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91dak239
Dodge Dakota
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5/16/2008
22:04:09

Subject: Larry? 3.9L to 5.2L interchangable parts
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I am getting ready to get my 3.9L Magnum rebuilt and want it built it up some. Though obviously 3.9L specific performance parts are pretty limited, but they should interchange with 5.2L Magnum parts. Here are the things I think will swap no problems.

-Pistons
-Valves
-Valve Springs
-Rocker Arms
-Oil Pump
-Water Pump
-Timing Chain?

Can you confirm for me what all is interchangeable between the engines?



dakota49
Dodge Dakota
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5/17/2008
16:25:23

RE: Larry? 3.9L to 5.2L interchangable parts
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I think you are correct on the items you have listed. When I rebuilt my 3.9 I wound up buying a set of pistons for a 5.2/318 because it was cheaper than ordering a set for the 3.9. I then sold the other 2 pistons to the machine shop that did the machine work. I also ordered a set of ARP rod bolts for a 340, because ARP doesn't have a rod bolt for the 3.9, even though they are the same size, again I sold back to the machine shop the extras. I had a lot of things done to my engine, mill the heads, block, line hone the main bearing bores, resize the rods, ect.
Good Luck
Dakota49
1988 3.9 4X4 5speed



91dak239
Dodge Dakota
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5/17/2008
16:49:19

RE: Larry? 3.9L to 5.2L interchangable parts
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You said you had the heads milled, how much did they take off and what is your Compression ratio sitting at? also are you running 1.7RR if so any clearance probs with having the head milled?



J and J Auto
GenII
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5/17/2008
22:39:53

RE: Larry? 3.9L to 5.2L interchangable parts
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3.9 to 5.2

Pistons - same

If you want more compression hughes engines has a
nice selection 10 to 1 for street 10.5 and you
will be running premium fuel stock 9.5 to 1

Valves - same

There is nothing wrong with the stock valves
unless for some reason you want to replace them
3 or 5 angle valve job is fine

Springs - same

The springs stock springs will only handle upto
a .500 lift than bind so unless your going with
a high lift cam stock is fine

Oil pump - same

The melling HV pump also sold by mopar performance
works well

Water pump same

Rocker arms same I recomend the harland sharp a
very stable system over the crowers the alignment
system is the best in the business 1.6 or 1.7

Timing chain, I recomend the cloyes true roller
and used with the tensioner # CLO-9-1103 this
is a .250 roller seamless roller chain this chain
alone will add 10 hp to the motor

stay away from the mopar performance roller chain
I have seen a lot of those off and as much as 6
degrees, not good run straight up 0

Rods

stock are fine but if you want to add some beef
find a machine shop that will mod your crank to
except the 318's wider journal and use them you
can get any 318 rod to use than the V6 rod
journaks are thinner oh ya use the 318 rod bearing
with them

All depends what and how far you want to take ithe stock 3.9 is a very strong motor as is
t


Larry
J&J Auto

91dak239
Dodge Dakota
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5/18/2008
00:02:59

RE: Larry? 3.9L to 5.2L interchangable parts
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Awesome! Thats what I was looking for, Right now I have the HER 0814AL-V6 CAM, 1110 valve springs(what hughes suggested) w/ retainers and new lifters. And I just ordered a double roller timing chain w/ tensioner, melling high vol. oil pump


I was looking to have the motor bored out a little (not sure how much is safe thou) and take the CR to 10.5:1, I am concerned a bit about the valve to piston clearance with the 1.7 roller rockers, will this be fine? And would i see some gains opening up the valves to slightly larger ones? I am asking or this info to get to the machine shop that I'm gonna have work on the motor, since no one around here is familiar with the 3.9L... The shop said also that i would need to have adjustable valve train for them to adjust for decking the heads for the compression ratio, now forgive my noobishness but is this referring to the adjustable rockers?

Thanks you so much!



Fed
GenII
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5/18/2008
11:46:59

RE: Larry? 3.9L to 5.2L interchangable parts
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i have that cam 91dak239... it is very nice! and i believe you are right about the adjustable rockers.


