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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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Honestly, you're fighting an uphill battle. IMO the only way you're going to get more power out of a 3.9 is either supercharge it or turbo it. What little you can do with that engine isn't going to make much of a difference.

Ed
 

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If you're going .060 over, be DAMN sure to get it sonically tested first.

Word from the engineers that designed the Magnum blocks is that .030 is starting to be dicey.

RwP
 

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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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No, most builders will go with 5.2/5.9 V8s due to the paucity of parts for a 3.9. Plus, "There's no replacement for displacement!"

The info is somewhere on Allpar.COM - where the actual engine designers used to post articles (not forum posts, articles.)

One article on the 3.9 is at The 3.9 liter LA-series Dodge V6 engine but the Magnum is mostly notes at the bottom.

Again, before I bored one much if any, I'd get it sonically tested to make sure there's enough wall there after the bore. That's just good common sense.

Don't forget, one of the big changes from the 50's A blocks to the 60's LA blocks was a thinner cylinder wall - hence the "Light A" for LA. Magnums were a slight bit lighter.

RwP
 

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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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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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Sounds like you want to "play" with upgrades and spend an awful lot pf money and time. I would have to say it is probably not worth 20HP or so.
It's your project so I wish you luck.
The easyiest way I helped my son, in NJ, was to eliminate the mechanical fan and just use the electrical fan after replacing the water pump.
 

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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
No need for increased oiling. I forget where I saw years ago but it also does not seem to help with windage trays for these Mopar engines either. The biggest improvement I made to my 3.9 was to put a 3.91 gear set. I put headers and a better y-pipe on along with a cold air intake and a 50 cfm tb. It made some very nice gains.
I would not bother with intakes, cams and such because all you're doing is moving the power band up for an engine designed to move an almost 4000 lb truck. Low end torque is your friend.
If you want to rebuild the engine, I wouldn't up the compression beyond 9.5 cr. Forget MSD ignition components. The Mopar coil puts out all the spark you'll need.
The headers helped the entire power band.
 

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Honestly, you're fighting an uphill battle. IMO the only way you're going to get more power out of a 3.9 is either supercharge it or turbo it. What little you can do with that engine isn't going to make much of a difference.

Ed
Other than the novelty of it isn't it cheaper and easier to make it a V-8
 

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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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Just think carefully.

If you're pulling 2000 pounds, you want low end torque, not raw HP.

MOST improvements move the torque band UP; can even kill power below about 1,800 to 3,000 RPM (where the torque curve actually starts on some motors.)

For towing ... There's No Replacement For Displacement. I'd STILL recommend building a 5.9 for towing, and replacing the 3.9.

But eh, it's your truck.

RwP
 

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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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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
I didn't do that. My exhaust was 2.25. 3" exhaust on the little v6 may not build enough velocity. I think you can attain what you are looking for w/o tearing into the engine at all. My headers were Edelbrock with 1.5" primaries. Between the rear gear set change, exhaust performance products along with a cold air intake, it became a different truck. I was able to tow a horse trailer that came to 4500 lbs much easier than before I did anything. It was just the right combo for that engine.
 

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More power out of a 3.9. How much money you got? You can change the cams, bore, throttle body, injectors, reprogram the ECU, all the usual. Gonna get you bout' 50hp more. For a lot of money. Going up hill without downshifting from the OD a couple gears on the interstate was my pet peeve with it. Best bang for buck is a turbo. As long as you don't go overboard on it, minor engine mods should keep it entact. Call the different companies, tell them what you're looking to do, the worst response you'll get is a no.
 

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Remember the 3.9 magnum is rated at about 145, maybe 150hp base. I'm thinking you want around 250 or more. That's a tall task.
 

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Remember the 3.9 magnum is rated at about 145, maybe 150hp base. I'm thinking you want around 250 or more. That's a tall task.
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.
 

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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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