doesnt leaving the stock cat defeat the purpose of getting a catback exhaust?

and sorry just to clear it up my dx does or doesnt have a tach cable pre wired?

 

No. The reason you would buy a cat for the EX exhaust is because the EX exhaust has the cat after the exhaust manifold. On the DX and LX, the cat is basically part of the exhaust manifold. The reason you would need a test pipe for your exhaust if you use your DX exhaust manifold is because the EX exhaust is not long enough for the DX and there will be a gap between your exhaust manifold and exhaust. On the EX, this is where the cat would be. But since you already have a cat in the exhaust manifold, you should just buy a test pipe to fill in the gap.

yes. the tach wire is there.

 

thanks my questions are answered