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91dak318
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2/20/2005
17:36:40

Subject: pre mag mods
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i have a 91 dakota 2wd with a 318 and an automatic tranny. i was wondering what mods i could do to increase my HP and torque. i was wondering if magnum manifolds or header would fit. also i have heard that i could use premag 360 throttle body and computer for some hp gains. is this true? what options do i have for cams that will work with my computer? any help will be greatly appreciated.



gen1dak
Dodge Dakota
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2/21/2005
16:57:03

RE: pre mag mods
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Magnum exhausts or headers will help, but this would require mods to run the A.I.R. pump if emissions testing is an issue. If you use Magnum exhausts and the matching crossover pipe, you can just route the A.I.R. pump line to dump into the crossover like the early 360 Magnums did.
Mopar Performance marketed the 360 TBI/PCM/and a low restriction muffler as an "off-road" mod for increasing 318 power. The PCM had a more aggressive ignition curve, and the combo alone was said to give 20hp/30lbs torque. Any stock 360 TBI and pcm would give an improvement without the premium fuel requirement of the aftermarket kit, as well as more headroom to cover hotter cams and any other mods.
Any reputable cam maker can suggest a cam that will work with your setup. CompCams lists the 254HR-12 as an OEM-replacement cam for the 318....meaning, it'll work with the stock electronics, BUT with the greater lift of the cam, you must use the 901-16 valve springs (these have been around for 20 years, very good springs). The 254 has lift numbers in the .450" range, while the stocker is just under .400". It really helps the upper rpm power. They also list the 262HR-12 which may require computer mods (or a 360 TBI/PCM), as well as the 264HR-12, which is a little hotter, and definitely needs computer mods.
These engines respond to all the usual mods. Cleaning up the heads with a mild port job, aftermarket (better flowing) valves, 3-angle valve job, etc. If you can find a 360 TBI donor, get the intake and heads too. These will flow more air than mildly ported 318 heads, and with a decent cam, it'll really wake up the top half of your rpm range.
A low-restriction air filter will help too. Also, these could still be tinkered with regarding the initial ignition timing. Bump it up a couple degrees. This will help perk up that soggy low rpm power a bit.
Keep in mind that the 318 has been built featured several times in the past two years making between 350 and 400hp at 6,000rpm. Granted, these were carbureted engines with headers and no emissions equipment, but the potential is great.
Anything like an MSD ignition will help as well.



Zac
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2/21/2005
20:56:12

RE: pre mag mods
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thank you for that info. that what i was looking for. for the 360 TBI/PCM mod what are the years i would be looking for and does the PCM just plug in to where the stock one is? where is the PCM on a fullsize dodge? and what all do i need to get with the throttle body? do i have to use the 318 injectors if i use the 360 PCM?



gen1dak
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2/23/2005
21:54:38

RE: pre mag mods
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First, I don't suggest mixing injectors. Use 360 injectors in 360 TBI, with 360 PCM. It'll still run if you mix with 318 parts, but why do that? It'll only limit overall performance. They're matched for a reason and do not adapt like more recent automotive computers. The SBEC or SMEC (the name changed around 1990, but they do the same thing, and look the same) controller will be on the left inner fender (driver side). The connectors are the same. The setups are the same for the 318/360 TBI, so you should have all you need in yours. Never hurts to have spares, but there's not much connected to the TBI that's unique...fuel lines, vacuum lines, kickdown linkage, throttle cable. Keep in mind that to use the 360 TBI on your 318 intake, you will need to slightly open the intake to clear the larger throttle blades on the 360 TBI (just a small amount of grinding), or you could mod a spacer with the offset bolt holes...you'll see what I mean as soon as you get into it. The 4 bolts that hold the TBI to the intake are the same pattern, so that's not a problem. In fact, looking at the TBI's, you can see how the top part of the TBI's are identical. The 318 has a narrower lower section from the injector bowls down. Now, if you're using the 360 intake and heads, you won't need to grind anything. Again, don't mix parts here. Either use the 360 intake and heads, or 318 intake and heads. The pre-Magnum engines (LA's, as they are known, had different size intake and exhaust ports. Mixing intakes and heads causes an intake port mis-match, and that defeats the purpose). Either way, it's only a minor hassle, well worth the returns. The 360 got advances about a year after the 318, so the first TBI 360's (I think) appeared in 1988, definitely by 1989. The last year for TBI 360's was 1992. Yes, 1992. Magnum 360's didn't appear til 1993. Best bets are full-size pickups and the larger vans.



