Benefits of Removing Cat and Running Straight Pipe?

[Nexus1155]

Oh Black Yaris you're my hero I was skepticle on commenting on a couple other peoples in thoughts of getting trees bashed over my head or something, but if what people say is true that it will lower the compression and create a downgrade in performance i would not want to do that per say, but i will toss him a PM and see what he says too....

[alhope34]

Well from what I know, USUALLY a free-flowing exhaust will free up a few extra top RPM hp but will take low end torque away. The Yaris's low end RPM range is already bad enough for power/torque without taking more away form it. That's just my opinion, though.

[Bdaslug]

I gutted my cat. and also I made my piping larger than stock. now I have a 2.5 in exhaust all the way. without the cat it's get a little bit louder. Depending if you have a straight through muffler like a N1 style. But it doesnt sound like a honda. Also your gas mileage will go down alot, Because the check engine light stays on without the cat. I actually tried both O2 simulators (mechanical and electrical) and the check engine light still comes on after a few miles. But you can feel the difference from the stock 1-3/4 inch to 2-1/2inch piping only at higher speeds. I am going to install a high flow cat to get rid of the check engine light and it should help my gas mileage a bit.

[eTiMaGo]

If you have a dedicated track race car, then maybe, yeah. But for a car that will spend most of its time on public roads, you really should consider other people's ears (and lungs). I'd recommend you get the cat replaced for a less restrictive high flow one, it would be an ideal compromise.

[loafer650]

you can run straight pipe...but dont change size of pipes..backpressure is your friend....

[acdaazn]

Not really trying to be an emission nazi or anything.... but putting out so much nox and slowly killing trees off is just going to make your life worse. Everything comes with a chain effect.

Trees, especially elder trees, are like air conditioners that are on for 10 hours a day. The less tree we have, the worse it becomes for us. Then we would have to resort to A/Cs; making electricity more of a scarce resource than it is now. Oil prices goes up along with that, then that would reflect on to your gas bill. Yes, I know you drive a Yaris. But the point is, why would you want to be a part of it for that "at most 5 hp" gain?

[Nexus1155]

Eh, im probably not going to do it for the simple fact it will toss a CEL and kill the MPG because it cant give proper o2 readings, but acdaazn do you have a blown up picture of your sig?

[blueskana]

High flow cats are pretty damn high flow... seriously, you can practically see right thru them, yet they allow for burning of "evil" gasses. Considering if you ran one right after your header and then ran straight pipe back it would pretty much have all the benefits of a thru-system, no CEL, hippie approved and emmisions/inspection good too along with the power... plus it's something to show the cop and say "Eh, I got's me a cat rite theh'!".
Good luck with whatever you run. A full exhaust is on my plate too once I figure out how exactly I want to do it.

[WolfWings]

Originally Posted by BailOut

"Nox" is short for "noxious emissions". Gasoline-burning vehicles produce 3 kinds of emissions:

No, incorrect, wrong, wrong, wrong. As wrong as claiming Annie Lennox wrote a song about walking on propane gas.

nox stands for a single chemical family being tested for: Nitrous OXides.

Petrol-based engine emissions-testing systems aren't even remotely categorized like you listed. The 'bad chemicals' they produce are:

• Nitrous OXides (two Nitrogen atoms and a random number of Oxygen atoms)
• Carbon Monoxide (two Carbon, one Oxygon)
• Unburnt HydroCarbons (one Hydrogen, one Carbon) actually.

These (NOX, CO, HC) are what are tested for in a tailpipe test, also. A three-way cat converts NOX better if you're running a rich mixture, or converts the other two better if you're running a lean mixture. Basic chemistry, replace a cat, adjust the fuel mixture and you can pass an emissions test almost always. California is so hard to pass because of their inspections, which include the most common ways to adjust the fuel-mixture having to be factory-spec.

At least research your claim a little before spouting it off like it's gospel, 'kay?

[BailOut]

Originally Posted by WolfWings

At least research your claim a little before spouting it off like it's gospel, 'kay?

Either I was misinformed at the testing station I asked lot of questions at, or Wikipedia is wrong. Either scenario is highly possible.

The end result is the same regardless, though:

Catalytic converter == good, hence why it is mandatory in most parts of the developed world.

No catalytic converter == acid rain, contaminated water, etc.

[Nexus1155]

ahhh you see, but it doesn't effect Ozones! so the big thing is a lie ! it all gets soaked into the atmosphere and clouds... not up way past there and burn holes like wut! purely scientfic! zomg ... Americas way of scaring idiots to try and get more moneys!

[eTiMaGo]

Originally Posted by Nexus1155

ahhh you see, but it doesn't effect Ozones! so the big thing is a lie ! it all gets soaked into the atmosphere and clouds... not up way past there and burn holes like wut! purely scientfic! zomg ... Americas way of scaring idiots to try and get more moneys!

