# Muff delete...



## goatboy_2004GTO (Sep 7, 2006)

I know this has been talked about before...I've read all the threads. I really, really love the sound with the mufflers taken out and everything else left stock (cats, resonator). 

Will this really affect the performance and will it damage the engine (as I've talked to some people who've done this to other vehicles and it messed them up). If it's going to cause even minimal damage, I'm not going to do it.

Drone isn't too big of a deal, but I can imagine it might get old after awhile, but I don't imagine it is too bad at around crusin' speed.

Also, the popping and rasping. I've heard people say its the worst in the world and people say it isn't bad at all. I can deal with a little, but if it makes it sound like something's wrong, can't go with it!

I really wish I could meet up with somebody in the East, Texas area that has done this so I can hear first hand. I just love the deep sound! 

Thanks all you GOAT heads :cool for a great forum!


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## DAH GTO (Mar 5, 2005)

goatboy_2004GTO said:


> I know this has been talked about before...I've read all the threads. I really, really love the sound with the mufflers taken out and everything else left stock (cats, resonator).
> 
> Will this really affect the performance and will it damage the engine (as I've talked to some people who've done this to other vehicles and it messed them up). If it's going to cause even minimal damage, I'm not going to do it.
> 
> ...


The effects of back pressure


A muffler is an ambiguity in the performance world, as it can have both good and bad effects on power output. Back pressure is essential for peak power in almost any application, even 6000hp alcohol-burning Top Fuel dragsters have some built-in back pressure. Before we begin this discussion, take note that 1 atmosphere is the pressure that air is at naturally (uncontained) at sea level.

During the combustion process, when the exhaust valve is open, all of the compressed (and depleted) air-fuel mixture spills out from the cylinders as fast as it can, through your exhaust manifold, into your catalytic converter(s), the muffler, and finally out the tail pipe. The problem with this is, just before your exhaust valve is about to close again, your intake valve opens up, allowing the fresh air-fuel mixture to rush into the cylinders. This is called overlap, and one of the things you take into consideration when choosing a cam, because it can be used to your advantage.

If there was no valve overlap, it would be 100% impossible to completely irradicate all of the spent gases from the cylinder. This has a two-fold effect on power output, depending on what RPM the motor is running at. At low RPM, this effect actually increases torque, because the least amount of compression is lost during the intake stroke, and the ratio of intake to exhaust gases is high. Unfortunately, as the RPMs increase, there is increasingly less time to evacuate the exhaust gases during the exhaust stroke, and more and more depleted air-fuel remains in the cylinders when the exhaust valve closes. The motor becomes incredibly inefficient near its readline. A motor designed for high-torque applications, such as towing, tends to exhibit less valve overlap then normal. The type of cam used in this application is often called an "RV" cam, because a recreational vehicle doesn't need horsepower as much as it needs low-end torque to get it moving.

Your car would also run terribly if there was too much valve overlap as well. When exhaust gases rush out of the cylinder, they create a low pressure area in the cylinder and the exhaust system, sucking the intake charge right into the cylinder, and right back out into the exhaust system. This is called scavenging. When that air spills out, so does the fuel it was carrying, so the O2 sensor reports a rich condition to the computer, often causing further decreases in the amount of fuel the computer injects. At low RPMs, this effect is most pronounced as there is sufficient time to suck out a significant portion of the intake charge, reducing torque. As the RPMs increase, however, the extra velocity imparted to the intake charge increases the amount that squeezes into the cylinder after the exhaust valve closes, as the valve closes so quickly at high RPMs that barely any intake charge escapes through the exhaust system.

No doubt you see the dilemna posed to designers when they choose a cam for the motor - the right combination of power must be achieved at the intended RPM range of the vehicle - if this is a tiny four cylinder, which must spin high RPM to make any power at all, you have to design in a higher amount of overlap. If the vehicle is mostly intended for low speed towing, you design in a smaller amount of overlap for more low-end grunt. Overlap is one of the reasons why the four-cylinder Acura Integra GS-R makes 170hp at almost 7000 RPM, and your 3.0L makes 171lb-ft of torque at 2000 RPM.

