I have so far rebuilt 2 Cherokee 4.0 motors and I wouldn't go over. 30 ever. You're messing with really thin cylinder walls,head millings not matching wall bores, and squirrelly compression results. Stay away from boring the 4.0 motor out that much and move up to the 4.2 258 or look at a swap with a nice 350 or 327.

 

Can not see the point with the thin side wall.
This pic is from my 4.7 L Stroker with 060" over size pistion and from stroker bulilder this are an reliable size for the block. I even run Nitrous on it without any problem and if Stroker with 060" pistons fail, I never had any with an crack in the block. if you go for 4.9 or even 5.0L then it get tied with the reliability.

 

Wake up guys! Compression ratio is deterrmined by several factors. Result in compression change are provided all else is held constant:
1) CCV Combustion chamber volume (more volume = lower compression) deck the head you get less volume, remove material in the chamber you get more volume.
2) HGT Head gasket thickness (thinner = higher compression)
3) PV Piston dish/dome volume(more dish = lower, more dome = higher)
4) CDV Cylinder deck volume (remove deck height from block, move rings higher on pistons, or push piston further up with longer stroke crank or longer rods = higher compression)
5) CD Cylinder displacement (increase bore or stroke = higher compression)

CR= (CD+CCV+(HGT*bore*bore*pi/4)-PV (subtract volume for domed pistons or add for dished)+CDV)/(CCV+(HGT*bore*bore*pi/4)-PV+CDV)

Bigger bore = more swept volume of piston = higher compression.

 

For the CR it is importen what left when the pistion is in the highest position. Easiest way to get low CR is with "low compression pistons" like mine in 2 post above. Kheit Black 944 with -22cc dish, head gasket thickness, ported head volume, deck hight. 9,6 /1 CR is perfect for strokers.

 

OK guys I already have the .060 over pistons that are stock type and will be using MLS (very thin) head gasket so I am SURE that the COMPRESSION and the COMPRESSION RATIO will both INCREASE. Compression IS NOT determined SOLELY by the volume above the piston at TDC. It is simply a matter of determining how much volume is created at BTC that gets compressed at TDC. The miniscule amount of increase in volume at TDC (because the piston does not travel to the exact TOP of the cylinder) is only about 1/8 inch of exposed cylinder bore I believe. Consider the MUCH greater volume from a .060 bore which adds to the BDC combustion area. It is FAR greater amount of combustion volume (the entire stroke) added at BDC compared to TDC so this increase is COMPRESSED into virtually the same TDC volume as before,..therefore RAISING compression and compression ratio. Its actually pretty basic but I just really wanted any FIRST HAND experience from ANYONE who has overbored .060 without any other modifications to see what difference it mad and any other recommendations they might have. Cannot afford the stroker kit at this time! Thanks

 

I just wanted to explane it simply, but if you want to have the 100% clear SR and CR, check this link

http://www.jeepstrokers.com/calculator/

BTW: if you rebuild the 4.0 the difference to an stroker is just the crank for about 150$....The rest you need in boths cases!

 

Thanks NOTOP46, that is an excellent explanation and formula for Compression Ratio. Since the ONLY difference I am making is Cylinder Displacement,..my Compression and Compression ratio will increase. Good to also hear from another member that the .060 overbore was successful even with NoX. I am not very concerned that this is a BAD idea to do the .060 overbore so thanks for the reassurance.