Hi all,

I have a 92 Dakota LB which is soon going to be in the process of an engine swap from the 3.9 to a 318, and I have a couple of questions regarding some mods. For starters, this is going to be primarily a work truck and my ride to and from school which is about 250 miles highway, so I would like efficiency over stupid amounts of power. I'm looking to do a mild cam, roller rockers if possible, all while maintaining the factory computer/MPI. I know carbs are easier but with it being a daily I don't want to be mucking around with a carb all the time and lose the "efficiency". I'm posting here as I'm new to internal engine stuff, primarily all the numbers that go into the grinds of a camshaft as I have no idea what I'm looking for.

As a rundown, here are my goals:

• Mild cam
• Long tube headers if possible, but just headers in general
• True duals with an X pipe, 2.5" out one side (I know it's weird running duals out one side but I personally don't like the look of dual exits on opposite sides)
• Intake manifold
• Roller rockers if possible
• Hopefully more than 15mpg highway (70mph in OD)
• Engine rebuild kit (rings, pistons, bearings, etc.)
• Potentially a DIY head job, depends if I can spare the funds for new heads or not
• Rebuild transmission preferably (not sure where exactly to look)

Also should mention, this truck is currently a 5 speed 4x4, and I want to keep it that way. I know I can't use the current 5 speed at least for very long behind a 318, so from other forums I've read, an NV3500 off of a Dakota is a good place, and the T-case I can just rebuild and reuse. Feel free to give me some advice or input, as like I said, I'm new to this and am looking for some knowledge on what I need to fit my goals. I currently get anywhere from 16-19mpg on the highway, I know I'm never going to get that with a 318 unless I'm going downhill with the engine off, but I'd like to hopefully stay above the 15 mark.

 

Thinking 15 is gonna be about it. Particularly if you mix in a few highway miles.

 

Yeah I figured lol, I know it's a lot to ask for a good mpg cammed 318, but I'm hoping with the taller gear ratio I have in the axles it will somewhat help me. Although literally my main purpose for this truck out of college is to be the junkyard part hauler, so MPG isn't going to matter to me at all once I'm not driving 500 miles frequently.

 

Be careful what cam you choose, a good percentage of them won't be real friendly with the PCM, and yours isn't flash programmable..... Mopar Performance PCM would likely help, but, those are getting hard to find.

 

Your 5speed is an AX15 and it will hold up just fine behind a 318, I like it better than the NV3500. For all of those mods you plan on doing a tune would really help take full advantage of them, but since yours is a 93 you can't use a programmer, I think there may be some aftermarket ECMs that will work though.

 

Well here is my opinions......
1. I would save your money and keep the stock cam that comes in the 5.2 magnum engine. As already said, you cant tune the pre 96 computer.
2. Headers, I dont believe long tubes are available for a 4wd dakota...... and if you look at the Y pipe, I think you will see why. Just no room for them. Then with shortys, which are available, all I have seen are designed to use the stock Y pipe.
JMO, but for the HP gains on a stock or near stock motor, I dont think they would be worth it. especially on a daily driver.
3. Intake manifold. Again, without a cam change, (which will require tuning) I would save my money....... In fact, it may hurt performance on a stock setup.
4. Roller rockers, would help, but I would go with a 1.7 ratio, and I believe you may need new springs to handle the additional lift. Not sure though. And if you do need springs, put a set of new seals on the valves while you have it apart.
5. Gas mileage may not be any worse then the 3.9.....
6. If you can do the rebuild yourself, its a good idea. These engines are getting old...... When I did mine, I basically did a backyard rebuild. Cleaned block as best as I could, got a reman. crank, cleaned pistons, honed block, put cam bearings in and put the short block back together.
7. Heads are a big debate. Almost all magnum heads are cracked between the seats. Some say, it really does not hurt anything. My machinist suggested I scrap the set I had and go new. I ordered a set and they were around $500.00 a few years back....... IMO for a stock or near stock build, new is the way to go. Machine work is expensive and adds up fast. I would not want to spend the money on just a basic valve job, ie: grind valves, clean heads, and check for guide wear, flatness etc. IMO its better to put the money towards new heads.
7. Transmission....... you have the AX15...... are you having any problems with it? If not, I would change the oil, and run it. May last a long time. If you are having problems, then I would upgrade to the NV3500. I have heard the argument that the AX15 is stronger then the NV3500....... Personally, I dont believe it for one second. FWIW. Dodge used the AX15 behind the V6 engines in the dakota's from 92-99. They always used the NV3500 with the V8 and started using it with the V6 after 1999 in all the 2nd gen dakota's . I trust Chrysler engineers on what is the strongest.

