                   349MagnumRT (James)

Original thread: Magnum Heads on LA Blocks Thread

Some of the advantages of the Magnum heads are: 8mm valve stems (lighter than the LA's 3/8 stem) "swirl port" technology in the intake runner, 63cc closed chamber, great port velocity, improved exhaust runner, stock 1.6 ratio rockers, ability to support 400HP out of the box.

To put Magnum heads heads on a pre-Magnum small block, here's what you need:

different pushrods
oil through lifters
different head bolts
magnum heads
magnum rocker gear
different intake (potentially)*

You can custom measure and get custom length ones, or MP offers these:
Special hydraulic pushrods
Designed to allow the use of magnum heads and
standard magnum rockers on standard 1967-91
"A" short block/engines.
MP Part number: 5007477
Magnum head on standard "A" block-set of 16 7.625"

Some guys have reported that these pushrods may be a touch too short because of differences in head gasket thickness and block deck height, etc.

If you are running a lot of lift (small base circle on the cam) with standard non-adjustable rockers, or adjustable rockers (depending on how much lift), you may need to get custom length ones. Or, you might be able to find some off the shelf Ford/Chevy parts to work.

The thing to remember is there is no “ONE SIZE FITS ALL” when it comes to pushrods.

They need provisions for pushrod oiling. If you have stock lifters (stock cam) they probably don't. If you have an aftermarket cam, you probably do. The way to check: find out your lifter manufacturer (i.e. are they summit lifters? comp? crane? etc) and see if the part number for a Mopar is the same part number for an AMC motor. If they are, then you have pushrod oiling capable lifters. Most do. I know for sure Comp & Summit do.

NOTE: Stock Mopar roller lifters WILL NOT work in a non-roller block. The lifter bosses in a roller block are approximately 0.40” taller than a non-roller block. Since the roller lifter is much taller than a standard hydraulic, the taller boss in necessary to keep the oil holes covered at max lift. Otherwise you will have little or no oil pressure. The lifter bores *could* be bushed taller, but that is getting a little more involved than most guys want. Retrofit roller lifters ARE available but are kind of expensive. CAT has listed retrofit rollers on their site, but are not yet available.

The bolts are different length than old LA ones. Luckily they're cheap:

MP part number: 4876759 Magnum engine

Any '92-up 318 or '93 up 360 will have them. You might have issues finding cracked heads, or you might not find junkyards to sell you heads, they may want to sell the whole motor. If you get them from a junkyard, make sure you get the rockers and valve covers. If you can't find them in a yard, what are you to do? Well, Mopar Performance sells them as brand new castings:

MP PN: 4876256 (1.92/1.625 production castings)

Or you can purchase Magnum R/T heads, which feature stock port locations, and a W2 style bowl, and improved exhaust port. Arguably the best iron small block head you can find.
MP PN 5007140 1.92/1.625 valve
MP PN 5007140 2.02/1.625 valve

Magnum head flow results by :
Magnum Head Flow Results

Magnum R/T head flow results by :
Magnum R/T Head Flow Results

>Springs: Magnum heads use a smaller diameter valve spring than an LA head does. While this makes getting at the head bolts easier, it makes selecting the right spring for your cam a pain. MP offers 2 different valve springs for the Magnum head. Of those, the ‘6062 spring is the only one to really consider in my opinion. Crower also offers a decent Magnum spring (dual).

The REAL ticket is to open up the spring pockets to 1.5” and use any one of the zillion 1.5” diameter springs offered by any of the cam or spring makers using the seat cutter available through Goodson or any of the major cam manufacturers.

Goodson PN VSS-1550 (spring seat cutter 1.55” dia. – other diameters are available)

>Locks: Limited availability due to the 8mm round groove valve stem used. MP sells them and LS1 Chevrolets use a compatible lock.

>Retainers: Stock Magnum springs are a conical style spring with a rather small diameter retainer. These WILL NOT work with aftermarket or MP springs. MP sells retainers for their Magnum springs as well as Crower. Chrysler 2.2L retainers can be used with 1.5” dia springs as well.

>Valves: Again limited availability due to the 8mm stem. This IS NOT the same as a 5/16” stem valve unless you want some sloppy valves. As far as I know, MP is just about the only game for stainless steel valves. Ferrea offers one, but their catalog shows it to be 5/16” stem…  FWIW, Chevrolet LS1 valves are virtually the same length, 8mm stem and use round groove locks. Diameters vary though.

OR if you want, you can purchase assembled heads. I believe the assembled production heads have the crate motor valve springs. These should be good for cams up to .510" lift. CAVEAT: Magnum heads start running into seal to retainer clearance at valve lifts much above 0.525 lift, so if you want to go higher you'll have to machine down the valve guide for clearance. A tool is available through most cam manufacturers to shorten the guide and remove the spring step. Best thing is, you can do it in your garage with minimal hassle and excellent results.

