New 4.2 or new 4.0?

[carnuck]

Grand Cherokee 4.0Ls also have the centered fan (That's what I put in my '84 J10)
I would really suggest doing a '91 to '95 Wrangler 999 converter and flexplate off a 4.0L together to ensure it doesn't go in too deep, but I was under the impression the factory sensor was the same as the Hesco (mounted on the harmonic balancer)
   The 4 cyl is on the flexplate (I have one of those flexplates for sale for Renix TBI)

[olymunch]

In my research I came across this: http://www.jeep4.0performance.4mg.com/stroker.html
It describes all the different stroker options for the 6cyl. At the heart of the stroker kits looks like a lot of parts from the 258ci 4.2L. Now I've decided to stay with the crate 258 because instillation requires way less mods to the engine bay and bell housing etc.. I'll prob just upgrade the 4.2 to a 4.0 and add the mpi, however, if I was going to upgrade all the way with the stroker 4.6, could I still keep the crate 258? I'd like to get a wider stance and posi anyway.
Also upping to power with the 4.0 and mpi kit only, do I need to upgrade my rear end?
Oh and if there is a write up on converting the 258 to a 4.6L stroker can someone please let me know. There's info on converting a crate 4.0 to stroker but nothing that I can find on the 258.

[doc65]

The jeep stroker is by definition a 4.0 block with a 4.2 crank(or 232 crank for the newer "mini" stroker) there is not a way to use a 258 crate engine for a stroker as you couldn't bore a 258 that far unless it's a very rare block, the cylinder walls aren't going to take it. On that page you referenced (that's Dino, or Cheromaniac on Jeepstrokers.com) you could build a "poor man's" stroker.

I have one running 4.6 in a ZJ and am concurrently building 2 more for my 98 Ex-USFS XJ and my 82 SX/4  I'm using the heavy 12 cwt crank & short rods for the XJ one(66 lb. crank; more inertia, better for crawling), and a light 4 cwt crank & long rods with KB 944 pistons for the SX4 one(46 lb. crank faster spin up & better throttle response in a car for running around the dirt roads etc..).

A minimalist approach would be to take your 258 crank & have it ground(if needed, but often they can be re-used with just a re-polish), rebuild the 258 rods, then get a good running 4.0 that has good compression and pull it down, substitute the 258 crank & rods for the 4.0 ones using the 4.0 pistons(back into the same holes) have the cylinders re-honed/just break the glaze(you could even do this yourself with a cylinder hone & a power drill).  Put it all back together with new gaskets & possibly new bottom bearings as needed to match your 258 crank.  I personally would rather build from the ground up but the outlined method will work & get you to around 240 HP.  If for some reason you want to keep the Carb you could still do that however you'd need to convert to an electric pump as the 4.0 block has no provision for mounting the manual pump. If your 4.0 donor was sold due to a spun bearing(a great finds as it'll be cheap & you are going to be replaceing the crank & rods anyway) then you should be able to get it for around $200 which should put you all in at $500-$700 depending on need for bearings & how much machine work you decide to do.

By the way that scenario where you just break the glaze on the cylinder walls so that the rings will re-seat will actually give you a 4.5(.020-.030 over is 4.6 and .060 over yields a 4.7)   

[olymunch]

Oh! Well I guess that's why I couldn't find any info on it then. Well I guess the extra power and range I'll get from the 4.0 and mpi will have to do. What do you think, do it need to put a better rear end in?

[doc65]

I'd do something about the 2 piece axle shafts, otherwise it's probably fine.  There are millions of D35's(your aAMC-15 is basically a D35 with different shafts & the wheelbearings are different) on the road behind 4.0's they get a bit of a bad rap from the hard core 4x4 crowd but in an Eagle it should be fine.  Most anything that you could easily swap in is going to be lower geared than your Eagle.  That's not a terrible thing, but it opens the can of worms of needing to make the front match.  I haven't done the research for what it would take to put D35 solid axles into an AMC15(I'm sure they could be made to work with a different bearing or some ingenuity) If I were doing it and trying to keep my original ratio while getting rid of the 2 piece shafts I'd probably get a D35 from a wrecking yard, grind the welds to pull the shock mounts from both axles then put the Eagle shock mounts on the Cherokee axle & finally put the Eagles ring & pinion into it(I've setup R&P's before by the way, even for a NewB it's not terrible, just time consuming). 

My SX/4 is getting a Cherokee 8.25" rear axle with 3.07 gears & ZJ rear disc's a little later(next fall) she'll get later model axle shafts to go the the 29 spine and an Eaton worm-gear driven positraction     

[carnuck]

Eventually. I'm doing mine sooner than later. I have an XJ 8.25 with 3.08 to go in and non-vac front to match.
The axle tubes on the Eagle are a bit thinner than XJ as well.

[olymunch]

Sounds good, yea Im not yet that familiar what the different ratios do but it sounds like the one I have is good.
I'm just going to be going fast and doing some hill climbing and trails, no hard crawling.

[mudkicker715]

I can give he ll to my stroker on the trails it comes back for more.

i have a stroker 4.7 to drop in wifeys car. aftually i did. now to integrate it

[mick]

I also firmly believe that ignorance and frustration is the reason so many Eagles end up in the scrapyard.

Truer words never been spoken!

One calculation that is crucial to engine performance is quench.  Before I disassemble any engine I plan on rebuilding I measure piston height at TDC and mark it on the block in each corner if a "V" engine or at each end on an inline.  For instance if the pistons are more than .010" in the hole at the top of their stroke I have the deck milled to a measurement of .000" The reason for this is Felpro or Victor head gaskets are .043" crushed thickness.  The original shim type gaskets the manufacturer use are much thinner .023" the increase in gasket thickness with pistons deep in the hole at TDC causes reduced compression.  At a wimpy 8.2 to begin with, I will not tolerate anything less, let alone the fact that you get diminished returns on your cam selection with low compression.  Another reason why 4.0L have HP advantages over a stock 4.2L....COMPRESSION.  It's all the little things that make one engine run better than another, attention to the details.  If 9:1 pistons were redily availible for the 4.2 this wouldn't be as critical, but even if they were, I'd still get my quench to around .045".

[eaglefreek]

In my research I came across this: http://www.jeep4.0performance.4mg.com/stroker.html
It describes all the different stroker options for the 6cyl. At the heart of the stroker kits looks like a lot of parts from the 258ci 4.2L. Now I've decided to stay with the crate 258 because instillation requires way less mods to the engine bay and bell housing etc.. I'll prob just upgrade the 4.2 to a 4.0 and add the mpi, however, if I was going to upgrade all the way with the stroker 4.6, could I still keep the crate 258? I'd like to get a wider stance and posi anyway.
Also upping to power with the 4.0 and mpi kit only, do I need to upgrade my rear end?
Oh and if there is a write up on converting the 258 to a 4.6L stroker can someone please let me know. There's info on converting a crate 4.0 to stroker but nothing that I can find on the 258.

 

The jeep stroker is by definition a 4.0 block with a 4.2 crank(or 232 crank for the newer "mini" stroker) there is not a way to use a 258 crate engine for a stroker as you couldn't bore a 258 that far unless it's a very rare block.   

I know this is an older post, but I came across it while doing some searching for something else. The bore has nothing to do with a "stroker" it's the stroke that makes it a stroker. All stroker means is making the stroke longer. With the 4.0L stroker you have the same stroke as your 258 but the larger bore of the 4.0L gives you the added displacement.  Flatlander makes a kit to stroke the 258 so you can retain your stock block. http://www.flatlanderracing.com/strokeramc-258.html