zac
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2/23/2005
22:10:38

RE: pre mag mods
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thanks again for the info. you were very helpful. now i just have to start scouting junkyards and such to to find the stuff. if i did the 360 intake and heads swap do i have to get them milled or anything. i thought that if you used those heads it would decrease the compresson ratio?



gen1dak
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2/24/2005
14:51:59

RE: pre mag mods
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Yeah, using the 360 heads will cause a mild decrease in compression ratio. It's a relative thing. Chrysler did the same thing with their police package 318's in the mid-80's as a way to improve performance, and these were direct bolt-ons, not milled. The advantages are that you will have no problem running regular gas. Also, you will be able to really bump up the initial ignition timing, which will help low rpm power, as well as improving upper rpm power since 32-34 degrees total timing is optimal for these engines. This is generally considered an equitable trade for what few horses are lost from roughly 1/2 point in compression ratio. Remember, a better street cam will also compensate for the CR loss because it, by design, builds higher cylinder pressure because of better cylinder filling. Now, granted, if you wanted to mill the heads, you can certainly do that for even a bit more power. The only real caveats are that you may have to bump up your fuel to a higher octane or lower your initial ignition timing a few degrees to avoid detonation...depending on what fuel octane is being used, what your actual CR becomes, and what environmental conditions are usual for you. Also, tthe intake will require milling to maintain the proper gasket and port orientation. If you remove 0.020 from the heads, you should mill the manifold 0.020 from each side, and 0.028 from the bottom. Milling 0.040? Take 0.040 from each side of the intake, and 0.056 from the bottom. Any decent machine shop should know this. Personally, I'd do a direct swap, install the CompCams 264HR-12 grind cam, open up the exhaust, advance the ignition, and smile every time I drove by the gas station.



gen1dak
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2/24/2005
14:56:03

RE: pre mag mods
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Yeah, using the 360 heads will cause a mild decrease in compression ratio. It's a relative thing. Chrysler did the same thing with their police package 318's in the mid-80's as a way to improve performance, and these were direct bolt-ons, not milled. The advantages are that you will have no problem running regular gas. Also, you will be able to really bump up the initial ignition timing, which will help low rpm power, as well as improving upper rpm power since 32-34 degrees total timing is optimal for these engines. This is generally considered an equitable trade for what few horses are lost from roughly 1/2 point in compression ratio. Remember, a better street cam will also compensate for the CR loss because it, by design, builds higher cylinder pressure because of better cylinder filling. Now, granted, if you wanted to mill the heads, you can certainly do that for even a bit more power. The only real caveats are that you may have to bump up your fuel to a higher octane or lower your initial ignition timing a few degrees to avoid detonation...depending on what fuel octane is being used, what your actual CR becomes, and what environmental conditions are usual for you. Also, tthe intake will require milling to maintain the proper gasket and port orientation. If you remove 0.020 from the heads, you should mill the manifold 0.020 from each side, and 0.028 from the bottom. Milling 0.040? Take 0.040 from each side of the intake, and 0.056 from the bottom. Any decent machine shop should know this. Personally, I'd do a direct swap, install the CompCams 264HR-12 grind cam, open up the exhaust, advance the ignition, and smile every time I drove by the gas station.



gen1dak
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2/24/2005
15:00:13

RE: pre mag mods
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Ooops. Sorry about the duplication.



gen1dak
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2/24/2005
15:10:59

RE: pre mag mods
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You hadn't mentioned if emissions testing is an issue for you. Holley makes a bolt-on TBI that even has an O2 sensor feedback option. They state they're for carbureted vehicles, but that's essentially what those early TBI's were too. In fact your TBI has "Holley" in the casting. You could go that route. I'm not talking about the multi-port Commander unit Holley sell, I'm referencing the true injectors-in-the-throttle-body injection system. I think they call it Commander TBI nowadays. Depending on your luck finding an OEM 360 setup and the costs of everything, it may even be cheaper. Then, just keep the stock heads, add a 50-state legal Edelbrock Performer EGR intake, and you're set. Leave your PCM in place to run everything else, and have a free-standing PCM (included with the Holley TBI) to run the injection. Naturally, this is not emissions-legal. But if all you have to do is pass a tailpipe sniffer test, and not a visual, run it with the O2 sensor, and you're golden. Some careful routing of wiring might even pass a visual. Just another option to consider.



zac
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2/24/2005
21:27:46

RE: pre mag mods
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im in alberta, canada and we dont have emissions testing so im good there. just to clarify the 360 head/intake swap is a complete bolt on? what would my compression ratio work out to after the swap and what is it now?



