Magnum Heads Swap
Below is information about Chrysler's Magnum heads, and what is needed to swap them to LA engines. This topic is based on information from Patrick Grossman's excellent Moparts.com Magnum Heads on LA Blocks
topic with additional information from James Pringle's www.bigblockranger.com
Magnum heads were introduced in 1992 on 5.2 truck engines, and in 1993 on 5.9 truck engines. They were never used in passenger car engines. Advantages of Magnum Heads
Differences Between Magnum Heads and LA Heads
- Lighter Valve Stems (8mm valve stems vs. 3/8" LA valve stems)
- "Swirl Port" technology in the intake runner
- Closed Chamber Design (63cc)
- Improved Port Velocity
- Improved Exhaust Runners
- Higher Ratio Rocker Arms (stock 1.6:1 ratio)
- Larger Exhaust Valves
- Improved Valve Cover Design (less leak-prone)
- Improved Rocker Arm Oiling (more direct)
- Able to Support 400HP in Stock Form (Note: This means they can support up to 400 HP with other engine modifications, such as cam, induction and exhaust changes. It does not mean that they will make 400 HP by just bolting them on to your 2BBL 318.)
Similarities Between Magnum Heads and LA Heads
- Valve Covers: Magnum valve covers are squared at the ends. LA covers are rounded at the ends.
- Valve Cover Bolt Pattern: Magnums have 10 bolt valve covers for better sealing. LA covers have 5 bolts
- Combustion Chamber: Magnums are a closed chamber design. Most LA heads are open chambered except for 302 and similar castings and some early 273 castings
- Intake Valve Size: Stock Magnums have 1.920" intake valves. The larger LA intake valves range from 1.88" to 2.02". (Note: Mopar Performance does offer Magnum R/T heads with 2.02" intake valves.)
- Exhaust Valve Size: Magnums have 1.625" exhaust valves. The largest LA exhaust valves are usually 1.60"
- Valve Stem Size: Magnums have 8mm sized valve stems, which are lighter than the LA 3/8" sized valve stems.
- Heat Crossover: Magnums have no intake manifold heat crossover like LA heads.
- Rocker Arm Mounting: Magnums have stud mounted rocker arms. LA rocker arms are shaft mounted
- Rocker Arm Oiling: Magnum rocker arms are oiled through the pushrods. LA rockers are oiled through the shafts from block passages
- Rocker Arm Ratio: Magnums arms are 1.6:1 ratio. LA rocker arms are 1.5:1 ratio.
- Pushrods: Magnums have hollow pushrods to feed oil to the rocker arms. LA heads work with solid pushrods. (Note: There were some LA roller cam engines that were built with hollow oil-through pushrods.)
- Intake Mounting Bolt Holes: Magnums have vertical intake mounting bolts. LA heads have angled intake mounting bolts.
- Head Bolts: Magnums require different head bolts than LA heads.
- Accessory Bolt Holes: Magnums have 5 accessory bolt holes on each end. LAs have 3 accessory bolt holes on each end.
- Intake Airflow: Magnum intake airflow is about 190 CFM. LA intake airflow is about 160 CFM.
- Exhaust Ports: Magnum exhaust ports do not have the "point" on the floor like LA exhaust ports.
Swapping Magnum Heads to LA Series Engines
- Head Bolt Pattern: Magnums have the same head bolt pattern as LA heads. They will bolt directly to any of the LA series blocks. 273 engines will require clearancing around the cylinder bores for the larger Magnum valves.
- Exhaust Bolt Pattern: Magnums have the same exhaust manifold bolt pattern as LA heads, and will mate to LA style headers. Because the floor of Magnum exhaust ports is slightly different than LA exhaust ports, there is a bit of overlap which provides some anti-reversionary effect when mated to LA headers.
- Water Passages: Magnum and LA water passages are the same.
Despite the differences, Magnum heads can be swapped to any LA pre-Magnum small block. Below is a list of parts needed for the swap:
Sources: Additional information:
- PUSHRODS: You can custom measure and get custom length ones, or Mopar Performance offers MP Part number: 5007477 (Magnum head on standard "A" block-set of 16 7.625", listed as Special Hydraulic Pushrods designed to allow the use of Magnum heads and standard Magnum rockers on standard 1967-91 "A" short block/engines.
- Some people have reported that these pushrods may be a bit too short due to 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 pushrods - Or - you might be able to find some off the shelf Ford/Chevy parts to work.
- It is important to remember that there is no “ONE SIZE FITS ALL” when it comes to pushrod selection.
- LIFTERS: You will need lifters that have 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 lifter, the taller boss is necessary to keep the oil holes covered at maximum 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.
- HEAD BOLTS: You will need MP part number: P4876759 (Magnum engine) Magnum head bolts
are different length than old LA ones. Fortunately they are inexpensive.
- HEADS: Your sources for Magnum heads are:
- Junkyards: Any 1992-up 318 or 1993-up 360 will have them. You might not find junkyards willing to sell you just the heads instead of selling the whole motor. If you get them from a junkyard, make sure you get the rockers and valve covers. Production Magnums have induction hardened seats that are prone to cracking between the exhaust and intake valves, so you should have them magnafluxed to check for cracks.
