If i drop a trd filter into my 2003 IS300 5spd, will it be noticable gain in speed or power, cause the stock filter really holds the car back.......?

 

IF you want a realy noticable gain take a Foreced Inducton rout
Turbo/Superchrger.

I got TOM's drop in in my 02 auto IS, i cant say that i see this 5hp gain but it feels that the engine can breath easyer. Just my .02$

 

This very much depends on the car.

In my 90LS for example, adding a drop in conical K&N filter took away close to 10 torque and 7 HP.

Stock air filter works best in my case.