I have to pass emissions and I have duel pipes with no cats. What was the gain to have duel pipes. If I use stock exaust pipes and a good muffler would I notice a big drop in power?

It depends on the engine. You need to have enough flow to let the exhaust out, it's easier if you've got a 305 than if you've got a 454.
A properly designed single exhaust can flow better than a poorly designed dual exhaust.

The stock exhaust is not considered to be well designed.
Will you lose a lot of power? Maybe not.

The real question for you is whether they will check for the cats or not.

Why don't you tell us where you are, and what year your car is? This will help us to help you.

Sometimes you just need the "right" smog tech. If you open the hood and he says any of the following:
"Your AIR system is missing"
"Why is your EGR port plugged"
"Ummmmmm..."

Find a different tech.

on the other hand:

"Let's see what we can do"
"GM Performance parts has some valve covers that will look nice on there!"
or if he grabs a screwdriver as soon as you pull up, you have found the right guy.

Speaking from experience.

I have straight duals, headers, no crossover, no cat, no egr, No AIR, and I passed.

I live in AZ. I have a 77 camaro 350 edlebrock carb, intake and duel flowmasters that all. It has the egr and efe but no cats. The duel exaust is poorly done they come out before the tires look like crap! I can get all the pieces for the oe exaust at the junk yard cheap then just buy a cat and muffler. I also dont like the sound very much. They are flowmasters 40s.

You would never pass in Indiana. They don't much care if you have duals or not, but they will check for cats. I used to fake it with heat shields and the car would always pass. The trouble is if they don't see cats they won't even test your car! :mad:

I put duals on the 76 I used to have, expecting a big boost in performance. Took it out and floored it and nothing happened! Same as with stock. I thought what a waste of dough. Then I got a Mr. Gasket breather. THAT made the car fly. On that car the stock breather was the limiting factor just as much as the stock exhaust.