gen1dak
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2/25/2005
12:30:18

RE: pre mag mods
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Your advertised CR is 9:1. I say advertised, because production tolerances tend to lower this number nominally. The heads and intake are a direct swap....same rockers, pushrods, head bolts. The Magnum head swap is another story, but LA to LA swapping is almost too easy as interchanging goes. Just remember to use 360 gaskets for the heads and intake. Valve covers and gaskets are the same. The swap will cost you easily 3/4 of a point compression, so it'd put you in the low 8:1 range, or a lot like most of the LA engines throughout the 70's, and early 80's. On my first car, I had a 318 with CompCams High Energy 260 cam, an old SP2-P intake, and initially, a Holley 600. It ran pretty well. The car was a 3800lb '69 Charger with 727 automatic (B&M kitted) and 2.76 gears. The 318 repeatedly revved to 5800rpm shift points on a daily basis. I ran the bejeezus outta that thing. It never broke. Later, I put the 360 swap on, and it was obvious that I'd lost a little bottom-end grunt, but not that much, and partially compensated by advancing initial timing. On top, whoa! It was the only time that car actually got rubber in second gear, and that was doing something. Just a little chirp, but it was there. That tranny was one slam-shifting mutha. I eventually did go back to the 318 setup. The tall rear gear with the weight of the car, and the driving I did....hey, the engine stuff I had. New gears, different size tires...I didn't have, and it was tight enough $ then. The 318 setup averaged a slightly better gas mileage figure. Your situation would be better in that you'd have fuel injection, which helps bottom-end power, so you'd lose less torque, and mileage wouldn't suffer as much, and newer cam designs help as well.




Zac
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2/25/2005
20:22:27

RE: pre mag mods
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Basically what i am thinking is the entire top end of a 88-92 360 plus PCM, CompCams 264HR-12, new valve springs, and manifolds or headers off of a 92 and up dakota, and true dual 2 1/4 exhaust. does that sound right? what kind of power increases am i looking at here roughly? i am just trying to make sure that the swap will be worth it. my mileage is fairly bad already but i guess it is still cheaper than a new truck payment. Are the 360 manifolds different or bigger than the 318's?



Mike S.
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2/26/2005
06:27:54

RE: pre mag mods
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I've got a TCI Breakaway stall converter for the 91 A-500 trans. This will help that bottom end loss. I'd be willing to take 150 for it and I'll pay for shipping. Converter is in perfect condition.
Now back too your subject. Let me tell you what mods I did too my 91. I put a set of 360 heads intake and throttle body from a 90 Ram, It was a straight swap. I used a Hughes engines cam (flat tappet) spec were 214/223 duration @.050 and a set of crane roller rockers,this required swapping push rods too. Also I added a electric fan,Mopar headers(which are no longer made) and a flowmaster dual outlet system. I used the above mentioned converter and a set of 4.10 gears.
I did all that swap at one time so the difference was night and day. But too put some numbers on it my best E/T (1/8th mile) was 10.71 stock after the mods it ran 9.86. This was with a bottom end with 115,000 miles on it. I was very happy with the results. Now of course I've went crazy with the truck. LOL, Hope this helps.

Mike S.
91 CC Carbed 390 w/nitrous
Best ET 7.47@94.23 (1/8th)



Zac
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2/26/2005
14:14:24

RE: pre mag mods
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thank you i needed someone who had done it to a dakota just to convince myself. I was on the comp cams site yesterday and was looking at cams. what type of lifters do I have and are the 360 ones any different? also what does a stall converter do exactly? Mike S. how was your mileage after that swap?



gen1dak
Dodge Dakota
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2/26/2005
15:58:19

RE: pre mag mods
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Zac, regarding the 318/60 manifold size, the Magnums are the same size on either engine. The LA 360's tended to have bigger exhausts, but they are still more restrictive than the Magnums. Also, remember, the best ones are 92 to early '93 models. Later '93's and up are smaller, but still very good for stockers. Your 318's hydraulic roller lifters are the same as the LA 360's. Briefly, the torque converter has a rated stall speed at which point the converter will slip no more and applies max power to the tranny. As you move the power up in the power band, it helps to have a higher stall rating to allow the engine to spin up to it's power band more easily against a given set of gears. There are several variables. Just changing gears makes it easier, or more difficult for the engine to pull the load, and this will also influence the stall rating of a given converter to some degree. Typically, a stall rating of around 2000-2400 rpm is good for most typical street performance, but I'm hangin' with the stocker (1600rpm)in my setup for now. Wouldn't mind kickin' it uo to a 2200rpm unit later on. With 3.90 gears, it's not much of an issue. Mopar fit a 2000 rpm stall unit on the Shelby Dakotas in '89, as opposed to the stock 1400 and 1600 rpm units.



