Old School vs Magnum on 86 Dodge W100

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Rolltide6019

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Team, I'm new to this forum - thanks for giving your time. I have a decision to make. My son (who is 17) is taking an old W100 4x4 I had sitting around and decided to revive it. It originally had a slant 6 but was converted to a 318 many years ago. That 318 is about dead. He purchased a running 94 5.2 magnum from a Dakota with the intentions of replacing the 318. He got all the electronics, wiring harness, and fuel system from the Dakota to help the conversion. Before installing, I recommended we tear the magnum down to inspect it. He did and it need a complete rebuilding. Block is fine, Cam is bad. Crank is fine. My question at this stage is whether to spend time/money rebuilding the old engine (which we have not torn down yet) or continue with the magnum? It seems to me the advantages of the magnum is fuel injection (and maybe one or two more) but the disadvantages are we have to do the electronics, wiring, & fuel conversion. If we stick with the old style, I feel we need a 4 barrel intake and carb (as opposed to the original 2 barrel it came with). That's a new intake and carb cost on top of a rebuild. And probably a newer distributor and ignition system. I would appreciate any thoughts for carbureted vs Magnum approach. Pretty soon, I'll be making decisions about machining, cam, pistons, etc so I could use the advise.
 
I would go with the magnum if they both need rebuilding anyway. If you can’t make the efi work you can always throw a carb on it, either way it will run better than a stockish LA 318.
 
Welcome to the site! Glad your son is interested in the truck. I would think you could buy a running magnum from a local yard, CL, or marketplace for about 200 bucks. Most of these will run countless miles if given any care, so buying one with a 150k on it wouldn't be a problem. If you are bent on rebuilding one or the other, then pick the one that needs the least would be my 2 cents
 
Rolltide6019 said:
Team, I'm new to this forum - thanks for giving your time. I have a decision to make. My son (who is 17) is taking an old W100 4x4 I had sitting around and decided to revive it. It originally had a slant 6 but was converted to a 318 many years ago. That 318 is about dead. He purchased a running 94 5.2 magnum from a Dakota with the intentions of replacing the 318. He got all the electronics, wiring harness, and fuel system from the Dakota to help the conversion. Before installing, I recommended we tear the magnum down to inspect it. He did and it need a complete rebuilding. Block is fine, Cam is bad. Crank is fine. My question at this stage is whether to spend time/money rebuilding the old engine (which we have not torn down yet) or continue with the magnum? It seems to me the advantages of the magnum is fuel injection (and maybe one or two more) but the disadvantages are we have to do the electronics, wiring, & fuel conversion. If we stick with the old style, I feel we need a 4 barrel intake and carb (as opposed to the original 2 barrel it came with). That's a new intake and carb cost on top of a rebuild. And probably a newer distributor and ignition system. I would appreciate any thoughts for carbureted vs Magnum approach. Pretty soon, I'll be making decisions about machining, cam, pistons, etc so I could use the advise.
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Carbed and Magnum are not exclusive to each other.
This is a 96 5.9 (360) roller motor and uses the LA motor accessories.

SANY0006.JPG


MagnumswapLA.jpg
 
The Magnum's higher inherent compression ratio will make it a better engine (torquier for low RPM use). You can get there or better with the older LA318 with a piston swap, but you need to re-balance the crank too, so the $$ add up to around $500 to exceed the CR of the Magnum.

In the cam department: You don't need to be fussy over the oil used with the roller cam, like you do with the older flat tappet cam in the LA318. But for a performance cam, the flat tappet system will usually be cheaper than the roller cams. IDK where you are thinking of changing the cam from stock; but be aware that you can't change the cam a lot for the factory FI as the manifold pressure signals will get changed enough to where the factory FI will not operate well with much of a cam change.

FI will keep the oil a lot cleaner.

I prefer the older ones for other reasons (like the shaft rocker system), but I suspect for your son's use, which is not demanding, the Magnum seems like the better way to go. You have all the FI parts.

You'll want a high out alternator to run the FI system.
 
