Lavrishevo

iTrader: (1)

99 LS400:

So I'm about to either replace my cats or remove them totally, not sure which yet. I'm not that concerned about horsepower gains but rather making the engine operate more effenceintly. Personally, a little more mpg would make me more happy then a few HP.

Anyway, I do realise the headers would be the best way to do this but I wish to start off with piping and removal of resonators and maybe new mufflers. I'm looking to do the most I can at my local muffler shop and not order an exhaust system. Can you guys recommend the best way to free up flow but not increase resonance or cruising level to be overbearing. I realize this is subjective but what do you think if I remove cats and resonators, leave stock piping and mufflers. How much volume increase will there be? Any general suggestions?

PureDrifter

iTrader: (10)

removing cats won't make any substantial improvement in performance, will make the car smell like fuel, and trip multiple CELs.

please read.
https://www.clublexus.com/forums/ls4...stem-mods.html

radiokilla

^ Agreed. You can increase the diameter of the exhaust piping after the center catalytic converter/resonator (depending on what state the car is from) and delete the resonators. It won't be substantially louder if you retain the mufflers. This will have your exhaust be more free flowing and you will still be able to pass smog.