Help Sourcing Correct Pistons for 2003 Jeep 4.0 (Low-Mileage Block, Future Turbo)
Posted: April 28th, 2025, 3:11 pm
Hi everyone, new member here. First, just want to say thanks — I've learned a lot already just reading through the posts here.
I'm hoping to get some advice on sourcing STD or possibly custom-sized pistons for a 2003 Jeep 4.0 project. I ran into some trouble after ordering a Std-Pwr STD piston set. Skirt measurements came in at about 1.8732/3", and with OEM (A through E) bore specs between 3.8758" and 3.8775", that would leave way too much piston-to-wall clearance, even before any deglazing or honing. Frustrating to see, even more to learn the reasoning why, but not entirely unexpected these days.
The block I'm working with has relatively low mileage. Bore measurements at 69°F range from 3.8763" to 3.8772", and it's no more than 0.0004" out of round. There's some skirt wear, but the main reason for replacement (along with a failed lifter) is to avoid the risk of skirt breakage down the line, especially since I am planning a mild turbo setup (under 5 psi boost). I've already invested in a new crankshaft, so going the stroker route is off the table.
While I have some background from earlier years working around repair and machine shops, I realize a lot has changed. I'd really appreciate some guidance — especially from anyone experienced with these engines — on sourcing/buying hypereutectic or forged pistons, or buying/working through a machine shop for custom sizing if needed.
(Happy to provide any additional measurements or details if needed.)
Thanks so much for any help or advice you can offer.
_-------_-------------------------------------------
— Former industry tech, back to learning.
— Here to learn, not to argue. Thanks for sharing your experience.
I'm hoping to get some advice on sourcing STD or possibly custom-sized pistons for a 2003 Jeep 4.0 project. I ran into some trouble after ordering a Std-Pwr STD piston set. Skirt measurements came in at about 1.8732/3", and with OEM (A through E) bore specs between 3.8758" and 3.8775", that would leave way too much piston-to-wall clearance, even before any deglazing or honing. Frustrating to see, even more to learn the reasoning why, but not entirely unexpected these days.
The block I'm working with has relatively low mileage. Bore measurements at 69°F range from 3.8763" to 3.8772", and it's no more than 0.0004" out of round. There's some skirt wear, but the main reason for replacement (along with a failed lifter) is to avoid the risk of skirt breakage down the line, especially since I am planning a mild turbo setup (under 5 psi boost). I've already invested in a new crankshaft, so going the stroker route is off the table.
While I have some background from earlier years working around repair and machine shops, I realize a lot has changed. I'd really appreciate some guidance — especially from anyone experienced with these engines — on sourcing/buying hypereutectic or forged pistons, or buying/working through a machine shop for custom sizing if needed.
(Happy to provide any additional measurements or details if needed.)
Thanks so much for any help or advice you can offer.
_-------_-------------------------------------------
— Former industry tech, back to learning.
— Here to learn, not to argue. Thanks for sharing your experience.