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I was thinking about removing my OEM cats and replacing the left and right side with cat bypass pipes - they are basically two T304 stainless steel pipes that'll replace the pipe from the headers to my X-pipe. Basically, the exhaust will be open from the headers back. The pre- & post- O2 sensors will still be in place.

My only concern at this moment is torque loss down low, but that torque will come back with software and it will gain a good deal of power on WOT and in the upper RPM range.

I just don't want to lose a great deal of down low grunt. I figure with the PC 93, that will take care of that.

Thoughts? Experiences?
 

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if you have stock exhaust manifold you will not loose to anything noticable down low. After speaking with a few guys in the business of building e39 monsters (D/A Dinan) I do not think you will gain more than 3-5whp running without cats and you will get a check engine light for the cats inefficiantcy.

Remember dinans S-3 runs through the stock cats. That is what 600+ through the cats on a boosted application. Like I said 3-5 whp i think is all you will see. Maybe as much as 10whp but at the expense of what????

I am goign to be running random tech race cats and wi most likely see the same gain you would runing no cats but I will retain my emissions.

Ryan
 

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Discussion Starter #3 (Edited)
if you have stock exhaust manifold you will not loose to anything noticable down low. After speaking with a few guys in the business of building e39 monsters (D/A Dinan) I do not think you will gain more than 3-5whp running without cats and you will get a check engine light for the cats inefficiantcy.

Remember dinans S-3 runs through the stock cats. That is what 600+ through the cats on a boosted application. Like I said 3-5 whp i think is all you will see. Maybe as much as 10whp but at the expense of what????

I am goign to be running random tech race cats and wi most likely see the same gain you would runing no cats but I will retain my emissions.

Ryan
My main concern is that I don't want to lose any torque down low, and I have heard that deleting the cats will cause this.

I plan to do the PC software along with deleting my cats, so hopefully the ECU will adjust and I will get some added flow in the exhaust.

I do not expect much gains, if at all, but my cats are beginning to foul out, so I have been searching for some alternatives.

Thanks for the post.
 

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Discussion Starter #4
Any other opinions? thanks..


Again, I plan to do custom software with the deleted cats.
 

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I'd like to know if you can delete the cats and not run software with it, will the car still run fine and operate normally?

Granted, there will be a SES light, but that will be taken care of when I actually get software.

For now, can I delete my cats without getting upgraded software? Will the car run like before after deleting the cats and stock software???

Thanks.
 
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