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Discussion Starter · #1 ·
Hey guys, I tried searching but couldnt find an answer. I was under the truck the other day and noticed that theres two catalytic converters up on the y pipe near each manifold, then a big 3rd cat that is mounted near the transfer case. The aft most cat has no sensors anywhere near it, so my question it, besides not getting a sticker, any cons to just straightpiping this bad boy? :049: I got a 40 series, just worried about lack of backpressure messing anything up. Thanks in advance
 

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nope, if you don't have to worry about inspections then rip it out, gut it, or fab up a test pipe. the 3rd cat is only for emissions and doesn't affect the engine at all. i have dual exhaust and no 3rd cat, and mine does have sensors but i have no codes. don't worry about back pressure unless you are going with too large of an exhaust. if you are going single, then you should have a 2.5" Y-pipe made that runs into single 3" the rest of the way back to the muffler for best results.
 

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Discussion Starter · #3 ·
i got dual 2.25" pipes exiting right before the rear wheel and like i said flowmaster 40 series, i should be ok then? If so that sucker's comin out tonight. How does it sound by the way? I see yours is a 5 speed, thats sickkk
 

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so you have a single in, dual out 40 series muffler then. is that going into all stock pipe the rest of the way? if so, you should really get a 3" pipe and larger Y-pipe because it's way better for performance. the stock system is too small, and just adding a new muffler isn't enough.

mine sounds great, it's pretty loud.
 

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Discussion Starter · #5 ·
nah its all stock up to the muffler (single in dual out) then about (2) foot and a half long pipes exiting out in front of the rear wheel on the passengers side
 

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Discussion Starter · #7 ·
ahh, too little backpressure can burn up valves and be bad for the motor, i guess since i still got the two primary cats on it should be fine
 

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ahh, too little backpressure can burn up valves and be bad for the motor, i guess since i still got the two primary cats on it should be fine
Not true, many people get back pressure confused with velocity. When you put on an exhaust system that is too big for your engine you lose power..... people assume that it's due to a lack of back pressure since the new exhaust flows much better. It's actually due to a loss of velocity, the exhaust gases are traveling much slower out of the cylinder and through the exhaust because there is much more room for them to expand. A good exhaust is big enough to let the gases escape the cylinder with as little restriction as possible but small enough to keep it moving as quickly as possible

As for the burned valves...... People get burned valves cause their engine ran lean. This used to happen on older motors that weren't able to actively adjust fuel delivery, you open up the exhaust and get more air through the motor but the fuel delivery doesn't change
 

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we actually had a guy burn his valves on the 4.7 by running open exhaust, just headers. he had to rebuild the thing. now whether or not that was all due to no backpressure or just his beating on the truck i don't know, but it happened.

amberfire is right though about the backpressure vs velocity. the terms always end up being confused on forums.
 

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Discussion Starter · #11 ·
thats what i love about these forums, learn somethin new every day. Thanks for the clarification guys. Tried gettin the cat off last night, the cutoff wheel just didnt fit all he way so im waitin on my buddy to bring his sawzall over, the one tool i dont have. Then its ready to straightpipe that bastard
 

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we actually had a guy burn his valves on the 4.7 by running open exhaust, just headers. he had to rebuild the thing. now whether or not that was all due to no backpressure or just his beating on the truck i don't know, but it happened.

amberfire is right though about the backpressure vs velocity. the terms always end up being confused on forums.
Were his O2's hooked up and in the headers?
 

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Were his O2's hooked up and in the headers?
that i don't know, but normally it wouldn't make that big of a difference. it would stay in open loop all the time, but that really only affects gas mpg and efficiency. it would have to be running an extreme rich or lean condition in open loop to really hurt the engine. if the map is working right then the pcm will still adjust the A/F to keep it running decent, but just not perfect. a lot of racers only tune in open loop, and disable the O2 sensors since they spend a lot of their time in open loop at WOT anyway.
 

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that i don't know, but normally it wouldn't make that big of a difference. it would stay in open loop all the time, but that really only affects gas mpg and efficiency. it would have to be running an extreme rich or lean condition in open loop to really hurt the engine. if the map is working right then the pcm will still adjust the A/F to keep it running decent, but just not perfect. a lot of racers only tune in open loop, and disable the O2 sensors since they spend a lot of their time in open loop at WOT anyway.
I can't guess as to why he burned a valve, but I strongly doubt it had anything to do with backpressure...... unless your running open shorties or no exhaust at all
 

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Discussion Starter · #15 ·
regardless, the cat is now straightpiped... quickest exhaust ive done on the truck, 40 mins start to finish. sounds nastyyyy, got a nice snarl now and just better sounding overall. thanks for the help fellas
 

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ok so i just recently put an off road y-pipe on my 04 dak and got rid of the cats. the exhaust runs to a single chamber flowmaster. i was told that would not effect my motor in a bad way.. should i be worried about backpressure or anything?????
 

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the only thing you need to be worried about is being in cali with no cats. how are you going to pass smog inspection? it will also be very loud like that.

as long as you have a full exhuast you can run straight pipes and still be fine. backpressure isn't the issue, it's velocity and heat. with a single pipe system you don't have to worry about much. what size is it?
 

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i know about the smog deal and i know people that can take care of that for me =] its a 4.7. next week im puttin a throttle body spacer and some stuff for looks but im hoping for a decent gain from the throttle body spacer. do you have any suggestions on programers or super chips???
 

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before you get flammed, forget about the spacer and just get a ported TB from fastman or others. the spacer is a gimic and the biggest pice of crap you can buy. if anything you will loose power not gain it. invest in a 70mm TB and superchips.
 

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so iam in pa i have a 00 4.7 and i have a cherry bomb muffler .not the best but wife bought the wrong one so i put it on anyways .but my question is if i cut the cat wich one do i cut out can i leave the one with the 02 sencor and cut the others i have to pass emmisions in pa .but i want MORE POWER iam thinking about the throttle body and a super chips but i want to do eveything thing cheap first 3 kids + hoilidays = not alot of cash .so i can cut and clamp or weld a piece in there .thanks for the help guys .maybe some one that has done it should start a thread for the cheap or the easy upgrades .in maybe a step form.most know intake exshaust .
 
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