Help me decide 2.8 to 3.4 or 4.0?

[Jacob Ochs]

Ive been debating this ever since ive got my MJ. An engine swap and which one to do! My father has the 4.0 in his cherokee and I love the power of it and everything about it. It is also a bullet proof motor. If I were to go this route I would get a whole new donor cherokee and swap the engine, tranny, TC, wire harness, ect.. and I can get one for under 1000 here in St. Louis.

 

Now on the other hand I could get a 3.4 from a camaro for $400 with 80k on it and have it bored and stroked for under $ 1,000. And from what ive been told this is a direct swap to my MJ as it is.

 

So I need help deciding which Is the better route to take! The 4.0 with more power and work Involved or the direct bolt 3.4. Also trading my MJ for one with the 4.0 is not an option. I love this thing to death it was my first vehicle and I plan to keep it forever if possible.

 

Any oppinion is appreciated!:) ide like to get as many oppinions as possible! This is all for future refrence so I can look back when this project comes up In time.

[onlyinajeep726]

Keep it Jeep... lol.

 

I may be biased, though hehe. :yes:

[nitroxsteve]

I'm guessing you have an 86 with a 2.8, I'd go 3.4

[Eagle]

I would go with the 3.4, but I would NOT try to bore it -- unless it needs a basic .030 overbore for the rebuild. And I have no idea how you would stroke it. The 4.0L to 4.6L strokers are possible because the older AMC/Jeep 4.2L used the same block but had a longer stroke and smaller bore to achieve it's displacement.

 

The 3.4L will be a significant improvement over the 2.8L -- especially if you set it up with the Camaro fuel injection, or even a good Weber carb. Don't try to push the envelope so far that you create an unreliable or short-lived engine.

[Dadinator]

3.4

[johnj92131]

... Don't try to push the envelope so far that you create an unreliable or short-lived engine.

 

^ Those are very wise words.

 

Here is a link to some good information on the 3.4 V6 engine:  http://www.ls1.com/forums/f68/some-insight-into-3-4l-ohv-motor-4706/

 

Stay with the V6 and use the latest stuff GM put 15 more years of engineering time into and built the factory parts required.  In the end, you will have a much more interesting truck than just the common 4.0 swap into an 86.  And that 3.4 V6 modified to 99 specs will run so much better than the 85/86 2.8 V6.

[dasbulliwagen]

There are write ups about adapting the Camaro injection as a standalone system. This would be the best way to go for power reliability and economy.

[benjy_26]

I'd also do an injected 3.4. Just do a basic rebuild for reliability with quality parts, keep the overall weight of the vehicle down, and enjoy driving it.

[Jacob Ochs]

I would go with the 3.4, but I would NOT try to bore it -- unless it needs a basic .030 overbore for the rebuild. And I have no idea how you would stroke it. The 4.0L to 4.6L strokers are possible because the older AMC/Jeep 4.2L used the same block but had a longer stroke and smaller bore to achieve it's displacement.

 

The 3.4L will be a significant improvement over the 2.8L -- especially if you set it up with the Camaro fuel injection, or even a good Weber carb. Don't try to push the envelope so far that you create an unreliable or short-lived engine.

Thank you, really good advice!

[dasbulliwagen]

Too much power will also eat an AX4 or AX5 alive. If you have the A904 auto you should be OK as those were used behind slant 6's and small Chrysler V8's. There are upgrade kits available for the auto to improve its shifting that are bolt on as well. I have a couple of 86 parts vehicles that I want to build one out of and the XJ has the A904 and NP228 with the 2.8. A 3.4 inj engine with the A904 may be a future drive train for the 86 MJ I have parked. I'd like to build it in the future for my daughter to drive. I have 10 years at this point to get it done. That SHOULD be enough time!

[Jeepman]

3.4 is my Vote...

[Jacob Ochs]

Too much power will also eat an AX4 or AX5 alive. If you have the A904 auto you should be OK as those were used behind slant 6's and small Chrysler V8's. There are upgrade kits available for the auto to improve its shifting that are bolt on as well. I have a couple of 86 parts vehicles that I want to build one out of and the XJ has the A904 and NP228 with the 2.8. A 3.4 inj engine with the A904 may be a future drive train for the 86 MJ I have parked. I'd like to build it in the future for my daughter to drive. I have 10 years at this point to get it done. That SHOULD be enough time!

