Just curious...

[Jayce 1971]

I live in a state where, fortunately, we have no annual vehicle inspections. One of the first things I've always done to my cars was to pull the catalytic converters. (Makes a HUGE difference on turbo 4's). Does anyone run an LS with an open exhaust? Just mufflers? I haven't crawled underneath to check out the layout of the O2 sensors yet. This hasn't been a factor, as all my previous vehicles had the sensor to the front of the cat. I would think that opening up the exhaust, especially on a 32V engine would really help on the higher end. Prolly sound mean, too But I certainly wouldn't want to throw the computer into a tizzy if it has a post cat sensor. I guess I'm just gonna have to crawl underneath after this frickin' ice melts and take a look. I've already found some aftermarket mufflers a buddy runs on his '07 GT 'stang. The company makes the same muffler that looks like it would fit....post rear end...(sawzall the factory cans)... Makes his 4.6 sound mellow untill the green light, then, WOW!!!

 

[NYC LS8]

Small V8 + no cats = too raspy sounding for my liking....especially on an LS.

 

[NateRW21]

I can't recall if the O2 sensors are IN the cat, or behind it. But either way, with modern vehicles, you always have an upstream and downstream O2 sensor; your upstream sensor (before cat) tells your computer how to adjust your engine's settings, or when something isn't running correctly. The downstream sensor (IN cat, or after cat) tells the computer that your emissions system is functioning. If you remove the downstream sensor, you will get emissions error codes that will not go away.

Plus, you know it's a felony to remove functioning cats on a highway bound car right?

 

[luttersj]

a felony? damn. I mean, I knew it was illegal, but man, that's a serious charge!

 

[NateRW21]

Yeah... i guess they take this environmental crap serious!!!

I think max they can charge you something like $10,000 and up to 5yrs... If my memory serves me correct.

But that is the extreme... certainly most people only have to pay a fine; just depends how far the authorities want to push it.

 

[Eric0508]

IIRC you can drive a car that has no cat as long as it didn't have one to begin with. ie. old cars.

 

[Jayce 1971]

I know that exhaust shops face a serious fine for tampering with converters. The relevant point being, if you service your vehicle regularly i.e., change plugs, filters, adjust timing as necesary, etc..., there shouldn't be much for the cats to do. Catalytic converters should be there only to burn off unburnt fuel particles, utilizing a catalyst {platnium is common}. Correctly tuned engines do not need them. Hell, my neighbors would have you believe that poorly tuned engines don't need them... (I think the government regulated their use for people too lazy to get a tune-up). As I said previously, I reside in a state that has absolutely NO inspections, whatsoever. I'm not afraid of leo pulling me over and crawling underneath my car to check my exhaust. My Daytona iroc dynoed at 260 hp stock, by simply removing the converter, and installing a full 2.5" exhaust. Again, it's a turbo engine, but also a 4v. I was just wondering if anyone has tried running the 3.9 V-8 without cats, or without mufflers to see if there are any performance gains or if someone runs like this just for the sound. I would think that with the 32V engine coming on so strong in the higher rpm band that someone would have tried. I'm guessing that if the car does indeed have post cat O2 sensors, then the point is moot as it will show up as a "check engine" code of some type and probably default to a less than desirable tune. If not, then I will happily pull my cats this spring...(perhaps keeping mufflers of some type...[glass paks would do] and give you all a report on the experience. Drive safe, but drive hard.

 

[NateRW21]

I know that exhaust shops face a serious fine for tampering with converters. The relevant point being, if you service your vehicle regularly i.e., change plugs, filters, adjust timing as necesary, etc..., there shouldn't be much for the cats to do. Catalytic converters should be there only to burn off unburnt fuel particles, utilizing a catalyst {platnium is common}. Correctly tuned engines do not need them. Hell, my neighbors would have you believe that poorly tuned engines don't need them... (I think the government regulated their use for people too lazy to get a tune-up). As I said previously, I reside in a state that has absolutely NO inspections, whatsoever. I'm not afraid of leo pulling me over and crawling underneath my car to check my exhaust. My Daytona iroc dynoed at 260 hp stock, by simply removing the converter, and installing a full 2.5" exhaust. Again, it's a turbo engine, but also a 4v. I was just wondering if anyone has tried running the 3.9 V-8 without cats, or without mufflers to see if there are any performance gains or if someone runs like this just for the sound. I would think that with the 32V engine coming on so strong in the higher rpm band that someone would have tried. I'm guessing that if the car does indeed have post cat O2 sensors, then the point is moot as it will show up as a "check engine" code of some type and probably default to a less than desirable tune. If not, then I will happily pull my cats this spring...(perhaps keeping mufflers of some type...[glass paks would do] and give you all a report on the experience. Drive safe, but drive hard.

