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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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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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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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I don't blame ya for playing with the 3.9. I'll be curious to see if you can begin to match hp with a regular 318. Heads will be huge in your endeavors so anything you do to improve flow in this regard will pay off big.
The thing that drove me nuts with my 91 3.9 were cam sensor issues.
Just putting headers on and using 3.91 rears woke up the truck considerably.
Good luck and keep us abreast.
 

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Thanks, I have been thinking about this project for some time. As we know there is little the aftermarket does for this engine. Hughes Engines do or did offer a mild camshaft that works with the PCM. They also offer a plenum repair kit to seal the manifold. I degree every camshaft I install so a performance timing kit. Also the spring cap and keeper kit to handle additional lift.
I replaced cam sensor and had to have a shop put it on computer and we adjusted just like you do any dizzy. I'm fairly sure my timing chain is badly stretched. Anyway all parts should be here Thursday. Steve
You may also consider 1.7 rockers to get a bit more lift and a slight duration bump. All of this will depend on head flow as to viability of performance adaptations.
I know a few guys who installed stroker kits and were disappointed w the results mainly for failing to regard any symbiotic relationship to the rest of the engine.
You can also cut the heads some and use thinner head gaskets to increase compression.
 

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I enjoyed chatting with the guy at Hughes Engines. It seems they at one time offered stroked cranks. I have read what I can find on V6 design issues. Having spent a life time building inline 4 cyl engines, natures worst balance design. It seems just about every V6 design takes a different path to deal with the balance issue. I hope to visit the only somewhat local shop with bob weights for a V6 crank. There seems to be some question as to percent of reciprocating mass used for bob weights. I'm very happy with the smoothness of my current engine. I'll pick up a core tomorrow and begin stripping it to see what I have. I have heard from local machine shop the heads are prone to crack. I expect chamber cracks so I'll pull valves wire brush, check with magnet and dust. If cracked, deep valve seats or wrapped I'll order new casting, may anyway. Weather new or used mild port matching, bowl work and a little around the guide bosses. Correct seats with the Serdi setting angles and margins. A little back angle on the valves (all new) correct springs, caps and keepers. New mild performance cam, roller rockers, push rods and rockers with pivots. I have in the past used extended rockers on engines and found improvement at upper end of RPM at expensive of bottom end. With a 3.55 CWP I'll try and keep my low RPM torque up.
Parts are showing up all day.

I'm sure it is clear this is not a cheap thing to do. Went to the Dodge dealer looked at new Ram $84,000. Makes me feel much better about spending $4000 to repower my ride. Even if I end up spending another $1700. on a remaned 5 speed I'm good. Steve
Your intake quits around 4200 RPM. It is strictly designed for low end torque so increased ratio rockers won't hurt and will liven up the entire rpm range.
The infamous cracks you allude to seem to happen more to V8 heads.
I have a set of heads taken off my R/T and at 36K, they are crackless. I think some of these "crack" issues have gained a rather urban legend. They weren't cracked on my 318 with 156K on it either.
 

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Thanks for your input. I made a quick run to Pa yesterday to pick up my core engine and SS headers from a fellow board member. It was fun to meet someone with interest to match to help each other out. Can't wait to get it on a engine stand and start pulling parts. The throttle body will come off and go out for mods, I'm thinking this will have better result than going to the V8 TB directly. The Hughes Keg plate has arrived so the Keg will receive attention. I'm still reading about Keg mods. I don't expect to get a lot out of Keg and TB but each small improvement will pay off. I think I started a thread on cyl head porting. I'll look around for it I'd like not to reinvent the wheel. Steve
Don't waste time or money on the keg. The mods I've seen on kegs which began between 190-192 cfm were improved to a best of 194.
There is simply a wasteland for intakes for these Magnum engines.

The Mopar TB for the Magnums start off at a certain size. On my R/T it started at 50mm at the opening and taper reduced to 47mm at the intake side. There is more to it than gross air flow. I forget what the 6 cyl tb starts off at (46mm?). I'm thinking the 6 cyl tb might do the same if not altered. After you're done with the engine, the V8 tb may be perfect.
I Switched to a 52mm Fastman with heads, intake, cam and exhaust changes.
 

