Have you ever even looked at a non turbo exhuast set up vs your turbo set up? They are completely different. There is no way to get non turbo headers to work on your turbo. Why worry about getting headers anyway? The stock manifold is pretty good and if you wanted you could just have it port matched to gain a little extra flow. Of course as mentioned already if you have the money have some custom made. Still plenty of people obtain 400+hp with the stock manifold so why worry about it? If your are truely ****** just go to a junkyard and get a stock set of manifolds for really cheap. Then as I said go to a machine shop and pay 100-200 bucks to have them port matched. My question to you is how did you mess them up and what do you mean by ******? The exhuast manifold is pretty strong so you must have done something stupid to mess them up or they aren't as bad as you think. If it's just and exhuast leak it's probably just coming from the gasket.
thats what exhuast leaks sound like. It makes your car sound like an old V8. Regardless if you need new manifolds or not you will need new gaskets. So get the gaskets and replace them. While doing this inspect the manifolds. If the manifold is bad you will see a crack or hole in it. Like domdogg123 said I'm about 99% sure it's an exhuast like and not the manifolds. As I mentioned before the manifolds are very strong and would require something drastic to break them.
Passanger side and cross over pipe from a non turbo is the same but the turbo side you will have to replace it with a turbo manifold. Check to see if the crack is in the middle of the manifold cause if its cracked start your motor let it run for a while then find somebody to weld it with a cast iron rod. Its a little tight but can be done, As long as you heat cast iron and can be welded. If its a gasket though youll just have to pull the manifold off and replace the gasket.
Sounds like an exhaust leak at at the gasket to me as well. I had the same problem with my daily driver (not my Z). You can have a muffler shop check it out and they can confirm. Just have them price and if you decide to it yourself tell them you are going to wait on it for now because you don't have the cash flow.
Does headers make a big difference in the performance of a 86 300zx non turbo and if not what way can I go to get a bit more power other than paying for a turbo motor w/upgraded turbo and intercooler (not to mention the 6G's they want me to pay). Can someone out there in Z land help me??