4" Bore Piston and Compression height

[redrider2911]

Any reason I couldnt/shouldn't run the below setup?

4.2L 3.895" stroke crank
4.0L 6.125 rods
KB 9956HC (4" bore, 18cc, 1.433 pin height)
Skim down piston pin height to 1.398
Compcams 68-232-4
FelPro 9076pti .051 head gasket

-.021 deck clearance
.030 quench height
10.76 SCR
9.21 DCR

Any input is much appreciated.
Kris

[IH 392]

You may have to go thru several blocks before you find one that will take that much over bore??, and even then keeping it cool will be a challenge.

[redrider2911]

I have a 98 and 91 block. I read somewhere the late model blocks have thicker walls. I already have standard .060 over pistons. Was just thinking of using the 4.0 rods and saw those pistons, they are a better price than the IC944. I guess I could use the 4.2 rods and the .060 pistons if that would be a better idea

[Cheromaniac]

You may have to go thru several blocks before you find one that will take that much over bore??, and even then keeping it cool will be a challenge.

Even if you find a block that'll accept a 4" bore, I'd be concerned about the longevity of the engine with the cylinder walls reduced to the minimum thickness after a 0.125" overbore. One overheating episode could result in a cracked cylinder and it's goodbye engine.
Stick to a safe 0.060" maximum overbore.

[DaemonForce]

One overheating episode could result in a cracked cylinder and it's goodbye engine.
Stick to a safe 0.060" maximum overbore.

This. This is more threatening than the typical wear of a high mileage engine. I went with 0.060" overbore due to serious wear and cleanup issues but if I had to go any further, I would have picked another block and started over. 0.010-0.060" is the safest range and it's where parts are available without getting expensive. There are many reasons to stay within these bounds.

[racing89]

This combo will work. Get your 91 block sonic tested, as these have been the blocks( 91-92), from my experience , that are thick enough. I havent had any overheating issues, on the street or off-road racing.