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As someone mentioned before, 5.2 swap would be a lot cheaper for those kind of ponies. He only want 20 hp more. What I did to mine was relatively cheap and satisfied my desires for the truck.
That's I get for skimming the posts.
20 should be pretty easy to get. I know some that just retro fitted a bigger throttle body, added a super chip, got 15 more horse. Yes he actually put it on a dyno. That being said I'd be surprised if you could find a new chip.
 

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Discussion Starter #22
To be fair I don't read all replies to the threads I follow. I share a concern about what parts will be around later. My trips to the dealer has resulted in NLA reply each time. That's why I want to buy and build now. My last two Fords went to the big Ford junk yard with 250,000 plus on each. takes me about 17 years each to do that. This over weight mid size pickup is already 17 with170,000. I bought it for $1000 with a right front brake on fire. All four tires were the same size but with flat spare five different brands. Body clean and straight no rust normal roof peeling. Recent removal of trashed drop in bed liner exposed nice bed. A complete repair and replace wheel bearings, suspension, steering and brakes. Alignment with 5 new 255/65 16s on those nice 8 inch rims covering four wheel disc.The AC system and the belt system got the works. If I knew then, I'd have done the intake, water pump and timing chain. Ideal, I don't want or need a full size like my Ford F150, 9 to 10 MPG towing or not. I have friends with a chassis dyno, guess I could do a before and after. Steve
 

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I love Daks, but you nailed it. The power/weight ratio sucks.

I forgot if you have a standard trans. One thing I discovered on an automatic transmission, turning off the O/D when going up hill dramatically improves the power. Of course you're running at 3,000 rpm because Dakotas have no low end torque. Anyway, good luck.
 

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Discussion Starter #24
It's a lot to do with where you come from. People laughed at the 10,000 tach in my autocross car. Till they realized I was shifting at 9200. 3000 is where the cam wakes up on some of my engines. Thanks Steve
 

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Other than the novelty of it isn't it cheaper and easier to make it a V-8
V8 swaps aren't cheap any more, epecially if the "new" engine is in need of a rebuild Then there are supporting mods like a trans swap and all the other details that can nickel and dime a project to death. It's been done often with the help of a donor which helps to bring down some of the costs, but it still ain't cheap any more.

Turbo swaps aren't cheap either, but the good news here is thanks to the popularity of diesels, turbos are slowly becoming more affordable...that being said, you still need to make supporting mods to the engine to survive boost.

Ed
 

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I'm more after low hanging fruit, 5 here 10 there I have no expectations I'll ever be able to pull the trailer in 5th gear and pass on a hill. Twenty five HP and 38 Lb Ft increase sound perfect to me. Inline 6 cyls have the best natural balance. These split pin V6s suffer from balance issues. They do not like to be lugged in higher gears. You only have to hear the sound once to know that's not good.
It's a matter of engine design and the physics of making power. Inline 6s are inherently balanced and V6s are less so. This is why V6s (especially 90 degree V engines) incorporate split pin cranks, so that the engine can operate with an even firing 120 degree crank interval.
By design, the 3.9 is basically a V8 with two less cylinders. As such, it's architecture is not ideal for a V6. Case in point, A V angle of 60 degrees is better suited for a V6 than a 90 degree V angle. A 60 degree V would produce much less imbalance. The 3.9 has a 90* V angle (as used by the V8s) Next, a V6 would benefit by the use of balance shafts. The 3.9 does not contain them.
When it comes to power, you have two elements; Horsepower and Torque. HP is a mathematical formula consisting of torque by rpm (divided by 5252). Torque is the twisting force produced at the crank. Torque is directly related to displacement. Every cubic inch holds a given amount of air/fuel which we burn to make power. More displacement means more air/ fuel we can burn at any given moment. 3.9 liters is not a lot of displacement. Since torque is fixed by displacement (which is also fixed) the only means to make more horsepower is to increase rpm (HP = TQ X RPM [/ 5252] ) The problem with increasing rpm in a given engine is volumetric efficiency at higher rpm...ever notice why all the common hot rod tricks seem to have something to do with breathing? i.e, cam, bigger valves, port and polishing, intakes, headers, etc.

