I own a tc3 and i am looking for speed i am thinking of getting an irrgang one way diff will i see much diffrence in speed what else will make my car faster hop-up wise

IT wont make it faster It will make your car handle different.

Really there are three things that can make a difference in your speed: gearing, batterries and motors. For the most significant difference I would change the motor. Try a modified 19t if you want to keep your esc and still have good run times. The p2k2 pro is good and so is the epic binary 2. Matched cells will also give you some extra punch and higher gearing will give you more top speed but you will lose acceleration. And of course the reverse is true too.

which car are we talking about? the nitro version or the electric version??