i have no resonator and i need to cut my cat, what should i do with exhaust?

what do you need to make you car run normal w/o a cat. Is there anyway to keep the pcm stuck on the mode it's in until operating temperature. what about o2 sensor/readings?

[chris_gt_74]

Originally Posted by jd99gagt

what do you need to make you car run normal w/o a cat. Is there anyway to keep the pcm stuck on the mode it's in until operating temperature. what about o2 sensor/readings?

You have to disable rear o2 codes with a programmer but I think that's about it if it's all stock. I think a high flow is better than no cat just for emissions and being able to legally drive your car on the highway's.

[AaronGTR]

Originally Posted by locoman99

and be cheaper, less complex and make better power...gonna throw a code with an aftermarket cat anyway...your gonna need a tune anyhow if you do much exhaust work.

You have no idea what you are talking about.

The HP difference on an NA car will be 1hp or less. You will NOT necessarily throw a code with an aftermarket cat versus an OEM (mine never did). And you will NOT need tuning with exhaust work. You will always make more power with tuning, but it's not required.

You also forget that running without a cat will make the car smell and sound like sh!t. And also a cat won't cost $300 dollars. This would be a pretty good size cat for a performance exhaust on a grand am. http://www.summitracing.com/parts/MPE-94006/ $74. Stays legal, sounds better, smells better, better for the environment. I see no downsides.

[AaronGTR]

Also both you guys should stop arguing about power and back pressure. Neither one of you sounds like you really understand the concept.

FYI, it really has nothing to do with back pressure or no back pressure. That is a side effect. What is important is exhaust velocity. Smaller piping = higher velocity, but more back pressure. That will make better low end torque because the speed of the gas stays higher at lower rpm so the gas wants to keep moving, but at higher rpm and flows the engine has pumping loss from trying to force more gas through a small pipe, so peak power is lower. That is a lower power band setup.

Larger exhaust piping will allow more flow with less resistance at higher rpm which equals higher peak power, but the gas velocity slows down at lower rpm, so there are pumping loss at low speed from the engine having to push more to keep the gas moving, so you lose low end torque. This shifts the power band higher.

Ideally if you can keep the piping size small but design it to reduce the internal resistance, you can increase the flow (to a degree) AND keep the torque up. Methods to do this would include using mandrel bends instead of crush bends for uniform pipe diameter, using smaller degree bends such as 30 degrees vs 45 degrees for less direction change, and making the smoothest joints and/or shortest exhaust system possible. You can also do this with a small increase in piping diameter for higher peak power with no loss or minimal loss in low end gas velocity. The trick is picking the right design and pipe diameter for the engine design, rpm range, and power level.

[locoman99]

[quote=AaronGTR;1178847]Also both you guys should stop arguing about power and back pressure. Neither one of you sounds like you really understand the concept.

FYI, it really has nothing to do with back pressure or no back pressure. That is a side effect. What is important is exhaust velocity. Smaller piping = higher velocity, but more back pressure. That will make better low end torque because the speed of the gas stays higher at lower rpm so the gas wants to keep moving, but at higher rpm and flows the engine has pumping loss from trying to force more gas through a small pipe, so peak power is lower. That is a lower power band setup.

Larger exhaust piping will allow more flow with less resistance at higher rpm which equals higher peak power, but the gas velocity slows down at lower rpm, so there are pumping loss at low speed from the engine having to push more to keep the gas moving, so you lose low end torque. This shifts the power band higher.

Ideally if you can keep the piping size small but design it to reduce the internal resistance, you can increase the flow (to a degree) AND keep the torque up. Methods to do this would include using mandrel bends instead of crush bends for uniform pipe diameter, using smaller degree bends such as 30 degrees vs 45 degrees for less direction change, and making the smoothest joints and/or shortest exhaust system possible. You can also do this with a small increase in piping diameter for higher peak power with no loss or minimal loss in low end gas velocity. The trick is picking the right design and pipe diameter for the engine design, rpm range, and power level.[/QUOTE

I have a cat on my car,btw

in all practical terms the only place were an exhaust can be truly " tuned" is the design of the headers and collecters. I agree that no cat vs hiflow cat is almost zero in terms of power and there are practical benefits to having one.
I disagreed with chris when he starts calling people stupid and makes up things like an engine needs backpressure.

[[ChaosweaveR]]

He just pisses me off.

But my point remains, eliminating a cat on a street car is stupid and pointless.

[[ChaosweaveR]]

not relevant.

[AaronGTR]

Originally Posted by locoman99

in all practical terms the only place were an exhaust can be truly " tuned" is the design of the headers and collecters. I agree that no cat vs hiflow cat is almost zero in terms of power and there are practical benefits to having one.

Again, this just shows your lack of knowledge on the subject. You can "tune" the performance of the exhaust from the cylinder head port all the way to the exhaust tip. Not just in the headers. And there are many practical reasons for having a cat. I just listed all of them.

