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and I asked them to install just mufflers,Magnaflow's, and they told me NO. The mufflers on our cars are only 9" long with no space to spare. The smallest they had were 12".
I was looking to make the car sound better by changing only the mufflers. I plan on doing other exhaust mods later down the road but right now I want the sound.
I also asked him to cut the cats off and he said no. DAMN.
 

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What did you/do you have in mind w/regard to possibly bringing the passenger side exhaust over to the other side of the car?
 

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tdimasi said:
What did you/do you have in mind w/regard to possibly bringing the passenger side exhaust over to the other side of the car?
I was looking to keep leave the system the same just change out the mufflers.



Also I was looking at my car the other night. Under the trunk there is a black panel behind the right wheel, that panel comes off and there is a lot of space for an exhaust pipe to pass through.
 

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i like the exhasust setup its different differnet is cool bringing the pipe to the other side is asking more than it's worth cause you will have to get a aftermarket bumper with dual cut outs paint it or do cut outs on yours which sometimes can cause paint to start peeling. My brother wanted to do this with his regal Gs but it was going to cost him a bit of money
 

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Sorry to be blunt, but what did you expect?

Modern cars are designed to run with their emissions controls in place, and no muffler shop would risk getting in trouble with (in your case) the state of Illinois, the EPA, the DEC and everyone else who would be on their case for chopping of your cats.

Is it really worth it for five horsepower or a minor improvement in sound? I can guarantee that you aren't going to shave even a fraction of your E/T. I don't think it's worth it at all, but that's just my sensible side talking...
 

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I hear the need for a little more sound. OE exhaust, no matter how good they are (ie GTO), never have that amount of volume i like because of government regs. After running a aftermarket on my TA i don't want to go back to OE ever.

After looking at the GTO i figured some problems may occur with just replacing the mufflers because of there size. Looks like either catback or cutouts are in order.

I'm waiting for some budget catbacks such as magnaflow because i'm not gonna drop big bucks for a minimal 5-10rwhp gain.
 

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CrispieGee said:
Sorry to be blunt, but what did you expect?

Modern cars are designed to run with their emissions controls in place, and no muffler shop would risk getting in trouble with (in your case) the state of Illinois, the EPA, the DEC and everyone else who would be on their case for chopping of your cats.

Is it really worth it for five horsepower or a minor improvement in sound? I can guarantee that you aren't going to shave even a fraction of your E/T. I don't think it's worth it at all, but that's just my sensible side talking...

I think the cats Net more power than people think. I have a 97 Ford Probe GT that I pulled the cat on. I gained 11 WHEEL HP with NO other mods. Remember that car only pulls 135 WHP stock. Thats close to a 10% gain.
These GTO cats may be more efficient, but when they get some miles on them, they'll be robbing more and more.

Also its a $25,000 fine for a shop to remove your cats! :)

I really think someone should make an aftermarket pipe that goes from the Manifolds right back to where the pipes are flanged. (like 5 foot long pipe) GM Crushed those Pipes on top so they fit under the car better, so the flow is hampered. With an aftermarket pipe we could eliminate the cats, and eliminate the restrictive pipe----Then we could also Swap the cat'd pipe back in for emissions testing. (where applicable). That would be a GREAT idea for you aftermarket guys, or even a muffler shop guy looking for a few $$$$. :cool:
 

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At least you guys have heard the exhaust note. I have yet to see a GTO let alone hear one. Oh well, one more month. I HOPE!
 

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Same here. I think the exhaust note is just fine. I have my other Pontiacs that are loud. I don't need three of them. :D The exhaust has a nice rumble to it, even when cruising. And like everyone said. No shop with any sense of honesty would remove those items and risk fines and possibly being closed down.
 

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I ran into the same problem trying to swap out the stock mufflers for Flowmasters.. but my exhaust guy said the stock cases were 10" length.. in any case, the flowmasters were about 3" too long.. (hit suspension parts) .

Flowmaster told him they have some 6 or 9 inch single chamber race mufflers.. but would probably be too loud inside the vehicle.

I've researched several brands and have decided to wait for a specific fitted system. The stock exhaust sounds pretty good.. and seems louder to me now that the temps have risen into the 60s-70s.

Maybe you could have em gutted, bet that would sound different :D
 

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CrispieGee said:
Sorry to be blunt, but what did you expect?

Modern cars are designed to run with their emissions controls in place, and no muffler shop would risk getting in trouble with (in your case) the state of Illinois, the EPA, the DEC and everyone else who would be on their case for chopping of your cats.

