Exhaust 3"------->2.5"

[My92cashtrap]

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...

Engine is a 347.

 

[Potomus Pete]

Im thinking I doubt it. Still flows well.

 

[General karthief]

Depends on how far the engine is built.
4-500 hp I doubt much loss
600+ yeah maybe
700 + yes.

 

[Gs1987GT]

I agree with the General on this one....

Along these lines but different, can you run MACs 3" exhaust (cat back system) with a 2.5" H-pipe?

I'm thinking about what exhaust to use with my GT this coming summer hopefully

Thanks

 

[Blown88GT]

If you're still running cats, you will need hi-flow ones.
As for the cat back exhaust, I still like the sound of the Flowmaster Force II.

 

[General karthief]

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.

 

[Gs1987GT]

If you're still running cats, you will need hi-flow ones.
As for the cat back exhaust, I still like the sound of the Flowmaster Force II.

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.

 

[General karthief]

3x2.5 adapter

 

[Noobz347]

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.

you will need hi-flow ones.

Yep!

 

[7991LXnSHO]

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.

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