a few questions first i have been reading a lot of posts and threads and gained a lot of knowledge but just bought a 91 rs took dash speakers (stock) out and got infinite reference 4 by 6 dont fit now i heard of cutting plastic with ac ducts and i dont need ac but ima probably sound stupid but arent those ducts for heat tooo i need heat i live in ohio sucks and also heard about taking out ac completely can someone give me a complete walkthrough with everything i need to know thnx

 

when i added 4x6 mine woulnd fit, so i added little 1/4 inch plastic nuts between the speakers and mounting points to act as spacers. worked perfectly

 

IF its not deep enough you can try adding spacers those work somewhat. If they still dont fit Id take a heatgun and massage the plastic a bit and just get it bent nough to fit the speaker in. I had to do that on my drivers side with my firebird. My heat and AC still work properly also.