Is it really worth it for five horsepower or a minor improvement in sound? I can guarantee that you aren't going to shave even a fraction of your E/T. I don't think it's worth it at all, but that's just my sensible side talking...
FYI, In most states, Illinois included, a sniffer test is no longer done for OBDII cars. The OBDII scan test is administered instead. This test does the standard gas cap (evaporative system) test but then a scan device is hooked to your DLC port and a system DTC check is run as well as readiness monitors are checked to be in a "ready" state. The test takes 15-30 seconds and you are done. Sometimes a visual inspection is done, sometimes not. It's really hit or miss here. Our cars being as low as they are, generally get nothing more than a check under the rear for a muffler.

While I am running cats on mine and have passed this test, I know many a fellow F-Body and Corvette owners that DON'T have cats that have passed without nary a flinch from the Illinois EPA knowing any better. Since the owners plugged the downstream (post Cat) O2 sensor pigtails with Simms, the PCM thinks the cats are there and that normal switching between trims is going normally and therefore no DTC is set, hence the scan test won't pick it up. And if worse comes to worse, you get a setup like FLP that allows to swap out an off-road section with a catalytic converter section for testing.

Rocket,
Removal of cats generally will increase your peak HP but decrease your peak torque due to lack of some backpressure. But sometimes the gain in HP isn't worth the loss of torque, sometimes it isn't. Also, many choses to eliminate the cats just to thwart the emissions control device and fail to realize that the LS1 without cats actually sounds bad. It's too raspy.
 

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This all brings up a question. The resonators are in there to adjust the sound right? How many people plan on trying to use the resonator with long tube headers, aftermarket mufflers and highflow cats?

Oh, and since I finally heard one in person yesterday, and I had my dad rev it up to the redline while I was standing outside to listen, it sounds just fine to me. I wouldn't change the exhaust just to get a louder sound, only because I was doing headers and needed to adjust.
 

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Rocket said:
I think the cats Net more power than people think. I have a 97 Ford Probe GT that I pulled the cat on. I gained 11 WHEEL HP with NO other mods. Remember that car only pulls 135 WHP stock. Thats close to a 10% gain.
These GTO cats may be more efficient, but when they get some miles on them, they'll be robbing more and more.

Also its a $25,000 fine for a shop to remove your cats! :)

I really think someone should make an aftermarket pipe that goes from the Manifolds right back to where the pipes are flanged. (like 5 foot long pipe) GM Crushed those Pipes on top so they fit under the car better, so the flow is hampered. With an aftermarket pipe we could eliminate the cats, and eliminate the restrictive pipe----Then we could also Swap the cat'd pipe back in for emissions testing. (where applicable). That would be a GREAT idea for you aftermarket guys, or even a muffler shop guy looking for a few $$$$. :cool:
An off-road H-pipe is an old Mustang mod. The cats suck about 25hp. Taking them off is very noticable... An H or X crossover is generally good for another 10hp on a Mustang (w/ or w/o cats). Generally, the cat replacement pipe is an H or an X, so you get both benefits. Summit Racing is one source for that type of stuff. On a Ford, its a pair of ramps and 8 bolts to take it on or off-- a real do it yourself job. I have not been under my GTO yet, so I have no idea if it can be done w/o a torch...

What most people don't realize is the sound dampening effect that the cats have. An off-road pipe Mustang sounds like it has no mufflers. The 302s hhad 2 cats/pipe. The 4.6L has 3 cat/pipe. The GTO owner should consider himself lucky w/ only one cat/pipe.

The new GTOs will have probably be 1/5-1/10 of the Fox-body Mustang volume this yr-- and Fox body Mustangs have been around forever, so there must be literally millions of them. I will be surprised if an after market shapes up for the 18,000 GTOs/yr that GM is bringing over for the next 3 yrs.

My guess is the GTO would gain 20-40 h w/ a good set of shorty headers, highflow cat H pipe and a set of Magnaflows. The F-body guyes talk about O2-sensor-cheaters, so I am sure it is doable... However, I am w/ the StormGuy03-- I am going to wait until a specific system is made for the car.

-Foo
 

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rschumacherfan1 said:
This all brings up a question. The resonators are in there to adjust the sound right? How many people plan on trying to use the resonator with long tube headers, aftermarket mufflers and highflow cats?

Oh, and since I finally heard one in person yesterday, and I had my dad rev it up to the redline while I was standing outside to listen, it sounds just fine to me. I wouldn't change the exhaust just to get a louder sound, only because I was doing headers and needed to adjust.
It *is* louder outside the car than in it. My wife did a driveby and it sounded pretty darn good-- and loud.