Hopefully 10 years is enough! I have the ax-5 will that be a future problem for me? I don't drive wrecklessly or go hard on my transmission!

[Jeep Driver]

 

Too much power will also eat an AX4 or AX5 alive. If you have the A904 auto you should be OK as those were used behind slant 6's and small Chrysler V8's. There are upgrade kits available for the auto to improve its shifting that are bolt on as well. I have a couple of 86 parts vehicles that I want to build one out of and the XJ has the A904 and NP228 with the 2.8. A 3.4 inj engine with the A904 may be a future drive train for the 86 MJ I have parked. I'd like to build it in the future for my daughter to drive. I have 10 years at this point to get it done. That SHOULD be enough time!

Hopefully 10 years is enough! I have the ax-5 will that be a future problem for me? I don't drive wrecklessly or go hard on my transmission!

 

So everyone says........

 

 

But I have yet to read anywhere whereas anyone has grenaded an AX5.

 

 

My AX5 now shifts flawlessly with the new Core/Hurst shifter......flawless.

[Jeep Driver]

BTW, save yourself a ton of grief.

 

Build the 3.4 thoughtfully, do all your homework and choose the best parts you can afford. Combine performance with reliability, keeping mileage in mind.

 

Once the engine is built, you engine bay prepped, it's a one weekend swap. If you go headers, you may have to get to the exhaust shop on Monday....otherwise, you are back on the road.

 

Then if you want to go injected.....do your homework....gather parts....prep.........then that's another one weekend swap.

 

Be methodical.

[Jacob Ochs]

BTW, save yourself a ton of grief.

 

Build the 3.4 thoughtfully, do all your homework and choose the best parts you can afford. Combine performance with reliability, keeping mileage in mind.

 

Once the engine is built, you engine bay prepped, it's a one weekend swap. If you go headers, you may have to get to the exhaust shop on Monday....otherwise, you are back on the road.

 

Then if you want to go injected.....do your homework....gather parts....prep.........then that's another one weekend swap.

 

Be methodical.

I have, once I get my mind set on something it eats at me until I end up doing it! So all weekeed Ive been reading up on swaps and I would like to keep the 3.4L fuel injection system but am very confused on how to do this.

[johnj92131]

You should also look at the GM High Value engine.  It is more than 20 years newer version than the 2.8 V6 with all kinds of improvements.  The biggest version of this V6 is 3.9 litres (237 cubic inches).  It has 90% of max torque available between 1500 rpm and 5500 rpm.  Great for a truck.  Offers variable valve timing, fuel can be anything from  RUG to E85.  And it offered Active Fuel Management for improved highway mpg.  About the only thing missing is direct injection.  Here is a quick link:

 

http://en.wikipedia.org/wiki/GM_High_Value_engine

[Eagle]

But I have yet to read anywhere whereas anyone has grenaded an AX5.

You mean other than a certain Comanche Club member (who will remain anonymous) who tried to run them behind a Buick 3800?

[shelbyluvv]

Or the guy who has replaced 4 of them behind a 2.5? The AX-5 is fine for a street queen. Put bigger tires, deeper gears and rocks into the equation and they just can't handle it.

[ggcnash]

You should also look at the GM High Value engine. It is more than 20 years newer version than the 2.8 V6 with all kinds of improvements. The biggest version of this V6 is 3.9 litres (237 cubic inches). It has 90% of max torque available between 1500 rpm and 5500 rpm. Great for a truck. Offers variable valve timing, fuel can be anything from RUG to E85. And it offered Active Fuel Management for improved highway mpg. About the only thing missing is direct injection. Here is a quick link:

 

http://en.wikipedia.org/wiki/GM_High_Value_engine

+1 This could get very cool!

