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whitwt 03-16-2013 11:47 AM

2.5 to 4.3 swap
Hey guys, I am new to this site and joined because I have a very large undertaking in the works. My 2.5 died on me, died hard... After researching I have decided to drop in a 4.3. They are cheaper and easier to work on than the 4.0 (or so I have read). Also hear they have better mpg's.

I am switching over the transmission to the ax15. I know the battle between that and the nv3550 is a heated one, but from what I have read I am going with the ax15. Let's be honest, anything is a step up from my ax5. I am just rebuilding my 231 t-case. Do I need to modify it in any way to hold up to the additional torque?

I am going through Novak for the bellhousing and adapters and motor mounts. The also told me that if I send in my wire harness they will modify it to plug into the gm engine. Can it really be that easy? I hate electrical systems and am willing to pay for simplicity on this front. Does anyone have any experience with their modified harnesses?

So this will be a huge undertaking for me. The most difficult thins I have done on the jeep is putting in a new radiator, brake lines, starter and alternator. I think I have all of the tools needed and my Haynes manual and a very large supply of coffee and beer.

What am I forgetting/overlooking? Fuel pump adapter? Any tips? I saw one fellow said to take off the entire tub and put the drive train on bare frame and start from there. :confused: Any tips or suggestions to make this at least a little easier would be greatly appreciated.

Thank you much! And hopefully I can leave the garage within 3 months. I will probably just set up a cot in there...

joe_jeep 03-16-2013 06:05 PM

the 4 cyl np231 is 21 spline. the ax15 is 23 spline. they will not mate without the input shaft from a 6cyl np231. that means tearing into the np231.
it should have no issue with the power of a 4.3L. a slip yoke eliminator would be a great idea while its apart. it makes the rear output much stronger.
that is a weak link for np231's. it might be easier to find a used 6cyl np231 with an sye already on it and swap that in, rather than building yours?
there are custom harnesses to plug in the 4.3L and many other engines. they are not usually cheap. one of the new all aluminum 4.3L's would be sweet!
novak or advance adapter should have good motor mounts and a bell housing for the swap.

whitwt 03-17-2013 10:03 AM

Thanks man. I called up Novak and they told me that if I sent in my t-case and wiring harness they would modify them for me. And i am certainly getting a SYE installed while i am at it. They actually told me that they had re manufactured ax15 and 4.3's there and that they would send me the entire assembled drive train.

So I am waiting for multiple quotes from them. I will decide which route I go when there is a price tag attached. But I will certainly get the t-case, harness and motor mounts through them. I will let everyone know their pricing breakdown when I get it. Just waiting for the jeep to get back into my time zone so I can tear into her.

captainauti 03-17-2013 04:43 PM

good luck, you are gonna love it...i do.

whitwt 03-19-2013 04:36 PM

Ok, so I got the quote from Novak, wow sticker shock... God damn...:eek: For the whole she-bang it is 9,500. that is the entire assembled drive train, wiring harness, new ax-15, transfer case rebuild kit, clutch fun, radiator and everything else that I hadn't thought of.

I can cut the cost down by not paying them the $1000 ($84/hr) to assemble the drive train and not paying for the $600 deluxe custom radiator. And the remanufactured 4.3 engine is $2700. Is this just crazy high? I am most certainly on a budget both money and time wise, this 2.5 death could not have happened at a worse time. And I did not see it all costing this much. Maybe I just rebuild my crap 2.5 and ax-5 and try to sell it. But I have so many accessories on my jeep and I know i won't get close to what it would cost to repurchase all or my aftermarket stuff. And the 4.0 route costs just as much as the 4.3.

Being that I am not car saavy in the least (I am a carpenter, not a mechanic) Does anyone have suggestions on how to make the swap less horribly expensive? Donor car with a tranny I want to use maybe? What chevy 5 speed goes well with a TJ? Oh well, thanks for the help in advance guys. Back to the drawing board.

joe_jeep 03-19-2013 04:46 PM

nv3500 chevy trans and tcase (np231c) would be the best option. find a cheap used 4.3L they run forever. dont buy a new or rebuilt one.
i bet you could get an entire drivetrain from a 4wd s10 or k10 for 1500 to 2000. engine swaps are never cheap.

sduncan 03-19-2013 06:52 PM

Your cheapest route for a motor swap is using a 5.2 or 5.9 Magnum. Do a search for the threads which have a lot of info on the topic..

$9500 is WAY too much for a 4.3 swap...I'm only a touch more than that with my Hemi conversion and thats with a new NP 231J HD ($1500) from JB Conversions added to the ticket.