-Foo
 

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foobar said:
An off-road H-pipe is an old Mustang mod. The cats suck about 25hp. Taking them off is very noticable... An H or X crossover is generally good for another 10hp on a Mustang (w/ or w/o cats). Generally, the cat replacement pipe is an H or an X, so you get both benefits. Summit Racing is one source for that type of stuff. On a Ford, its a pair of ramps and 8 bolts to take it on or off-- a real do it yourself job. I have not been under my GTO yet, so I have no idea if it can be done w/o a torch...

What most people don't realize is the sound dampening effect that the cats have. An off-road pipe Mustang sounds like it has no mufflers. The 302s hhad 2 cats/pipe. The 4.6L has 3 cat/pipe. The GTO owner should consider himself lucky w/ only one cat/pipe.

The new GTOs will have probably be 1/5-1/10 of the Fox-body Mustang volume this yr-- and Fox body Mustangs have been around forever, so there must be literally millions of them. I will be surprised if an after market shapes up for the 18,000 GTOs/yr that GM is bringing over for the next 3 yrs.

My guess is the GTO would gain 20-40 h w/ a good set of shorty headers, highflow cat H pipe and a set of Magnaflows. The F-body guyes talk about O2-sensor-cheaters, so I am sure it is doable... However, I am w/ the StormGuy03-- I am going to wait until a specific system is made for the car.

-Foo
You're comparing apples to oranges. Comparing how a mustang which has what, 4 or 6 little cats compared to LS1 powered vehicles 2 is two different worlds. Actually our factory cats flow pretty darn well. Maybe not as well as a nice set of Random Tech hi flows, but certainly a lot better than most. So the difference in going from stock on the GTO to aftermarker WILL NOT net the same drastic difference as on a mustang.
 

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Great info guys, but remember a Cat with some miles on it usually flows much much less. So if you swap them out later on, then the effects will be more.

I know that cats can reduce torque and sometimes even driveability, but i just thought that they robbed more HP than they really do in reality.
 

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CMNTMXR57 said:
You're comparing apples to oranges. Comparing how a mustang which has what, 4 or 6 little cats compared to LS1 powered vehicles 2 is two different worlds. Actually our factory cats flow pretty darn well. Maybe not as well as a nice set of Random Tech hi flows, but certainly a lot better than most. So the difference in going from stock on the GTO to aftermarker WILL NOT net the same drastic difference as on a mustang.
Engines of similar displacement and build quality will make similar power and factory cats are factory cats. The concepts are the same. The Aussie board regualrly talks about "coring their cats" for their Monaros.

Cats are a plug in the pipe. A quick chg pipe w/ or w/o high flow cats would be highly desirable to me.
 

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Just a quick one re the cats on Monaro/GTO. Over here, it is definetly illegal to remove or punch out your cats. Exhaust guys on this side of the pond have found that changing each of the factory cats to a high-flow aftermarket version provides little gain. The usual cat mod is to remove them from the car, cut each end off to increase the diameter of the opening at each end. This allows us to have 2 1/2" pipe in and out of the cat i.e., minimal restriction. I'll get some pictures of my exhaust system and post them tomorrow.

Mick
 

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A 4.6L motor is of simliar displacement to a 5.7L?

Build quality? All are mass produced with a similar range of tolerances I would presume.

Coring out the cats is nothing new. We've been doing it for years and/or replacing them with high flow units.

Cats are the plug in ANY automobile. However, their presence does provide some benefit particularly on the torque side. I for one am one of those that beleives in retaining the cats vs. removing them completely. I'm running them still on my heads, cammed and built LS1 that I have in the garage.

I've been a part of the LS1 community since 1997 when they first came out and I bought my Camaro in early '98. I've since built mine and soon will be building #2 thats now in my driveway. I've seen the progression and had many a technical discussion with many owners on many boards over those years pertaining to the pros and cons of the cats.

Fact is, our stock catalytic converters used on GM vehicles are NOT the same that ford uses. They do flow *reasonably* well. Not fantastic, but not terrible either. As always with anything from a mass produced manufacturer, there is room for improvement. Coring (or more commonly referred to as "gutting") your factory cats OR replacing them with high flow units (like I have on mine) will always net positive results over the stockers.

My major contention was your comment about the gain to be had by removing them on a mustnag vs. removing them on an LS1 powered vehicle. It is NOT an apples to oranges comparison. Two completely different engines, two completely different displacements and two completely different power curves.

For you, I would highly recomend FLP's setup with an interchangeable off-road pipe (no cats) and a swapable pipe with a high flow catalytic converter. THis way you can have it both ways.
 
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