5.9L Magnum questions

Well, I was lucky enough to get my hands on a decent 1998 5.9 Magnum core locally. Supposedly out of a Dakota R/T. Stripped it down that day and was pleasantly surprised at it's condition, considering it supposedly had 100K plus miles on it. Virtually no ridge in the cylinders, and they still had crosshatch in them! Inside was very clean, no chunks or gunk inside. Heads were clean also. Had a couple broken studs, but I was able to extract them without any damage. Haven't got to the bottom end yet, but it spins free and and if it looks like the top, I'll be happy.
My goal for the motor is to do a "best bang for the buck" build I can while creating a reasonable amount of HP/TQ. I realize that everyone's definition of "reasonable" is different. Just hear me out...you can take turns kicking me in the nuts later.
Motor is going in a 66 Barracuda that has the original 273/904 in it. Want to transfer all the 273 parts (timing cover, pulleys, EX. MANIFOLDS, etc.) to the 5.9 if possible and keep the 904 behind the 5.9. Will try to be more specific below- not necessarily concerned with any hard numbers right now, just tell me if the info below makes any sense. I know you guys have been at this WAAAYY longer than I have, that's why I came here. All comments welcome.
Here we go- pretend I have a 20 yr. old's wallet, because I pissed away too much money on my Belvedere ll previously. (I'm 66 and still working. American dumbass).

1. Hone/re-ring motor with stock pistons. Would like to improve CR if possible. Deck/square up block, cleanup cut on heads, and .027 Cometic gasket? Maybe worth .040?
Pistons "in the hole" as follows- only checked the corners- #1 .045, #7 .044, #2 .044, #8 .051
2. Check/mic main and rod journals. If clean, new bearings and re-install.
3. New high volume oil pump. Double roller timing chain and gears.
4. Intake- Edelbrock Performer...or maybe even the Chinese version. Have one on the 5.2 in the garage, haven't run it yet. Looks well made and machined though.
5. Carb- something in the 650-750cfm range I would guess. Not partial to any particular brand.
6. Heads- stock, fresh valve job, stock 1.6 rockers, cleanup cut, home ported ala Charles Servidio videos. Fingers crossed.
7. Cam- see attached pic. I intend to go to Oregon Cams and get a regrind based on the Hughes cam numbers shown. If anyone can give me a yea/nay on this choice, or provide a better grind for this combo, I'm all ears. Required springs, too. 5500 rpm max should keep me out of flying parts territory, and most of my driving will be midrange anyway.
8. 3000 stall converter, manufacturer unknown at this point.
9. 3.55 SG in rear. I have a 3.91 in the Belvedere...and a 5 gal. gas can in the trunk. You know, just in case...
10. Exhaust- this is where I'm a little stumped. By that I mean efficiency versus $$. The headers I WANT are $1000+. The manifolds I HAVE and I know will fit, are FREE. Question is, what is the loss in efficiency/fitment between the Doug's (or any) headers and the iron manifolds? Can I modify the iron to improve flow? Dunno. Yes, planning on using a header flange on the drivers side if I use manifolds.

I'm sure I forgot about 100 things, but please feel free to remind me. Best I can do on a Sunday morning. Any and all responses will be considered to get me to the most efficient, economical build. Thank you.

MechNerd said:

Well, I was lucky enough to get my hands on a decent 1998 5.9 Magnum core locally. Supposedly out of a Dakota R/T. Stripped it down that day and was pleasantly surprised at it's condition, considering it supposedly had 100K plus miles on it. Virtually no ridge in the cylinders, and they still had crosshatch in them! Inside was very clean, no chunks or gunk inside. Heads were clean also. Had a couple broken studs, but I was able to extract them without any damage. Haven't got to the bottom end yet, but it spins free and and if it looks like the top, I'll be happy.
My goal for the motor is to do a "best bang for the buck" build I can while creating a reasonable amount of HP/TQ. I realize that everyone's definition of "reasonable" is different. Just hear me out...you can take turns kicking me in the nuts later.
Motor is going in a 66 Barracuda that has the original 273/904 in it. Want to transfer all the 273 parts (timing cover, pulleys, EX. MANIFOLDS, etc.) to the 5.9 if possible and keep the 904 behind the 5.9. Will try to be more specific below- not necessarily concerned with any hard numbers right now, just tell me if the info below makes any sense. I know you guys have been at this WAAAYY longer than I have, that's why I came here. All comments welcome.
Here we go- pretend I have a 20 yr. old's wallet, because I pissed away too much money on my Belvedere ll previously. (I'm 66 and still working. American dumbass).

