Sounds like you lost all sense of back pressure and air is sucking in backwards through the exhaust and causing some valve lag.

 

Yep you've lost a lot of back pressure. I would've left the cats on it

 

the magna pack being a glass pack???

 

^ Yup. Get a decent, full exhaust system and that annoying pop and crackle will go away, and you will have a much better sounding and better performing truck. Take the tune off as well, it's honestly just a waste of money. You're better off investing that 2-300 on an air intake and then buying yourself a good custom tune. That'll make a noticeable, good difference.

 

i have a flowmaster delta flow 40 thats just sitting around. if i replace the magnapack with it will that fix the back presshure problem

 

yes its a glasspack that magnaflow makes. i have a intake 4in tubing with a spector cone filter. i have been thinkin about black bear for a tune is it worth it. and what if i install headers or intake ect. will they moddify the tune to account for changes. and could it be multiple tunes such as towing gas milage and perforance

 

i have a flowmaster delta flow 40 thats just sitting around. if i replace the magnapack with it will that fix the back presshure problem

No, not completely. You need to just get some high-flow cats, and then get yourself a cat-back system (preferably not flow master if you're concerned about flow) to finish it off. Trust me. The straight piped get OLD after a while and other people will thank you.

 

In my opinion, put cats back on, and a decent muffler. The 5.3 stock is not a high compression race motor. It will be hard to find that "deep throaty vroom vroom I make 450hp at the crank" exhaust note. I would definitely put a muffler/cats on it as soon as possible. No back pressure can cause quite a bit of stress on a motor when it doesn't have the power to constantly push air out instead of inhaling it back in

 

yes its a glasspack that magnaflow makes. i have a intake 4in tubing with a spector cone filter. i have been thinkin about black bear for a tune is it worth it. and what if i install headers or intake ect. will they moddify the tune to account for changes. and could it be multiple tunes such as towing gas milage and perforance

Blackbear would be a great place to start. I'd suggest to do all of these first before you get your tune.

 

did the check engine light not come on?? sounds to me like a bad knock sensor....when they go bad it retards your timing and runs like a dog..take it to autozone and have them put there scanner on it...its free

 

what brand cats do u recamend. and i have been planing on getting a borla pro xs or the xr what do u think. should i stay with 2.5 off the y pipe or bump it up to 3. and for an intake what do u recamend aem spector volyant...

 

yes the light was on before i installed the tune and i ran codes and it came up with two knock sencors with low imput.

 

Sounds like you lost all sense of back pressure and air is sucking in backwards through the exhaust and causing some valve lag.

In my opinion, put cats back on, and a decent muffler. The 5.3 stock is not a high compression race motor. It will be hard to find that "deep throaty vroom vroom I make 450hp at the crank" exhaust note. I would definitely put a muffler/cats on it as soon as possible. No back pressure can cause quite a bit of stress on a motor when it doesn't have the power to constantly push air out instead of inhaling it back in

Okay, I thought you were joking the first time, but are you serious?

 

I wouldn't joke on a topic such as this. The OP is asking for help so I won't troll.

I can only say that with vehicles that have EGR, reducing the backpressure does not allow the proper exhaust flow (pressure) to operate the EGR system properly. Because of that, your engine will have an increase in combustion pressure which will increase the possibility of spark knock which the PCM will read from the knock sensor and now retard the ignition timing. So under certain conditions, you could actually have reduced power due to retarded ignition timing. Straight pipes without cats will certainly set failure codes and turn on your check engine light.

To cite personal experience, I knew a guy with a LS1 trans am who just installed headers and decided not to run any exhaust. About 3 months later, he snapped 2 valves because of valve burn. Just my $.02

 

No back pressure can cause quite a bit of stress on a motor when it doesn't have the power to constantly push air out instead of inhaling it back in

Wait- so if you open up your exhaust, the motor pulls air back in through the exhaust valves? Please explain how this is possible...

