2.5L swap to a 3.4L?

I've kinda seen on here a couple times about a 3.4L swap? I have a 86 Comanche with the 2.5L, 904. Can I get a 3.4 out of a Firebird with a manual trans( so I don't have to worry about the automatic wiring)Wiring harness,Computer, an Dash cluster. Will my 904 bolt to the 3.4L Engine? Or will I have to change trannys to? Also can I take my NP207 out an Put a NP231 in? Same spline count an bolt pattern? I'm new to the whole JEEP thing some I'm kinda try to figure out what will work an what won't. This truck is not a DD so Streetabilty is not a big Issue.

The Jeep 2.5L engine was engineered to use the same bell housing to block bolt pattern as the 2.8L GM V6, which is the same block as the GM 3.4L. So you can swap in a 3.4L and use your existing transmission. An early (1987 through approximately 1990) 231 transfer case can be used instead of the 207, because both are 21 splines on the input shaft. About 1991 Jeep changed to a 23-spline input shaft, which will not mate up with your tranny.

What flexplate would I use? Does the 904 converter bolt to the 3.4 flexplate? Thanks for the info on the T case.

I put together this pile of info a few years ago but until now it was always a word document. I figured now's as good a time as any to see if it'll fit on a forum. :D It's not complete though. I'm still waiting for someone to try it and report back with the details and a whole mess of photos.

Jeep on!

--Pete

 

 

 

Swapping out a 2.5L Jeep engine for a 60* Chevy V6

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First, I feel it’s my responsibility to start off with all the negatives and typical nay-say that would generally be brought forth if this were to be asked on a open forum/message board.

 

-It would be *infinitely* easier and probably more cost effective to sell the Jeep and buy another with the 4.0L.

-Swapping engines, even among identical blocks, is a HUGE undertaking. They always require more time and money than planned. And always *expect* surprises!

-you’ll likely need parts from both a Chevy car and/or a Jeep XJ/MJ equipped with the 2.8L

-Another option is that you could build up the 2.5L. Mopar Performance carries hop-up parts as does Clifford’s. You're not going to get v8 power out of it, but v6 numbers are attainable.

-The state you live in might require all of the proper smog equipment to be there at the next inspection.

 

 

If all that still hasn’t scared you out of the project, then let’s continue with the facts, rumors, hearsay, and theories I’ve sought out and collected concerning swapping the Jeep 2.5L I4 for a Chevy V6.

 

The bellhousing-to-engine bolt patterns are supposedly identical between the 2.5L I4 and the 2.8L v6. (They share transmissions)

The 2.8L v6 is really a Chevy 60* v6 engine.

This means that the 2.5L shares a bolt pattern with the 2.8/3.1/3.4 family of Chevy engines.

 

The engine mounting locations are supposedly identical between the 2.5L I4 and the 2.8L v6.

The 2.8L v6 is really a Chevy 60* v6 engine.

This means that the 2.5L shares engine-mount locations with the 2.8/3.1/3.4 family of Chevy engines.

 

These are generally the hardest steps of any custom engine installation and they’re already finished for you.

 

There is one caveat though. I’ve heard that both the AX-5 and the T-5 were used in early Jeeps. You’ll need to know which you have. There might be differences. (and there might not, I’m still working on that.)

 

Check out car-part.com to gauge costs for the new engine. They don't have every junkyard in the world, but they have a whole lot and you might get lucky and find one near you. When using car-part, make sure you search for different years and cars. Car-part organizes each search by EXACT matches. Below is a breakdown I did a while back of interchangeability in Chevy engine years as sorted using car-part.com. The search was for a Camaro v6 engine of every year from ‘85 to ‘95. The Firebird's results should be the same. The S-10 and Blazer will be a tad different because they went directly from the 2.8L to the 4.3L somewhere in the early ‘90s. (The 4.3L is a 90* block and that’s a completely different family of engines).

 

93-95 - 3.4L

91-92 - 3.1L

90 - 3.1L

89-90 - 2.8L

88-89 - 2.8L

87 - 2.8L

85-86 - 2.8L

 

Unfortunately Car-part doesn't say *WHY* the years (of same engine size) are different from each other. If you had a '90 Camaro and wanted a direct swap of the *entire* engine assembly, then '90 is the only year. The change could be a major as adding fuel injection or as minor as an emissions tweak. (i.e. a search for just the engine block reveals that the '90 - '92 are indeed interchangeable blocks.)

