best parts to use

[wolfesgreenxj]

I have a 2000 xj with a good running 4.0 but smokes an im wanting to build a motor for it. I also have a good running 91 yj 4.0 motor with 59,000 miles an a 4.2 rotating assembly with low miles. Im wanting to build a stroker with the 91 block so i can still drive my xj for time being. What would be the best combination of parts out of the 3 motors? Im planing on boreing it .30 over an buying pistons an rings, cam and injectors. Which would be the best to buy?

[wolfesgreenxj]

Im also trying to go cheap but without losing too much power.

[Cheromaniac]

Use the crank/rods from the 4.2 together with Speed Pro H825CP pistons in the '91 4.0 block. The SCR will be ~9.6:1 and you could end up with a modified version of the 4.6L low buck stroker recipe at http://www.jeep4.0performance.4mg.com/stroker.html

[RenoF250]

Im also trying to go cheap but without losing too much power.

The best way to get cheap is check around. I used Amazon, Summit, Clegg, RockAuto, and O-Reilly for my parts depending on who was cheapest. The difference was regularly quite significant and there was not one that was lowest for everything. The best deal I think I found was Chrysler 24.6 injectors for ~$25/each from RockAuto on clearance. Also got a header for $86 shipped. I also ran a stock timing chain since they seem to last >200k miles. I did not see a reason to improve on that.

I had the same goal as you and went with KB IC944 piston, no decking, 24.6 lb. injectors, and Crower BajaBeast cam with camsaver lifters. It runs great, I am pretty happy with it.

[akadeutsch]

I like your build. You will have fun putting it together. But I dont understand why everyone here wants to use the forged pistons. Are you adding a lot of boost? IMO, a good hyper piston is a better fit for a naturally aspirated stroker. The hyper piston will expand less meaning you are allowed a tighter piston to cylinder tolerance. Tighter clearances here are a good thing as you will have less "slap" on cold start and less "blow by" all around. And not to mention that a good hyper slug can already handle a little (6-10lbs) boost Why spend 500 dollars on Forged pistons unless you are going to force feed the beast? Am I missing something?

[SilverXJ]

It is not so much the piston material but the fact that they go on the longer 4.0L rod. Plus forged pistons will also stand up to detonation on a poor tune better than hypers.

[RenoF250]

It is not so much the piston material but the fact that they go on the longer 4.0L rod. Plus forged pistons will also stand up to detonation on a poor tune better than hypers.

That and the IC944 has enough volume it does not need to be dished. Also, I did not pay $500 for them, they were just under $400 vs. $200 for Hypers + sending them to get cut was close enough to a wash.

Mine have 0.0035" clearance and have not made noise so far but they have only been down to 50F so far, we will see this winter.

[SilverXJ]

They will make a little noise when it gets really cold. Only for a minute or so though.

[purple_jeep]

I went forged for the possible improvement in life and the cost of Hypers plus 4.2L arms vs Icon 944 from Ebay for $380 was pretty much a wash.

Cheers

Chris

[wolfesgreenxj]

I was going to go with the kb 944 piston just because of the pin height. If there is a cheaper way to go using the 4.2 crank an 4.0 rods let me know.

[Retlaw01XJ]

I like your build. You will have fun putting it together. But I dont understand why everyone here wants to use the forged pistons. Are you adding a lot of boost? IMO, a good hyper piston is a better fit for a naturally aspirated stroker. The hyper piston will expand less meaning you are allowed a tighter piston to cylinder tolerance. Tighter clearances here are a good thing as you will have less "slap" on cold start and less "blow by" all around. And not to mention that a good hyper slug can already handle a little (6-10lbs) boost Why spend 500 dollars on Forged pistons unless you are going to force feed the beast? Am I missing something?

The KB pistons can often be had for about $360 on eBay from Titan/old yeller.
They work with the stock 4.0 rods.
They don't need the dish machined for correct CR.
The alloy KB uses only need 0.0025" to 0.0035" piston-wall clearance.
They are much more durable and won't break into pieces as hypers are prone to do when they reach their failure point.
My original engine failed due to a broken piston skirt. Didn't want that to happen again!
I don't mind spending a bit more for a better part.

[wolfesgreenxj]

What is the cheapest piston i could use? I cant find the kb944s for much less than 500$? Im starting the build soon. If i got to pay that much for pistons ill just got with the 4.2 rods an a .30 over stck type piston. Im trying to build this cheap as possible while still getting a lil more power.

[SilverXJ]

For a short rod I would go with Sealed Power hypers with metric rings.

[wolfesgreenxj]

What would my motor be with 4.2 crank, 4.2 rods, .30 over 4.0 pistons in a 4.0 block? Would it be more or less reliable that way? Would i be missing out on alot of power?

[RenoF250]

What would my motor be with 4.2 crank, 4.2 rods, .30 over 4.0 pistons in a 4.0 block? Would it be more or less reliable that way? Would i be missing out on alot of power?

Clegg engine had IC944 for ~$400 when I bought them if that helps.

There should be no noticeable difference in power or reliability though. The longer rod is a little better but I really doubt you will be able to tell.