Jeep Strokers

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?

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

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

wolfesgreenxj wrote: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.

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?

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.

SilverXJ wrote: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.

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

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

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.

akadeutsch wrote: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.

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.

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

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?

wolfesgreenxj wrote: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.