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Discussion Starter · #1 ·
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
 

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Discussion Starter · #4 ·
I guess some info is better than none. Perhaps a link to the cyl walls to thin to bore info would be nice. I'll check with the local machine shops in as far as poor boring results. I have heard they are common to crack cyl heads. I have also heard they have issues with oil control rings. I'm not looking to reinvent the wheel just want 20 more HP.

I'd still like to hear from anyone who has rebuilt a 3.9 V6 to what ever level. It seems there are not many engine builders here. Thank you Steve
 

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Discussion Starter · #6 ·
Thanks for the warning, seems to me Ford started the light block casting program in the early 60s when they decided to win the Indy 500. It took awhile to locate a shop who has bob weights for a split pin crank balance. Testing a block should be no problem. I'll let you know what I find out. I checked Clifford's 6=8, 225 slant 6 only. Seems all Kenny Bell wants to do is super charge. Worse comes to worse it will just be fresh and not burn oil. Steve
 

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Discussion Starter · #7 ·
Just got off the phone with my 1st choice machine shop. They have just received their new Sonic tester. We will be able to find out what the cyl walls look like. It appears pistons are listed std -.060 by industry leading suppliers. Things may take a new direction on my engine build. The search for a core goes on. At the same time repairs on the current engine will go on. Steve
 

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Discussion Starter · #8 ·
Starting a parts list for a complete rebuild and upgrade of our 3.9. It looks like the parts will run in the $1000 region. This does not include any of the performance parts not made for a 3.9 or parts for the cyl heads. Since all the power is made above the piston the cyl head prep will be the key to pulling some more power out. I'll follow up. Steve
 

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Discussion Starter · #9 ·
Just got off a very helpful phone call with Hughes Engines. It seems more is out there than is common knowledge. I have to completely rethink this build. As I suggested all the power above the piston. A camshaft kit with springs, retainers and keepers which sounds like a Comp Cams product they like to do that. There is a claim of 25 HP and 38 lb ft improvement at the wheels with the cam kit alone. We know about claims. Steve
 

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Discussion Starter · #13 ·
Thanks for the replies, good to know people are thinking. I agree rebuilding a V6 will cost as much as building a V8. After spending a year with the stock power unit running great covering 13,000 miles with no issues. Other than needing a headliner, carpet and a little freshening up of the seats I'm good. Yes, rolling up and down I 95 pulling 2000 lbs I'd like 20 more HP. Just like when I was a kid, I read everything I can find in print then talk with anyone who will share info. Up until very recently I have had little positive said about the 3.9 V6. With a cam that will improve breathing without upsetting the computer, heads with bowl work, port matching, manifold and throttle body improvements with 3 inch exhaust end to end. I'm thinking 25 HP and 38 lb ft of torque would be ideal for my purposes. I will share what I learn. Steve
 

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Discussion Starter · #15 ·
Thanks again, seems one of us is just not getting it. Can't recall how many times I pulled this same trailer and car combo from Hampton Va. to Charlotte Motor Speedway and back with my 73 Ford 2 liter Pinto. A mild cam, HC pistons, header, head work and a pair to 45 DCOE Webers and brakes were the only issue. It's not always what you have it's what you make of it. Steve
 

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Discussion Starter · #20 ·
Thanks for the replies. I have yet to hear from anyone who has addressed a performance build of a 3.9 V6. I also have read some place that the change to a smaller exhaust system reduces advertised HP by 5HP. There is a small figure quoted for a throttle body upgrade. Hard to put a number on cyl head bowl work, port matching and intake mods. The most interesting is that there are a couple of cams. One gives a real improvement without changes to the computer. The other requires a chip and computer work. That kind of support is offered with the cam.

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.

There is a lot of talk about any mod moving the power curve up in RPM. More gear has been suggested as well. which of course will increase RPM at any speed. All these things have to be considered and cost is a part of it. I did a little list last night of parts I'd replace if doing a intake oil leak repair. That list is just over $400. plus shipping. Being an in frame repair catching the water pump and all hoses, fans and related parts to include a new radiator. If our engine had fewer miles I'd add a cam and timing kit. Steve
 

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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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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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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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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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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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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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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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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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Discussion Starter · #42 ·
With a little machine work and $300. You can have a set of light weight Eagle rods new in the box with two spares. A set of ARP bolts, press off and on and recondition labor would cover it or near the cost, and I suspect the balance will be close. New rods have to beat 100,000 plus mile rods. Steve
 

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Discussion Starter · #44 ·
OK it looks like the late engines 3.9 and 5.9 went to press fit rods. And all the aftermarket rods are floated. Not a problem as there are 318 flat top pistons with clips. These rods are 100 grams lighter than stock. Claim safe for 500 HP at 6000 RPM. Now that would be a nice 3.9. The plan is to pick up a core engine strip it and have the bores tested and crank checked and turned or polished. Once that info is in hand I'll order pistons, rings, bearings and the rods mentioned. I'll also need the ring gear and clutch. This is what I'll need to do the balance work. Stripping the cyl heads, crack, surface and guide checking will determine if I order new castings. The cam kit comes with new springs, caps and keepers so valves and all new. Steve
 
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