[locoman99]

Originally Posted by AaronGTR

Again, this just shows your lack of knowledge on the subject. You can "tune" the performance of the exhaust from the cylinder head port all the way to the exhaust tip. Not just in the headers. And there are many practical reasons for having a cat. I just listed all of them.

After the collecter it is just backpressure. Once pulses are merged any scavinging effect is lost and gasses are cooling (expanding) and slowing down. Any "tuning" effect after the collecter is only the effect of backpressure on the effecincy of the engine and the corresponding "flattening" of the torque curve on the powerband. Period.

[AaronGTR]

Originally Posted by locoman99

After the collecter it is just backpressure. Once pulses are merged any scavinging effect is lost and gasses are cooling (expanding) and slowing down. Any "tuning" effect after the collecter is only the effect of backpressure on the effecincy of the engine and the corresponding "flattening" of the torque curve on the powerband. Period.

And yet again.... you show your lack of knowledge on a subject. Yes, you can design a header to have a scavenging effect on exhaust flow from the engine... which NONE of our header designs do. But who said that is the only thing that constitutes "tuning"? Anything you do that can improve the power or driveability of the car can be considered tuning. Since cars are required to have an exhaust system to be technically street legal in all 50 states, and anything you can change on the exhaust that improve flows and lessen restriction will lower power losses and effectively increase the maximum HP at the wheels, that can be considered "tuning". Duh . Oh yeah... PERIOD!

[surfermatt95]

well, that was interesting to read , i may be moving to oregon here soon anyways so i will need a cat to pass emissions

[locoman99]

bad advice again...

[surfermatt95]

Originally Posted by locoman99

Only worry about it if they have a visual inspection or sniffers. Most places just have obd2 plugin testing. I know lots of cars that pass emissions here without cats. There puter only knows what yours tell it. It is not the end of the world to run catless, regardless of what a couple of self appointed know it alls might say.

i dont think ill be racing it since the previous owner didnt take too good of care . so ill just put one on to be safe

what about how how it runs,if i disable rear 02 codes than it won't run in open loop mode?I was gonna run no cat and stock muffler.

[rocketfast123]

Originally Posted by [ChaosweaveR]

But my point remains, eliminating a cat on a street car is stupid and pointless.

You just mad because your state has inspections.


But if you have the right O2 sim, it will run fine. I don't have a cat or res on a 90 tech 4. It just has some mangaflow knock off muffle with a res tip. No ses,no hard cold starts, no bad smells, and sounds like a bad ass little diesel tractor. The tech 4 was not the best sounding engine. Can't say if power was lost since it only has like 92hp.

[mfuller]

Whether your region does emissions testing or not, if your car came from the factory with a catalytic converter, it is illegal to remove it.

Catalytic Converter Laws
Rules for Replacing Converters
In 1986, the U.S. Environmental Protection Agency issued new guidelines for the construction, efficiency and installation of aftermarket catalytic converters. All CleanAir converters listed in this catalog have been designed, tested and manufactured to meet this policy.

In addition, CleanAir converter listed in this catalog is appropriate for use under the current requirements of the California Air Resources Board (C.A.R.B.).
E.P.A. guidelines state that replacement converters may be installed only in the following situations:

1. The vehicle is missing a converter
2. A state or local inspection program has determined that the existing converter needs replacement
3. Vehicles manufactured prior to 1996 must have more than 50,000 miles, and a legitimate need for replacement must be established and documented
4. In cases of OBD Il-equipped vehicles (1996 and later), the O.E. manufacturer's 8-year/80,000-mile warranty must have expired and a legitimate need for replacement must be established and documented.
Please note that Federal law prohibits removal or replacement of a properly functioning O.E. converter.

When replacement of the converter is appropriate (as outlined above), the E.P.A. further requires that:

1. It be installed in the same location as the original
2. It be the same type as the original (i.e., two-way, three-way, three-way plus air/three-way plus oxidation)
3. It be the proper model for the vehicle application as determined and specified by the manufacturer
4. It be properly connected to any existing air injection components on the vehicle
5. It be installed with any other required converter for a particular application
6. It be accompanied by a warranty information card to be completed by the installer.


Source: http://www.catalyticconverter.org/law/index.htm

[locoman99]

not relevant to thread.

[AaronGTR]

Originally Posted by locoman99

jeeeeez dude ...

Who said that comment was directed at you? I meant the epa types in the government that try and tell us what to do...

Its alwaaays about aaron...

Same thing. I think the EPA serves a useful function, and I also think running a daily driver without a catalytic convertor is irresponsible, regardless of whether there are any technical merits or not. If it's not a race car, there is no reason to run without one, except for being a stupid douchebag.

[[ChaosweaveR]]

Originally Posted by AaronGTR

Same thing. I think the EPA serves a useful function, and I also think running a daily driver without a catalytic convertor is irresponsible, regardless of whether there are any technical merits or not. If it's not a race car, there is no reason to run without one, except for being a stupid douchebag.

Thank you.

[locoman99]

The thread is related to cats...