Questions for compression with KB pistons

[JASON 77]

have a 98 TJ wanting to do a stroker. goin to use the 4.2 crank,4.0 rods with KB pistons. was wondering what compression would b with either KB 944's and KB 945's. head casting is a 0630.

also is decking block a necessity? want to run this on 87 octane

[unlimitedrubicon]

The pistons are designed to be used with a decked block per the KB tech line. I had a falling about with my ex-machine shop when they charged me for decking the block, but did not do it and still charged me and did not say anything about it when I picked it up. As for static compression ratio, that depends on your head volume but should be in the 9.5-10:1 range with the IC944s and higher with the IC945s and will drop depending on your camshaft selection. A cam with longer duration will close the intake valve later dropping your dynamic compression and in turn allowing you to run with lower octane fuel. If you want to stick with 87 octane I would recommend staying with the IC944s to reduce your compression and still have great quench with a thin MLS head gasket on a decked block.

[BDD]

I've got a 98 tj,used kb944s,stock 630 head,505 performence stage one cam with stock springs.I didnt deck the block, but did shave the head.010.I love it,i can climb long hills at 1400-1500 rpms in 4th or5th gear, and I,ve never heard it detonate.I run 87 octane and didnt notice a difference running 93.Im sure I could of made more power with a different cam and springs, but for a daily driver I'm really happy.it pulls like crazy,I dont even think about pulling out in traffic now or passing in a to tight spot.I live in michigan, so I'm close to sea level.

[Cybershot]

I have the IC944KTM-060 with the 4.0 connection rods and the 0630 head miled around 0.015" . Runs fine even in hot weather (I am in the desert )

The 4.0 Connection rods did not fit to the KB piston and needed some adjustment. You can see my pics here.

http://www.jeepstrokers.com/forum/viewt ... 98&start=0

[SilverXJ]

You don't have to deck the block if you don't want to. The piston will be about .020" down in the hole, maybe more depending on your block and your quench distance will increase. On mine, with a 0 deck and a fairly long duration cam (for this engine anyhow) it will ping if I don't give it premium.

As for compression: http://www.jeepstrokers.com/calculator

[gradon]

The KBs will be .030"(.0295" with the 9.453" deck height) down in the hole. KB assumes you have the block decked .020" with their 9.433" deck height spec. Taking .010" off will get you a smidge better than stock deck clearance, but if you're gonna cut, might as well take at least .025" off. Don't assume you have a 9.453" deck height--measure(2x) before you cut. Again, I don't know what KB was thinking when they chose their 1.353" comp height(why not 1.373" and then no cuts are necessary?). For custom pistons on the 4.0 rods, 1.38" comp height is money, For the eagle 6.150" rods, 1.35" comp height is what you want.

[SilverXJ]

Again, I don't know what KB was thinking when they chose their 1.353" comp height(why not 1.373" and then no cuts are necessary?).

Yeah, I don't understand the logic behind that either.

[Mopud]

to add my 2c.

i have 944s with the deck zeroed (20thou off) running comp cams 68-231-4. comp ratio is 9.7:1. Also running a well ported 0630 which was milled flat (58cc) with std 4.0l con rods.

my engine pings its head off if i don't run the highest octane pump premium. a bit annoying when out in the remote but the car goes like the clappers and pulls hard no matter where i am in the rev range.

[dragginwagon406]

What valve springs and keepers did you use for the 68-231-4 cam? Did it require any other machine work?

[Mopud]

Mopar Performance Valve Springs : P5249464 
Mopar Performance Valve Spring Retainers : P4452032 

Yes. The camshaft was the most annoying part to install in my stroker thanks to it using the pin/spring retention instead of the thrust plate. If your engine is pre 1998 you'll have the special camshaft bolt, pin and spring so it'll be easier for you. If it's post 1998 you'll have the thrust plate and will need to modify the timing cover and get some new parts to install the cam.

[dragginwagon406]

Thanks for that. I forgot all about having a friend who is a parts manager at a Dodge dealer, I wonder if he will cut me some slack on parts