What size exhaust to run? - Off-Road Forums & Discussion Groups
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post #1 of (permalink) Old 08-05-2001, 06:58 AM
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What size exhaust to run?

Should be getting my 258 this Monday(finally!) It has an RV cam, header, and 390cfm 4 bbl. Should I run 2 1/2" exhaust or leave it with the factory 2" exaust?

Thanks for any input


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post #2 of (permalink) Old 08-05-2001, 09:55 AM
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Re: What size exhaust to run?

With a 4.2L head a two inch (2") pipe is fine.
If you are upgrading to a 4.0L HO head then two and a quarter inch (2.25") pipe is all you need. Your new mill will breath just fine in either case.
You'll loose your bottom end torque on the trail if you go to a larger diameter pipe (trust this ... cams and headers are a science).
A 4* advance on the cam with the small tail pipe nets lots of grunt.
My 4.2L with a ported 4.0 HO head, cam, etc ... blows through a '91+ 4.0L Borla 2.25" header with a transition to a Borla CJ 2" cat back (no cat) via a see through Borla muffler and easily revs through a 4.0L HO's 5K red line.
Check my Jeep site (below) for details ...

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post #3 of (permalink) Old 08-05-2001, 06:06 PM
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Re: What size exhaust to run?

As always thanks for your input, once I get started on going back together with mine I'm sure I'll have more ????????????????????



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