...if a guy wanted to replace a 5.2 engine with a 5.9 engine in a 99 Ram with auto trans, would the computer need to be swapped as well? Anything else need to be changed, torque converter maybe? What about rearend gears, can a guy go from a 3.55 gear to a 3.91 without any other changes other than the rearend itself? Thanks for any help.

IIRC yes on computer needs swapped. * or flashed?

yes on TC swap = needs 360 magnum balance. LA 360 is slight different than magnum 360.

yes, on gear swap, will need speedo pinion change going from 3.55 to 3.91. everything else should be fine.

**you may research computer flashing. IIRC there is a trick they do flashing it to 5 speed specs or like adding a chip? some kind of performance flash on it or something?

I remember reading some users stating the OEM calibrations were overly rich at full throttle in stock configuration, if that's true I would try the 5.9 on the 5.2 calibration. Failing that, a 10% larger injector set from the junkyard might get you right in the zone too.

yes something like that. I think they use the big yellow ford injectors

Done that swap many times both ways with no computer issues, they can both run the other engine just fine. The 318 has more compression and a better cam so the power is a lot closer than you would think based on CID alone.

You do NOT need to swap TQ converters, just use the flex plate that came with the engine, the weight is on the plate not the converter.

You will also NOT need to swap a speedo pinion, there is not one. The speed is read off a tone ring on the ring gear carrier and the only thing that will change it is tire height not gear ratio since it is read after the gear.

The yellow injectors are a nice upgrade for MPG but they flow the about same. The blue ford injectors are good if you soup it up a little but they are a little much for a stock engine.

Forgive my ignorance, could you say this another way, particularly that part about tire size, not exactly sure what you're saying there. Thanks

The tone ring turns at axle speed so it will be the same at any speed, regardless of the axle ratio. The rollout of a tire is determined by its diameter so that will affect speedo accuracy. IOW, a 28" tire will travel a different distance in one revolution than a 30" tire so, since the tone ring counts revolutions, it needs to know how far the vehicle travels in one revolution. (speed is about distance over time)

Thaxs for the explanation of this as i'm also looking to upgrade the rear gear in my 95-Ram from a 3.55 to the 3.91 or a 4.10. And to the op. not meaning to jack your thread .

yep.... gear change won't change the speedo, but tire size will. On that era of truck the programming can be changed with a DRB scan tool.

Ok, thanks guys.