pulled my engine and sent it to the machine shop boring it out .60 over and putting a 4.0 head on, with a 4 brl carb any one know the power gain about from what im doing?? i know the head swap alone is around 40 or so from what ive read on other sites from people doing it
1989 yj 4.2L, 3" rough country lift, 2" body, 1.5" shackle lift, sye, 35x12.5 cooper discovery stt's, costom rear bumper with d ring mounts, 4 brl holley 390cfm, offenhouser 4brl intake manifold, hollowed out cat, dynomax straight through muffler, t-case out of a ram, 4.11 gears, super dana 35 kit with detroit
I had a 4.0 head on my 258 with the 390 holley and offenhouser intake and let me tell you that puppy would break the 35's loose with ease. Out ran my wifes new Liberty until my gear ran out(4.10). Boring it out will only increase the power. You may even want to look into a HEI distributor from about a 72 chevy van with the 250 six cylinder. Only thing is you have to put a v8 drive gear on it from an amc v8. That helped me out by opening up the gap on the plugs. You may even be able to up the carb size to the newer 470 cfm truck avenger.
89 YJ upgraded with 95 Chevy LT1 small block, NV4500 5spd, tera low 231 SYE, Custom built crossmembers and skids, 2003 Corvette Electron Blue paint, 3 inch custom spring lift with 2 inch shackles, 2 inch body lift, locked 8.8 with discs, 4:10's and 35's, spray lined tub, and a few other unmentionables