Yeah totally got into a nice discussion about cat's, the EGR and the engine today in
Fuel & Ignition at school tonight.

I got totally bashed on by my teacher for running a CATLESS exhaust system on my car. He said that the CAT is NO RESTRICTION on the car's power. I kept my mouth shut throughout the whole entire conversation/arguements people were having so I could better understand this.

He went on to say that having no cat, mean no back pressure which therefore in turn harm your EGR which then in turn can hurt your PCV and then your engine....

AYE AYE AYE, seriously I have a headache now from tonights lessons

So to the auctal SMART, INTELLIGENT people on the forums, what are YOUR opinions on running an exhaust. Can someone please shed some light on this?

I am sure I will never prove my instructor wrong, but he is known to hate the "rice burners" and I have a kid in my class who owns a old school beetle who constantly says his car is far greater than any "tuner" car

 

well show him up with ur tC

 

I've been thinking about it for about 3 days b/c this is all we have been going back and forth on.

I just dont like to reveil my hand on what I got....b/c i'm sorta "sleeperish"

 

Take him to your local dyno, have a downpipe with a cat in it ready, dyno that.. then have a cat less dyno and show him the gains...
Then proceed to make him pay for the dyno time and lunch.

 

I've already been challenged by a kid at school to put my car on the dyno we have on campus...

he calls bs on my setup...so we'll see

as for this topic, i just need some input i think that engineeferr (spellin) knows quite a bit too

 

Just`show the dynos of people of stock (with cat) header versus aftermarket (no cat) header dynos. Show how there is no power loss at any RPM and only gain.

 

haha cat is needed for back pressure thats intersting. Those poor guys in the 70s with catless cars and huge v8s thats what they were missing a cat for the extra power. Perhaps some logic to that could be rephrased to something like current exhaust setups accomodate for the cat and calculate that into the backpressure for the system (because a certain amount is still good on na applications) So when you take the cat off you have less back pressure then intended. But saying itll ruin your engine is kinda going too far i think.

 

I have seen comparisons of cars with no cats, showing almost zero performance gain (at least a gain you will feel). I have run straight pipes (removing the cats all together) with flowmaster mufflers on ford 2.3L 4 cylinders with no noticeable effect (didnt dyno it, but could tell zero difference other than sound). So there is a debate as to what you will see. The mandrel bending and better curves of a cat back probably gain you more performance than removing the cat itself.

As far as the EGR. Some engines used (and some may still use) backpressure to partially control the EGR valve. They needed about 1 - 2 psi of backpressure to operate properly (dont quote me exactly, I am not an EGR "expert"). But even if ours WAS that type of valve I believe that even a straight piped, non muffled exhaust on one of these engines will produce that much backpressure on its own.

But I wouldnt bother with removing the CAT all together. I dont think you would see a noticeable gain over just running a good, mandrel bent cat back exhaust system.

 

I would have to agree completely. A good madrel exhaust system is going to show you the best gains in my experience and the cat is a wonderful sound buffer. Now, if you are running a stock cat on an NA-T application, over time you could see some power loss due to the added heat. Especially if you run race gas as it will kill a converter along with your 02's quickly.

However, on a stock vehicle I doubt you will see any real gains by removing the cats. In fact, some small 4 cylinder NA cars have lost power by using a staight through exhaust. They need the backpressure to increase the "scavenging effect" in the cylinders and produce a cleaner burn on the next power stroke.

Charles

 

Ok I guess I just needed to hear it from another persons view point to better understand this. My instructor did say MOST EGR's are operated by backpressure and that if you run no cat, you have at minimum .5 psi of backpressure.

I'm not saying you will gain a noticeable power increase, I just simply say its the end user's decision to run cat/no cat on their exhaust

I will further discuss this topic at school on monday with him.

Thanks for the input engifineer! By the way I quoted you...so deal it it

 

well toyota motors dont have an egr 'valve' to begin with so i dont think youll have that problem, toyota controls its egr functions through the VVT-i which is why all recent motors are VVT-i. it snaps the valve close before all the gases are let out. as far as restrictions go, straight mandrel bent pipes are your best bet youll probly see some hp gains from that, as far as your cat compared to a high flow cat there is no real difference, technology has gotten better since the older days where they were highly restrictive. anyways just my 2 cents

 

since this is in the f/i section i thought you meant on fi cars, why would you even want to take off the cat on na stock cars. I have no experience but everyone that i know with aftermarket turbos has said they felt quite an increase running catless. Now ofcourse that oculd be due to the fact when they went catless they went with a larger exhaust but most still say on fi cat is restrictive.