1. Hone/re-ring motor with stock pistons. Would like to improve CR if possible. Deck/square up block, cleanup cut on heads, and .027 Cometic gasket? Maybe worth .040?
Pistons "in the hole" as follows- only checked the corners- #1 .045, #7 .044, #2 .044, #8 .051
2. Check/mic main and rod journals. If clean, new bearings and re-install.
3. New high volume oil pump. Double roller timing chain and gears.
4. Intake- Edelbrock Performer...or maybe even the Chinese version. Have one on the 5.2 in the garage, haven't run it yet. Looks well made and machined though.
5. Carb- something in the 650-750cfm range I would guess. Not partial to any particular brand.
6. Heads- stock, fresh valve job, stock 1.6 rockers, cleanup cut, home ported ala Charles Servidio videos. Fingers crossed.
7. Cam- see attached pic. I intend to go to Oregon Cams and get a regrind based on the Hughes cam numbers shown. If anyone can give me a yea/nay on this choice, or provide a better grind for this combo, I'm all ears. Required springs, too. 5500 rpm max should keep me out of flying parts territory, and most of my driving will be midrange anyway.
8. 3000 stall converter, manufacturer unknown at this point.
9. 3.55 SG in rear. I have a 3.91 in the Belvedere...and a 5 gal. gas can in the trunk. You know, just in case...
10. Exhaust- this is where I'm a little stumped. By that I mean efficiency versus $$. The headers I WANT are $1000+. The manifolds I HAVE and I know will fit, are FREE. Question is, what is the loss in efficiency/fitment between the Doug's (or any) headers and the iron manifolds? Can I modify the iron to improve flow? Dunno. Yes, planning on using a header flange on the drivers side if I use manifolds.

I'm sure I forgot about 100 things, but please feel free to remind me. Best I can do on a Sunday morning. Any and all responses will be considered to get me to the most efficient, economical build. Thank you.

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Your plan sounds pretty good so far save for the cam lift.
I think your cam duration could be a little higher for one.
I did exactly what you are planning, with some slight differences.
My Oregon regrind is 214/224 and .512 lift on 110and sound wise I can barely tell it has anything other than stock.
Ken at Oregon agreed that this grind would be for good torque, and it is but still gets good economy when driven that way.

Also I think your lift values may be a bit of a problem.
Hughes sells a retainer and locks set that give more clearance between the retainers and stem seals, but if I remember that kit allows up to .520-.530?

Also you might consider some aftermarket heads instead of the hone and rering, and possibly even the bearings and hi volume pump.

Hi volume is not necessary.
Rings and bearings are probably just fine.(mine were) and I have a 96 that had 98k on it.
Runs great and uses zero oil.

A roller timing set and aftermarket heads is the only thing on the motor I changed.
Well that and all the LA front accessories.
The bearings were barely touched so I left them.

I was lucky enough to find a set of New Zealand cast 318b heads with the LA intake bolt setup, but I think those are long gone.

Of course this is just my opinion and the way I did it.

OH, and if you decide to go with headers beware of the casting on the drivers side of the block that needs cut off.
It interferes with most headers.

And with 3.55 gears and that motor in a 66 Barracuda you could save quite a bit by not needing a 3k converter either.

