i got the small set up on my 89 now and i want to go to the bigger one like the gxl calipers, do i have to put the bigger rotors or will it fit with the thiner ones, iam just doing the backs, will the 13 15(cast number on the calipers) rotors work with bigger caliper

 

The whole point of the wider rotors are to accommodate the vented rear rotors. If you are not going to use the vented rear rotors then there is no reason to go to the wider calipers.

 

i just want to drive my car, old ones are f'ed up i can buy gxl ones for cheep now

 

You will also have the problem that at the end of your pad life the caliper will be missing the extra width of the vented rotor and you may pop out the pistons. That would be very bad.

look up www.r1concepts.com for cheap rear blanks.

 

so they would fit on there??

 

I can't stress enough how important it is NOT to cut corners when messing with brakes. Even the rear ones. If there is a modification/repair you are planning on doing to your braking system, take the extra time/money to do it RIGHT. Don't just change out your calipers for the wider ones and just hope that it works. Not smart.

 

all they do is slow you down, joke, sorry yeah ill just buysome remans in a few weeks