okay not 100 % doin but its been bothering me that i cant figure it out. i have a 99 dakota sport 2wd with a 3.9v6 i want to know what is the biggest possible engine i can fit into my truck without making any engine bay mods

 

A 5.9 will fit. It came stock with one.

 

What Dan said. But you can punch a 5.9 out to 408 somewhat safely and a 426 if you want to be on the ragged edge of cylinder walls thickness. Or go get you an aftermarket block and build up a 500+" mill.