A couple of things to consider:
The '66 transmission has the small support nose on the convertor, the Magnum has the large diameter crank pocket. You will need a spacer/adapter to run an early style convertor on the late motor. Many convertor suppliers may have issues supplying an early style convertor. No, a later '68 and up convertor will not fit an early 904- different input shaft splines. Consider finding a later ('68 and up) 904 to mate to your Magnum- no adapter bushing needed, virtually unlimited convertor choices, and all the hardware (shift linkage and levers, cooler lines, speedo drive) is a direct swap-over from your '66 904. If you use a '904 from the early/mid '70s you will have the added benefit of a valve body with part-throttle kickdown.
Linkage for the Magnum-
The early As used a kickdown linkage with a bellcrank that bolted to the rear of the driver's side head with 2 bolts; the Magnum only has one bolt in this location, so a means of stabilizing the bracket will be needed. A small added bracket or "finger" to locate it to a convenient section of the head is all that's needed.
The '66 (and earlier) 273 had a throttle cable clamp that bolted to a boss on the intake manifold, aftermarket Magnum intakes don't have this boss so you'll have to get creative with a later throttle bracket.
Throttle Bracket for Magnums
This method may also allow you to use a later kickdown linkage.
I'm not sure about your '98 Magnum, but somewhere around that time they switched to a one-piece balancer/pulley. If you have that, you'll need to switch it out for an earlier two-piece unit that will allow you to bolt on the early LA pulleys. You will need to oblong one hole in the early LA pulley for it to fit the balancer- a five minute project with a rat-tail file. You will also need to re-mark your balancer for the early LA passenger side timing marks.
Speaking of filing an oblong hole, you'll need to do that to one hole of the Magnum flexplate also to get the 904 convertor to fit. You need to run the Magnum flexplate due to it's unique balance.
As far as the exhaust manifolds, I assume you're referring to using the early A manifolds. Yes, they'll fit- sometimes with just a thick exhaust gasket on the driver's side, sometimes you'll need to go with the header flange. Just mock it up ahead of time and check your clearances. If you don't have power steering, you can get Magnum manifolds to work. Passenger side drops right in, and the drivers side will need a bit of shimming/grinding but has been made to work.
And regardless of which way you go with exhaust (manifolds/headers) remember that you'll need to modify the transmission crossmember to clear a dual exhaust.
Dual Exhaust Crossmember Modification on 64-66 A-Bodies?
The motor mount brackets from the early A will fit the Magnum, but will need a bit of work to do so.
(Photos posted by @65 Cuda 340 )

Modified passenger side bracket

And while we're talking about motor mounts, you might want to consider this (especially since correct early A biscuits are becoming increasingly difficult to find):
https://earlycuda.org/techdocs/JimBowenTheHolyGrailofMotorMounts.pdf
That's all I got for now.

If you have the flex plate that was on the 5.9, you will need to use that back because it has balance weights on it. Three bolt holes for the converter will line up and one will be about a quarter hole off. Rat it out to fit with a round file or a die grinder and you're good. You probably know, but 5.9 external balance is different than LA 360 external balance, even though both are 360's. Others have tried to use LA 360 balancers and weighted converters on 5.9 Magnums and then wondered why their motors sh sh sh shook! lol. As far as exhaust, there are some Magnum manifolds that breath better than the early A specific ones like you have. I think they actually came on Dakota R/T's like the truck your motor came from. you may have to fiddle with them on the drivers side by cutting the collar back on the steering column. They do get close to the firewall in pics that I have seen, so you may have to add insulation. Doug's D450's fit pretty well. Sounds like you have a good plan, plus @TrailBeast offered excellent advice based on hands on experience! Good luck with the build.

Here a mild cam upgrade

Your plan sounds solid, but the cam and converter don’t play well together. With that cam you could use a stock converter. And if you use a 3000 stall you could use a bunch more cam. For your plan, I’d pick small cam and stockish converter. Regarding exhaust, I wouldn’t even do the swap if I had to use stock 273 manifolds on a 5.9, just leave the 273 in there. If you do the 5.9 find a header that fits it’s that simple. Doug’s and TTIs are your choices. Have fun

BTW- you do know that the 273 oil pan doesn't fit the Magnum- you need to use a LA360 passenger car pan/pickup tube/dipstick, and either an LA360 pan gasket set, a one piece Magnum pan gasket with a bunch of sealer at the front seal corners, or the one piece gasket modified with an LA front seal and RTV at the joint.

Professor Fate said:

BTW- you do know that the 273 oil pan doesn't fit the Magnum- you need to use a LA360 passenger car pan/pickup tube/dipstick, and either an LA360 pan gasket set, a one piece Magnum pan gasket with a bunch of sealer at the front seal corners, or the one piece gasket modified with an LA front seal and RTV at the joint.