Just helped a friend do the same thing over the span of the past two weeks. 88 W100 318 with 3.21 gears and and 31X10.50-15s It's been converted from 727 to wide ratio NP-435. Installed a 1993 magnum out of a Dakota with 130-135 PSI cranking pressure. Used the front accessories off the LA. It also had a bad camshaft, but we had a good 360 LA roller cam in my '88 block. The stock magnum cam is .432 lift I/E and 240/248 duration I/E. The stock LA 360 roller is .410/.417 with 249/269 degrees duration. When combined with the magnum 1.6:1 rockers, it becomes .438/.445 lift with about 2-3 degrees more .050 duration. (Really would liked to have a set of 1.7:1 rockers on the intakes for .464 lift but valve guide to retainer clearance gets iffy) The two cams intake valve closing is within a half degree of one another (between 60-61 degrees ABDC), so no loss of cranking compression. We added a chinese knock off air gap on it and a 650 Edelbrock carburetor. Exhaust is through a set of '68 model 318 truck manifolds (I would advise using the magnum manifolds or if you have an automatic, better yet headers) and 2-1/4 inch to 2-1/2 inch Y pipe with a single glass pack. Recurved a distributor and it seems to work optimally at 18 degrees static with 35 degrees all in at 2200 degrees. It runs really well for what it is, especially considering the gearing.
All in all, this combination works so good that I can't imagine wanting to mess around with the stock magnum fuel injection and all the headaches of adding it into the older truck. Then there's that "kegger" intake that really needs some internal runner work to make it work properly, and sometimes needs extra work to ensure it seals properly.
 
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Garrett Ellison said:
Just helped a friend do the same thing over the span of the past two weeks. 88 W100 318 with 3.21 gears and and 31X10.50-15s It's been converted from 727 to wide ratio NP-435. Installed a 1993 magnum out of a Dakota with 130-135 PSI cranking pressure. Used the front accessories off the LA. It also had a bad camshaft, but we had a good 360 LA roller cam in my '88 block. The stock magnum cam is .432 lift I/E and 240/248 duration I/E. The stock LA 360 roller is .410/.417 with 249/269 degrees duration. When combined with the magnum 1.6:1 rockers, it becomes .438/.445 lift with about 2-3 degrees more .050 duration. (Really would liked to have a set of 1.7:1 rockers on the intakes for .464 lift but valve guide to retainer clearance gets iffy) The two cams intake valve closing is within a half degree of one another (between 60-61 degrees ABDC), so no loss of cranking compression. We added a chinese knock off air gap on it and a 650 Edelbrock carburetor. Exhaust is through a set of '68 model 318 truck manifolds (I would advise using the magnum manifolds or if you have an automatic, better yet headers) and 2-1/2 inch duals with glass packs. Recurved a distributor and it seems to work optimally at 18 degrees static with 35 degrees all in at 2200 degrees. It runs really well for what it is, especially considering the gearing.
All in all, this combination works so good that I can't imagine wanting to mess around with the stock magnum fuel injection and all the headaches of adding it into the older truck. Then there's that "kegger" intake that really needs some internal runner work to make it work properly, and sometimes needs extra work to ensure it seals properly.
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Great input from you guys...
@jas0162 - Good point
@318willrun - You are correct; that's what he did. Until we pulled to pan off, we thought it might have been a good deal. But so many issues (200k miles, pitted Cam, scored crank, etc) it doesn't make sense to drop it in without rebuilding.
@Trailbeast - Good point.
@nm9stheham - I will have to change the Cam as the one in the Magnum is pitted on several lobes. I guess I'll go back with a stock cam unless someone gives me better ideas. FYI, I don't know what "FI" means.
@Garrett - Nice write-up, thanks for the input. You know much more than I do at this stage regarding the cam :) I'll send you a PM.

I haven't made a decision yet but all the input is helping!!
 
FI is fuel injection.
Something i always wanted to do, 360 magnum in my 80 power wagon. I have passed truck down to my son, i hope he is willing to do something like that.
Think it would be nice with the fuel injection.
 
I'm putting a 1998 360 Magnum in my 72 B-body. It had an original 318LA that died. Im doing just what Trailbeast did by swapping the entire front end of the 318LA onto the Magnum 360. I went with a carb and tossed all the efi. The biggest expense was the intake manifold. I went with an edelbrock air gap, that actually cost more than the $200 I paid for the engine. It is a very easy swap that should run very well bolted to my 904 trans.

Good luck!
 
66 Valiant wagon said:
I'm putting a 1998 360 Magnum in my 72 B-body. It had an original 318LA that died. Im doing just what Trailbeast did by swapping the entire front end of the 318LA onto the Magnum 360. I went with a carb and tossed all the efi. The biggest expense was the intake manifold. I went with an edelbrock air gap, that actually cost more than the $200 I paid for the engine. It is a very easy swap that should run very well bolted to my 904 trans.

