Catless Exhaust Pipe
 

Keep the stock DP, but 'core' the 2nd cat, with a piece of 2.75" tubing.
You don't even have to remove the DP to do this.

This will work better than an aftermarket DP catted , or catless...
Try it , you'll like it...:twothumbs:

A FREE mod that works...
12.39 in the quarter mile.
30 MPG with E47 ethanol, staying out of boost, which is very hard to do.
And best of all, NO CEL

Here's why.
The stock ECM is so complex , with more tables that we will
never ever know about.
The 1st cat is very important, because some of the ECM tables,
were designed around a set amount of flow/charge pressure, in the total intake track.
This is very important at low speeds, cruising, & really in any driving mode,
when & where, no boost is present.
This is very noticeable, if you have an automatic.

Coring the 2nd cat, removes a big restriction, & at the same time, helps the
Flow thru the 1st cat.

it's also all about where the 1st cat sits, as close as possible, to the exhast manifold.
This means it will be hotter, which means that flow will be better also.
AND the ECM is programmed around this 1st cat, for excellent off idle response...:twothumbs:

The 2nd cat is bad, very bad for good HP , torque, & throttle response...:skull1:
'Coring' it, will remove the only restriction, in the stock exhaust system.
The remaining 'cat' guts will stay in place forever, as mine have stayed in
place for years...:twothumbs:
Also this modded 2nt cat will still get hot, so if an emission inspector would happen to touch it, he will think that this cat is working correctly.

I've 'tested' this 2nd cat position with straight piping, & 'soda' can aftermarket
cats, & 'off-idle' response isn't as good as just 'coring' it.
The only cat the I have found to be equal to just 'coring' this cat, is a
big 5" diameter, $400, Random Tech 100 cell cat.
Definitely not worth it, but I had used this cat before in a 'test' DP, in which I had this as the only cat, having it welded into a catless CIA DP, in about the same position, as the 2nd cat sits.
That setup still wasn't as good as having a stock 1st cat, with a 'cored' 2nd cat.

I've spent too much time, & too much money, to only discover, that a simple 15 minute FREE mod, works best...:gnonespet:
https://www.chevyhhr.net/gallery/fil...0669_thumb.jpg[/QUOTE]

Thanks so much 2005HH. You just saved me $200.00.

Boydie


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I already have that, guess I'll sell the ZZP catted down.

Have you even tryed it out ???

In the mid-range, it really rips...:twothumbs:

i have the cat on but no resonator and no muffler w a 3 inch ZZP catback
love the sound
with the 2.5 in charge pipes and exhaust, trifecta tune the thing is a beast and really pulls for a manual