Last, I want to make one suggestion. Instead of swapping in a 5.2, consider a 5.9.
1. Used engines are close to the same in price.
2. There is a considerable power difference especially in the lower rpm which is where most trucks operates.
3. Heyyou could probably answer this, but I think, you can use a ecm from a ram in the dakota. So, basically find a 93-95 computer for a 5.9.... and the rest is the same as the 5.2
4. You will need the 5.9 flywheel for the correct balance.

I have a 87 that I put a 2000 ram 5.9 in, along with a NV3500 transmission. But I used a carb and an HEI ignition.
If you have any questions I may be able to help with, please ask, here, or pm.......

Good luck and keep us informed on what you do.

 

Yep, PCM out of a full size truck should work just fine, just make sure it is a 5.9 with a manual. Otherwise, it will be constantly whining about the trans.

Do they make an off-road Y-pipe for the dak? Either that, or find a shop that does custom work, see how much they would charge to do ya up a 3" single exhaust. (I used to do that kind of thing for a living, it was fun. Today though, shops that will do it are few, and far between.)

So far as I know, you can do the harland sharp 1.7 roller rockers without changing springs. It's worth about 10hp/tq. (another member with a full size truck dynoed his truck before and after making that one change, so, the numbers are pretty solid.) Or, you could talk to someone like hughes performance, tell 'em what ya got, and they can likely recommend a cam that will work with the stock computer. Probably cost more than the rockers would, and may not get you as much of a bump in power..... Worth chattin' with 'em at any rate.

Clearwater and Odessa cylinder head (same company, but, different names for some strange reason) make NEW casting heads with thicker decks, last I checked, you could get a pair, fully assembled, for around 600, but, yeah, that's been a couple years for me as well. Likely closer to 1K by now....

Going by another thread that I read, the Fastman 52mm throttle body is worth a nice bump in power as well..... There are other places that just punch out the stock throttle body, and it likely works just as well. Those are for the MPFI engines though..... I *think* that's what you are looking for anyway, right??

 

I couldnt find any offroad pipe..... But the factory pipe does not have a converter in it. That is after the y pipe. I think the one on the rams may be a larger dia. as well as mandrel bent.....

Not meaning to get off topic, but especially to heyyou.... what is your opinion on shorty headers, and specifically the collector. My concern is the collector is designed to bolt to the stock y pipe, which is 2in or a little less I think.
Really wonder how much even dual exhaust with 2.5 pipes would help with the bottle neck of the collector or for that matter the stock exhaust manifolds.
Would like to hear your opinion.
And to the OP Im sorry if I am getting off topic.

 

Yeah, the "ball" on the end of the headers that seals to y-pipe IS a restriction. However, the y-pipe is large enough, that you can waller the ball out to 2.5"..... If you can find a shop that does custom exhaust..... (good luck...) they could make up a 2.5" Y-pipe without too much trouble, with a 3" outlet, then 3" all the way out the back. Cat, and muffler of your choice. That would flow much better than stock, and the larger diameter pipe would give it a deeper tone.....

On my Firebird Formula 350 (I know a chevy engine....) I went with a 3" Edelbrock cat back system, and while installing that, the cat seems to have 'fallen off'..... and got replaced with a test pipe. The Y-pipe exit was already 3", so, it flowed REALLY well, and sounded so good, I never turned the radio on again. I wanted to hear my exhaust. (and I own the car for another 6-7 years after that.....)

 

Yes you can use 1.7 roller rockers with stock springs, that's what I have in my 5.9.
The AX15 is a far better transmission than the NV3500, the Jeep guys figured that out long ago. New Venture has been out of business over a decade, and the majority of parts you find to rebuild the NV3500 are made overseas and subpar. The AX15 on the other had is made by Aisin a Japanese company that is still alive and well, It is very similar and shares many of the same components as the R154 transmission put in the old Toyota Supras, there is a ton of good parts still available for them and they can be built to handle 500hp or more, you can also still buy brand new units from Aisin. People have ran the AX15s on small block and LS swapped Jeeps for years without any issues. I wouldn't trust Chrysler engineers on anything related to transmissions they didn't design the NV3500 or the AX15 but they did design the crappy auto transmissions all the trucks used.