I have another dual exhaust question. My Dad was wondering, with a stock 305 with stock headers. How big of a pipe to use, and what kind of free flow mufflers, and cat' converters have given the most reduction and back pressure...

Hello Ken
A 2 1/2 inch pipe well work with a set of Flowmaster well well work.
You well love it :mrgreen: :thumbsup:

I have another dual exhaust question. My Dad was wondering, with a stock 305 with stock headers.

If yours is like mine, stock headers join under the right side of the engine into a single cat. To get duals, you'd have to start with new headers....
which is on my list of near term fixes.

...stock headers...
Am I correct in assuming that you mean stock "exhaust manifolds"? Headers are aftermarket items. You can have a true dual exhaust while still using stock exhaust manifolds. An good exhaust shop can bend a custom 2.5" dual exhaust for you in a few hours.

Have you read all posts concerning dual exhaust systems? Have you replaced or modified your transmission crossmember for the installation of a true dual exhaust system? 2.5" pipes is the most common conversion, but even 2'' or 3'' can be done by a good muffler shop. There are no such animals as stock headers on Elkys, stock exhaust manifolds is probably what you mean. If you do convert to true dual exhaust, I would install aftermarket headers in the process, if you do it later it will cost a little bit more to rebend or make some new pipes from the header collectors to the catalytic converters. This is my opinion and someone will probably blast me for spending your money. To them I say HAVE A NICE DAY :)