Jeep Strokers

Like many of you I am building a 4.6. This is my first one. I have a degree in auto mechanics and am ASE certified so I should be able to handle the assembly but I am unsure about the math. Here is my recipe. Think it will work?

-4.0 block bored +.030, line honed, and decked -.020
-Jeep 4.2L 3.895" stroke crank, not sure what the machine shop will tell me that I have to do to it yet.
- Jeep 4.0L 6.125" reconditioned rods
-KB +0.030" bore pistons/rings with a ????? pin hight
-Clegg stage 3 cam/lifter/timing kit, Cam duration 266/272. Duration at .50 214/218 Gross Valve lift .490/ .488
-Mopar Performance gasket kit
-Ported big valve 2.02"/1.60" cylinder head cast #0331 "Tupy"
-Mopar Performance 0.043" head gasket
-???? quench height. why is this important?
-ported 63mm TB
-stock injectors...for now
-Kolak ceramic header inside and out with 2.5" tubes all the way to high flow cat, and flowmaster exhaust.

Thoughts?

I just learned that there were different counter weight crank shafts in the jeep 258 4.2L engine. I just bought an old 258 out of an 88 YJ. How many counter weights does it have? I'll search around a little bit and find some information and post it here.

Maybe of your questions will be answered here: http://www.jeepstrokers.com/forum/viewforum.php?f=34

Good day to you and welcome to the forum. Sounds like a fun project and a good set of parts list to start with.

As for the cw on the crankshaft it's probably going to be a 4lb cw. There are casting numbers found on the crank and when you search for those casting numbers (be it google, jeep strokers, jeep forum, naxja) you should be able to find out more information on it.

There is a wealth of information on this site alone and I find myself re-reading information 2 and 3x. After all repetition has been known to be the mother of all skill.

Quench from my understanding will effect your combustion. It's location is between your cylinder head and the top of your piston. It has been known to play a role in how efficient your combustion will be, detonation, swirl in the chamber, and emissions. If you have a question more times then not regarding this build just use the search. Chances are it's been touched on at least once like a fat guy in a las vegas buffet.

Any 258 crank newer than 81' will be a 4cw light version. The 12cw cranks ran from 72'-80'. There are differences with the snout length tho. The newest 258's using a serpentine setup have the short snout and will drop into the 4.0 platform with no modifications.

Mine is the 4 CW crank. I count 9 but I weighed the crank and it weighed 44 lbs. Which means it has four CW. The 258 that it came out of had a serp belt so I am not worried about the snout length. My next question is about rods. I have searched and searched for a thread on which rods to use. I could go with 4.0 rods or 4.2 rods.
The stock 4.0 rods = 6.125" and the 4.2 rods = 5.875"
Rod Ratio = (rod length / stroke) so...
4.2 rods...5.875(4.2 rod Length)/3.895(258 stroke) = 1.5 rod ratio higher rod angle and greater propensity for failure!!
4.0 rods...6.125(4.0 rod length) /3.895(258 stroke) = 1.7 rod ratio Lower rod angle for greater reliability!!!
I will use the 4.0 rods.
Next I need to find pistons.

have Diamond machine you up a set of forged pistons that will net a zero deck height. Not that much more then off the shelf KB`s. Sorry I am not an advocate of milling the block deck surface anymore then to flatten it out and certainly not .025.

Yeah, I don't want to push it too far, but my compression ratio will suffer if I don't go for a zero deck height.
Question. I imagine pre-assembly is required to get a zero deck height. I am shooting for a CR of 10:1. Will I be able to achieve this without a zero deck height? Will I need domed pistons? I have not seen much written about CR above 9.5:1. Is this because it would require racing fuel?

I have decide to change up my recipe a little bit.
4.6L "poor man's" stroker

Jeep 4.2L 3.895" stroke crank ground .030 under on mains and rods...total weight 44 lbs
Jeep 4.0L 6.125" rods shot peened and polished
Keith Black UEM-IC945-030 forged pistons
Comp Cam 68-232-4 camshaft
DIY Ported HO 1.91"/1.50" cylinder head
Mopar/Victor 0.043" head gasket
adjustable Map
Clevite Bearings
Doug Thorney Header from Kolak
63 mm TB
Accel 24lb/hr injectors,

SCR= 9.81:1 DCR=8.24

I brought my block and head to G and S auto parts and machine shop in Littleton CO. They cleaned and magnifluxed both and I just got the call that everything checks out with no cracks. Great news!!!
Next, I will DIY port my head and then bring it in to have a nice 3 angle valve job done. Then I will start building my block

With your above recipe, what does the 'squish' work out to be?

jeepxj3 wrote:With your above recipe, what does the 'squish' work out to be?

Way to high. In the area of .070

akadeutsch wrote:Question. I imagine pre-assembly is required to get a zero deck height. I am shooting for a CR of 10:1. Will I be able to achieve this without a zero deck

Yes you will have to setup any motor you are building to measure where zero deck will be. After the block is cleaned up and bored to the new piston size you can slide them in and measure with a depth mic. Be aware that there are sometimes variances in rod lengths from resizing and/or factory tolerances, and possibly slight variations in crank throws... so don't assume they are all the same length.. Measure so you know exactly how much you can take from the deck. If you plan on running 10:1 I'd highly recommend running a tight .038-.045 total quench height. But, with it that high and with an iron head... you'll still be flirting with potential ping issues when hot and under load w/ pump gas. Why not play it safe and keep it in the low/mid 9's?

akadeutsch wrote: Will I need domed pistons?

No, not with a stroker setup. Most strokers need dished pistons to compensate for the increased volume from the added stroke.

What will this motor be used for?

Sorry akadeutsch you were warned about deck height, compression and quench a long time ago.

You did not want to spend the time or maybe the money to do it right. Hopefully you can back track on the 945`s `cause unless you have some magic formula this engine will not live up to your expectations.

jsawduste wrote:

jeepxj3 wrote:With your above recipe, what does the 'squish' work out to be?

Way to high. In the area of .070

That's what I thought. So you need 0.030" longer rods $$$$ or custom pistons made with 0.030" more pin height than the KB 945s.

Which is why folks have been saying custom pistons. I chose Diamond (Diamond also supplies Hesco) as they are well respected and local to me.

The other course of action is folks taking .025 ish off the deck. Not fond of this as now you have to come up with the volume in the chamber which is not easily done. The other side is the structural integrity of the block itself after taking that much metal off. Failing head gaskets are not uncommon as the block is quite long by comparison which makes it susceptible to warpage.

Either way creates a compromise. Simply buying the correct pistons avoids all this and you can spec out exactly what you want.

I`ve been running a set of .080 over Diamonds with a zero deck and an actual compression ratio of 9.65 since 2006.

Last I looked 944`s were going for about 550 plus pins and this is for a simple hyper piston. Talked with Mike Panetta at Diamond a week or so ago and they were making forged to your specs for about 125 a hole with pins.

So if we guess that 944`s with pins works out to 625. The custom made Diamonds come out to an extra 125

With so much riding on the relationship of the quench (squish), compression, longevity, reliability why wouldn't you spend the extra few bucks to get the correct parts ?