 

I also found a website that specializes in the above push-rod engines.

http://www.60degreev6.com/

 

The engine has to be from a rear-wheel drive vehicle. Some of the front-wheel-drive versions of the 60 degree engines are internally identical to the rear-wheel drive, but they have different locations for the engine mounts, oil filter, water pumps etc. Newer fwd 60* v6 engines are overhead cam and are VERY different.

 

The following items would be needed if you were replacing a 2.8L engine, so I’m assuming they’ll be also needed for replacing the 2.5L. You’ll need to acquire an electric fuel pump and likely an oil pressure cut-off switch for said pump. The 3.1/3.4 blocks apparently don’t have any provisions for a mechanically driven pump. You’ll need to modify or replace the flywheel (which will be externally balanced) with a neutrally balanced one suitable for use with the internally balanced 3.1/3.4L. I don’t know if the flywheel from the 2.5L would bolt to a 3.1/3.4, nor am I certain that a flywheel from a 3.1/3.4 will work with your clutch. Both propositions might work. I’ve heard from two sources that 2.8Ls found in early ‘90s S-10s are internally balanced and that means a flywheel from one should fit the bill. Or you could snag a flywheel from an externally balanced 2.8L engine. It’s a simple matter to get it neutrally balanced at a machine/automotive shop. There is a solution, but I’m not positive which it is. Similar problems exist with an auto tranny’s flexplate.

 

There is a concern with which flywheel works with which starter. I do know that a Jeep 2.8L flywheel (neutrally balanced) will bolt to a 3.4L engine and function with the 2.8L’s starter. The theory is that, since the 2.5L and 2.8L Jeeps used the same tranny with the same bellhousing bolt-patterns, it’s reasonable to assume that the starters are also identical. My parts manual only goes back to 87, so I can’t verify that myself. At the very least, you should be able to use a starter for a 2.8L engine. I found an old post online from a guy that swapped in a 2.8L from a Jeep into his 2.5L equipped XJ and he didn’t mention any problems with the starter. I haven’t been able to get a hold of him though, so I can’t ask him any questions.

 

Those replacing a 2.8L will only need the block/heads etc., but when replacing a 2.5L, you’ll need a complete engine (or piece together a complete engine) from the belts to the wire harness.

 

There’s always a concern with putting more power through a stock tranny. Advance adapters sells kits that’ll bolt a 4.3L up to the AX-5 tranny, and that engine makes more ponies than any stock 3.4L, so I’m quite confident that this trans will do fine under responsible driving. (NO 4wd burnouts! ;-)

 

You could make your life a bit less complicated by being a bit less greedy on horsepower. Go for the latest year carbureted engine or swap the entire carb, harness, and accessories from a 2.8L Jeep engine onto your newer Chevy block. I’ve heard that the Jeep wire harnesses from the 2.8 and 2.5 are very similar and may even interchange at the firewall.

 

Some of your sending units might need to be changed to the correct year in order for the gauges to all work properly. Not a big deal, but that’s why I’d try to get a gauge cluster from a 2.8L Jeep (one with all the gauges if your current Jeep is cursed with the idiot lights) just in case. Don’t pay for it until your sure you’ll need it (unless you’re upgrading), but also don’t pass up a free or next-to-nothing one either.

 

Here is what I would do:

-Find a donor 2.8L engine from a Jeep Cherokee or Comanche. The cheaper the better. A locked-up/frozen engine would be fine. The closer the vintage is to your year Jeep, the better. Buy a whole cheap Jeep if you’d like. It’d be a spare parts bonanza! I bought an entire ’78 Bronco for cheaper than the axles would have been from a junkyard. And now I’m selling off the extra parts and will make up more than the original cost!

-Get basically the entire 2.8L engine compartment, and I mean EVERYTHING you can that touches the engine, including the starter. You may also need parts of the body wire harness and the gauge cluster.

