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  #1  
Old 01-28-2003, 11:36 PM
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92whitedak 92whitedak is offline
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Default 3.9L (238) Cylinder Heads

Does anyone know or has anyone ever purchased aftermarket cylinder heads for the 3.9L magnum post-92 engines? What about cams? Persay, ANYTHING aftermarket like new rockers, pushrods, valves, valve covers. I know Hughes sells Throttle Bodies for the 3.9 magnum that supposedly flow almost 60% more cfm at .5" merc and was wondering if there was anything else I could plant in this bad boy to take advantage. Also, they claim these throttle bodies are for 93 and up magnums. But the 3.9L magnum came out in 92. What gives? I'm just dying to turn my little 3.9 magnum into a street eater. I was debating whether or not this belonged in the performance forum but I believe it does, if other people can talk about their slant sixes with pride, I sure can talk about my v6


-Deacon
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  #2  
Old 01-29-2003, 09:56 AM
CudaMike CudaMike is offline
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Cool

I don't know a whole lot about the Magnum engines, but there is no reason why rocker arms, pushrods, valves, and everything else that is not affected by having 2 cylinders missing, shouldn't work just fine. I know Mopar Performance has a small selection of parts. I THINK I have seen cams, chrome valve covers (good for 5-10 HP ;-) , intake manifold, as well as the interchangeable parts with the Magnum V-8's. If you don't have a MP catalog, get one.
Hughes Engines and others I'm sure could supply cams.
Since the 318 and 360 Magnums have a lot of potential, I don't see why the 3.9 wouldn't respond very nicely, of course taking the cubes into account.
Good luck! Hopefully some other folks can chime in too.
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Old 01-29-2003, 10:10 AM
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Thanks for the reply. Understandably so, the 3.9 is a 318 minus two cylinders. I know i've heard it said just as much as everyone else but was unsure of how "interchangable" the parts from each engine were (i.e pushrods, rockers, springs) Another question that has come to light would be are my pistons the same as a 318? If so, couldn't I just buy 6 rather than 8. Are my valves the same diameter and stem as a 318's valve? If so, i could just buy 12 rather than 16. I guess I'll just have to keep pushing forward and searching. Keep the replies coming though.

-Deacon
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Old 01-29-2003, 10:20 AM
CudaMike CudaMike is offline
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Yeah the pistons and rods should definitely be the same as the 318 Magnum, no problem. Also, the valves are the same as the 318 and 360 Mag. Keep up the research, as it should be an easy project to do.
I have often thought the 3.9 would go good, say, in an early Barracuda (64-66) or early Valiant where you didn't want or need a monster engine, but would still be quite peppy. The two cylinders missing off of the front would help with weight distribution, which would contribute to better handling.
If you don't have the MP catalog, get one, it will get you started.
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Old 01-29-2003, 10:27 AM
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Mike, thanks for the inspiration. I've never heard anyone so enthusized by the 3.9 except for me To start, I think the engines are amazingly high output for their small displacement, let alone in a heavy pickup. Window Sticker advertised 185 rwhp stock. I think I should be able to do much better than that. Quick question again though. What sets the magnum apart from a regular engine. Is it the block? or the heads? or anything else? Whats the difference and why did they do it?

-Deacon
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Old 01-29-2003, 10:31 AM
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Update from Hughes:

Quote:
Fox,
The part of the web site where it says the modified 3.9's only
fit '96 and up is a mistake. They are all the same back to '92.
We will get that fixed. We can grind any of our V-8 camshafts to
work in you 3.9 engine. We can also port your heads. It would
cost 80% of the price of porting the V-8 heads.
Well. That settles my heart a little. Its no 850 cfm carb but for an engine to receive 50-60% more air than it was originally getting can't be that bad. If a v8 cam has specific ends and beginings (sprockets and gear drive), how can a v8 cam be "ground" to fit a much shorter v6? If they say they can do it, I guess they can. Off to order that Mopar Performance cat. (My first one yippeee).

-Deacon
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Old 01-29-2003, 10:55 AM
CudaMike CudaMike is offline
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Biggrin

It looks like progress is already being made. 3.9 cams are obviously shorter also, so I think Hughes was just saying they could put their V-8 Magnum cam lobe profiles on the short stick.
The MP small block engines book has a section on Magnum engines. However, MP has an entire book on The Magnums.
The Magnums do have some significant changes from the older small blocks. The shortblock is almost the same the same as previous small blocks. The heads are different, and the intake uses vertical mounting bolts, and more of them. The heads are oiled through the pushrods, rather than passages through the block and head to the rocker shafts. And, speaking of rocker shafts, there are none because rocker arm studs are used instead on Magnums. Anyway, the books will tell you more. These changes seem to be an AMC influence.
If I have time tonight I'll see what I can find in the 2002 MP catalog and pass it along to you. The 2003 catalog should be available in March.
While I am gathering parts to build a 408 stroker for my 68 Cuda, I still like to see people persue something a little different. I orginally was going to do a slant six project, but eventually decided on a 360. But, since a 408 can be built for only a little more than the 360, why not? Anyway, all I have ever owned is Mopars, all of them are cool!
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Old 01-29-2003, 02:49 PM
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Mike. Interestingly enough, I'm also putting together a 408 stroker. If you look on the first page in the performance post section, there is the thread:

http://www.moparchat.com/forums/show...7&goto=newpost

I there you'll find my buildup plans so far for the 408.

I, like you, am always interested in things being done a little less conventionally and like doing things that aren't always the easiest of paths (one of the many reason I'm a mopar-ite). I'd be very very "delighted" if you could somehow pass along the mopar performance book. Have you got the one specifically for the magnums? They use studs? There was only one time that I had the valve covers off and it was pitch black outside Anyway. What you're saying is I can use rockers and studs from a 318 magnum application? Where can I order/get this Mopar catalog from? Sorry if I'm all over the board right now. I just did my tax returns and got royally effed. You've got to love the government... Please reply and lighten my day...

-Deacon
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Old 01-29-2003, 03:08 PM
CudaMike CudaMike is offline
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Unfortunately I don't have the Magnum book, but I want to get one later on for reference.
Any of the MP vendors (Mancini, Hensley, Barton, Moparts Racing, Fred Smith, etc.) should have the catalog, as well as the parts dept. of a local Dodge dealer.
Yeah, the studs and rockers from a 318 Magnum will work on your engine. The studs are a screw-in type, instead of press in type. Larger O.D. studs are available along with matching rockers. Oh yeah, the rocker ratio is 1.6 for the Mag versus 1.5 for the older small block.
Be sure to thoroughly go through the Hughes Engines website for their various parts for Magnums.
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Old 01-30-2003, 09:06 AM
CudaMike CudaMike is offline
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Unhappy

92, I had a busy evening so I didn't get to post the items in the MP catalog. I should have something posted by 7 pm this evening, however.
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Old 01-30-2003, 12:27 PM
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Thanks alot mike. I'm going to be out and about most of the day anyway. I check my mail just as much as I watch the boards so feel free to email me if you'd like. Perhaps we could also talk about your/our 408 projects. Thanks again.

-Deacon
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Old 01-30-2003, 08:15 PM
CudaMike CudaMike is offline
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:shock:

92, I can't seem to get your e-mail address from this board. So, please e-mail me at mdyonce@att.net and I'll give what info I can find.
Later,
CM
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  #13  
Old 02-11-2003, 11:52 AM
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Interesting, I am about to do the same thing. My daily driver is a 92 Reg cab 2wd v6 5speed Dakota. Last night I set my new v6 on the stand, and plan on getting it apart friday night. The engine I will be rebuilding is a '98. I'm just starting to look into some perf upgrades, and I'm not sure to what extent I will go?? Does anyone know if there is a difference between the '92 Mag and the '98? I have to get the heads redone anyways, and was thinking of a little porting? V8 t.b. and possibly some intake work? That one I'm not sure on. Also a camshaft. I have to get the engine apart and then decide if I am going to bore the thing or not.

As I said this is my daily driver, not a drag truck (I just want it to be a little more fun to drive)

Any other ideas, or help would be greatly appreciated.
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Old 02-11-2003, 12:39 PM
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For my 3.9 (239) magnum also a '92 I was going to just order the parts for the magnum 318 and put them in. Keeping the spare parts for extra's incase something breaks. From what I understand everything is the same between the 3.9 and 5.2 except the 3.9 is missing two cylinders.

It's a good performing engine in a light car or truck. Back in the day (about 5 years ago) when my dakota had way less miles I got the little V6 to catch 2nd gear rubber with the stock A500. I've thought about building a 3.9 but it's just not cost effective. For me it's cheaper just to build a 360 (5.9). Which is going to be my summer project.
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