A couple things to note...
First, it doesn't matter how well tuned the engine is, there will ALWAYS be unburnt hydrocarbons and carbon monoxide (at best, Gasoline, IC engines are usually no better than 80% efficient; this means 20% of the energy in the fuel is lost to heat, friction and just simple unburnt fuel); the cats are always working to decrease the output of UHC and CO. It is true, the extent to which they are effective is variable dependent upon efficiency of the engine (to the point where, in order for them to actually function as intended, the engine must be in correct tune). If not the case, you could install the down-stream O2 sensor after a test pipe, and on a correctly tuned car, not throw any codes... And I promise... you would certainly throw codes. (read up: http://courses.washington.edu/me341/oct22v2.htm)

It isn't just the facility whom removes the emissions components who is culpable, it's you too!

Size-able amounts of torque would be lost in opening up the exhaust to that extent, with the addition of what would be relatively minimal HP gains when compared to the lost torque. Keep in mind... a 350 IROC is at best 1980's technology (in reality, more like late 1970's since GM took so long to jump on the MPI and digital ignition bandwagon). Exhaust systems at that time were really VERY VERY poor from the factory. Here you have a car with dual walled headers (the dual wall makes them insulated, retaining heat... improving velocity), factory "X-pipe" section, flow through resonators and small mufflers. Most charts will say a dual 2" exhaust will flow an N/A application up to 350HP (less in FI). In conclusion, I'm sure you'd gain a couple HP... but lets be honest, is that worth the legal risk (keep in mind, if you take it to a dealership to be serviced and they see the cats are removed, they are required by law to inform authorities), the cost for a new system, headers back that will net you maybe 10HP, but suck 10 Lb Ft, and the difficulty in resale (if you don't inform the buyer, they can, and will... come back on you)

all-in-all, that's just me... you've gotta make your own choices.

 

[NateRW21]

Oh, one more thing... it's illegal to remove FUNCTIONING cats. In theory, you could install high-flow cats if yours were "broken". But you're still left with too much flow for the engine size and power out-put.

(I installed a Bassani stainless high flow cat'ed Y pipe, converted to an H-pipe on my truck, with true duals out the rear corners, in 2.5". This set-up has only two cats instead of four, and is only barily legal: http://www.catalyticconverter.org/law/index.htm My truck is a 98; fortunately, the four converter set-up is a cheap way out; the first cat preheats the second when in a row. So if you use a better converter that doesn't require preheating, you can get rid of the secondary cat)

Also, I don't know if the plugs match up, but if you decide you want to do the cat delete anyway... look for MIL eliminators for mustangs (I'd look for 05-up); they go in place of your downstream O2 sensors, giving the computer a constant resistance saying everything is "Okay". But again, issue could be the plugs.

 

[thethirdeye88]

so if i added some high flow cats it would open up too much,losing back pressure and power?...just from high flow cats?...really?..

 

[NateRW21]

It's a possibility. I don't think anyone has dyno'ed this though. But, keep in mind, he was talking about pulling his cats and running a full 2.5" dual. There is a big difference between factory 2" duals, minus cats and custom 2.5" duals, no cats, high flow mufflers and no resonators. The first is likely to net you a very small gain across the board. The second is very likely to make low end power and torque suffer, but giving a decent increase in the top end. That's fine if you race your car, but for a street driven car, you're looking at loss of throttle response and possibly a gas mileage decrease.

 

[lseguy]

You want the short, but informed answer?

For a street LS, leave the cats on.

Period.

 

[NateRW21]

yeah... pretty much what lseguy said

 

[cammerfe]

Cat/Con theory and experience

For an alternative answer, back pressure is the car equivalent of breathing in through your nose and exhaling through a soda straw. You may be able to get away with it while sitting in a chair but try to run around the house that way and see how long you can keep going. The idea that back pressure is EVER good is an old wive's tale. Simply not true!

That said, your O2 sensors are all in the cats, which bolt directly to the exhaust manifolds. If your engine is stock, it probably doesn't make sense to remove them. If you plan on serious modifications,you may want to either rid yourself of them completely. Or go to aftermarket HP versions. I have 111K on my '02 LS and by running N2O and methanol through the original cats this past fall, I set one mile Land Speed records in two classes at 140+ and 138+ MPH. I am making +/- 400 HP.