99_TJ_Wyoming 03-19-2013 07:11 PM

Ok, so your a carpenter and not a mechanic. But. . . . . You were going to have to weld in new motor mounts, transmission mounts, bolt in the drive train, do the wiring, lots of fabrication, welding, and making things fit. This is not mechanical? Did you have a contingency plan for all that, I'm guessing you weren't going to send the Jeep to Novak.

Whatever your plan was for doing all that work, that's the hard part, the rest, aside from the wiring, is fairly simple. You need to keep in mind you aren't replacing a drive train, your'e upgrading a drive train, and upgrades aren't cheap, or easy, or quick, or painless. But it isn't insurmountable for someone who has the ability to weld, fabricate and has the mechanical knowledge to swap in a drive train.

If you want a new engine / transmission / transfer case you're going going to have to pay for it, no matter if Novak charges $9500 (not unreasonable for bolt in ready) or you buy a drive train out of an S-10, or if you piece together a GM 60 degree engine with an Isuzu bell housing and a Chrysler / Jeep transmission, it's going to cost some cash and the less cash you spend the longer it will take.

Do some serious research, do a hell of a lot of reading, even threads that don't specifically say 'engine swap' will have amazing amounts of information. It's all here. You can do it, it's just knowledge, and all you need is here (and a few other forums).

whitwt 03-21-2013 10:05 AM


Originally Posted by joe_jeep (Post 15159959)
nv3500 chevy trans and tcase (np231c) would be the best option. find a cheap used 4.3L they run forever. dont buy a new or rebuilt one.
i bet you could get an entire drivetrain from a 4wd s10 or k10 for 1500 to 2000. engine swaps are never cheap.

So I took your advice and found the used 4.3 with and nv3500 and a np241 t-case. I found it on the forum. A fellow jeeper is taking it out of his rig to put in a diesel drive train. So he is shipping it all my way when he is done.

But i have plenty to keep me busy until i get it. My poor ole Jeep will be dropped off by my uncle today. It was stranded outside of Albuquerque when she threw a rod. Thank goodness my uncle is a trucker and had a route that went right through there.

So this weekend will be full of prep work. Removing the grill and fenders and lifting off the tub. Take out the old drive train and clean up the frame. Let the adventure begin!!!!

captainauti 03-21-2013 10:33 AM

pics lots of pics.

Mcjeeperson 03-24-2013 01:37 AM

1 Attachment(s)
Here's the wiring harness. Engine and trans/tcase pics soon to come.

Mcjeeperson 03-24-2013 08:25 PM

1 Attachment(s)
The 4.3 in all it's glory! I'll send it your way soon as I pry it out of my jeep. Better pics to come hopefully next weekend.

whitwt 03-27-2013 07:17 PM

Just walked in the door after a long half day of taking out all of the elements the mount to the fenders, the wiring harness, the radiator, and I actually got the grill and the fenders off. More than I anticipated! I also used a full can of PB and hit the suspension and all of the body mounts. My hope is to pull the tub this Saturday. It is kind of a blessing having a wife that often works weekends. It means that I can work on pet projects guilt free.

I think that I may as well put in a lift kit while I have it stripped down to the frame. I am thinking about going with a 2.5 suspension and 1.25 body lift from rough country. Any suggestions? Should I just go with the 3.25 suspension lift? I am not sure yet. I guess I always have more reading to do. Pics soon. My phone's camera took a **** on me a few weeks ago.

So for the easy part has been easy. I expect it to be much harder from here on out...

Mcjeeperson 03-30-2013 09:57 PM

5 Attachment(s)
Now to figure out how to crate it up and send it your way!

theGiantPanda 03-31-2013 12:22 AM

congrats on taking on the swap. you can do it for WAAAAAY less than those quotes as you are already finding out. I am working on putting together a cost effective LS series swap kit together for us garage DIY guys. I have a new fuel adapter in cad design right now and hopefully will have 5 made this weekend. I am trying to provide most of the little key things needed to get the LS/vortec etc motors in the TJ and cut research, sourcing parts and install time down even more. Ill let you know how the fuel adapter and fuel line kit turns out, maybe it will work out that you can try one and let me know how it works..?

for sure do the body lift, you will appreciate the extra room here and there. I use the zone BL kit... 100 off ebay shipped... be ordering kits number 3 and possibly 4 this week.

get a bolt in aluminum 2 core ebay radiator 180 and then a efan and shroud kit for 100.... primary cooling system parts, done.. 280. the shroud does need a set of adapter plates to make it just abit wider and a 'bolt on'.. yes we are working on having some of those plates made up too. I have some pics in my 5.7 hemi build to show you how we did it. your pcm can run your efan relay if its programmed/reprogrammed to do it.

we just started gathering parts for our 5.3 swap into a TJ. we are going to make our version of a few things for it !!!

good luck on your swap. plenty of guys that have done it and are doing it here to help out.

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