Ozone? I don't think anyone brought that up before, but it's got very little to do with exhaust fumes.

BTW as WolfWings mentioned:

. A three-way cat converts NOX better if you're running a rich mixture, or converts the other two better if you're running a lean mixture

This is very true, the ECU, in our cars at least, keeps oscillating the mixture between rich and lean in order to maximize the efficiency of the cats

Anywayy, as I said before, it's just irresponsible to have a daily driver without a catalyzer

[Joker]

As I sit back and read this post I wonder what some of the people think they will gain by either removing the cat or going to huge (at least for our cars) 2 1/2" exhaust pipe? Like someone said in this thread some backpressure is good, take it all away and you lose your bottom end. For most of us losing your bottom end means more sluggish acceleration, etc. Most of us dont tool around in the 5000 rpm + range all the time.

If solid gains were expected and proven by removing the cats or going to larger pipes then by all means I'm in but the reality is that on newer vehicles the cat isnt as restrictive as most people think.

I have a long history of drag racing both cars and motorcycles. There is no new magic here, our cars are normally aspirated and will benefit from the normal bolt on parts such as header/intake/exhaust IF chosen wisely. More air in + more air out = better performance. This is the same thing people did back in the old days, replace stock exhaust manifolds w/headers, replace small carbs with larger ones, etc.

The only thing we need to contend with is the ECU. If you feel you must override the stock ECU there are options such as the E-Manage and if you have the need to go full stand alone then there is Haltech and the like.

I appreciate this forum as it provides feedback from real people on many of the things we like to do which for most of us is to mod their car. Just givin' my 2 cents here....have a good morning....

T

[joey1320]

you are not lowering compression you are lowering backpressure.
the compression is inside the engine, inside the cylinder and the head. thats where the compression is rated.

the less backpressure the better on any engine. scc did a test years ago about all the aftermarket headers for hondas and none of them made any more whp than no header at all. all thru the rpm band, the no-header run made the most horsepower and torque.
(i'll see if i can find the mag somewhere...)

the only reason why people burn valves when using open headers, no cats, test pipes and what not, is that the car wasn't tuned properlly after the removal of these parts and the car ran lean, since you are making more power.

theres really no reason for you to remove the cat. converter on any car. try to make clean power other ways and keep the cat. for last...

[Joker]

the less backpressure the better on any engine. scc did a test years ago about all the aftermarket headers for hondas and none of them made any more whp than no header at all. all thru the rpm band, the no-header run made the most horsepower and torque.
(i'll see if i can find the mag somewhere...)

Less backpressure is better, NONE is not...by putting 2 1/2" pipe on any of our normally aspirated cars is overkill in every sense of the word. If you think your car is slow now go ahead and try it.....

To clarify I assume when you say "no header at all" you mean the engine was tested w/its stock exhaust manifold? The only other meaning would be the car had no exhaust manifold at all, esentially running the cylinder head "open" which makes no sense.

A header w/a good design should make some gains on our cars, when I say good design that doesnt mean the 4 into 1 DC header that recently came out. 4 into 1's are for higher (5000+ rpm) applications which means on the lower end your dead...unless of course you drive around at or near redline all day. Do some research, DC's own website highlights this fact!

Just trying to help out the inexperienced. Peace.....

T

[alhope34]

I'll have to agree with Joker on the backpressure thing... Take it away and you'll have absolutely no acceleration from a dead stop at all. An engine NEEDS backpressure to work and run properly. If a 2.5" pipe was better, why wouldn't Toyota use it? A lot of people buy the Honda Fit because of its 3 extra hp. If a larger pipe was really necessary Toyota would have used it. It's because the car needs to have the backpressure there to have decent enough low RPM torque.

[largeorangefont]

Originally Posted by Bdaslug

I gutted my cat. and also I made my piping larger than stock. now I have a 2.5 in exhaust all the way. without the cat it's get a little bit louder. Depending if you have a straight through muffler like a N1 style. But it doesnt sound like a honda. Also your gas mileage will go down alot, Because the check engine light stays on without the cat. I actually tried both O2 simulators (mechanical and electrical) and the check engine light still comes on after a few miles. But you can feel the difference from the stock 1-3/4 inch to 2-1/2inch piping only at higher speeds. I am going to install a high flow cat to get rid of the check engine light and it should help my gas mileage a bit.

The check engine light for cat inefficiency (code (p0420) has no effect on anything. You mileage went down because your exhaust piping is too big and you lost low end power. 2.5 inch piping is too big for a 100 HP car.

[largeorangefont]

Originally Posted by Nexus1155

Eh, im probably not going to do it for the simple fact it will toss a CEL and kill the MPG because it cant give proper o2 readings, but acdaazn do you have a blown up picture of your sig?

The car will run fine without a cat. the front 02 sensor handles fueling, the rear checks catalyst functionality and has no influence on fueling.