4.0 head on 4.2 - considered a stroker?

[gijombo]

First post, first question:

I have an '85 CJ7 with the 4.2L Not to bore you with the same sad stories anyone who's ever had a carter carb, but you can appreciate why I'm ready for something different.

Question: Is swapping a 4.0 head, intake, pcm, essentials, etc. onto a 4.2L block considered a stroker?

I have a donor 4.0L and I have a tired 4.2L, so I have the crank and rods along with the advice on this forum I'm certain I can build at least a 4.5L or 4.6L. But then I'll have a useless 4.2L. Or I could go find a donor 4.2L crank and rods and keep the 4.2L stock for a later build up.

OR use the 4.0L head I have from the donor and put it on the 4.2L for now. Then build up the 4.0L block and take my time.

Thoughts?

Finding this site has certainly broadened my perspective and knowledge of the subject. Kudos to the founders of this forum and the brave souls who dared to be different!

[seanyb505]

A 4.2 short block with a 4.o head and intake stuff is just a 4.2 block with a 4.0 head and intake stuff. Stroking comes in when make the stroke of an engine longer. In our case its taking the 4.0 stroke from 3.413" to 3.895", by means of the 4.2 crankshaft.

Which direction you take is pretty much up to you. Will you need two engines? If not Frankenstein them and just make a stroker out of the 4.0 block and 4.2 crank and rods. But if you want two separate running engines, youll be faced with two situations. 1.)You stroke the 4.0 with your donor 4.2, and have to buy a new crank and rod set to rebuild your 4.2 block. 2.) You rebuild your 4.2 engine and save the 4.0 for later, youll have to buy a new crank and rod set to stroke your 4.0.

If you want two engines youll have two stock engines or youll be buying a crank and set of rods.

[gijombo]

Which direction is still the big question. I have a budget of about $3,000 but that includes everything. I need a new clutch, tranny work, new radiator and add 10% of unknowns.

The bore on a 4.2L is much smaller than the 4.0L, too correct?

I started this journey simply wanting to convert to fuel injection and getting rid of the carb. The engine rebuild has been part of this venture from the start, but as I go along I'm learning about more options. First, I was led down the path of swapping in a 4.0L head. After more research and finding this forum, the thought of stroking a 4.0L has become quite intriguing!

I really wouldn't have any use for the 4.2L if I go with a stroked 4.0L. My dilemma is wanting to keep the integrity of the CJ with matching numbers. It is still a bone stock Jeep and aside from a few minor accessories, is very clean. I don't know why I fight with that question because I don't ever see me selling it so does it matter if the numbers match? Not that an '85 is all that special anyway. An '86 w/ factory air and factory D44 might be a different case.

Thanks for the clarification

[Flash]

Personally, i say, build the stroker............If you are after a numbers match project.........you had better keep the 258............and that POS carb

If your interested in putting the 4.0L head and fuel injection on your 258......Look in "Swapology" here.

Not a bad idea any ways an, even if you go with the stroker........Your still going to need to learn how to do the fuel injection conversion!!!!!!

[John]

Which direction is still the big question. I have a budget of about $3,000 but that includes everything. I need a new clutch, tranny work, new radiator and add 10% of unknowns.

The bore on a 4.2L is much smaller than the 4.0L, too correct?

I started this journey simply wanting to convert to fuel injection and getting rid of the carb. The engine rebuild has been part of this venture from the start, but as I go along I'm learning about more options. First, I was led down the path of swapping in a 4.0L head. After more research and finding this forum, the thought of stroking a 4.0L has become quite intriguing!

I really wouldn't have any use for the 4.2L if I go with a stroked 4.0L. My dilemma is wanting to keep the integrity of the CJ with matching numbers. It is still a bone stock Jeep and aside from a few minor accessories, is very clean. I don't know why I fight with that question because I don't ever see me selling it so does it matter if the numbers match? Not that an '85 is all that special anyway. An '86 w/ factory air and factory D44 might be a different case.

Thanks for the clarification

A well done 4.0 efi head swapped on a 258 looks right at home and most would not notice. Nice power upgrade though. As far as stroking it, if you decide you want to stay with the block you have and want a stroker, http://www.rpmmachine.com/amc-stroker-kit-258.shtml
John

[gijombo]

I'm leaning more toward stroking the 4.0 adn setting the 4.2 aside for...ya'know, something else.

Thanks for the link. I'll read more tonight when I get home.

[Shark]

if you had the 4.2 block bored for 4.0 pistons and a 4.0 head i really dont see much difference between that and a stroker. except for the fact that it isnt stroked.

[oletshot]

My opinion, after the 4.0 was introduced the 4.2 became useless except for donor stroker parts. If the 4.2 needs a rebuild anyway, you might as well invest the money into the 4.0 or a stroker, cost is close to the same. Either motor will be better than a 4.2 (even if you put the 4.0 head on it). Your best idea is getting rid of the carb!

[Jeep-Power]

Question: Is swapping a 4.0 head, intake, pcm, essentials, etc. onto a 4.2L block considered a stroker?

This is the setup I have-- it has the same issues as far as timing, fuel pressure, injectors, etc. as a stroker, but no, it is not a stroker. The piston issues/options are not something I have have had to deal with (yet!).

I chose the head swap because I had recently rebuilt my 4.2. The thorrle body EFI I had (Electromotive JFI) had died and I was looking for an affordable and easy way to get it running again with fuel injection. A quick web search led me here, and the rest has been happy history!

Don't let them fool you (especially Simon )-- the 4.0 head WAKES UP the 4.2-- I still get surprised at the power this thing puts out. Now don't get me wrong-- next time I'm rebuilding the 6, it will be stroked with a cam. For now, the 4.0 head swap can't be beat as far as ease and inexpense. This of course assumes that the 4.2 that it is goin' on has a healthy bottom end (--not burning oil or knocking).


Yeah, I'm a bit of a black sheep around here, but alot of the issues we all have with fuel, spark,and sensors are all the same. The list serve and now this forum have been indespensable for me.



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