Id like to put true dual exhausts on my 75 cutlass supreme, currently its a single and i believe it has a catalytic converter. I already have a pair of flowmasters that someone gave me so Id like to know if all I would need are the pipes done or would i need new exhaust manifolds/headers or would the stocks work? also knowing the approximate cost of the work would help as the shops in my area tend to overcharge. Thanks!

 

Price depends upon the going rate for labor in your area so hard to say and also would depend upon the following. An exhaust shop can run a new downtube from your existing exhaust manifolds, cut off the crossover, and weld the old openings for the crossover up, then run duals from the downtubes back to mufflers and then turn downs after the mufflers. That would be about the cheapest (except for you doing it yourself) as it would take the least amount of tubing and labor. That might be as cheap as $150 to $300 if you supply the mufflers and he isn't trying to sell you his own. From there it goes up. If you buy true dual exhaust manifolds and pay someone to install them first, then go the above route it would run a little more for his labor but be better than cutting the crossover and welding it closed. That of course would probably be better in the long run performance wise. Then there are always headers, add the price of headers which may or may not run more than true dual exhaust cast manifolds, because they aren't cheap. Then you would add more if you want larger diameter pipes, stainless vs non-stainless, mandrel bent vs standard bending, tail pipes instead of turn downs after the mufflers, etc.... It can get very pricey and your wallet will end up being the limiting factor. One other thing I almost forgot. I know on my '77 the transmission support has only one hump for the single exhaust and if I were to put true duals on it I would have to replace that with a "double hump" support. I think they run about $150, your '75 is probably the same way. And finally, I forgot about the cats, they aren't cheap either. Sorry for the rambling answer. You will probably get a better more concise answer from another member.

 

I paid $300 for true duals, aluminized 2.5" pipes, an X pipe, and 18" chrome tips on my 71 98. Of course, it didn't have catalytic converters, and I had two Thrush glasspacks I wanted installed. The pipes weren't mandrel bent but I am very happy with the results. I plan on installing headers soon and having the downpipes modified.

 

Because you have a 75 you don't have a double hump cross member. It would be good to source one from a 73-74 A body to make routing the pipes a lot easier.