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It's a new day now, I started stripping the core engine yesterday. Having come from up North it shed a bunch of rust scale in my truck bed. After spraying it down with PB Blaster/ WD 40 and high pressure air it looked better. The old " you can't judge a book by the cover" is still true. The TB is dirty underneath. The Keg is very clean inside viewed though the TB bores. I have worried about the timing chain on my engine but this one seems very tight and the rails and gears show no wear. It's beginning to look like someone may have been in this engine before. The water pump appears almost new. I had concerns about the timing cover and water damage to it. Glad I didn't order a new one this one is perfect cleaned up. Removed one cyl. head and was surprised at the size of the pistons and valves. While I did not remove the valves to mag seats I did wire brush between the valves and see nothing to concern. The bores on that side show no cyl. wall wear and the hone marks are still faintly visible well up the walls. I noticed the flat top pistons and a slight chamfer and look to be .050 down the bore. I have been looking at aftermarket rods and pistons for this job. Scat offers floated rods with ARP and come 8 to a set. My plan is to buy a set machine them for the correct side clearance and notch for V6 bearing tangs. Searching around KB offers a 318 floated pistop flat top with valve reliefs which is listed wit .050 more pin to deck height. The valve reliefs hold 5 CCs so some math will be required to figure the best way to come up with 10 to 1 CR over the current 9 to 1 CR. While the core was a std tranny unit the flywheel is not with it. If some one has a 3.9 flywheel to sell or trade please let me know. I have ordered a new ring gear so gear condition not a big deal. Looking forward to getting this project done, I take lots of pictures. I can text them to a phone. I have not figured how to post them here yet. If someone want to post them for me I'll be glad to share. Steve
If any use, I cut my heads 30 thousandths. Obtained a 58 cc chamber and then used Felpro 1008 gaskets which I doubt they make for the 3.9. All in, 9.5 cr from 9.1.
Static and dynamic are gonna to be different so it depends how much overlap you're new cam has. Can't be much.
Cut the head, use the 10 to 1 pistons at zero deck and with the squished gasket, you could come close.
 

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I have ordered a set of pistons that should put me right where I want to be. There seems to be a common approach to zero deck the piston to deck. Use a .039 compressed gasket giving a correct quench of just under .040. Figure in the 5 CC s for valve reliefs and a 52 CC head and 10 to 1 may be closer than expected. Steve
Sounds like a fun v6.
 

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ok. If you insist on "keg mods" even though every known test on these has proved this fruitless.
If you're going with a single 3" exhaust, go with a complete "straight through" muffler.
With a "baffle type" muffler, you could lose horse power.
Try and use a legitimate "y" pipe and not one that just "butts" into the other exit tube.
Your cam should be on a 110 lsa if you have a choice.

You obviously are not doing this simply for "more power".
It is the challenge of making something out of that which others have been more practical or even "disdainful" in their advice.
"Challenge" is a much more exciting horse to ride than "practicality."
.
 

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ACTUALLY it depends on which "kegger mod" you're talking about.

See Marty's work at Kegger VRP - UTAWESOME PERFORMANCE sometimes.

RwP
Most people didn't go through the trouble Marty went through with his plate design. They simply cut the runners down and all of these tests proved fruitless.
Marty'sdesign increased air velocity and that was what really made the difference.
I always stated there was more to intakes than total cfm output.
At any rate, you are correct. It does depend on what mods you're talking about.
 

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Thank you both for you interest and input. Please understand just because I don't always take advice does not mean I don't consider it and see how it fits for me, A little back ground may help. I bought this 03, extended cab, SXT with a 3.9 V6 and five speed. Having never owned a V 8 or automatic for my personal use, it with timeless styling four wheel disc, big wheels and tires had to give it a shot. It was not hard to spend a couple thousand on brakes, suspension, AC, alternator and drive belt parts. At that point I could not stand the sound a std V6 makes. It sounds like it is sucking, so on went the complete single 3 inch exhaust system. My exhaust guy is third generation and does the NASCAR exhaust school every few years it is made of the correct parts. For a whole year it was great and ran fine. It did not begin to show issues till I started making long high speed trips pulling 2000 lbs. The first one went fine no codes no issues. I had learned a few things about the ride. Just a wild guess but I feel it's at least 20 HP short of what I need. Just running up and down 95 even small hills are an issue in O/D 5th. Having never heard a V6 in lugging distress it scared the crap out of me. I though the engine was coming apart. OK, no towing in 5 th gear. Even in 4 th it's a little short of power. Many have suggested more rear gear which would move things up the RPM scale. With something in the 175,000 miles on the OD the engine could use a freshening up. The cost of a std rebuild using stock parts with no effort to improve is big money. So I'm spending a few more dollars looking for something that may not be there. We have a local shop that holds an open Dyno day a couple of times a year. Once done I may give it a go. As for the Keg issue I believe there is something to be had there. If not HP it may be something that supports other power adders. Again, thanks and I'm about ready to start. If I had someone to text pictures to that would post them to a thread as I add text it could be interesting to some. Steve
I feel you would only improve performance. Better valve events with the cam. More compression. Better breathing in and out.
You have no choice but to see some nice gains in my opinion.
 

