Building a Stroker For the First Time

[Aero_MX]

Hey guys, been lurking for a little while, and was trying to avoid posting and asking a dumb question, but here it goes.

The 4.0 in my 99 Xj with 180k decided to do what many other 4.0s do. lost a skirt and the piston rattled around, made horrible noises.

anyway, pulled the motor and tore it down, had everything sent to the machine shop for a rebuild. So far head and block have checked out good. no cracks, just minor hone would have repaired the jug. But why build a stock motor when you can upgrade?

So far my shop is ordering a rebuild kit for me, and the price seems reasonable,

258 crank
kb421 pistons
rings, bearings
refurbish my rods
arp rod bolts
head bolts
gaskets (.043 head gasket)
oil pump
timing set
cam (not sure on type yet, Comp 8-232-4? maybe)
bore .030
typical machine work
valve job and new mopar springs

all for $2300

So my question is, decking the block. math says deck it .031 to bring it to 0 and get .043 quench and a 9.1:1 static. My machinist recommended only .020 off, but that puts me in the .054 range for quench and 8.9:1. (this was all calculated with a 57cc head

So what way do I go? is it safer to have .011 deck clearance, but a higher quench? or 0 deck the block and have a slightly higher CR? Im sure I'm beating a dead horse, but my block hasn't been machined yet so I guess i need to make a decision. I want, like everyone else, to run 87 but of course I can wiggle on that.

Also, man reason I went with the KB piston was because of the price the shop was giving me for the whole kit. Maybe i'm off in left field, but seemed like a reasonable price to pay for a complete engine.

[Russ Pottenger]

The problem with the KB421 Pistons is that it has a lot of compromises built into it.
Running a piston with a full circular dish compromises the efficiency of a quench area.

The piston that I sell is based off of a reverse mirror dome piston. The dish is the same shape as the chamber therefore allowing a potential quench if you put the piston at .030 to .045 from the cylinder head at TDC.
Furthermore this could be achieved in the piston design without requiring the surfacing of the block. By not having to deck the block it brings the price point of my forged piston much closer to your cast Hypereutectic piston. I sell my Forged Pistons for $495.00 a set pinfitted with pins and locks.

Lastly you're welcome to shoot me an email and I could forward you information on my bushed steel rods.
One of the many benefits is both ends of the rod is fully profiled without balance pads making it much easier to retain the factory main girdle. At $325.00 a set they're not that much more expensive than a fully rebuilt stock cast 4.0 connecting rod. If purchased with my Pistons i'll upgrade the wrist pin to a much lighter and stronger .927 Chevy pin at no additional cost.


Russ Pottenger
Bishop-Buehl Racing Engines
531 N. Lyall Avenue
West Covina, California 91790
Work (626) 967-1000
Fax (626) 967-7836
Cell (626) 673-2203
Email/PayPal: [email protected]

[Aero_MX]

Hey Russ, thank you for your input. I'm mostly going for Budget, and the kb421s seem to fit the bill nicely. Not saying they're perfect, but for a mild on/off road rig hyper pistons just seem to be better suited cost wise for me. The shop is billing me 250$ for the whole set including rings, and he said he would press them Off and on for free. But I do recognize the compromises with this piston, the quench area being one of them, and the other being the decking requirement, However in this case the block is already going be be milled clean, so having him mill .020 off while he's at it doesn't cost me anymore.

I did get an answer(ish) after calling UE and then Clegg as well.
Clegg said they use the kb421s in almost all of their builds and they usually deck it down .020. This leaves you with about a .011ish DC, and a .054 Quench with the right head gasket. Clegg claims to have great success with this set up running 87 up in SLC,UT. Its a compromise, but that's where I'm at.

So now that the lower end is in the works, I need to decide on the Cam, and the injectors.

Cams seem to be hard to get a definitive answer on the forums. None of the Comp cams I could find online seem to work with the '99 ECU or the stock springs. I know there are several custom ground cams out there to choose from, just don't know what to look for or where to go.

Injectors. This is another hard to answer question. My jeep is a 99 with EV6 connectors and 49psi. so tracking down exactly which injector is confusing. Right at this moment I'm looking at the Bosch 0280155849. Its a 4 hole 24/lb injector. I know most of these are rated with 43psi so will it will flow higher than 24lbs, but is that something to worry about?

again beating a dead horse, but just need some clarity.

[SkylinesSuck]

I know you decided against Russ's pistons and I'm not trying to push his stiff, but I would highly recommend a cam he has custom made that's a lower lift version of a version Comp Cam that would allow you to run stock springs. Seems to fit your build perfectly.

[SkylinesSuck]

Oh, and ignore that not working with a factory ECU crap. Most of then say they wine but they do just fine. I had the must aggressive cam Comp made originally in my Golen stroker and the computer was fine with it.

[Aero_MX]

Good to know. I don't have any experience with cams other than just replacing a stock one. So as far as performance, I'm a noob, so I appreciate all the insight i can get.