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I've had my 4" exhaust with cat delete pipe on since my truck was new and have had no problems or issues with it. It helps to keep egt's lower when towing.
you will actually gain some free flow and notice the improvement in the higher revs. but with stock programming and no cat, your power band will higher, therefore the low end suffers a bit. not really bad, just you will have to keep the rpms higher to see the benefit.
That is my understanding as well LvTitian. I'm thinking that all the internal pressures in the motor would actually improve since both the incoming air (with the AFE installed) and the outgoing exhaust (free flow exhaust) is less restricted. Thus, blowing seals and what not should not be contributed what so ever to a modified exhaust system.
IMO the number one improvement is the sound the exhaust makes without the cat. It sounds good with the muffler gone, but with the cat gone it sounds great. The only downside if it is one is the increased diesel smell at idle.
Hmm, funny I found this thread tonight. I jsut got done installing my new MBRP 4" turbo back 304 stainless exhaust. I opted to leave the stock cat in for warranty purposes. I was told by my tech at the dealership that it is best to leave the cat on there until warranty is up. My dealership does not really care about it, but if I were to be travelling and have problems somewhere else, that dealer might void my warranty for the exhaust. I have 29k to go and I will put the cat delete pipe in. I did notice when I drove it that the low end grumble is not quite as pronounced as everyones videos. I also had a little trouble with the cat bolting up to the downpipe, the mbrp pipe is obviously a 1/2 bigger around but the flange nuts used on the stock exhaust get hung up before the nuts get the flanges all the way together, so I currently have a very slight hiss from a leak there. I will fix this tomorrow with some homemade spacers to get the nuts away from the weld on the flange.
Thinking of removing the cat myself.Will lv the muffler in and was wondering ppl say the sound is great..What type of sound r we talking about.....Kinda hoping the whine from the turbo is that sound... Thx Guys
The turbo whistle is more pronounced when the cat and muffler are both out of the system. Either one left in will diminish the tone rather significantly.