No disrespect intended: I still maintain
There are some free/cheap modifications that can be done to the 2.9 that make it perform a little better and that give it a little more snap on the throttle:
Free ones:
-Zip ties on throttle cable to draw up slack
-Spacers under intake rain plate on core support (rain plate is restrictive to airflow)
-Gasket match port your plenum (THIS MAKES A HUGE DIFFERENCE)
-Gasket match port your lower, and smooth out your injector "humps"
-Rebuild distributor and clean out years of sticky varnish on distributor shaft
-Clean the crud out of your rocker arm shafts and polish them. Polish inside of rocker arms
-Clean the oil and carbon out of your intakes. There's a lot in there.
-Polish pushrod contact surfaces
Low dollar (all less than $50)
-CATCH CAN (EVERY 2.9 SHOULD HAVE ONE EQUIPPED) Amazon $20-30
-High flow air filter (Fram air hog is $6-8 on rock auto)
-1986 throttle body (I have a small pile of them, pm me if you're interested)
-Electric fan (new 16" kits on eBay, $40-50, make sure to reuse factory fan shroud. See my build thread for photos. Lots of junkyard options. C230 Mercedes dual fan fits perfectly)
-TFI module relocation and hest sink (improves idle and ends the "TFI slump") Search the forums and tech section for instructions)
-Install new Motorcraft brand name distributor hall effect sensor (best modification I've made yet, even over everything else I've done, including my performance heads, headers, etc.) $24, Rock Auto
-MSD blaster coil, $46, various
-8-10mm plug wires, varies but under $40
-Brass distributor cap and rotor, $20-30
-New O2 sensor. I like the Bosch ones, $20-40
-Synthetic fluids (I'll get criticized for this, but I'm a firm believer in Lucas Synthetic Oil Stabilizer mixed in at 20%. Gets rid of the 2.9 tick. I also run 2oz of Bells X-tra lube in my oil)
-Bosch iridium plugs, under $50, Rock Auto
-Shifter bushing kit (you'd be surprised at how sloppy it is and you don't notice) $24, Rock Auto
-3g alternator. Mine came out of a 1995 Windstar. $20 with harness, U Pull
-Volvo electric power steering pump, $15-30 at a U Pull
-Seafoam spray can engine cleaner and Lucas blue bottle injector cleaner -varies, Walmart
Most of these focus on improving airflow. The 2.9 intake.and exhaust system is highly restrictive. I know I jump on this stump often, but the UK and German guys figured this stuff out years ago as the 2.9 was a European sports saloon engine; before that it was a carbureted V4 economy engine that could be modified to hum along nicely. Cleaning up the restrictions on the intake and exhaust tracks net impressive gains in regard to passing power and throttle response. The rest are focused on reducing parasitic load on the engine.
Keep in mind, the 2.9 IS NOT A TRUCK MOTOR. The intakes and exhaust system are restrictive to push the power band down on the rpm range. This comes at the cost of top end speed and power issues, which is why everyone on the interstate hates you. My truck now passes readily at 70-75mph without issue.
There's definitely more that I've done, and that works. If there's interest I'll add to the list. The plan is to dyno the little guy before supercharging with the Merkur and Ranger intakes to post results with my changes made. No point in claiming any of this works without real data.