Goodson PN VSC-530312 (cutter and 5/16” guide for 0.530” seals – other seal diameters are also available)

Assembled Magnum head:
MP PN 5007086

Assembled Magnum R/T heads:
P70005 (1.92/1.625)
P70005 (2.02/1.625)

NOTE: MAGNUM R/T HEAD USERS!  The pushrod holes machined in the R/T heads offer MINIMAL (if not zero) pushrod clearance standard hydraulic lifters. It is HIGHLY recommended that you enlongate the push rod holes in the casting TOWARDS the intake face almost to the valve cover rail all the way through the casting. Roller lifter users may only need to clearance the lower portion (deck side) of the hole to have adequate clearance. Failure to check this can result in a trashed motor and a very bad day.

Stock magnum rocker arms are actually the same rocker arms as the old AMC 290-401 engine series, and are 1.6 ratio instead of the LA 1.5 ratio. To determine the valve lift with 1.6 rockers, take your LA cam's valve lift and multiply by 1.067 (1.6/1.5).
Aftermarket roller rockers are usually the same pieces as SB Chevy pieces, and may require different rocker arm studs. Some kits may include them. Most aftermarket rockers are available in 1.6 or 1.7 ratio. Small Block Ford specific roller rockers (1.6 ratio) are reported to be a better fit because of minor differences in the rocker pivot to roller tip dimensions. CAT Chevy roller rocker have been successfully used as well.

Crane: offers a stud and guide kit: PN 36655-16, which is the same part number for a Ford 5.0L conversion. The rockers PN 11746-16 (1.6 ratio) are the same rockers for 5.0L Fords and SB Chevy's. These are the same parts as the roller rocker arm kit available through MP.

COMPCams: Now offers a “real” Magnum guide plate and it is preferred over the Crane Teflon thingys. In older Comp catalogs (and possibly their website) they list a PN4842 & PN4843. These are INCORRECT.  This is an Oldsmobile guide plate and it WILL NOT work properly on a Magnum head.

Crower also has Magnum roller rockers available in rail (no guide plates necessary) or non-rail (guide plates required) as well as the other necessary hardware to install them.

If you're running a moderate hydraulic cam, stock rockers are fine. If you don't have junkyard ones new ones are available from MP:
Consists of 2 rocker arms,2 pivots,2attaching
boltsand 1 guide.for use with hydraulic cams
only,production 1.6 design ratio. NOT for
4.7L V8.
MP PN 4876050 (one cyl, need qty 8 )

NOTE: Roller rocker arms WILL NOT clear the baffles inside a stock valve cover. There are several ways to fix this:

1. Buy MP cast aluminum valve covers (spendy)

2. Cut the stock baffles out.

3. Bash the baffles in with a hammer.

4. Build a valve cover spacer out of wood or metal. I ended up bolting a valve cover to a piece of wood (maple or something) trimming around it with a flush cut router bit and made myself a 1/2" spacer. Painted it good and installed it with 2 valve cover gaskets and longer bolts. No leaks so far. Small Block Chevy valve covers will even fit if you enlongate the valve cover holes a bit. I had this setup for a while, but couldn’t keep it from weeping around the top of the bolts (didn’t really try too hard though) and went with a spacer. Some SBC valve covers can be purchased without the holes drilled. You could drill your own and possibly eliminate the weeping problem I had.

MP  intakes:
MP PN 5007380 dual plane

MP PN 5007381 single plane                                                         

MP PN 5007398AB 2BBL MPI W/EGR (92-96 truck replacement)

MP PN 5007852 2BBL MPI W/O EGR (97-02 truck replacement)

Edelbrock: Air Gap PN 7577

Professional Products: Crosswind  #55025 – Polished, #55026 - Satin

*Also, Moparts board member 349MagnumRT has come up with a simple yet ingenious jig to redrill your magnum heads for an LA bolt pattern, so any LA intake can be used. PM him for details.

That's basically the gist of adding Magnum heads to an LA motor. For a 318, the 1.92 valve is about the perfect size. Any larger (to say 2.02's) will physically fit, but the shrouding caused by the smaller bore on the larger valve will negate any flow increase. besides, ported, the stock valve will flow over 260 CFM, enough to support 500+ HP. Look in the “Best Of Moparts” section for some of RyanJ's flow results from Magnum heads, both R/T and standard Magnum.

I'd like to thank the board members who have over the years contributed information, and to Mopar Muscle, Car Craft, and Steve Dulcich for the articles they've written/published on the matter who I have gained some of the info from. This is a great forum with a lot of knowledgeable guys, hopefully I've been able to contribute a little to help others out.

Steve D also had a great article in building a non-ported head 318 using Magnums here: The Little Mopar that Could which is a great reference article.

One last note: Magnum heads *can* work on a 273 (I have one), but you had better be ready to break out the carbides and notch the cylinder bores, as the stock Magnum valves will hit the bore.
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