You can't control your overlap without changing the cams, but the effects caused by changing the back pressure are the same. When you reduce back pressure, it is equivalent to increasing valve overlap, and when you increase back pressure, it is the same as decreasing the amount of valve overlap. That's why some people will say, "you need a muffler for torque", or, "you'll have more high-end, but less torque, if you run straight exhaust". They are right, but a muffler's purpose is to reduce sound output, not horsepower! By reducing back pressure in an exhaust system, you increase high-end horsepower at the cost of low-end torque.

You can compensate for this by increasing the velocity of the intake charge. Increasing the intake velocity has the added side effect of increasing back pressure, because there is more air to be evacuated during the exhaust stroke. Note that if you increase intake velocity past the limits of the exhaust system, the gains you achieve are diminished to the point of being non-existent. That power will be there when you do upgrade the exhaust system, which is why something as simple as upgrading the exhaust system can result in huge horsepower gains.

You can decrease back pressure by increasing the size of your exhaust manifolds, or using separate tubes for each cylinder (called headers). Increasing the size of the exhaust pipe and decreasing its length also helps, as well as installing high-flow catalytic converters and mufflers. Of course, you could just cut them off. Although it is illegal in the United States to remove the catalytic converter in a registered vehicle, the muffler is a different story...


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## goatboy_2004GTO (Sep 7, 2006)

Thanks...that for sure helps out some. I'm going to go to a muffler shop and talk to them about all this.


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## pickinfights (Oct 3, 2006)

To: Dah GTO.
This forum is the best place on earth (other than my drivers seat) Because of people like you. That was like a 9 paragraph thread of pure knowlege. You rock.:cheers


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## Good 2 go (Sep 7, 2005)

My base line dyno was done without the mufflers, and it seemed low to me, but there was nothing to compare it to. I didn't notice any seat-of-the-pants difference, but a tremendous attitude change. Yes, it does pop, sometimes pretty loud. If that would annoy you, don't do it. If not, be prepared for compliments and thumbs-up from bystanders. Don't know if the mufflers contribute at all to back pressure, especially since there are crimps and pinches already in the pipes ahead of the mufflers.

I'm not in East Texas, or I'd be glad to take you for a ride. I do have LT's now, which changed the exhaust note considerably (the word NASCAR comes to mind), but you might decide to go that route yourself one day. At any rate, I only paid $50.00 for the muffler-ectomy, pretty cheap, and reversible too!


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## goatboy_2004GTO (Sep 7, 2006)

Good 2 go said:


> My base line dyno was done without the mufflers, and it seemed low to me, but there was nothing to compare it to. I didn't notice any seat-of-the-pants difference, but a tremendous attitude change. Yes, it does pop, sometimes pretty loud. If that would annoy you, don't do it. If not, be prepared for compliments and thumbs-up from bystanders. Don't know if the mufflers contribute at all to back pressure, especially since there are crimps and pinches already in the pipes ahead of the mufflers.
> 
> I'm not in East Texas, or I'd be glad to take you for a ride. I do have LT's now, which changed the exhaust note considerably (the word NASCAR comes to mind), but you might decide to go that route yourself one day. At any rate, I only paid $50.00 for the muffler-ectomy, pretty cheap, and reversible too!


Yeah, I've been reading on ls1gto.com forums and it really is a matter of opinion. The Stock exhaust system is honestly one of the best I've ever seen or heard, I just want her louder. I would think the cats and the resonators would eliminate any backpressure, plus the pipes are long and curved enough to cancel any of it out.

I was also thinkin' about glasspacks, as I've had 12 inch on my first ride (79 GMC sierra...YEEEEEE FRIGGIN HAWWWWWW!!!). That truck would set off car alarms it was so loud! 

What I'll more than likely do is get bolt on straight pipes, keep my stock exhaust that way if I wanted too all I'll have to do is change em out. Either that or get the super 40's or something...heard good things about them.

Thanks guys...I knew I could count on ya :cheers

No clip Good 2 go?? Nice color choice as well...as it is the fastest


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## DAH GTO (Mar 5, 2005)

pickinfights said:


> To: Dah GTO.
> This forum is the best place on earth (other than my drivers seat) Because of people like you. That was like a 9 paragraph thread of pure knowlege. You rock.:cheers


Thanks but I can't take the credit, I came across this some time ago, glad to share it.


