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Hi, First post so please be kind. I'm considering deleting my cat and adding an original 40 flowmaster exhaust. Emmisions are not required where I live. I'm having problems finding a kit. Any suggestion? Also have Volant CAI and diablosport Trinity tuner. Wanting to complete the package. Any suggestions/ experiences would be much appreciated. Thank you
 

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'05 ESV Platinum, 250,000 still looking fine, really fine!
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I deleted my CATs a couple months ago. I used straight pipes, it was simple and cheap. One was plugged up causing very poor running.

After delete you will need to tune computer to write out the code which will cause the check engine light to illuminate or purchase 2 spark plug antifowl caps. They will need to be modified simply by drilling out the base on the inside a little bit so the downstream O2 sensors can be fitted. This will eliminate any codes thrown as well.
 

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2004 ESV
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475 Posts
Unless you are having issues with the converters, I'd just leave them in. You aren't going to see any real horsepower gains by removing the cats. Get the exhaust for sure. But removing the cats just to remove them isn't going to give you any improvements.

The legit street cars channel is doing a build in a C5 where he has all his emissions equipment installed. His car is tuned and puts down C5 Z06 level power numbers, and gets 40 mpg highway. It is possible to gain power and efficiency as well.
 

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Discussion Starter #4
Thank you guys for your replies. So let's say I just change the muffler. Flowmaster original 40. Which one? Inlet outlet size, qty...etc
 

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'93 SedanDeville 60 Special
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230 Posts
Due to the age of the Cats and the use of Ethanol in gas they may be clogging up and increasing the back-pressure which also hurts the exhaust pulses to help fully extract exhaust out of cylinders so next time a cylinder fires off is not a clean charge.

Best case is replace the CATs with a X-Pipe (not H pipe) and that will solve both of those issues and increase the bottom end torque which will be gained by the tuning changes

Just leave the rear O2s in.
 

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'93 SedanDeville 60 Special
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No I do not but if you search for mufflers for your car it should say what the pipe diameter is
In my case it was about best performance and as you see the X-Pipe I used was a direct swap where
the CATs were

575958
 

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2004 Cadillac EXT
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Hi, First post so please be kind. I'm considering deleting my cat and adding an original 40 flowmaster exhaust. Emmisions are not required where I live. I'm having problems finding a kit. Any suggestion? Also have Volant CAI and diablosport Trinity tuner. Wanting to complete the package. Any suggestions/ experiences would be much appreciated. Thank you
Hey man I was lost also at first when my Cats started clogging up my truck would run but it was sputtering and i could tell something was not right. Mechanic said it was cam after he kept it a day. I knew that was not right. I remember when I was a kid (back in the early 80s) my dads Buick station wagon did same thing, rev but no power. I remember the old Chevron Mechanic put it up on lift and beat the hell out of the catylitc converter, and little pellets shooting out. It ran way better after that. SO I took it to muffler shop and told them to cut cats and replaced muffler with MagnaFlow 12599 Exhaust Muffler and I can tell you WOW what a difference. Like night and day. only charged me 50.00. I was sooo happy.
 
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