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That was one of the questions I forgot to ask. Thanks!

TT5.9mag said:

Your plan sounds solid, but the cam and converter don’t play well together. With that cam you could use a stock converter. And if you use a 3000 stall you could use a bunch more cam. For your plan, I’d pick small cam and stockish converter. Regarding exhaust, I wouldn’t even do the swap if I had to use stock 273 manifolds on a 5.9, just leave the 273 in there. If you do the 5.9 find a header that fits it’s that simple. Doug’s and TTIs are your choices. Have fun

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I might have chosen to leave the 273 in there, but the drivers side is currently doing double duty as a mosquito fogger. Had to come out anyway...

MechNerd said:

I might have chosen to leave the 273 in there, but the drivers side is currently doing double duty as a mosquito fogger. Had to come out anyway...

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The 5.9 is a much better option. I was just saying I wouldn’t kill it with 273 manifolds.

On a mild 5.9l I wouldn’t overly worry about the manifolds, headers definitely better, not huge hp difference between manifolds.

So...any methods for improving compression/quench? Necessary, or not so important? Do Magnums really have 9.1 factory compression? Given the low octane gas we have, it almost seems like you could leave it alone...

MechNerd said:

So...any methods for improving compression/quench? Necessary, or not so important? Do Magnums really have 9.1 factory compression? Given the low octane gas we have, it almost seems like you could leave it alone...

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You expressed an interest in keeping the cost down, so all of my suggestions are based on that.
Yes 9.1
I run 87 without any problems.
93 gives about the amount of better gas mileage that it costs, so it’s kind of a wash.

KB 107 will bump the compression up, but then you have the expense of balancing the bottom end.

273 said:

On a mild 5.9l I wouldn’t overly worry about the manifolds, headers definitely better, not huge hp difference between manifolds.

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Gotta say I disagree. If you leave the stock cam in it I’d agree with you, but any increase in performance be it from a cam or compression or other is negated by putting manifolds on it. Especially so with the worst small block manifolds there are, the 273s.

If you don't have power steering, the Magnum manifolds (or a set from a different truck) might be a nice, low restriction option.

General consensus/opinion is .520 is the upper limit of valve lift on Magnum heads before cutting the guides is necessary.

You'll want to check that pretty carefully.

sireland67 said:

KB 107 will bump the compression up, but then you have the expense of balancing the bottom end.

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Agreed, I think for the OP's goals and since the short block is already in good shape it's not worth the expense of swapping pistons and rebalancing everything. 9:1 isn't excellent but it's better than the 8:1 (or less) of stock LA 360's and still allows you to run regular gas which saves quite a bit on fuel these days.

Here a manifold header shootout on a stock 4bbl magnum, there's another out there somewhere that has magnums and there basically on par with 340 ones, they found the best combination to be one 340 and one magnum manifold, I forget which ones but was only better by a hp or two.

As for 273 manifolds who knows probably slightly less than 318's, only dyno test I've seen was a set of tti headers gained 10.8 hp on a stock 273 Commando.


Legend318:Stock '69 A-Body exhaust manifolds with 24-inch extensions360:Stock '77 360 iron log-style exhaust manifolds with 24-inch extensions340:Stock '70 340hp exhaust manifolds with 24-inch extensionsSHT:Hedman 151/48-inch-tube shorty headers with 24-inch extensions 1 58: Hooker Competition 1 58-inch ceramic-coated header tti: Tube Technologies Inc. 1 58x1 34-inch chrome step header 1 34: Hooker Super Competition 1 34-inch header; bare, uncoated

https://www.motortrend.com/articles/mopp-0307-installing-exhaust-headers-into-300hp-crate-engine/

273 said:

Here a manifold header shootout on a stock 4bbl magnum, there's another out there somewhere that has magnums and there basically on par with 340 ones, they found the best combination to be one 340 and one magnum manifold, I forget which ones but was only better by a hp or two.

As for 273 manifolds who knows probably slightly less than 318's, only dyno test I've seen was a set of tti headers gained 10.8 hp on a stock 273 Commando.

