CAI and Supersprint combo, though I think that is probably realistic for a 97/98 2.8 at 5500 RPM. The 2.3 breathes too easily as is. I'm not sure that the trade off of lower coolant circulation flow and possible charging problems are worth the expense of underdrive either..though I have nothing to go on but Internet Lore. How long have you had your UDP's and for how many miles. ANy problems/trade offs? I think that the improved 0-60's say a lot, that put's it in 2.8 territory easily..I just don't think it's worth $2500 either.