[smokinAMD]

With my draxas header and exhaust, I don't have any catalytic converters on my car which doesn't bother me, I passed emissions just fine without them. But anyways, several people I know have kept arguing with me that having no cats on your car is horrible for the engine and can cause damage to it. That the air/fuel mix will be affected by it and you can cause serious damage to your engine. And lets not forget the backpressure...I'm loosing all my backpressure and that can cause damage as well. Etc, etc, etc. I just ignore them for the most part because my car runs fine without them, I haven't had any problems at all.

My training and what not tells me its all BS. Yeah, I might have lost a bit of backpressure and in turn some low end torque, but I gained top end power. I still have a muffler and a resonator, so I shouldn't have to worry too much about it. They are just driving me nuts! Everytime I see them "Did you put a cat on yet?"

 

[biped]

quick question - how loud is your car compared to a test-pipe and stock manifold? i'm considering a header and if the sound gain isn't too too much i'd like to go for it.

anyway, my buddies with obd1 trucks all harp on me for my lack of even one cat. it doesn't bother me. like you said, the car runs fine and i've yet to see the "damage" accumulate in any way. my top end is sweet too.

catless is the way to be for some NA fun.

 

[the415]

cars doesn't need a cat to run. all they are there for is emissions.

a header will make your car significantly louder.

 

[smokinAMD]

[quote author=biped link=topic=66972.msg1149990#msg1149990 date=1168837945]
quick question - how loud is your car compared to a test-pipe and stock manifold? i'm considering a header and if the sound gain isn't too too much i'd like to go for it.

anyway, my buddies with obd1 trucks all harp on me for my lack of even one cat. it doesn't bother me. like you said, the car runs fine and i've yet to see the "damage" accumulate in any way. my top end is sweet too.

catless is the way to be for some NA fun.
[/quote]

Loud! Hence the reason for my insanely expensive stereo upgrade.

 

[small town king]

if you're talking about no cats on your speed3, thats probably better, no back pressure.


[quote author=the415 link=topic=66972.msg1150028#msg1150028 date=1168839212]
cars doesn't need a cat to run. all they are there for is emissions.

a header will make your car significantly louder.
[/quote]

+1

your friends dunno what they are talking about. the less restrictive your exhaust is, the better gains you will see.

 

[boardumb]

Scismic, after he went to the exhaust shop, said his car isn't all that much louder than before the install. I'm starting to wonder if we put in the wrong header :lol:

 

[smokinAMD]

I know they were wrong, but they totally flipped shit when they found out I had no cats. Like the world was going to end. Basically I was wondering if anyone has heard of any risks form running no cats besides legal and emissions. I never have, but then again, everyone has different opinions, so lets hear them out.

Thomas, scismic also has a high flow cat, and a different exhaust then I do.

 

[boardumb]

Anyhow, I've always viewed backpressure as a myth in modern fuel injected cars. We aren't talking about the old days when we had super restrictive cats in which we had to rejet the carbs.

Less back pressure, always the better. Now, if we started talking about exhaust velocity....

 

[the415]

there's no risk. i had a race header on my focus for 2yrs with no problems.

 

[smokinAMD]

Thats what I tried to tell them, but no one listens to me, ever. Even though I'm the one with the ASE's and they uh, mow yards?

 

[raptor3]

I think the lack of backpressure will lose you some low end power because some of the intake air will pass through the exhaust valve at lower speeds/rpms because of the valve overlap. But I can't see how that could be damaging to an engine. Even if some of the mixture leaves the chamber during the intake stroke you would still maintain the same A/F ratio in the remaining mixture.

Please someone correct me if I don't know what the hell I am talking about!

 

[surfwagon]

If you're talking about your Speed3, then back pressure is less of an issue since the air must travel through the turbo prior to entering the exhaust system. It's not a "straight through" system as it is on the NA 3's.

 

[the415]

he's not talkng about a speed3.

 

[JustROLLIN]

I actually read a book on exhaust tuning and it stated that, as mentioned above, backpressue is a thing of the past. With today's vehicles there is absolutely no need for any backpressure. The book had multiple dynos and testing to back this theory up. Basically, in the old days, they were having valve issues due to the lack of backpressue. Not a problem anymore. You will likely throw a CEL though, as the PCM monitors catalyic covertor efficiency.