This brings up another problem with using the 3.9L It's V8 origins was never really designed for high rpms. The cam is in the block with a relatively heavy valve train that's prone to float at high rpm. A V6 is really better suited to overhead cams, to support higher rpms.

There isn't much you can do to increase the torque of a naturally aspirated engine. As mentioned torque is fixed by displacement. Having said this, I6s also do not make much torque as they too tend to be rather smaller displacement, but unlike V6s, many inline 6s makes more of the torque it does at lower rpms. The reason for this is, many I6s tend to be square or undersquare engines (meaning the bore is as small or smaller than it's stroke) The longer stroke means it takes more time for a piston to travel from TDC to BDC which means a slower crank rpm for any given piston speed. The 3.9 is overquare, meaning the bore is wider than it's stroke. This is ideal for higher rpm HP, but it also tends to make the torque it makes at a higher rpm. Butthat also means the truck will not acellerate as well or pull loads as well

This is why I mentioned the supercharger or turbo. Since displacement is fixed, and there isn't much displacement with a 3.9L V6, the only way to get more air into the engine is to "push" more of it in. And that's what superchargers and turbo chargers do. The boost these devices produce can effectively overcome the lack of volumetric efficiency in all rpm ranges and allow a small engine to breathe with as much air as a much larger engine (just add more fuel)

There is a lot of talk about any mod moving the power curve up in RPM.
As mentioned, displacement is fixed, therefore torque is fixed. The only variable is rpm. You push the rpms up to make more hp and this is why the power curve moves up.

More gear has been suggested as well. which of course will increase RPM at any speed.
Lower gears creates mechanical advantage trading speed for torque. A 4:1 ratio, for example will increase output torque by a factor of 4, but reduce output rpm by dividing by 4. This can offset some of the disadvantages of moving the power curve up.

Ed
 

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Discussion Starter #27
Thank you Ed. Having operated an auto machine shop for 25 years and a paid part of the auto after market since 1965 I understand the design issues with this engine. An engine is little more than an air pump. The greater the volume of air / fuel the more power output. Yes you can pump air / fuel in or you can attempt to improve NA breathing.

I agree all the power happens above the piston. Once bore, stroke and CR are determined, cam lift and duration, valve size, rocker ratio, porting, manifold work and throttle body size can be adjusted to improve flow. Just as important is getting spent gasses out. Again port, valve size, manifolds and system on back are a part of the big picture.

I have always been a big believer in balancing every engine I build. I have located a shop with V6 Bob weights that will balance the assembly. With a new balancer, resurfaced flywheel with a new ring gear and pressure plate we will get the balance perfect.

I have found a camshaft which will improve breathing I have plans for the heads and intake. and a throttle body will be sent out for mods. The exhaust was my first project and should match the balance of my plans. I realize the standard answer to how to get more power from a 3.9 V6 is swap in a V8. I'm not looking for an European 100 HP litre, I'll be happy with the lazy US std. with a little hot rod influence. Steve
 

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I'd like to begin a serious rebuild on a 3.9 V6 looking for a little more power. I have read the Haynes book of lies cover to cover. I have spent hours reading and looking for info on the net. It appears no one is interested in offering a camshaft or for that matter anything for the 3.9 performance wise. I'd like to hear from anyone who has raised the compression from 9.1 to 1 to say 10 to 1. I see 1.7 rockers offered and std being 1.6 I don't expect the improvement to be worth the cost. My experience with extended rockers is I gain a little top end loose some bottom end, not sure that's what I want. Current plan is a set of quality .060 pistons with file fit .065 O/S rings. Zero deck and square the block, balance assembly with new balancer , resurface flywheel w/ new ring gear and clutch. Mod the throttle body and intake manifold. Port match intake, heads and exhaust manifolds. A little bowl and port work on the heads should help. I have a compete 3 inch in and out exhaust system. If I can locate one a 4.5 qt oil pan and a oil cooler system with a thermostat. A quality timing kit and degree the cam in. A high volume oil pump and water pump. I'm sure there are some other things tried some that work some don't. I'd be interested in hearing anyway. Steve
Cooper!
I just completely rebuilt my 3.9L for my 1988 b150. Almost back together. My machine shop bored it out 0.20, ported the heads, and short blocked it. Flat pistons, new cams, heads, bigger valves, clevite bearings and everything high end. Definitely added some horsepower. Yeah you could go V8 but I'm happy with my V6 pulling better gas mileage and plenty of dodge pep. Good luck with your build!
 

