Saw a kit for 12% over pulleys for the XJR. Listed a 25 horsepower increase. Sounds low, but with stock intake and exhaust the top end may be restricted. Would hope the over speed blower will improve the midrange pull significantly. Also bring the boost in at a little lower rpm.
Got fresh plugs and O2 sensors and everything looks healthy on scanner. No oil consumption at changes.
From people here with overdrive pulleys, is just a pulley kit worthwhile? What else do I need, a catch can?

 

Its worthwhile if you accompany with a few other mods. It will wake it up more in the mid range and you will feel more response, but on a warm day... you could lose a bit on the top end because it creates so much heat. That's why originally i went with the 6% pulley, less heat. Once i had more cooling mods and cleaned out the intercoolers, i switched up to the 10% and it made good power.

Definitely clean out the intercoolers though; they are typically covered in all the oil gunk and do not transfer heat as efficiently as they would if they were clean. Just cleaning these out helped me pick up 14 whp on the dyno. A catch can will greatly help maintain them.

How much modding are you thinking about doing?

 

Mild mods in mind. But instead of an overdrive blower pulley, maybe I just need to clean out the inter cooler. At 115,000 miles it may be a little build up.
One bank was throwing a code on start up every six months or so. O2 sensor not ready. The other bank was running rich all the time. Replaced the four O2 sensors and A/F ratios look good, and car is running crisper. But it is winter time here. Winter in Houston is no 90 degree days.
Saw the pulley kit on eBay. Honk I will lean the inter coolers first. With hot days ahead a 12% pulley may not be good. It is 32C+ here nine months a year.
Between new OEM O2 sensors and cooler weather it is running great as it is.