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

My92cashtrap · Jan 16, 2020

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 · Jan 16, 2020

Im thinking I doubt it. Still flows well.

General karthief · Jan 16, 2020

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

Gs1987GT · Jan 17, 2020

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 · Jan 17, 2020

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 · Jan 17, 2020

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 · Jan 17, 2020

Blown88GT said:
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 · Jan 17, 2020

3x2.5 adapter

Noobz347 · Jan 17, 2020

General karthief said:
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.

Blown88GT said:
you will need hi-flow ones.

Yep!

7991LXnSHO · Jan 19, 2020

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.

What Size Exhaust Pipes Work Best?

In this month's editon of Quick Tech, Tech Editor Marlan Davis discusses what size exhaust pipes work best.

www.hotrod.com

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

My92cashtrap

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Potomus Pete

I'm still waiting for the fully nude shots

General karthief

wonder how much it would cost to ship you a pair

Gs1987GT

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Blown88GT

General karthief

wonder how much it would cost to ship you a pair

Gs1987GT

Active Member

General karthief

wonder how much it would cost to ship you a pair

Noobz347

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7991LXnSHO

wanna catch the space herp

What Size Exhaust Pipes Work Best?

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

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I'm still waiting for the fully nude shots

wonder how much it would cost to ship you a pair

Active Member

wonder how much it would cost to ship you a pair

Active Member

wonder how much it would cost to ship you a pair

Stangnet Facilities Maint Tech... Er... Janitor

wanna catch the space herp

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