[JDesjarlais]

So both my catalytic converters failed the precat first (had to pay $2000 for a junkyard engine and $1000 for a new pre cat), then my main cat failed and the guys at the local minute muffler told me they can just hollow it out and it'll work fine. So i said go ahead, then after they gutted it it sounded like a rez rocket and i abolutely hated it, so i asked how they could get rid of that awful droning. To them the answer is backpressure, so i had them put in a resonator as they suggested. Now my car pops and sounds like its backfiring (not carb'd so i know its not) and i was just wondering, is this bad? What exactly could the popping be? Is it backpressure?

PS: I read a few posts on backpressure, just want someones opinion

 

[i68k]

the backfires are from a few reasons, but your mostly seems to be from lack of back pressure. most of us will gut the precat and leave the main cat. check online you can get a universal cat for under $100, and just have them weld it in. between another cat and a resonator in the exhaust you should be taming the beast. not sure why youd pay $1000 for a precat, instead of a $100-$300 catless header as recommended in the precat and butterfly faq here:
http://www.b15sentra.net/forums/showthread.php?t=135241

 

[B15pwr]

So both my catalytic converters failed the precat first (had to pay $2000 for a junkyard engine and $1000 for a new pre cat), then my main cat failed and the guys at the local minute muffler told me they can just hollow it out and it'll work fine. So i said go ahead, then after they gutted it it sounded like a rez rocket and i abolutely hated it, so i asked how they could get rid of that awful droning. To them the answer is backpressure, so i had them put in a resonator as they suggested. Now my car pops and sounds like its backfiring (not carb'd so i know its not) and i was just wondering, is this bad? What exactly could the popping be? Is it backpressure?

PS: I read a few posts on backpressure, just want someones opinion

Having a gutted cat and not having a cat at all is pretty much the same thing. The resonator will only help with the noise cut out but honestly nothing to do with backpressure or atleast not a big part of it. It backfires cuz your cats gut and allowing unburnt fuel throught your exhaust hence the backfire

 

[undertakernismo]

^^^Exactly. I've been running a full catless exhaust for the last 4 years (car's been with me 5 years and counting) and it pops and backfires all the time. Whenever you eliminate a catalytic converter, be it by gutting or cutting it out altogether, unburnt fuel goes into the exhaust stream and like B15pwr said, there's the backfiring. And what makes it more evident in our cars is that our engines don't have an EGR system. Unless you want to replace the cat you gutted I guess it's just a matter of learning how to live with it.....

By the way, if you're still rocking the Pre-Cat I'd suggest replacing it with a catless header and weld an aftermarket cat to the midpipe. Your engine will thank you in the long run...