I wouldn't joke on a topic such as this. The OP is asking for help so I won't troll.

I can only say that with vehicles that have EGR, reducing the backpressure does not allow the proper exhaust flow (pressure) to operate the EGR system properly. Because of that, your engine will have an increase in combustion pressure which will increase the possibility of spark knock which the PCM will read from the knock sensor and now retard the ignition timing. So under certain conditions, you could actually have reduced power due to retarded ignition timing. Straight pipes without cats will certainly set failure codes and turn on your check engine light.

Please stop posting about back pressure- it is a myth that doesn't apply to modern EFI motors the same way it applied to old carb motors. While changing exhaust components will affect engine performance, it is not because "your motor needs backpressure" to run right.

OP- It could be any number of things affecting your HP at this point. With added miles comes added things that can go wrong- not necessarily enough to get a CEL but enough to affect the HP/TQ your motor is making. Also- putting mods on the truck will also have an affect on things as well. Running almost an 'open exhaust' such as you have is going to impact your torque/hp curve and if you don't have an appropriate tune to compensate you are going to lose power. Your motor does NOT need backpressure to run properly- it is set to run with the flow capabilities from the factory. Change those parameters and your tune should be changed as well.

There are pages that could be typed on the topic. But anyone who claims your motor needs "backpressure" to run right doesn't understand exhaust dynamics and how they apply to how a motor operates.

I would recommend ditching the tuner you have now- get a quality tune from a source such Blackbear and tell them what exhaust system you decide to go with. As far as exhaust it is personal preference- but I would go with some long-tubes, high-flow cats (to help smooth out sound and clean up the smell) and a 'cat-back' of your liking. A 3" cat-back isn't going to be overkill IMO for a 5.3 and give you a little room to grow if you decide to swap out heads or cam down the road.

To cite personal experience, I knew a guy with a LS1 trans am who just installed headers and decided not to run any exhaust. About 3 months later, he snapped 2 valves because of valve burn. Just my $.02

Did he adjust his tune at all? What other mods were there? And if someone is running open headers I doubt they are just driving around like grandma on a Sunday cruise...Also- the whole "I knew a guy" doesn't count as personal experience in my book.

 

Knock sensors it is... Look at the sticky when the sensors start to go bad they retard your timing and it runs like a dog

 

Wait- so if you open up your exhaust, the motor pulls air back in through the exhaust valves? Please explain how this is possible...

Please stop posting about back pressure- it is a myth that doesn't apply to modern EFI motors the same way it applied to old carb motors. While changing exhaust components will affect engine performance, it is not because "your motor needs backpressure" to run right.

OP- It could be any number of things affecting your HP at this point. With added miles comes added things that can go wrong- not necessarily enough to get a CEL but enough to affect the HP/TQ your motor is making. Also- putting mods on the truck will also have an affect on things as well. Running almost an 'open exhaust' such as you have is going to impact your torque/hp curve and if you don't have an appropriate tune to compensate you are going to lose power. Your motor does NOT need backpressure to run properly- it is set to run with the flow capabilities from the factory. Change those parameters and your tune should be changed as well.

There are pages that could be typed on the topic. But anyone who claims your motor needs "backpressure" to run right doesn't understand exhaust dynamics and how they apply to how a motor operates.

I would recommend ditching the tuner you have now- get a quality tune from a source such Blackbear and tell them what exhaust system you decide to go with. As far as exhaust it is personal preference- but I would go with some long-tubes, high-flow cats (to help smooth out sound and clean up the smell) and a 'cat-back' of your liking. A 3" cat-back isn't going to be overkill IMO for a 5.3 and give you a little room to grow if you decide to swap out heads or cam down the road.



Did he adjust his tune at all? What other mods were there? And if someone is running open headers I doubt they are just driving around like grandma on a Sunday cruise...Also- the whole "I knew a guy" doesn't count as personal experience in my book.

You hit the nail on the head with this post. I was reading through the thread hopeing someone would correct him.