With my now-being-built engine, I'll remove the cat/cons. But I'm looking to double the HP. (See my thread in the High Performance section)

KenS from Ben's Place

 

[NateRW21]

For an alternative answer, back pressure is the car equivalent of breathing in through your nose and exhaling through a soda straw. You may be able to get away with it while sitting in a chair but try to run around the house that way and see how long you can keep going. The idea that back pressure is EVER good is an old wive's tale. Simply not true!

That said, your O2 sensors are all in the cats, which bolt directly to the exhaust manifolds. If your engine is stock, it probably doesn't make sense to remove them. If you plan on serious modifications,you may want to either rid yourself of them completely. Or go to aftermarket HP versions. I have 111K on my '02 LS and by running N2O and methanol through the original cats this past fall, I set one mile Land Speed records in two classes at 140+ and 138+ MPH. I am making +/- 400 HP.

With my now-being-built engine, I'll remove the cat/cons. But I'm looking to double the HP. (See my thread in the High Performance section)

KenS from Ben's Place

I just noticed you're from D town... I wouldn't mind seeing this engine once it's done. Maybe we could set-up a meet over on your side of the state?

I think as I recall, you're thread on the HP section did mention the fact that without a change in camshafts at the least, removing the restriction from the factory exhaust on the LS would cause it to loose low-mid power and torque. Naturally, restriction in an exhaust isn't a good thing, but in order to eliminate that restriction, and obtain a positive result, other steps must be taken. Steps, which unfortunately, with this car just are not practical (or affordable for that matter) for the average joe. I wouldn't disagree with the statement that restriction is never a good thing, but when a car is engineered with that restriction, and camshafts designed to operate within those perameters... generally, for a street driven car, totally eliminating that restriction without new cams does more harm than good. (interesting note; when trying to find exhaust parts for my F-150, Borla, Bassani and Magnaflow all told me the same thing; the reason there is no 2.5" true dual is because it opened the flow up too much for an unmodified engine and resulting in a change in the power band; decreasing low-mid and increasing high. They wouldn't even entertain the idea of making one. Said the percentage of owners who modify the engine itself is too small to warrant engineering and production. Long story short, I had to extensively modify off the shelf parts. I've got comp cams and patriot performance CNC'd heads... so my situation is rather different than your average truck owner).

I think we can both agree, long story short... given the fact that he has not stated any plans to modify the engine itself, pulling the cats and throwing on a full 2.5" true dual would be a total waste of money. He hasn't reached a point of max flow from the exhaust he has. It's kind of like wiring a house... If you're running a 15 amp circuit and code calls for a 14/2 run... don't use 10/2; you're throwing money and materials into something for which you'll see no reasonable benefit or requirement.

 

[97stscaddy]

The idea that back pressure is EVER good is an old wive's tale. Simply not true!

Take the manifolds off of your car and tell us how well the engine runs with no exhaust system. The last I checked an engine doesn't idle too well without the exhaust system hooked up. An engine that is tuned to run with no exhaust could maybe run fine no trouble. But from a practical or a manufacturers standpoint, you need back pressure in order to make the engine run reliably and efficiently for a long period of time. If you cant do that you won't sell anything.

 

[camthman]

I see where he is coming from though. With be Kenne bell Cobra I gained ALOT of Hp taking off my cats. In my 350z I saw AMAZING gains taking them off. I would be interesting to see what happens.

 

[NateRW21]

I see where he is coming from though. With be Kenne bell Cobra I gained ALOT of Hp taking off my cats. In my 350z I saw AMAZING gains taking them off. I would be interesting to see what happens.

mmmmmm kennnnnnnneeeee beeeeelllllll cobra....

what year?

I seriously have my doubts as to the benefit on this car though; both cars you mentioned are sports cars... that don't weigh that much. I think this is apples to oranges here.

 

[cammerfe]

backpressure again

If you open up the exhaust and leave everything else alone you have simply reversed my example above. Now you are breathing in through a straw and out through your nose. YOU MUST HAVE BALANCE. Get one of the intake systems that Ken (not me!) offers at LSK and perhaps, if going all out, get a larger throttle body and MAS. Then your breathing in and out will be back in balance. Back pressure has nothing to do with it. You simply won't be able to take advantage of what is available if you only do one end. And along with the new hardware, you'll have to make adjustments to the fuel delivery curve and ignition as well.

I started out as a kid doing changes to the family flathead '53 Merc. Even with something that crude---over 50 years ago!---there was a very noticeable improvement when I put on a dual exhaust system. And that engine was only marginally larger than the 3.9, at 254 CID. It really woke up when I put three carburetors on but I also had to replace the distributor and coil and wires.

