I've seen websites about making your own cold air intake system with pvc piping but only for newer mustangs. Is it possible to make your own for 86-93 models and do they even work compared to a bought one?

cold air induction really does nothing. it adds in reality maybe 2 - 3 horsepower. i wouldn't even bother. if you have a k&n air filter already, thats good enough. i know on my 94 gt it already takes in the air from the fenderwell, so in essence, the cold air kit really isn't any different than stock.

Yes you can make your own, you can use bigger piping than the original so that you get more airflow, the factory tube is constrictive you can make it straighter and run it for cold air... its better in the end... just take your time, make sure all your connections are hooked up..
hope this helps
~*Adam*~

Adam do you know of a website that takes your through making it step by step? If not what kind of piping/fittings/etc. would u or anyone else recommend i use??

I don't want to offend any one but personally I don't believe in Cold Air Intakes at least not on road cars. Cold air intakes need high speeds at least 90mph+ to produce the positive pressure and give you worth while gains. Even then you have to setup the intake in the presurized part of the car eg front bar and to do this you will need technical devices such as manometers...etc. to find the optimum location and get the effect to work properlly. You will get a minimal power increase out of it and you will not feel the difference. At the most you migh get few bhp and a slightly better mpg. The only time you will feel a major differece is if you where running an exposed air filter in your engine bay and you are changing to the above mentioned setup. If you are still keen to try it out then try this site.

www.sn95.com/projects/coldair.htm

I'm not going to be racing the car just trying to push out extra HP. Would it just be smarter/cheaper to remove the air silencer and put K&N Filter in there? Any opinions?

I must interject on the aspect of Cold Air kits..... regardless of actual horsepower gains and what not... the do remove the engine heat from the induction and that is less chance of detonation or just plain better for an engine... plus running an open element air filter in the engine compartment can get "air-wash" from the fan and throw off the mass air flow sensor (if applicable) and cause it to run ruff. If you want another CAI homemade kit, this one says for 94-95 but you can use it to get a good idea of what to do...
~*Adam*~
stallionmotorsports.tripod.com/id42.htm