I have mac LT headers with 3" collectors. Would i take a performance hit if i used a 3" to 2.5" collector and ran 2.5" for an X-pipe and exhaust? I'm thinking yes...
This is how I would run the 3" into 2 .5" exhaust , I would make the merge gradually maybe over a length of 4-6" , if running cats the merge would be after the cats.
This is not based on any actual flow data, just a cartoon in my mind.
I have a bbk off road H pipe to install, no cats. Was just wondering if the mac 3" cat back would mate with the 2.5"bbk off road H pipe or if the flange size is different or not.
Sorry to take this off the OPs origional question.
This is how I would run the 3" into 2 .5" exhaust , I would make the merge gradually maybe over a length of 4-6" , if running cats the merge would be after the cats.
This is not based on any actual flow data, just a cartoon in my mind.
Yep... Give those cats as much flow as possible. Gasses will do a great deal of cooling in the converters and be more dense going out than it did coming in. This is a good place to begin reduction and maximize exhaust scavenging.
3” pipes the whole way will add weight without adding much benefit for most 347’s. Even flowmaster and Hot Rod’s chart shows you need to be making at least 400 hp at that engine size to use 3” duals.