Well the guy I bought my 88 gtu off of, had re done the exhaust and just ran a straight pipe with no main cat. So my 5&6 ports aren't working, and I know theres many alternatives to getting them open while still running a straight pipe.
I called the exhaust shop to get prices on replacing the cat, and of course he questions me on why I'm even wanting to run one, and I tell him I need more backpressure. He insists that running another muffler in place of a cat will get me the backpressure I need.

My question is, will an extra muffler provide the backpressure I need, and if so will it cause a decrease in power compared to adding an oem replacement cat, or should I just be saving the money to get a hi-flow cat.

 

Alot of people do a air pump mod where the air pump opens the 5/6th ports.

 

Yea I've researched the air pump mod, but I was just wondering if the the only a cat would provide enough backpressure, or would the extra muffler I was talking about work also, and if the muffler works would it cost any more extra power than a cat would.

I guess the air pump mod would be the cheapest and best choice, but I was just wondering about the whole muffler idea.