Horsepower
RPM	318	360	340	SHT	1 58	tti	1 34
2500	186	185	187	189	187	189	187
3000	223	223	225	226	228	228	226
3500	269	271	272	276	280	281	279
4000	299	301	306	307	314	318	312
4500	311	313	315	321	319	326	321
4600	211	314	315	320	317	327	319
5000	303	304	308	315	312	316	311
5400	281	291	289	295	282	296	289

Legend318:Stock '69 A-Body exhaust manifolds with 24-inch extensions360:Stock '77 360 iron log-style exhaust manifolds with 24-inch extensions340:Stock '70 340hp exhaust manifolds with 24-inch extensionsSHT:Hedman 151/48-inch-tube shorty headers with 24-inch extensions 1 58: Hooker Competition 1 58-inch ceramic-coated header tti: Tube Technologies Inc. 1 58x1 34-inch chrome step header 1 34: Hooker Super Competition 1 34-inch header; bare, uncoated

https://www.motortrend.com/articles/mopp-0307-installing-exhaust-headers-into-300hp-crate-engine/

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That test was pointless. The stock cam doesn't even have lobes (exaggeration, but close) so the exhaust isn't the limiting factor and this didn't show anything. They should have done the test with the 380 HP crate motor not the 300 HP crate motor. Completely worthless test.

If it was me, I would look for a big outlet early PS Magnum manifold and a later 340/360 DS manifold. Generally the '73/74 freeflows are cheaper ($300?) and if you are lucky you can find the magnum manifold for $12 at a Pull and Save. Then compare those costs to the cost of headers. If the manifolds are significantly less, run them and accept whatever HP loss they have.

Note, I am assuming the later freeflow manifold fits the DS of an early A. Maybe that is wrong?

Wouldn't say the test worthless, could be better, 380hp crate is a little excessive not many gonna run manifolds on one and from the sounds of it the dude is building a fairly mild 5.9l maybe 50 hp higher than this engine so about 17% more airflow. The overall numbers of gain and losses probably go up slightly maybe around 17%.

Some info is better than no info, you generally can extrapolate, engine performance is somewhat predictable.

DionR said:

Note, I am assuming the later freeflow manifold fits the DS of an early A. Maybe that is wrong?

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If it's manual steering, they can be finagled in there and made to work. Power steering is a no-go. Hits the factory box. Don't know if it will clear a Borgeson box, never had one.

As far as the cam goes, I think I'm going to go with an Oregon regrind. Here are the cams that Ken proposed- any benefit to one over another? Was looking for the same lope my buddy's 69 340 Dart used to have, and it wound up fast. Sadly, he's no longer with us, and I can't ask him if he upgraded or not. He did mention a Purple cam though. Not sure of specs.

#1458

206/212 @ .050”, 258/264 adv, .512”/.520” lift(1.6:1 rocker)110 lobe sep

#1429

210/214 @ .050”, 260/264 sdv, .506”/.506” lift, 110 sep

#2204

213/220 @ .050”, 265/275 adv, .480”/.498” lift, 110 sep

MechNerd said:

As far as the cam goes, I think I'm going to go with an Oregon regrind. Here are the cams that Ken proposed- any benefit to one over another? Was looking for the same lope my buddy's 69 340 Dart used to have, and it wound up fast. Sadly, he's no longer with us, and I can't ask him if he upgraded or not. He did mention a Purple cam though. Not sure of specs.

#1458

206/212 @ .050”, 258/264 adv, .512”/.520” lift(1.6:1 rocker)110 lobe sep

#1429

210/214 @ .050”, 260/264 sdv, .506”/.506” lift, 110 sep

#2204

213/220 @ .050”, 265/275 adv, .480”/.498” lift, 110 sep

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Highly doubt there's gonna be a huge difference in power especially in the lower rpm bands, each cam gonna have probably a slightly higher peak hp over the one below it.

The biggest one is similar to Richards in that video except on a 110 instead of 114, he makes 350 hp at 5000 rpm and think he gains another 10-15 hp in another video with an air gap.

Magnumswap.com

WIth stock manifolds you could lose as much as 20 HP over headers, depending on your engine combo

Even 340 and Dakota R/T manifolds
Are only a few HP more than 273-318

I'm happy with this cam (4 speed 3.23's). I cleaned the lifters, installed a good timing chain, and swapped out the cam bearings.