RIght now I have 2 K&N filters in my garage. One is the stock replacement and the other is the one that goes right on the TB. Which one would you use?

 

The one that goes on the TB if you've got a modded 350.

 

i have a 91' Formula TPI, i have a k&n in the intake box right now, would it be worth the money to get a new one to put right on the throttle body? and what are the dimensions of that filter that sits on the TB?

 

First off, he doesn't and second off that's not such a hot idea anyways. Putting a cone type filter right on your throttle body isn't a good idea because it will pull in air that has just passed through the radiator/ac condensor. This air will be way hotter than ambient air and will kill power due to the loss in density of the air charge. Your stock air intake, on most FI vehicles anyways, will pull air from in front of the radiator/ac condensor which will be closer to ambient temp which is what you want. The only advantage to the cone type filter right on the throttle body is the increase in flow capapbillity over the stock ducting (even with a stock type K+N), which wouldn't even be of any help on your mostly stock 305 tbi. If you can't use the extra flow, what good is having it, especially if you pay a price for it (ie. the hotter intake charge). The best of both worlds would be the cone type k+n filter mounted remotely (ie. upstream of the radiator) with a free flowing pipe connecting it to the throttle body.

Stick with the stock application k+n until you make some serious mods that require a better flowing intake.