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Unread 05-14-2013, 06:43 PM   #1
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1988 YJ Wrangler 
Join Date: Mar 2013
Location: Canyon Country, CA
Posts: 28
Exhaust header upgrade Questions

I have an 88' 4.2L yj all stock exhaust with a new cat. i welded on.
I can get a good deal from my friend for a new exhaust header but it turns in to a 3" pipe. My header i have now goes to a 2" pipe.

I was woundering if i can istall those headers and instead of running a 3" pipe all the way out and getting a new cat, if i can bring the pipe before the cat. to 2.5" then at the cat down to 2.25"?

would that work?

would it impove flow?

would their still be enough back pressure for the engine?

any advice of what i should do
--im looking to increase flow and mabey gain a little hoursepower at the same time

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Unread 05-15-2013, 12:56 PM   #2
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1987 YJ Wrangler 
Join Date: Sep 2006
Location: Hernando, Mississippi
Posts: 2,426
I haven't ever decided to replace my factory 4.2 manifold with a header for a couple of reasons
1 - I never seem to be able to put the money together to buy one
2 - It runs just fine now that I have the vacuum advance working correctly
3 - I have been informed (from another member here) that has done a 4.2 header swap and also a 4.0 head swap, that a plain header for the 4.2 is not worth the effort or money for what you might gain over a 4.0 head swap

To answer your question directly, no
You don't want to run 3" pipe up front and 2.5", 2.25" piping later on
IMO, the reduction in exhaust flow will be counter productive
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exhaust , exhaust header , exhaust manifold install , exhaust mods , exhaust system

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