Here are some plugs that work in your lexus GS400, i personaly would stick only with NGK or the denso plugs ..due to never ever having problems with them in my personal MKIV single tubo and the ones i worked on , some plugs are not listed but feel free to add them to the list.

.....BRAND........product name....................part # ..............GAP
-Autolite............Double Platinum.............APP3923........... .044

-Autolite........... Single Platinum ............. AP3923............ .044

-Autolite............. Traditional spark plug.....3923................ .044


-Champion......Premium Gold plug..........2071................ .044

-Champion.... Single Platinum................. 3071................. .044


-Champion.......Double platinum..............RC12PYP....... .044


-Denso..............Iridium plug.......................Ik20................. .044

-Denso............ Iridium plug ................... SK20R11.......... .044


-NGK..................IX Iridium............................BKR6EIX-11.......... .044


NGK .................Iridium plug............................IFR6T-11................ .044


-NGK................ GP platinum..........................BKR6EGP............... .044


-NGK................... Traditional spark plug............ BKR6ES-11...........044


- NGK ................ Traditional spark plug...............BKR6E-11.............. .044


-splitfire.............Platinum spark plug........... TP392C..................... .044


-Splitfire........... Spark plug..................... SF392C............................ .044


thanks to sparkplug.com ill also post the bosh # soon unless some one has it already also can some one post the torq master part#