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Discussion Starter #29
Found a V6 book that predates the 3.9 Dodge engine. The chapters on 60 vs 90 degree, even vs odd fire, difference in crank pin split in degrees and balance weather to over or under balance. There is a lot to learn and I'm interested. I now better understand the motor mounts. A serious build has to begin with a plan. Seems all V6 have to make a trade off on balance. I need to figure out the crank pin split in degrees. Funny where study leads. Steve
 

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The crank pins are 22° apart on our 3.9L V6's. 30° would be ideal, not for balance but for even firing. The engineers were concerned having that large a gap on the crank throws. As it is, the cylinders fire alternating 112° and 128° from each other. I'll try to find where I read this and post a link.
 

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I read that in a post on Allpar; but danged if I can find it now.

The 3.9 posting mentions the split crank; but it doesn't describe how many degrees it was split.

RwP
 

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Discussion Starter #33
I was reading an old SA Designs paper back I bought when thinking about putting a 2.8 Ford V6 in my Pinto to better pull the same load I now pull with the Dakota. That was about 1975 I even bought the core engine and rebuilt it although I never installed it. At the beginning of the chapter the author says he contacted 12 college physics professors and a couple of indy car engine builders no college wanted to explain what happens within a V6 balance wise and the engine builders said no one really knows. Seeing as Buick, Chevy and Dodge all split the crank pins a different amount. I'll read what I have found several more times to try and better understand. In Ralph's defense there are several mentions of light cast blocks being careful boring due to thin cyl. walls. I did read that a heavier flywheel and pressure plate while not helpful for engine acceleration it does help damp vibration. So a 12 inch clutch seems the right call. Steve
 

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CooperT you might be over-thinking this. For any 6 cylinder engine, the ideal firing interval is 120*
In an inline 6, each piston gets it's own crank journal and each crank journal can be separated by 120 degrees. It also results in the pistons to move in pairs (although each pair of pistons moving together are on a different stroke)

On a V6 this isn't possible. Each piston does not get it's own crank journal. In the V configuration, the piston on the left bank shares the same journal with the piston on the right bank. Factor in the angle of the "V" and even if the crank journals are evenly spaced at 120* the firing event for pistons on the left side ve the right side of the block were offset by the angle of the V. So for example, if the journals were separated by 120 degrees on a 90 degree V, the firing interval would be 90*-150*-90*-150* This is whats called an odd fire engine and it produced some interesting vibrations and a unique missing V8 sound.

To resolve this manufactures developed the split pin crank design. This restored the even firing 120* interval on a V6 reducing the odd vibration and funny noise. It is the current standard in most V6 engines today

Balancing a V6 is no different than any other engine. But balancing and blueprinting a V6 will not get rid of the inherent dynamic vibration of a V6. This is mostly due to it's configuration. A V6 will experience side to side vibration as the pistons are moving up and down in two different planes. An inline 6 runs smoother. In it's design, all the pistons are inline, so there is no side to side vibration. The cylinders fire at an even 120 degrees and this even spacing results in the pistons moving in pairs of three which naturally cancels up and down, as well as fore and aft dynamic vibrations. The V6 does not because the pistons are not paired with the firing order going back and forth, from the left bank, to the right.