-You’ll also need the exhaust. At least from the engine to the catalytic converter. Both Jeeps had a single exhaust pipe from the cat back, but you’ll need the headers and Y-pipe from the Jeep v6.

-Find your donor Chevy engine 3.1/3.4/or later year 2.8. You’ll need only the engine itself. All the accessories (water pump, alternator, maybe even stuff like the valve covers) will be coming from the 2.8L.

-You’ll also need the engine’s half of the motor mounts from one of these blocks.

-Go through all of your parts thoroughly. Treat it to an engine rebuild if you want. There’s no hurry if your Jeep still works as is. If any accessories from the 2.8 look questionable, buy a new part. You can buy all new/rebuilt parts if you want. The main reason for acquiring the whole Jeep engine is so you can see where all the wires, vacuum lines etc. go and you’d have every one of the necessary brackets. I personally think that this would make life a lot easier.

-Now merge the two engine assemblies together as best you can (for it being out of the Jeep).

-I would never think of using the woeful Jeep carbs. Get an aftermarket one. You could even get an aftermarket intake manifold (like Edelbrock) and run a small 4 barrel.

-When your new engine is ready, start work on removing the old engine from the Jeep. Take note as to where *everything* goes and came from. I’ve never done an engine swap, but I do know that attention to the details will make life easier. You never know what you’ll come across or have to replace or, at the very least, you might need to retain for your new engine. For my ’88 Comanche project (made it a 4x4 using Bronco axles and a TJ trans/t-case), I wrote up a spreadsheet and listed everything, step-by-step. That way I could continually update it as I went along.

 

The reasons why I would do it this way are thus:

The Jeep 2.8L and older Chevy 2.8L engines are notoriously weak both in horsepower and in longevity (although I have a 170K+ mile 2.8 in my ’86 and it runs okay. No horsepower though.) This is due to poor build standards and a poor design. The later year 2.8s and the 3.1s and 3.4s had an internal redesign with larger oiling passages etc. and are great engines. But they use fuel injection systems and I don’t like the idea of splicing wires till the cows come home. It isn’t exactly “hard” per-se, but it is monotonous, laborious, and you must be meticulous in the details. The Jeep 2.8L and 2.5L setups should be similar enough as to greatly ease the crossover work.

 

I haven’t touched the subject of emissions controls here as I have no idea what passes for legal in your neck of the woods. I live in Michigan and just about anything goes here. :-)

 

That’s about as far as I can take you. I haven’t done the swap myself, nor have I ever even seen a 2.5L up close. I have an ’86 2.8L, a an ’88 4.0L and shop manuals from ’86, ’89, and ’91. I highly recommend getting a shop manual for your Jeep. They are kinda hard to find for the older years (try eBay) and pre-87 versions are mucho inferior to the later ones, but 87+ don't cover the 2.8L at all. Get one that’s closest to your Jeep’s year. Another alternative is the alldata.com site. It’s like having a shop/parts manual online. They cost $25 a year for a subscription ($15 to renew and $15 for each additional vehicle). I have subscriptions for my parents’ minivan, my sister’s TJ and my Dakota. I’d probably have one for my Jeeps to if I didn’t already own three shop manuals and a parts manual.

 

It’s amazing what you’ll learn when you do it yourself. I had done nothing like my project before. It’s been a challenge sometimes (especially adapting those Ford axles) but fun none the less. Now I’m real close to having “my own” rig to take out on the trails. No more being a passenger in someone else’s’!

 

Here are some links that might prove useful:

http://www.off-road.com/jeep/cherokee/x ... 4swap.html

http://www.60degreev6.com/

http://www.naxja.org/forum/showthread.php?t=42278

http://jeepsunlimited.com/forums/showth ... light=3.4L

http://www.lunghd.com/Tech_Articles/Pro ... ect_XJ.htm

 

Remember though, it’s always physically and monetarily easier to just sell it and buy a new Jeep, but you won’t learn anything new from that and if you’re as attached to yours as I am to mine, you couldn’t do that anyway. ;-)

 

Jeep on!

--Pete

WOW thats alot of info. Thanks alot. I printed everything you had listed above plus a detailed description an pictures of one that has been done. It came from somewhere when I hit print but its a really nice article :lol: