I am making a similar decision: keeping a 1998 ls400 with 309,000 miles vs buying a 2006 ls430 with 184,000 miles. I was surprised to see the ls430 had less horse power, 278 vs 290, and worse in the MPG . 23 hwy vs 25 hwy. For the last 24,000 miles I have used regular unleaded and not noticed any problems. Im guessing the motor has loosened a little,saving me a bit of change. So after seeing the ls430 this afternoon, and reading the comments, im leaning to keeping what I got.

 

Not really. Depending on which source you are looking at, the hp ratings between the VVT-i version of the 1UZ-FE engine and the 3UZ-FE are pretty comparable with the 3UZ having better torque. As far as fuel consumption, the method used to calculate the fuel usage was probably different between the time those cars first were released. I'd look at real world data over at fuelly.com to see what you can really expect (likely not much difference between the two).

As always, drive what you want to drive...