1996 Dakota CC 3.9 manual
(rebuilt motor at 9.5:1 compression, Hughes 208 V6 cam, milled heads, 1.6 Hughes RRs, ported intake manifold, Tom Fox PCM flash, FMS 24# injectors, K&N FIPK, F&B 48mm tb, MSD coil & wires, underdrive pulleys, JBA ceramic headers, custom y-pipe to 2.5

91dak239
Dodge Dakota
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5/18/2008
12:18:23

RE: Larry? 3.9L to 5.2L interchangable parts
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I sure hope it is nice :D
I'm jumping up from an LA 3.9L to a more or less built up Mag 3.9L. Mostly concerned about the valve to piston clearance with the RR, thankfully Harland Sharp does have a set of adjustable RR. They are about the last piece of my parts puzzle. Also I'm gonna need new injectors for this baby when she's done anyone got PN for the FMS injectors everyones always using? and about haw many lbs/hr should I be looking for?



daddio
Dodge Dakota
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5/18/2008
12:39:05

RE: Larry? 3.9L to 5.2L interchangable parts
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they are probably referring to adjustab;le pushrods.



dakota49
Dodge Dakota
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5/18/2008
18:09:20

RE: Larry? 3.9L to 5.2L interchangable parts
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I don't know what my compression ratio is, but it now has 180 pounds of cranking compression.
As for how much the heads were milled, one needed .015 and the other could have gotten by with 12, but the shop made them both the same so it help to keep the compression ratio the same for both banks.Mine is the old style, mine uses rocker arms. They are 1.5 to 1. I did however polish the exhaust ports, cleaned out the exh. manifolds (ground the casting flash, and polished the rest of the exh. on the inside) I also ground the casting flash out of the intake ports of the heads. It was a lot of hand work, but I think it did help a lot. I used a drill, and several stones, and an extention so I could do all of the exh. manifolds. I also replaced all the lifters, cam, valve springs, ect. I wish I had bought a slightly higher performance cam, but I got such a good deal on the total engine package I went with the stock cam replacement.
I think Larry has given you some good tips, I also used the cloyes timing set.
Good Luck
Dakota49
1988 3.9 4X4 5speed



91dak239
Dodge Dakota
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5/19/2008
20:43:39

RE: Larry? 3.9L to 5.2L interchangable parts
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well everything is somewhat under way, though i need to order the roller rockers, does anyone have an idea of if it will be safe to use the 1.7:1 Harland Sharps with a decked head/block with Kieth Black Flat tops? (It'll probably run 10:1 to 10.5:1 Compression) Thats really my last important question as those rockers are the last bit I need to order, though the shop did suggest some hardened push rods but i don't think those are terrible expensive...

Thanks for your help guys I really appreciate it, With that last bit of info I need, I'm sure give it a month or two and I'll be rolling with one hot 3.9L!!!



not so good
Dodge Dakota
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5/19/2008
22:44:15

RE: Larry? 3.9L to 5.2L interchangable parts
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1.7 stock cam
if you are going to run a larger cam then go with 1.6 Roller Rockers



91dak239
Dodge Dakota
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5/19/2008
23:54:05

RE: Larry? 3.9L to 5.2L interchangable parts
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Nope most certainly not a stock cam :D

Hughes: HER0814AL-V6
Lobe separation:114
Installed centerline:111
Lobe lift: I - .320 E - .325
Valve lift: I - .480 E - .488
Advertised duration: I - 208 E - 214



J and J Auto
GenII
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6/03/2008
05:37:16

RE: Larry? 3.9L to 5.2L interchangable parts
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Stay with the 1.6 ratio with the cam your using

Hughes engines has the adjustible roller rockers
with a decient price

the crower rev kit is over $500

Use guide plates and hardened push rods and you
will be fine

The reason is the regrind cams have the base
circle altered you colud use harlands but you
would need slightly longer push rods you need
a .030 lifter preload for the roller rockers

Larry
J&J Auto

Zack
Dodge Dakota
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3/18/2020
18:55:52

3.9L to 5.2L interchangable parts
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I have a very tired 2001 dodge 3.9 l
magnum. I have looked for 2 years on good
info on getting it built up some without
boring it out. I just cant afford that. I
have read the posts and now I have more
conflicting information. I am looking for
bolt on and go mods for it and have came
up empty.



Zack
Dodge Dakota
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3/18/2020
19:00:27

3.9L to 5.2L interchangable parts
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I have heard to go to my local scrap yard
and pull tb, fuel rail, heads. Or just
drop in a v8. Is there parts out there
thats bolt on and go that could awaken it
or am I just in a losing battle with my
3.9 and should just let her die? Which I
dont want to do.



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