Zac
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2/26/2005
18:02:24

RE: pre mag mods
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severeal posts back you mentioned advancing the tming. how exactly would you do that? just adjustment at the distributor?



Mike S.
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2/26/2005
21:01:45

RE: pre mag mods
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Your stock lifters are roller. The reason that I changed too a flat tappet lifter was there are alot more cam choices. The lifters are no different for a 360 than a 318. My mileage after the swap was around 13 mpg, I know that sounds bad but I had 4.10 gears. Basically the stall converter controls what the engine revs up to before the trans starts too pull the truck. Stock is around 1600 - 1800 on the 91, the converter I have will put it around 2400. This will give you a faster take off. Also advancing the timing is done at the distributor the stock setting is 10 degrees at idle it can be taken up to 14 with no problems any higher you may get some spark knock. Now if you do the head swap to 360 heads you should be able to run 16 degrees with no spark knock.
Mike S.



Zac
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2/26/2005
21:07:38

RE: pre mag mods
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Excellent. 13 would be awesome for me. my last tank was ten mpg. granted my truck needs a tune up and i tend to drive with a heavy foot. what does spark knock sound like. will I definately be able to hear it? also for the exhaust i was thnk 2.25 true duals with an x-pipe. is that too small? i dont want to lose any bootom end torque.



gen1dak
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2/27/2005
10:14:38

RE: pre mag mods
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Initial very mild spark knock cannot be heard or felt, but that's when you're just barely getting it. Typical spark knock is easily heard, and sounds like , well, clatter, is a good word (sometimes sounds like a diesel). No way to miss it, and a definite clue to back off the initial timing. Another clue that the initial timing is too high is, when cold, it'll start right up, but when warmed up, the engine won't start, i.e., the started will barely turn the motor over, like the battery is weak. Back it down 3-4 degrees (or about 1/4 inch twist on the distributor, and try again. If it turns over freely, go out and do some runs, listen for clatter and feel for a definite loss of power. If it pulls, and doesn't clatter at normal operating temps, you're there! A lot of engines did this as leaded gas was being phased out, so it was a commonly heard noise in the 80's. Once you've heard it, you will know.
2.25 inch duals is great. Go any bigger and you'll sap some low-end power.
Along with what Mike said, originally, my '89 Shelby Dak (318-powered/3.90 geared) managed an average 15mpg on combined highway/city driving, with my heavy foot, 13 when it needed a tune-up, so there ya go. I NEVER saw the EPA 20mpg highway rating. On a related note, my old '69 318 Charger would run rings around the truck, had gobs more power, an managed 19mpg (with a carb. and single-point distributor!!!). So much for progress.
These LA engines (meaning pre-Magnums, 'cause even the Magnums are really LA's at their heart) were the last that could have any timing adjustments via adjusting the distributor. The ignition curve and advance are, however, controlled by the computer.



Zac
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2/27/2005
20:12:19

RE: pre mag mods
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Great!! So can i use any year 360 inatke and heads or is it best to pull the whole top end of one engine? Where is the computer on my dak? Is it the box on the pass side innner fender? There is a hose from the intake tube that connect to it.



gen1dak
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2/28/2005
02:44:07

RE: pre mag mods
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If you're gonna use the TBI, you'll need the TBI intake from the late 80's-early 90's 360. This is mainly due to the offset bolt pattern used in the TBI. So, unless you're handy with metal and want to fab your own adapter plate, you'd have fewer headaches using the TBI intake. Also, the matching heads would be good. The late 360 heads received the same improvements as the 318 heads, a lot of which were eveolutionary changes as they geared up for the Magnum make-over. Also, if you ever see a set of pre-TBI heads, you'll notice that the rear water passages are plugged. These were finally opened up on the injected engines. You really should try to use heads from a TBI 360 since these passages were opened with the injection in mind. Has to do with emissions, and overall heat balance for computer control. It'd probably run fine with any heads, but since you're looking for a 360 donor, why not get the whole top side?
Your computer is on the inner fender as you described. Wherever you get the heads, make sure to have them checked for cracks. Sometimes, higher mileage units will develop cracks between the valve seats.




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