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there is actually quite a bit you can do to the 2.9l I just finished rebuilding mine from the ground up I put a set of pace setter headers on 5.0 fuel injectors (19lbs) ram air, ported and polished the intake upper and lower as well as the heads (did them my self) put the bigger throttle body on the TB from a 86-87 2.9 is larger then 88 and up about 1.5 ci bigger to be exact did a set of free flowing rockers turned it in to quite the peppy lil thing I noticed a huge diffrence I know I am forgetting a couple of other things I did but if ya wat anymore info I got it all here I can scan it in and e-mail it to you
CDNCOWBOY, I too would be interested in reviewing the information if you could e-mail it to me when you get a chance.
86-87 had a 58mm TB and the 88-92 had a 53mm TB. The best thing you can do is to port the crap out of the 2.9 intake and remove the bumps for the valve cover bolts in the exhaust ports (make sure you silicone the VC bolts). Add some headers and a free flowing exhaust. Get an RV cam and do the Free floating rocker conversion (its basically just billet spacers in place of the stock rocker assembly springs, reduces friction) You can start getting more radical with the Mods when you do the MAF conversion (either a Cali 2.9 EEC or a Maf 3.0 EEC).
if ya goto http://www.therangerstation.com/tech_library/index.htm will show you how to make free flowing rockers you pretty much loose the springs and make spacers and the TB you want is off a 86-87 2.9 there about 1.5CI bigger then the ones on other years of 2.9 all that info is on that website as well done almost everything to my 2.9 and I notice a HUGE diffrence
Just get em new. Camcraftcams sells a complete rocker arm spacer kit ready to go for only $49!
If you want to feel the difference in the seat of your pants at a reasonable cost, give this a try and hang on the your hats.
A performance chip in the computer. A K/N filter. Next, check where the air intake tube to the air box starts behind the grill by the right head light. I found the flap to be broken and blocking the air flow. Cut away the flap and install a screen behind the frame to keep the bugs out. This will make a big improvement. Next get a TB from a '86-'87 2.9l engine. They have an opening of 58mm, where the '88 and newer are 53mm. You will feel the difference in the seat of your pants. To keep the air as cool as possible, insulate the air tubes and the air box.