Good luck!
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Yep, that's what I'm seeing too, the intake is more than the engine. I've decided for today I'm going to go ahead and do the rebuild of the magnum, polish crank, replace cam, etc while I'm deciding whether to go EFI or Carb. Carburation is simpler but will cost me more (intake and carb).
 
Rolltide6019 said:
Yep, that's what I'm seeing too, the intake is more than the engine. I've decided for today I'm going to go ahead and do the rebuild of the magnum, polish crank, replace cam, etc while I'm deciding whether to go EFI or Carb. Carburation is simpler but will cost me more (intake and carb).
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And I have to cut out the bell housing on my tranny to allow the CPS to fit.
 
Out of curiosity, what transmission, tire sizes, and axle ratios do you have?
 
That's pretty easy....just a hole saw and a hacksaw. I've got a low mile 5.9 and all the under hood wiring out of a 98 3500 straight drive truck, but just haven't had time to figure out the wiring to make it run in my 88 D100.
 
Put a 5.9 Mag in a 78 W150 a few years ago.

8Umodb.jpg
 
^^^ I didn't know Magnums came with aluminum heads.... what a bargain! LOL I want to go to your local junkyard now ....
 
nm9stheham said:
^^^ I didn't know Magnums came with aluminum heads.... what a bargain! LOL I want to go to your local junkyard now ....
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No Junkyard parts in that one, I put KB 107 pistons in it and a Comp roller cam, hughes 1.65 rockers. It was a strong runner compared to the tired 318.
 
Rolltide6019 said:
I will have to change the Cam as the one in the Magnum is pitted on several lobes. I guess I'll go back with a stock cam unless someone gives me better ideas. FYI, I don't know what "FI" means.
Click to expand...
As noted FI means 'fuel injection'.... Acronyms R US LOL

You can go up a step or so in cams. If you go to the cam mfr catalogs, you can find some that are suitable and won't upset the stock FI system excessively. For example, Lunati says their smallest VooDoo cams are suitable for factory FI; PN 10120700 is a tad larger than what Garrett's friend ended up with.

So you might want to look at cam catalogs and maybe call around to some mfr's and custom cam grinders with your engine configuration and see what you can get for a slightly bigger. For the stock FI, the duration cannot be too big and the LSA ought to be 112 degrees minimum. The objective is to keep the exhaust-intake valve overlap time low, so as to keep the idle and low RPM manifold vacuum up. Manifold vacuum is what the FI computer uses to determine engine load, and if you get a big cam in there with a low vacuum level at idle, then the computer gets confused.... "I see 10" of manifold vacuum. Am I at the off-idle transition or am I at 70% throttle?"
 
And on that note, the baby step 360 roller cam in the W100 with 31X10.50-15s and 3.21 gears doesn’t really start to pull hard until over 2000 rpm. If we had an offset key or a timing set we would have installed it 4 degrees advanced to pick up a little more cranking compression. With the 109 LSA, it would work well. The original plan was a 360 Magnum that had 160 psi cranking compression. Unfortunately, the two dead cylinders from improper storage at the junkyard relegated that short block to the scrap heap. A set of 3.73 or lower gears and some headers with an X flow muffler would help a whole lot with towing here in the vertical territory. But it’s still leaps and bounds ahead of the roller cam 318 with a base Performer intake and the same carburetor.
 
nm9stheham said:
As noted FI means 'fuel injection'.... Acronyms R US LOL

You can go up a step or so in cams. If you go to the cam mfr catalogs, you can find some that are suitable and won't upset the stock FI system excessively. For example, Lunati says their smallest VooDoo cams are suitable for factory FI; PN 10120700 is a tad larger than what Garrett's friend ended up with.

So you might want to look at cam catalogs and maybe call around to some mfr's and custom cam grinders with your engine configuration and see what you can get for a slightly bigger. For the stock FI, the duration cannot be too big and the LSA ought to be 112 degrees minimum. The objective is to keep the exhaust-intake valve overlap time low, so as to keep the idle and low RPM manifold vacuum up. Manifold vacuum is what the FI computer uses to determine engine load, and if you get a big cam in there with a low vacuum level at idle, then the computer gets confused.... "I see 10" of manifold vacuum. Am I at the off-idle transition or am I at 70% throttle?"
Click to expand...

Thanks nm9stheham. I'm leaning toward Carburation but may change my mind. I don't much about Cam selection so I may need to pick your brain. All I know at the moment is I need a new one b/c mine is pitted pretty badly. Crank and Cylinders seem ok although the crank will need polishing, maybe oversized as there is some scaring on 2 journals.
 
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