89 4runner with 4 cylinder engine. If for some reason the catalytic converter should somehow come up missing , how much more power would that give me? There is no smog check in this state. Thanks.

vmax84

 

my brother removed the one on his 94 with the 3.0 and it sounds more agressive and he says that it gives him more power. From the way his sounds and the more power thing i will soon be doing it to my 95. He also said somethin about a little better gas mileage with it.
-Kyle

 

lots of opinion on this matter a while back. Pls search...
for me, i remove mine from a runner w/ v6 though and i like having the cat, only thing is that i fried it coz of burnt valve that needs to be fixed yet.

No observable difference... just smelly exhaust which is bad for everyone....

i will buy a new one to replace it as soon as i got my motor problem fixed!

btw, my runner is on storage now because of its illness... i feel that its gonna die soon so better stay in the garage til it get fixed!-just to share this misery...

 

Removing back pressure can be very bad for an engine. Kinda like running 4" exhaust on a 4 or 6 cylinder engine. I think there are lots better ways to make the type of HP we may or may not be talking about by x'ing the cat. The way I understand this is that bigger exhaust tracks promote more power at high rpms but the power is less at low rpms than stock. As most of us are looking for off road power (low rpm) removing the cat would not help. Could be wrong. $.02 ?

 

Is your O2 before or after the cat? If it's after the cat, leave the cat in place. An EFI motor needs the proper parts/gear in order to run as it should. Remember, not all trucks/4Runners only had one O2 sensor, some have two...depending on the location of where it was originally sold.

 

does anyone have a good picture of where to find an O2 sensor on a 2nd gen?

 

There is always an O2 sensor before the cat. It's what the ECU uses to control the amount of fuel injected.

If you have two O2 sensors, the one behind the cat is not for fuel control, but to check the health of the cat and can be replaced with an O2 sim to prevent the CEL from coming on if you eliminate the cat.

In my GM vehicle, I am even able to eliminate the "test" on the 2nd O2 sensor using a PCM programming tool, obviating the need for O2 sims, but my GM vehicle is OBDII, and I don't know if a similar tool exists for Toyotas.

 

Just crawl under your truck about under the drivers seat, and look for wires going to the exhaust pipe ahead of the cat. Those wires are connected to the O2 sensor. It's hard to miss.

 

No, its a bad idea.


Lamm

 

About 5 peak horsepower from ditching a working cat. Obviously if the cat is plugged to some degree, you can pick up more, but about 5 bhp peak from factory.

 

There are several reasons why removing your cat altogether is a bad idea. Here's a few:

1. You're going to lose a lot of back pressure. What little hp that you will gain from this mod probably won't be noticed until 4k rpms or so. For most that's not even "usable" hp. You also run a chance of actually losing some low-end torque. The last vehicle I owned I put a free flow cat on and a glasspack. Later I had to put a more restrictive muffler on because my hp and torque were too high up in the rpm range.

2. The majority of the hp gain could probably be obtained simply by replacing your old clogged up stock cat with a free-flowing one or even a new OEM one for that matter. It's actually quite amazing how advanced these "free flow" catalytic convertors are. Unlike older cats you can see right through the new ones which makes you wonder how they even work. But they do work.

3. Just because your state doesn't have smog doesn't mean that you're not required to have a cat. In NC vehicles that are OBD I and older do not have emissions testing, but if a catalytic convertor was originally on the vehicle then one must still be present. I know because I have done many inspections myself.

4. It's just plain stupid to emit more pollution than necessary on a vehicle just so it will "sound better" or "take off a little quicker". There are plenty of other ways to gain horsepower without completely ditching your cat.

My .02

 

Removing the CAT or any other reasonable exhaust modification on the 2.4 will improve power all accross the powerband. I'd suggest that although removing the cat on that motor will open it up a bit you could see better increases running the stock manifold 2" pipe to a high flow cat then 2" to the muffler and 2.25" out of the muffler. Thats a solid upgrade that will net you about 10HP assuming all else is well.

Then talk to Ted at ENGNBLDR.com about one of his heads and cams and machine specs for more power...

 

Ive run my truck (with headers and 2.5" exahust) with and with out the cat. I didnt notice any performance diffrance with and without it only a significant increase in the amount of noise the exhaust made, which i quickly grew tired of and put the cat back in.

 

With that size of exhaust I'm not surprised you didn't notice any difference.

 

Yeh, small increases such as ~10 HP are hard to notice just using your butt-dyno.

To get any more HP increase from any mods like exhaust or intake (including heads/cams), you'll need to modify the fuel/spark tuning to take advantage of the increase air flow.

Changing out the exhaust doesn't necessarily mean losing back pressure (which helps low-end torque). A good, tuned set of headers will maintain enough back pressure to help with the low end, but flow freely enough to create more power at higher RPMs too.

 

You'll notice it on a 2.4, but I doubt that you would see a difference of 2hp on such an open exhaust as 2.5". My .02 would be to forget a header on the 2.4 as well as they apparently only get you about 2hp over the stock manifold as well.

 

When I was replacing my CAT, I decided to gut my old one and see if it gave me some power. You will loose some bottom end, but the higher end is a little better. It did make my exhaust WAY louder. t wasnt worth it for me, I lost too much bottom end.

 

I have always understood that the reason increased backpressure helps low-end is that it causes the cylinders to be more fully filled with air and fuel.

Now, I understand why this works on the intake part of it - for instance, an engine with high-flow intake ports and stuff will pump lots of fuel and air through the combustion chamber but at low rpms, there is not enough negative pressure to pull in a cylinder full of fuel/air. You get like 80% of a cylinder. But with a more restrictive port, it causes the air to flow through faster (venturi or bernoulli effect, take your pick) at low rpms.

But how does this carry over into the exhaust portion of the cycle?

 

Here is an article done by Ted that I think will make a lot of sense to some peeps here about building good, useable and dependable power for the 2.4. I have heard complaints about other builders products actually living up to their claims but I've yet to hear a viable one about him so here it is.

http://www.4x4wire.com/forums/showfl...5&o=14&fpart=1

 

Man, you guys are great!! Thanks for the info!!

vmax84