[Jeep Driver]

 

You should also look at the GM High Value engine. It is more than 20 years newer version than the 2.8 V6 with all kinds of improvements. The biggest version of this V6 is 3.9 litres (237 cubic inches). It has 90% of max torque available between 1500 rpm and 5500 rpm. Great for a truck. Offers variable valve timing, fuel can be anything from RUG to E85. And it offered Active Fuel Management for improved highway mpg. About the only thing missing is direct injection. Here is a quick link:

 

http://en.wikipedia.org/wiki/GM_High_Value_engine

+1 This could get very cool!

 

Those are all front wheel drive engines. Don't know how cool that would be.

[Jacob Ochs]

You should also look at the GM High Value engine. It is more than 20 years newer version than the 2.8 V6 with all kinds of improvements. The biggest version of this V6 is 3.9 litres (237 cubic inches). It has 90% of max torque available between 1500 rpm and 5500 rpm. Great for a truck. Offers variable valve timing, fuel can be anything from RUG to E85. And it offered Active Fuel Management for improved highway mpg. About the only thing missing is direct injection. Here is a quick link:

 

http://en.wikipedia.org/wiki/GM_High_Value_engine

thanks for the info, is this an easily done swap?

[Jacob Ochs]

Or the guy who has replaced 4 of them behind a 2.5? The AX-5 is fine for a street queen. Put bigger tires, deeper gears and rocks into the equation and they just can't handle it.

Mine for the time being is a street queen, I just graduated and don't have the money to replace parts that I would break on the trail or rock crawling but I would love to do it one day! For now I have a 6 inch lift and 33's with a rear ford 8.8 and front Dana 30 both with factory 4.10 gears! With this setup, in your opinion, do you think that my transmission would do well?

[Jeep Driver]

 

You should also look at the GM High Value engine. It is more than 20 years newer version than the 2.8 V6 with all kinds of improvements. The biggest version of this V6 is 3.9 litres (237 cubic inches). It has 90% of max torque available between 1500 rpm and 5500 rpm. Great for a truck. Offers variable valve timing, fuel can be anything from RUG to E85. And it offered Active Fuel Management for improved highway mpg. About the only thing missing is direct injection. Here is a quick link:

 

http://en.wikipedia.org/wiki/GM_High_Value_engine

thanks for the info, is this an easily done swap?

 

Go to his link, read my last post, other page.

[Jeep Driver]

Just to shed light on my comment-

 

The FWD block may not be adaptable to a RWD truck,  you'll have to compare blocks. The engine mount brackets are surely not the same. Oil filter may not be in the same location. Starter mount may not be in the same location and may not work with a RWD bell housing. Intake will likely be facing to the cowl and not the front of the engine in you truck. A lot of adaption may need to take place.....you'll have to compare the blocks.

 

Ignition and fuel delivery will be complicated by the Flex Fuel and variable valve timing........There is likely a lot to this conversion as it relates to the ECU/harness.

 

I doubt you will find headers or other exhaust manifolds to fit these heads.....etc.....

 

Wiki states the engine are no longer sold in the US and have not been since 2012......likely little support other than replacement parts.

[johnj92131]

 

You should also look at the GM High Value engine. It is more than 20 years newer version than the 2.8 V6 with all kinds of improvements. The biggest version of this V6 is 3.9 litres (237 cubic inches). It has 90% of max torque available between 1500 rpm and 5500 rpm. Great for a truck. Offers variable valve timing, fuel can be anything from RUG to E85. And it offered Active Fuel Management for improved highway mpg. About the only thing missing is direct injection. Here is a quick link:

 

http://en.wikipedia.org/wiki/GM_High_Value_engine

thanks for the info, is this an easily done swap?

 

NO.  I will take a whole lot of research.    Easily done is the huge advantage of the 3.4 V6. 

 

What the high value engine offers is a much more modern version of the original 2.8 V6 family.  But modern engines have become much more complicated.  Nothing interchanges from the original 265 cubic inch Chevrolet V8 from 1955 to today's Small Block Chevy. It is not that bad with the V6.  The 3900 v6 has been swapped into some Pontiac Fieros and they went out of production in 1988.  So the Fiero dated to the same time period as the Comanche, it just had a little longer run.