- Mopar Performance (MP): MP offers the following new Magnum heads:
- Bare Cast Iron Casting: P4876256 (1.92/1.625 production castings)
- Bare Aluminum Casting: P4876624 (set up for 1.92/1.625 valves)
- Assembled Magnum head: P5007086. As far as it is known, the assembled Magnum heads have the crate motor valve springs which 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 R/T heads: Magnum R/T heads are also available assembled. They feature stock port locations, a W2 style bowl and an improved exhaust port. MP part numbers are:
Some sources said that the Magnum R/T head is the "best bang for the buck" iron small block head you can find. However, Moparts member hotroddave40 observed that the Magnum R/T heads were probably the best of the iron heads only in a fully ported configuration. He noted that although they had a real nice bowl and runner design more like W2 heads, the castings were very rough - even worse than production Magnums. As cast, they didn't flow any better than the EngineQuest (EQ) or Pro-Topline offerings. He recommended that they were a waste of money if you weren't planning on porting them. Additional Note on Magnum R/T Heads: The pushrod holes machined in the R/T heads offer MINIMAL (if not zero) pushrod clearance with flat tappet 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.
- MP PN 5007140 1.92/1.625 valve
- MP PN 5007140 2.02/1.625 valve
- EngineQuest Magnum Heads: Clearwater Cylinder Head, Inc.sells the EngineQuest (EQ) Magnums (EQ # CH318A). EQ heads are high quality heads. They are much better than than production Magnums. They flow about 5% more, and they are less prone to cracking due to pressed in hardened seat inserts. They also have a smoother pushrod pinch area. They don't come with rockers or valve covers, so your cost to use them will be a bit more. However, they are still worth it. EQ also manufactures EQ # CH318, which is a Magnum designed casting that has the early(pre 92) type LA intake bolt pattern. Moparts member hotroddave40 was of the opinion that for most people doing the Magnum head swap with new parts, EQ heads are hands down the best deal unless you can find the Pro-Toplines somewhere. WARNING: There are places on ebay and other sites that sell cheap copies of the EQ heads from China. They are reported to be junk, so avoid them and look for real EQ heads
- Pro-Topline Magnum Heads: These quality heads have been discontinued, but you might be able to find them used. Out of the box, they flowed about 5% better than the EQ heads, and at least 10% better than stock Magnum heads. Moparts member hotroddave40 observed a fully ported set with 2.05" valves hit 300 CFM. He also noted that they had the most room for porting of all the heads that he observed.
- Edelbrock: Edelbrock Performer RPM Magnum Heads #61779, are excellent quality Magnum heads manufactured from lightweight A356 aluminum. They work with stock Magnum intakes and exhaust manifolds, as well as aftermarket headers, and they are good for up to 6,500 RPM. They also work with Edelbrock's excellent #7577 RPM Air-Gap Magnum manifold. Adjustable rocker arms and hardened pushrods are required. They have the following features:
- 58cc combustion chambers
- Stainless steel 2.02" intake/1.60" exhaust valves
- Heavy-duty 1.450-inch O.D. valve springs for up to .580" lift
- CNC profiled port entries and bowl blending for optimum air-flow
- 176cc Intake Runner Volume
- 75cc Exhaust Runner Volume
- 5/8" thick deck for positive gasket sealing and retention
- Heli-Coiled in the exhaust bolt and rocker stud bosses for maximum strength
- Hardened Steel 3/8" rocker studs and guideplates
that will accept most aftermarket 1.5:1 and 1.6:1 adjustable rocker arms
- ROCKER GEAR: Your rocker arm options are:
- Factory stock - Stock Magnum rocker arms are actually the same rocker arms as the old AMC 290-401 engine series, and they 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). If you're running a moderate hydraulic cam, stock rockers are fine. If you don't have junkyard ones new ones are available from Mopar Performance: Part number P4876050 - MAGNUM V8 ROCKER ARM SET (Consists of 2 rocker arms, 2 pivots, 2 attaching bolts and 1 guide. Designed for use with hydraulic cams only. Production 1.6 design ratio). The part number is for one cylinder so you will need to order 8 sets.
- Aftermarket - Aftermarket roller rockers are usually the same pieces as Small Block Chevrolet (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 rockers 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 also the same parts as the roller rocker arm kit available through Mopar Performance.
- 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.
- 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. James Pringle bolted a valve cover to a piece of wood (maple or something) trimmed around it with a flush cut router bit and made a 1/2" spacer. He painted it and installed it with two 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. James 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.
- INTAKES: There are now several intake options for Magnum heads:
- Mopar Performance Aluminum Intakes:
- P5007380 Dual Plane
- P5007381 Single Plane
- P5007398AB 2BBL MPI W/EGR (92-96 truck replacement)
- P5007852 2BBL MPI W/O EGR (97-02 truck replacement)
- Edelbrock Performer RPM Air-Gap Magnum (non-EGR), #7577. This aluminum intake is always highly spoken of by Mopar enthusiasts.
- Professional Products Aluminum Intakes:
- Crosswind #55025 – Polished finish
- Crosswind #55026 - Satin finish
- Another option is to redrill and tap Magnum heads for the LA intake bolt pattern. This expands your intake options to all of the new and used aftermarket LA intakes. James came up with a simple yet ingenious jig to redrill Magnum heads for the LA bolt pattern. He later sold it, and it has since disappeared. However, if you have welding and fabrication skills, you can make your own jig using any LA head as a template. Hughes Engines and other Mopar oriented companies also offer Magnum head redrilling services.
- SPRINGS: If you are using assembled MP Magnum heads, the springs should be good for cams up to .510" lift. If you are using Edelbrock Magnum heads, the springs are supposed to be good for up to about .580" lift. Any other Magnum heads (junkyard, EQ) will require a spring upgrade if you plan on using anything other than a stock cam. Magnum heads use smaller diameter valve springs than LA heads. 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 James' 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” diameter springs as well. YOU MUST USE MAGNUM LOCKS.
- 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… For what it's worth, Chevrolet LS1 valves are virtually the same length, 8mm stem and use round groove locks. Diameters vary though.