All by itself a Magnaflow cat-back system only makes about 4-5 HP improvement, and that is mostly above 5K RPM. Since the gain is higher in the RPM band the low end may seem sluggish by comparison. With both intake and exhaust there is about a 20 HP difference. An SCT tune adds to that by really making use of the hardware. But backpressure is never good. It's an 'old wive's tale'. Simply put, the exhaust gas held back in the combustion chamber by the backpressure cuts into the 'room' available for a fresh incoming charge. I could explain all this in great engineer-talk detail. But it would take three screens to do, and probably wouldn't be overwhelmingly productive. But it's true, nonetheless!

KenS from Ben's Place

 

[cammerfe]

New cams will alter the characteristics of the flow but have practically no effect on volume.

KenS from Ben's place

 

[cammerfe]

I you take the manfolds off, the close proximity of relatively cold air as the engine is shut off will have a severely debilitating effect on the valve metallurgy. Quick cooling of valve stems will make them brittle. The benefit that some degree of exhaust system---AA Fuel 'zoomies'--- provides is the tuning effect that augments the gas velocity of the spent charge. But now we're getting into 'engineer-talk'. I'd be happy to have a get-together.

KenS from Ben's Place

 

[Jayce 1971]

jeesh...didn't mean to start an arguement!

I have to agree with cammerfe. Running a "performance" restrictive exhaust of any kind is an old wives tale. Try to keep in mind that this is the first modular v-8, actually, first v-8 of any kind I've ever owned. My previous vehicles have all been 4 or 6 cyl engines (predominantly chrysler 2.2 TII, TIII and T4 engines. To make a turbo 4 a performance oriented engine, you MUST remove the cats. It's a 30 hp parasitic can that a well tuned car doesn't require. And, it's alot more pronounced when the displacement of the engine is smaller. Again, I will be the first to admitt I know nothing about performance v-8 engines. As this is my daily driver, and not a race car, I won't be removing my exhaust, or performing any other modifications. This car is very beautiful, and requires no improvements. This car is already fast enough, doing over 144mph. But I like to hear of other people's experiences of what works, and what doesn't. What is the point of putting on a cold air intake, and not opening up the exhaust? Only difference is, your bottle neck shifted from the airbox to the exhaust side of the equation. Remember, these things (engines) are essentially airpumps. More through-put=more power. The end goal for performance should still be to get them to the redline as soon as possible. (remember the redline is just there to let you know it's time to shift.... )
On another note, I'm not real pleased with the exhaust tone of the car, but its probably something that some magnaflow's would fix. In the end, this stock vehicle won't require any more exhaust than the 2" factory piping. Have a good holiday everyone, and let's put some miles on these hot rod lincolns.

 

[NateRW21]

I have to agree with cammerfe. Running a "performance" restrictive exhaust of any kind is an old wives tale. Try to keep in mind that this is the first modular v-8, actually, first v-8 of any kind I've ever owned. My previous vehicles have all been 4 or 6 cyl engines (predominantly chrysler 2.2 TII, TIII and T4 engines. To make a turbo 4 a performance oriented engine, you MUST remove the cats. It's a 30 hp parasitic can that a well tuned car doesn't require. And, it's alot more pronounced when the displacement of the engine is smaller. Again, I will be the first to admitt I know nothing about performance v-8 engines. As this is my daily driver, and not a race car, I won't be removing my exhaust, or performing any other modifications. This car is very beautiful, and requires no improvements. This car is already fast enough, doing over 144mph. But I like to hear of other people's experiences of what works, and what doesn't. What is the point of putting on a cold air intake, and not opening up the exhaust? Only difference is, your bottle neck shifted from the airbox to the exhaust side of the equation. Remember, these things (engines) are essentially airpumps. More through-put=more power. The end goal for performance should still be to get them to the redline as soon as possible. (remember the redline is just there to let you know it's time to shift.... )
On another note, I'm not real pleased with the exhaust tone of the car, but its probably something that some magnaflow's would fix. In the end, this stock vehicle won't require any more exhaust than the 2" factory piping. Have a good holiday everyone, and let's put some miles on these hot rod lincolns.

This argument that well tuned car does not need catalysts is just not true. Basic chemistry says it doesn't matter how well tuned a car is; it will put out hydrocarbons and Carbon monoxide; that is just simply the result of the combustion process and changes of substances at the molecular level. In terms of reduced emissions, there is absolutely no amount of tuning to the engine that will replace the effects of a catalyst.

