I have a 97 GTP and One of my 6x9s blew,so while I have the whole back seat out Im going to change all the speakers,but I dont know what size they are.I dont know either 3.5 or 4's.Any help would be great.
Thanks, Rich

they are 4" in combonation with 6x9s
but be careful I have found that some 4" aftermarket speakers do not fit...
at one time I was sure it was 3.5 because of this...but it is in fact a 4" spot...its just a tight fit

www.crutchfield.com

you can go there and they will be able to tell you which speakers would fit and which wouldnt (based on surrounds, actual basket size, top or bottom mount, etc) They are a good place to call if you just need a little help, but I wouldn't buy from them. far to expensive

They are a bit more expensive, but they also send you all the adapters and mounting brackets and wiring diagrams that you'll need to install aftermarket speakers, not to mention they have good technical support.