As for turbo engines, the straight through exhuast is even better, as the turbo causes a large amount of backpressure in the exhaust path.

But, without cats, you are helping to destroy the atmosphere. I know, I know.... I just watched the Al Gore movie about the environment, good stuff.

 

[m3-s]

mine is loud and i have a hi-flow cat header exhaust

 

[boardumb]

[quote author=JustROLLIN link=topic=66972.msg1151554#msg1151554 date=1168918968]
I actually read a book on exhaust tuning and it stated that, as mentioned above, backpressue is a thing of the past. With today's vehicles there is absolutely no need for any backpressure. The book had multiple dynos and testing to back this theory up. Basically, in the old days, they were having valve issues due to the lack of backpressue. Not a problem anymore. You will likely throw a CEL though, as the PCM monitors catalyic covertor efficiency.

As for turbo engines, the straight through exhuast is even better, as the turbo causes a large amount of backpressure in the exhaust path.

But, without cats, you are helping to destroy the atmosphere. I know, I know.... I just watched the Al Gore movie about the environment, good stuff.
[/quote]

How does a turbo create back pressure? From my understanding back pressure is merely resistance.

On N/A cars, you want the least amount of back pressure with the highest amount of exhaust velocity. Too little exhaust velocity is what causes loss in low-mid range power. Higher exhaust velocity aids in scavenging spent gases from other cylinders. To increase exhaust velocity you would use a shorter exhaust diameter, but that increases back pressure. So for N/A cars, you want to find the best balance of minimal back pressure to high amounts of exhaust velocity.

So what does this all mean? Mufflers, resonators, and catalytic converters merely create back pressure which is detrimental to performance. It will not hurt the engine in anyway removing these, just maybe the environment and people's ears. If you have any of these like I do, go for the least restrictive ones, such as high flow/race catalytic converters, and straight through mufflers/resonators.

 

[HouRman]

Backpressure definitely affects engines that don't have air/fuel management. Take a 1cc 2-stroke engine in it's fundamental form. If it was designed to work with the right fuel/air efficiency with an exhaust on it. But then somebody runs with straight headers... well then the engine runs very lean. This is because the reduction in backpressure is causing more air to be drawn into the combustion chamber than before. Then you "burn valves", overheat, etc...

Then again, going with the least restrictive high diameter piping can be bad. Exhaust gas is very hot. And it should stay hot throughout the exhaust system. The reason is because cold air is dense air, and dense air is heavy air. There shouldn't be "heavy" air that has to be pushed through the exhaust system.

So if our engines can not adjust the air/fuel ratio so it's not too lean or too rich, then YES, running no cats and a less restrictive exhaust may cause damage.

But since there are sensors and ECU to prevent those lean/rich conditions from happening (to a degree), then it's on the safe side I suppose.

Ideally, I'd want to map out A/F on a dyno for the range of RPMS and optimize it if I ever ran a catless setup + headers to see how the engine handles it. If only this were cheap and easy though...

 

[the415]

all this has been said in another post. people didn't seem to believe me and still think backpressure is a problem.

hourman, get a microtech and a wideband and go find a dyno.

 

[HouRman]

hourman, get a microtech and a wideband and go find a dyno.

I would if I had the money.

Heck, I want to find a dyno just to see what my stock engine puts out. Just have not gotten around to doing it yet.

 

[JustROLLIN]

[quote author=boardumb link=topic=66972.msg1151728#msg1151728 date=1168924352]

How does a turbo create back pressure? From my understanding back pressure is merely resistance.

[/quote]

Exactly. Your understanding is spot on. The turbine wheel lays directly in the exhaust flow of the exhaust. The expanding gases from the exhaust are what spin the turbine wheel, which is connected to the compressor wheel. The compressor wheel, well compresses the intake air charge. Effectively jamming more air into the combustion chambers, which in turn creates more HP. So yeah, a turbo has enough backpressure to choke a horse, or a 4-cyl. engine for that matter. http://www.howstuffworks.com/turbo.htm