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There is no working that motor that I can tell. Unless you are willing to do an engine swap, look for an IS350 at a minimum or an SC300 if you want to do motor work.
As of right now there isn't much work you can do on the IS250 engine. If you want to do some work on an engine, anything with an NA 2JZ is probably a better choice. If you want to stick to the 2IS lineup, a 350 or F is a better choice. The 350 engine has just recently been tuned by various companies and in addition, some of the internals of that engine may be changed and available for sale within the next few months. Look up 'OV Tuning' and check their Facebook page every now and then for more information. The engine in the 350 is really underrated.
Bought an IS250 and was way way way too slow. Sold it 1 month later and made $700 off it. Then bought an IS350. After owning an Infiniti G25 that felt really quick and responsive, I couldn't believe how sluggish the IS250 felt. What made me buy the 350 as well was the similar fuel consumption. I hear the gear ratios on the 350 from 0-60 are better than the ISF, and you get more out of the ISF on the track. but in terms of daily driving, the 350 is a decent competitor.