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## Good 2 go (Sep 7, 2005)

goatboy_2004GTO said:


> No clip Good 2 go?? Nice color choice as well...as it is the fastest


I've got a clip of her on the dyno being tuned after the Kooks installation. Can someone assist me in how to post it? I would like to upload some pics into the gallery too.


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## goatboy_2004GTO (Sep 7, 2006)

Good 2 go said:


> I've got a clip of her on the dyno being tuned after the Kooks installation. Can someone assist me in how to post it? I would like to upload some pics into the gallery too.


You have to upload it somewhere, like youtube.com or putfile. After you upload it, you copy the url on a thread. Hope this helps some.


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## Good 2 go (Sep 7, 2005)

Here we go!

http://www.youtube.com/watch?v=AVN6_BMlRhs


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## goatboy_2004GTO (Sep 7, 2006)

Good 2 go said:


> Here we go!
> 
> http://www.youtube.com/watch?v=AVN6_BMlRhs


WOOT! Very nice! I think you just made my mind up. :cheers 

I like how its kind of tame at the low end but when you get on it...cover your ears!


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## pickinfights (Oct 3, 2006)

Holy crap.:willy:  :willy:


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## AcePilot (Aug 10, 2006)

Is the resonator in the muffler? If it is then you will have a few more rattles in your car.
When I got rid of my Vetts mufflers I started to get alot little rattles at some RPMs (mostly crusing RMPs). 
And boy did I not get chased around by alot of cops. After 2 weeks I put them back!


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## pbmaniac2000 (Feb 13, 2006)

We actually left the muffler on. We took the cats and resonators off. There is only one reason you should not do this. If you have to do yearly inspections then either get a shady character to do your inspections, or don't do it at all. Colorado finally passed a law that says we don't need yearly inspections anymore, so off they came. It sounds crazy awesome though.

Edit: I did have a flowmaster muffler on there so those are not stock.


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## Good 2 go (Sep 7, 2005)

AcePilot said:


> Is the resonator in the muffler? If it is then you will have a few more rattles in your car.
> When I got rid of my Vetts mufflers I started to get alot little rattles at some RPMs (mostly crusing RMPs).
> And boy did I not get chased around by alot of cops. After 2 weeks I put them back!


The resonators are upstream of the mufflers, and I didn't mess with them.


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## Good 2 go (Sep 7, 2005)

goatboy_2004GTO said:


> WOOT! Very nice! I think you just made my mind up. :cheers
> 
> I like how its kind of tame at the low end but when you get on it...cover your ears!


It's not as tame as the clip suggests. In person, when idling you will notice that something has been done, but still is not offensive. When starting it up cold though, it is a little loud.


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## STI GUY (Oct 28, 2006)

do it!!


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## nagoat (Oct 21, 2006)

DAH GTO said:


> The effects of back pressure
> 
> You can compensate for this by increasing the velocity of the intake charge. Increasing the intake velocity has the added side effect of increasing back pressure, because there is more air to be evacuated during the exhaust stroke. Note that if you increase intake velocity past the limits of the exhaust system, the gains you achieve are diminished to the point of being non-existent. That power will be there when you do upgrade the exhaust system, which is why something as simple as upgrading the exhaust system can result in huge horsepower gains.
> 
> ...


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## Pennsylvania Goat (Jul 22, 2005)

I did this to my Goat. It was the most amazing sounding car I've heard in my life (besides stock cars). Almost as good as my Z06 w/ Billy Boat Bullets :cheers 

http://www.gtoforum.com/photopost/showphoto.php/photo/879/size/big/cat/500/ppuser/2429


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## DAH GTO (Mar 5, 2005)

nagoat said:


> DAH GTO said:
> 
> 
> > The effects of back pressure
> ...


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## Exhaust Depot (Oct 28, 2006)

Intake and exhaust go hand in hand. This is why people liek K&N use the word UP TO. 

For example, lets say you make 100hp with an exhaust. If you install an intake you will make say 75hp. Now if you had an exhaust then installed the intake, it would make 100hp. 

What im getting at is that if you have supporting mods, you will get more HP from your intake/exhaust etc.


a 500 hp gto will get more HP out of an intake/exhaust than a 400hp gto would.


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## aintmisbehavinn (Feb 9, 2006)

I think I will stick to factory until I can fork over $1500.00. It's putting out 400 for a reason, not sure I want to get involved in all that other stuff give or take a few ponies...:cool


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