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As I turn the corner on this build parts are arriving every day. I have parts at several machine shops One does my block and cyl. head work, one does custom piston and connecting rod work, and the last does V6 balance work. If we decide the crank needs grinding we will use another machine shop. Having managed a auto machine shop for 25 years I know you not only need the equipment but the talent to operate it. Reading back though this thread there is a lot more info and advice than first appears. Some of it comes from experience, some from reading some from mistakes made.

It was recently mentioned that I must have some other motivation for my failure to take good advice. That got me to thinking about the whole process. Going though the board there are two things you can depend on. One is the question "How to get more power from a 3.9 V6" seems to come up often. The second would be the common answer " Why not put a V8 in it?" seems to follow. I have been rebuilding engines and trannys for the last 59 years.

For anyone interested, I have a heavy truck with a under powered engine. My sore back will attest to everything about this V6 engine is heavy. So I have a big heavy lazy V6 engine. Being rated at 175 to 195 HP that's not even 1 HP per cubic inch. The V8 options are even heavier and lazier. Even with the V6 there is so much weight on the front end I believe the suspension needs reinforcement. My aim is to bring the V6 up to 1 HP per cubic inch. If this works having V8 power without the weight of two extra cyls I win. It has also been mentioned that I could spend a lot of money. Yes, I have and I have stopped counting, as it does not matter. None of us are driving 20 year old trucks because we can write a check for a new fully loaded Big Horn $84,000. Even the base at $53,000 is a little out of my range. Insurance and taxes if the payment don't kill you. The plan was to complete this project at $10,000. That shound have done the suspension and brakes complete. Engine and tranny rebuild, Paint job, AC service with all new parts and full interior redo. I'm going to miss my mark mostly due to the engine over runs. I'm still looking for someone who would allow me to text them photos and then post them to the 3.9 V6 engine build thread. Just got a text my headers are ready for pick up. I'd like to be able to share pics of that. I'm doing the work, spending the money and trying to figure it all out. Someone else can post the pictures if they like or we have none. Steve
Well Coop,
You travel on uncharted ground.
I am wondering if you'd hav better luck looking up any drag history of someone running a stock class with the 3.9 in anything.
That would at least give you a clue as to what gains could be made.
Personally, I think you will achieve your goal and this combo being as or more powerful than the 5.2
 

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I wouldn't count on that.
Even the 5.9 small block has a more and more limited following and the 3.9 next to nothing.. Everything Mopar is being usurped by the hemi.
Your project, to put it kindly, is about 18 years too late to begin to garner interest,
Mopar runs in my veins so I'd be like that hen's tooth you found.
 

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Thank you Binford, now that is what I call a tease. Yes, it looks like you have done it. Any chance of your sharing a little more info and some better pictures? While my direction was making additional power within the ability of the PCM to deal with it, old school throw what you can at it works as well. Thanks for sharing. Steve
Where you been Coop? Haven't received a notification from you in months.
You keeping the original electronics is what will hold you back.
I know they made a performance pcm for the 5.2. I know of none for the 3.9.
The above poster probably went to carb, coil and distributor.
 

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Hey Arrow, you mention the electronics being the hold back for my engine. I realize the PCM has been considered in every effort I have made. Using figures quoted by suppliers there is no telling how much power one can make. Benford suggests he is making 350 HP from his 3.9. If he has a 125 HP shot of NOS with a 750 Holley that's 225 from motor? The best quote factory was what 190? I'll be a little disappointed if the truck don't pull more than 225 at the wheels. Steve
First of all Coop, I think Benford bypassed all computer electronics. It was like the 4 cyl Indy Offenhauser engines making 600 hp with jugs the size of tomato cans. I doubt that would have happened with a pcm.
Even the high performance pcm was only good for 5200 rpm for the automatic tranny. It just doesn't have enough adaptive memory. You would get to wind yours higher than that w a stick.
I think you can get 225. That would have to be around 315 crank hp if an automatic.
A standard 5.9 made around 230-240. Throw on a carb with the proper intake (M 1) and it did 300.
I believe you have more than compensated for missing two other cylinders.
 
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