Hey. I recently unbolted the exhaust after the cats on my 07 5.7. I like the way it sounds but it seems like I have worse throttle responce and get a little less MPG. What can I do to restrict a little bit of air flow, but still have it sound like it sounds now? Do I need to get a muffler to help restrict the flow, or is there a way around that? If I need to get a muffler, what is a good muffler that will sound almost as loud as it does now?
Brandon772
I think you need to give it more than half a day to conclude one way or another.
did you reset the ecu and give it a few driving cycles to relearn?
did you reset the ecu and give it a few driving cycles to relearn?
twin 40 series flowmasters!!!! Closest I found with all the mufflers I tried versus straight pipes.
Backpressure has nothing to do with it. Your exhaust needs to have a high velocity in order to produce power, especially at low RPM. With the muffler removed, the exhaust run is too short. When the hot still expanding gas leaves the pipe, it begins to slow down and cool. This causes the pressure wave to collapse. Without a strong pressure wave, you do not get a strong scavenging effect, and that it turn means spend exhaust is left in the cylinders. Now the engine has to push that exhaust out, and that robs power from the engine. You never want the engine to have to do work that could otherwise be done by waste energy. Leftover exhaust in the cylinders also means less fresh fuel and air can enter the cylinders, and that means less power.
i have a x-pipe w/o mufflers and turndowns and havent noticed any loss in power. its not too loud at idle or normal driving but put it the the floor and it sounds like a beast from hell.
Again, as I mentioned, backpressure has absolutely nothing to do with it. Allow me to expain what is happening in this system that is causing the performance loss.
The exhaust as it exits the exhaust is moving in the form of pulses or pressure waves with varying speeds and pressures. These pulses have mass, and want to continue moving at a high rate of speed. These pulses if they are moving fast enough, will create a low pressure region behind them and will help draw out more spent exhaust from the engine, and will create a region of lower pressure inside the exhaust manifold.
If the system is too short, the fast moving pulse will collapse as it exits the end of the pipe, and the low pressure wake will also collapse, reducing the scavenging effect, especially at low RPM. This will be felt as a decrease in performance right off the line.
As RPMS increase, the speed and frequency of these pressure waves increases, negating some of the performance losses and restoring the scavenging effect.
Exhaust scavenging is a function of velocity, not backpressure. Having lower backpressure is a good thing. If a modification decreases the velocity, then a low RPM power loss will be the result. In the case of cutting off the muffler and not at least replacing it with a straight pipe, this modification is reducing the opportunity for the exhaust to built up and keep the speed, and it instead slowing down the exhaust as it exits, creating more backpressure than the stock muffler.
Rebels system is one that maintains velocity. He is running with very little backpressure and seemingly has gained power. The x-pipe creates a cross flow which allows the pressure waves to accelerate each other and create a positive induction.
If you replace your muffler with a piece of pipe, you will get the sound you are probably after without loosing the velocity that is essential to produce power.
The exhaust as it exits the exhaust is moving in the form of pulses or pressure waves with varying speeds and pressures. These pulses have mass, and want to continue moving at a high rate of speed. These pulses if they are moving fast enough, will create a low pressure region behind them and will help draw out more spent exhaust from the engine, and will create a region of lower pressure inside the exhaust manifold.
If the system is too short, the fast moving pulse will collapse as it exits the end of the pipe, and the low pressure wake will also collapse, reducing the scavenging effect, especially at low RPM. This will be felt as a decrease in performance right off the line.
As RPMS increase, the speed and frequency of these pressure waves increases, negating some of the performance losses and restoring the scavenging effect.
Exhaust scavenging is a function of velocity, not backpressure. Having lower backpressure is a good thing. If a modification decreases the velocity, then a low RPM power loss will be the result. In the case of cutting off the muffler and not at least replacing it with a straight pipe, this modification is reducing the opportunity for the exhaust to built up and keep the speed, and it instead slowing down the exhaust as it exits, creating more backpressure than the stock muffler.
Rebels system is one that maintains velocity. He is running with very little backpressure and seemingly has gained power. The x-pipe creates a cross flow which allows the pressure waves to accelerate each other and create a positive induction.
If you replace your muffler with a piece of pipe, you will get the sound you are probably after without loosing the velocity that is essential to produce power.
Back pressure is just a term used in exhaust work. just as in everything in electrical work is a short when technically most are opens, not shorts.
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