Also, the 3.9 is of the AJ series of engines; it is not a modular engine. As a matter of fact, the normal assumption that modular comes from the ability to swap parts from different engines is entirely incorrect (nor is it new; Ford FE engines, push-rod Windsor engines... list goes on). The name comes from the design of the factories the build the engine. They are set up to be modular, allowing for extremely fast production changes, and quick replacement of machinery that goes down. It really has absolutely nothing to do with the family of engines who carry the name.

 

[NateRW21]

If you open up the exhaust and leave everything else alone you have simply reversed my example above. Now you are breathing in through a straw and out through your nose. YOU MUST HAVE BALANCE. Get one of the intake systems that Ken (not me!) offers at LSK and perhaps, if going all out, get a larger throttle body and MAS. Then your breathing in and out will be back in balance. Back pressure has nothing to do with it. You simply won't be able to take advantage of what is available if you only do one end. And along with the new hardware, you'll have to make adjustments to the fuel delivery curve and ignition as well.

I started out as a kid doing changes to the family flathead '53 Merc. Even with something that crude---over 50 years ago!---there was a very noticeable improvement when I put on a dual exhaust system. And that engine was only marginally larger than the 3.9, at 254 CID. It really woke up when I put three carburetors on but I also had to replace the distributor and coil and wires.

All by itself a Magnaflow cat-back system only makes about 4-5 HP improvement, and that is mostly above 5K RPM. Since the gain is higher in the RPM band the low end may seem sluggish by comparison. With both intake and exhaust there is about a 20 HP difference. An SCT tune adds to that by really making use of the hardware. But backpressure is never good. It's an 'old wive's tale'. Simply put, the exhaust gas held back in the combustion chamber by the backpressure cuts into the 'room' available for a fresh incoming charge. I could explain all this in great engineer-talk detail. But it would take three screens to do, and probably wouldn't be overwhelmingly productive. But it's true, nonetheless!

KenS from Ben's Place

As you said... Balance. The ONLY way a true dual 2.5" exhaust with flow through mufflers and no cats will be in balance with the intake on a 3.9L would be through forced induction.

This is obviously leaving out many factors, but keeping it simple...
Area of a 2.5" circle (3.14x1.25x1.25): 5.8875"

Area of a 65mm throttle body (65/25.4=2.5591/2=1.27955 3.14x1.27955x1.27955): 5.141"

Obviously this doesn't factor in air flow dynamics involved with length of tube, air filter, muffler or bends. But... given the fact that a 2.5" exhaust tube has just slightly more area than a 65mm throttle body... I think it would be totally and 100% safe to assume that there is no where's near balance between intake and exhaust on a NA engine with a 65mm throttle body and dual 2.5" pipes.

The problem with an exhaust that is too large is, the velocity of the exhaust gas is decreased, there for, taking away from the savaging effect. I don't think I ever said anything about back-pressure being a good thing. My point here is that on a factory engine, there is a such thing as an exhaust that is too open. Instead of being allowed to PULL the gas out of the cylinders, when the velocity of the exhaust is decreased too much, the engine must PUSH out the gas (which it will not totally do). This is why a very very open exhaust does so well at the top end; the velocity of the gas coming from the engine is elevated, and the savaging effects are able to pick back up. So what you're left with is a low end that suffers due to all of the exhaust not being PULLED from the combustion chamber, but a high end that improves because the engine isn't fighting to push the gas out. In reality, it's physics/thermal dynamics... You can find yourself an all-around compromise, but you can not have the best of both worlds (the most potential out of the top and bottom of power band).

That is the bread and butter the entire performance exhaust industry has made it's money on. If it weren't the facts, Joe Snuffy's exhaust company would be pushing out mandrel bent 20" exhaust systems running 2.5" primaries on shorty headers all the while, putting companies such as Flowmaster, Magnaflow, Borla and Bassani out of business for using "restrictive" exhausts.

 

[NateRW21]

On another note, I'm not real pleased with the exhaust tone of the car, but its probably something that some magnaflow's would fix. In the end, this stock vehicle won't require any more exhaust than the 2" factory piping. Have a good holiday everyone, and let's put some miles on these hot rod lincolns.

btw... I agree... I've had mine for a little over a year, and I just find myself wanting a touch of a growl when I get on the gas.

But, I'm of the mindset that as a luxury sports sedan... it shouldn't be a loud rumble. So here I am, over a year later, still debating on changing the mufflers or pulling the resonators. Worried that what I do will end up giving it too much sound. I'd rather have not enough, than diminish the classiness of the vehicle with too much.

Maybe Gibson has some mufflers; their exhausts are pretty quiet...