Ed
 

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Discussion Starter #35
Thanks for the input. I don't plan to reinvent the wheel. There is suggested reading if we want to know more. Some papers from MIT. I'm sure it's entry level reading. It seems there are as many approaches to V6 as auto makers wanting one. It is clearly not a simple problem to solve. The change from single crank pin to split pin solved some issues and created others. Seems the two rods sharing the split pin apply force at a slightly different point depending on the number of degrees of split. These engines create a side to side as well as a up and down motion. By under of over balancing ( which just means what percentage of the reciprocating weight is added to the crank in bob weights for spin balancing) one of the movements can be reduced. I have balanced every engine I have built since 1968, during my years at the machine shop I must have balanced 1000 engines if not more. I never balanced a V6 because we did not have any call for it and no V6 bob weights. Normal balance for all other 4, 6 and 8 cyl engines is 50% of recip. That is the weight of piston w/pin, ring pack, allowance for oil and half the con rod. Steve

PS During my years at the machine shop we ran two crank grinders and put out as many as 16 sets of V8 heads a day.
 

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It is clearly not a simple problem to solve.
It's probably "solved" enough to accept the compromise in the design, especially for the intended purpose.

Seems the two rods sharing the split pin apply force at a slightly different point depending on the number of degrees of split.
Which is not really a problem with modern metallurgy and computer aided design. You can certainly adjust and improve the balance of reciprocating and rotating parts and reduce vibration of these components, especially at higher rpm, but the inherent imbalance of a 90* V6 cannot be "adjusted" out without changing the configuration of the engine. The best way to see it is to know that a 90* V6 like the 3.9 is a compromise design. It's based on the 90* LA V8, with two less cylinders, and was intended to fill the displacement and HP/economy void between the 4 cylinders and V8s with the added advantage of being very compact.

Ed
 

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Discussion Starter #37
Buick, Chevy, Ford and a bunch of others have proved it works and there are many ways to approach the problem. Sounds like Chevy built 5 different cranks with different crank pin splits. Built them into engines put in cars and driven by their engineering staff. Like a big blind taste test and that is how their crank pin split was determined. I believe they went with a 18 degree, I have read some engine builder think a 3.250 stroke with a 30 degree split and std. 50 percent balance would work best. After reading the material I have the question is ask "How much do I need to worry about it?" They work and do a good job, they respond to performance improvements, and if properly built and balanced they don't seem to hurt themselves. They do seem to crack things bolted to them. Brackets and mounts should be checked. My only reason for looking into this is building an engine for me starts with the balance job. Dodge not mentioned in my old book I'll need to find our if Dodge over or under balanced this engine. Looking at the balancer it appears internally balanced. Steve
 

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Discussion Starter #38
I just read another interesting paper on V6 balance. Dealing mostly with over and under balance. Seems a lot has to do with how you look at the con rods. I realize this is not like reading the funny paper for some. Once again a long story ended with it does not matter. Steve
 

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Buick, Chevy, Ford and a bunch of others have proved it works and there are many ways to approach the problem. Sounds like Chevy built 5 different cranks with different crank pin splits. Built them into engines put in cars and driven by their engineering staff. Like a big blind taste test and that is how their crank pin split was determined. I believe they went with a 18 degree, I have read some engine builder think a 3.250 stroke with a 30 degree split and std. 50 percent balance would work best.
They work and do a good job, they respond to performance improvements, and if properly built and balanced they don't seem to hurt themselves.
Totally irrelevant. As interesting as this discussion may seem to be, bottom line is you're stuck with the 3.9 and whatever it's split pin angle it was made with. As such, you could balance it's rotating and reciprocating components to near perfection, and it's still not going to amount to much of a performance improvement. The reality here is the 3.9 isn't well supported. You're only hope to get decent power out of that mill is adding either a turbo or blower.

Ed
 

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Discussion Starter #40
Ok, what can you tell me about V8 rods vs V6 rods? Seems they carry the same casting number. the V8 rod appears wider on the big end. The H beam rods are bushed but could be machined and have the locking lips re-cut other side. Just thinking about buying good rod bolts and have a set reconditioned. Running the numbers on a build while not cheap not as bad as I suspected. Steve
 
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