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Discussion Starter #1 (Edited)
Has anyone here experimented with making the factory cat a high flow
by cutting it in half and rewelding back together.
We've tested this at many viper dyno days and this custom version produced
equal or better power along with a much more durable unit. The aftermarket
fancy stainless versions burnt up or blew out after time, especially with power
adders.
At one of the world viper drags John Hennessey and I talked about it and he
also said it was the way to go. :thinkerg:
 

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Straight Up Beast SON!!!
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Never heard of any one doing this Scott. Although I have heard of guys hollowing out the stock cats before, but not like the way you describe it....
 

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I'd be curious to see how it works out; would it going to effect emissions testing?

Did John Hennessey say he was going to start selling these "modified stock cats" as "Hennessey Performance Hi-Flow Cats?"
 

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I just had my stock cats fabbed up to pass emissions in Allegheny County in SW Pa. The stockers are 400 cell and choked down from 3" to 2 1/2 with a pressed in inner pipe in each end. Pulling the inner pipes out changes the inlets and outlets from 2 1/2" to 3". This changes the inlet and outlet areas from roughly 5 sq inches to roughly 7 sq inches which is a significant increase. With this modification I did notice a difference with my modded stock cats. My impression was that they were very similar to the 300 cell high flow cats that I had on with the SW headers prior. I have a set of off road pipes on now and notice a bigger difference in throttle response and top end and at WOT. (A lot more sound too.) The amount of time and effort and expense to cut and repack and reweld the stock cats seems like a lot more trouble and expense than just making the cats interchangable. You could use the stockers for emissions or dealer service, and then easily replace them with an off road pipe with no restriction at all or go to a 200 cell or even a 100 cell high flow cat set up, any of which should flow way better than stock.
 

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Straight Up Beast SON!!!
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I just had my stock cats fabbed up to pass emissions in Allegheny County in SW Pa. The stockers are 400 cell and choked down from 3" to 2 1/2 with a pressed in inner pipe in each end. Pulling the inner pipes out changes the inlets and outlets from 2 1/2" to 3". This changes the inlet and outlet areas from roughly 5 sq inches to roughly 7 sq inches which is a significant increase. With this modification I did notice a difference with my modded stock cats. My impression was that they were very similar to the 300 cell high flow cats that I had on with the SW headers prior. I have a set of off road pipes on now and notice a bigger difference in throttle response and top end and at WOT. (A lot more sound too.) The amount of time and effort and expense to cut and repack and reweld the stock cats seems like a lot more trouble and expense than just making the cats interchangable. You could use the stockers for emissions or dealer service, and then easily replace them with an off road pipe with no restriction at all or go to a 200 cell or even a 100 cell high flow cat set up, any of which should flow way better than stock.
Rich how bad is the smell with the off road pipes? I asume you took the stock cats off already....
 

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Discussion Starter #6 (Edited)
ok just completed the stock cat conversion to high flow cat.
We cut an easy access hole into the stock cat so we could
easily weld back on. To our suprise the stock cat has two
sections. We removed the front section only. The mod can
be done by any fabricator in a couple hours. My guys are
slackers so it took a few including lunch. The rig sounds much
better at top end too. 12 second club make some room.
I've got pics but have to figure out how to post.
I sent Eric and Vic from our local a couple.
So far no check engine light.....
 

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Rich how bad is the smell with the off road pipes? I asume you took the stock cats off already....
Jose, not really that bad. I wanted to try the off road pipes knowing that I could swap back and forth pretty easily if they were too obnoxious. I've had them on for about 1500 miles now and I don't really notice it much. Pulling into or out of the garage I notice it sometimes but even idling at a stop it isn't really that noticeable. I think partly because the Johan tune burns pretty clean.
 

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ok just completed the stock cat conversion to high flow cat.
We cut an easy access hole into the stock cat so we could
easily weld back on. To our suprise the stock cat has two
sections. We removed the front section only. The mod can
be done by any fabricator in a couple hours. My guys are
slackers so it took a few including lunch. The rig sounds much
better at top end too. 12 second club make some room.
I've got pics but have to figure out how to post.
I sent Eric and Vic from our local a couple.
So far no check engine light.....
Let us know if you throw any codes with the altered cats. Looking forward to seeing the photos.
 

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Straight Up Beast SON!!!
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Jose, not really that bad. I wanted to try the off road pipes knowing that I could swap back and forth pretty easily if they were too obnoxious. I've had them on for about 1500 miles now and I don't really notice it much. Pulling into or out of the garage I notice it sometimes but even idling at a stop it isn't really that noticeable. I think partly because the Johan tune burns pretty clean.
Thanks Rich! Might have to give the off road pipes a try as well.....
 
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