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Old 08-19-2013, 07:06 PM   #1
Craig B
 
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How much HP 2.5 exhaust?

How much HP will 2.5 exhaust support in a N/A car?? Was wondering if it was worth it to go with a full 3in. system. Thanks.
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Old 08-19-2013, 08:24 PM   #2
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Quote:
Originally Posted by Criag B View Post
How much HP will 2.5 exhaust support in a N/A car?? Was wondering if it was worth it to go with a full 3in. system. Thanks.
Zero. The factory exhaust is 2.5'', and flows pretty well. There is almost no gain to be had in 2.5'' exhaust. 3'' is overkill on an N/A motor unless you have some bigger cubes, high flowing heads and a beastly cam.
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Old 08-19-2013, 08:25 PM   #3
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Zero. The factory exhaust is 2.5'', and flows pretty well. There is almost no gain to be had in 2.5'' exhaust. 3'' is overkill on an N/A motor unless you have some bigger cubes, high flowing heads and a beastly cam.
IIRC the stock system is good to ~600RWHP. Then the 3" is not just for sound anymore.
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Old 08-19-2013, 08:27 PM   #4
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You won't get a true 3" system unless you buy one. I think KOOKS and LG are about the only ones that make a full header to exhaust tip in 3".

Most headers and cat-backs have a 2.5" connection point.

Unless you're making really big HP I wouldn't worry about going to a full 3" system. However, a 3" will give you a little bit of deeper tone when idling.
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Old 08-19-2013, 08:27 PM   #5
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IIRC the stock system is good to ~600RWHP. Then the 3" is not just for sound anymore.
I stand corrected OP! You're gonna need a whole LOT of cubes then lol.
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Old 08-19-2013, 08:31 PM   #6
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the magic number is 2.2cfm /HP. Any more flow is a waste of money.

Here is a decent unbiased article with science behind exhaust system design
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Old 08-19-2013, 08:33 PM   #7
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Originally Posted by caverman View Post
You won't get a true 3" system unless you buy one. I think KOOKS and LG are about the only ones that make a full header to exhaust tip in 3".

Most headers and cat-backs have a 2.5" connection point.

Unless you're making really big HP I wouldn't worry about going to a full 3" system. However, a 3" will give you a little bit of deeper tone when idling.
Lots of companies make a full 3".
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Old 08-19-2013, 09:07 PM   #8
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n/a i dont think the gains will be but like 1-2 hp if that. the weight of the extra pipe. will counter balance that tho lol
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Old 08-19-2013, 09:25 PM   #9
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Thanks for the replies. Looks like it's not worth changing to 3in.
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Old 08-19-2013, 09:34 PM   #10
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Sure it is. A 3" sounds like heaven on these cars.
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Old 08-19-2013, 09:52 PM   #11
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JRE has an 800 rwhp on the 2.5" exhaust. Blower car though


I run the Kooks 3". It does sound evil at the track!
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Old 08-19-2013, 10:19 PM   #12
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Quote:
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the magic number is 2.2cfm /HP. Any more flow is a waste of money.

Here is a decent unbiased article with science behind exhaust system design
Great read
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Old 08-20-2013, 11:07 AM   #13
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Lots of companies make a full 3".
Not a true 3". I'm talking about 3" from the collector back.

Most 3" cat-backs have a 2.5" inlet so they can connect up to the stock mid pipes. KOOKS makes a 3" inlet cat-back as well as LG. I think ARH might have one setup that way as well.
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Old 08-20-2013, 01:32 PM   #14
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Not a true 3". I'm talking about 3" from the collector back.

Most 3" cat-backs have a 2.5" inlet so they can connect up to the stock mid pipes. KOOKS makes a 3" inlet cat-back as well as LG. I think ARH might have one setup that way as well.
And so does JBA. And so does SW. I know what you're talking about. I just know there are plenty of full 3" choices .
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Old 08-20-2013, 04:13 PM   #15
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I have 1 7/8 kooks, 3×3 cats. Cut off the 2.5 " end of flowmaster AT welded on 3 inch end. 3 inches all the way back. Love it.
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Old 08-20-2013, 07:58 PM   #16
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I have 1 7/8 kooks, 3×3 cats. Cut off the 2.5 " end of flowmaster AT welded on 3 inch end. 3 inches all the way back. Love it.
That's what I'm gonna do one of these days. I bought the neck-down version of the JBA 3" long before I got the headers. Simple problem with a simple remedy!
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Old 08-20-2013, 09:04 PM   #17
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I slapped a Flowmaster 3" catback and center mount exhaust with the kooks and I live it!
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