Catless

DangerRanger007 · #1 04-27-2010, 08:34 AM

If i have my cats removed and straight pipe welded in place on my 2004 2.3L will my ECU flip out? basically what im asking is (because we dont have vehicle inspections in AR

) will i ruin my truck?

im asking to not get chewed out please......im asking before making a decision because no one who works at an exhaust shop wants to give me a straight up answer.....probably cuz its illegal cuz of the noise ordinance they just passed like a year ago

TheStig · #2 04-27-2010, 12:57 PM

even without emissions testing...its still a federal offense

no...it won't "ruin" your truck
some say it increases power....others say it doesn't do anything

but unless you have done some serious head work and have a high flowing....high output motor....leave them on
they are there for a reason

Jp7 · #3 04-27-2010, 01:53 PM

Read posts by me and you will learn why it is a poor decision.

BAMA BOY · #4 04-27-2010, 04:48 PM

do it youre truck will be ok

CUTiger · #5 04-27-2010, 06:34 PM

Its not illegal because of the noise ordinance...even though getting pulled over for noise and ending up in big trouble over removing the CATs would be a hurt I wouldn't want to deal with. They aren't giving you an answer because its a federal offense to remove a CAT, or for that matter replace an OE CAT that is still under its 80,000 mile warranty with no documented need for replacement and I'm sure they don't want to get shut down for illegally removing a cat.

If you absolutely have to get rid of the stock CATs to make your truck obnoxious...I mean loud enough find a shop that will weld in an aftermarket magnaflow CAT or learn how to weld and do it yourself.

Scottg · #6 04-27-2010, 07:40 PM

what do you want out of removing the cat? Are you just looking for more noise? The stock cats are fairly high flow and create enough back pressure for everything to work properly

Jp7 · #7 04-27-2010, 07:49 PM

Quote:

Originally Posted by Scottg

and create enough back pressure for everything to work properly

a noobie comment (sorry!)

Backpressure = bad

Keeping the pulses moving fast enough so that they suck eachother down the hot side of the exhaust = good.

In the hot side of the exhaust, exhaust does not "flow" it "pulses". If you slow it down it begins to "flow" and this is what kills torque.

People imagine exhaust flowing like a river stream. Wrong. It is more like a tide moving in and out, high and low. It does not turn into a laminar flow until it gets cold enough, or slow down enough.

CUTiger · #8 04-27-2010, 08:31 PM

Would it be safe to say that a stock engine with no means of adjusting the fuel mixture "needs" some amount of back pressure to keep the engine from running lean?

Now assuming that the fuel injection system can sufficiently compensate then the back pressure should be able to be reduced and there be little loss in torque...as long as the piping is sized correctly keeping the exhaust velocities high.

The problem I see with reduction backpressure by removing the relatively restrictive exhaust components on a low power engine is that the slight loss in low end torque feels like a big one. From what I understand this loss is due to the fact that stock exhaust on most vehicles is so restrictive that it ends up "banging" the exhaust pulses together forces them along creating a lot of low end torque, where as a less restrictive exhaust will create a lot more high end power it also reduces low end torque because it can not "suck" exhaust gases along as fast at low rpms.

Basically what I'm saying is you can drop the backpressure down as long as you keep the exhaust flow moving and have a tuner to adjust for the correct air/fuel ratio which according to chemistry is 14.7:1 oxygen to fuel.

This is why headers, cat-back exhaust system, and a good tuner can gain you plenty of horsepower especially at higher rpms without even touching the cats. Granted it won't be crazy loud but it'll perform.

Of course what headers to get is a whole nother thing...but basically longer primaries=more low-mid ranger power and torque. Shorties produces more high end power and less torque.

ILFarmboy · #9 04-27-2010, 08:47 PM

No cats = BooKoo torque. its a night and day difference. but instead of taking them out completely just take of the y pipe and clean the "honeycomb's" out and put the empty catty's shell back up there so it looks legal.

Jp7 · #10 04-28-2010, 09:22 AM

Quote:

Would it be safe to say that a stock engine with no means of adjusting the fuel mixture "needs" some amount of back pressure to keep the engine from running lean?

This makes no sense whatsoever. Your primary oxygen sensor reads back to the ECU and makes adjustments to the fuel trim so that under closed loop conditions your truck is stoich. All catalysts are after the primary hego.

Quote:

Now assuming that the fuel injection system can sufficiently compensate then the back pressure should be able to be reduced and there be little loss in torque...as long as the piping is sized correctly keeping the exhaust velocities high.

No, no, no, no... you are totally confused. Loss of torque happens because the exhaust pulses are not pulling on eachother.

Quote:

The problem I see with reduction backpressure by removing the relatively restrictive exhaust components on a low power engine is that the slight loss in low end torque feels like a big one. From what I understand this loss is due to the fact that stock exhaust on most vehicles is so restrictive that it ends up "banging" the exhaust pulses together forces them along creating a lot of low end torque, where as a less restrictive exhaust will create a lot more high end power it also reduces low end torque because it can not "suck" exhaust gases along as fast at low rpms.

Basically what I'm saying is you can drop the backpressure down as long as you keep the exhaust flow moving and have a tuner to adjust for the correct air/fuel ratio which according to chemistry is 14.7:1 oxygen to fuel.

This is why headers, cat-back exhaust system, and a good tuner can gain you plenty of horsepower especially at higher rpms without even touching the cats. Granted it won't be crazy loud but it'll perform.

Of course what headers to get is a whole nother thing...but basically longer primaries=more low-mid ranger power and torque. Shorties produces more high end power and less torque.

You really are missing the idea of a tune. No matter what changes are made to the physical parts on the engine, you always want to make sure that the timing and fuel are optimal. Timing can sometimes be increased by using less restrictive exhaust hot-end parts. Too little timing will cause unburned fuel to make its way out of the engine because the mixture is less dense at time of the "umph" in the power stroke. Your AFR will always adjust to 14.7 because that's what OBD2 cars do, unless in open loop where it runs richer because of the higher load. Extra fuel is dumped on purpose to make sure that there aren't excessive lean parts of the combustion chamber. Leaning a mixture will allow you to actually burn more fuel instead of dumping it out the exhaust on purpose. This is why I say bolt-ons are not power adders, they are power-enablers.

Jp7 · #11 04-28-2010, 09:23 AM

Quote:

Originally Posted by ILFarmboy

No cats = BooKoo torque. its a night and day difference. but instead of taking them out completely just take of the y pipe and clean the "honeycomb's" out and put the empty catty's shell back up there so it looks legal.

Thousands of articles say you are wrong.

CUTiger · #12 04-28-2010, 09:54 AM

Quote:

Originally Posted by Jp7

This makes no sense whatsoever. Your primary oxygen sensor reads back to the ECU and makes adjustments to the fuel trim so that under closed loop conditions your truck is stoich. All catalysts are after the primary hego.

No, no, no, no... you are totally confused. Loss of torque happens because the exhaust pulses are not pulling on eachother.

You really are missing the idea of a tune. No matter what changes are made to the physical parts on the engine, you always want to make sure that the timing and fuel are optimal. Timing can sometimes be increased by using less restrictive exhaust hot-end parts. Too little timing will cause unburned fuel to make its way out of the engine because the mixture is less dense at time of the "umph" in the power stroke. Your AFR will always adjust to 14.7 because that's what OBD2 cars do, unless in open loop where it runs richer because of the higher load. Extra fuel is dumped on purpose to make sure that there aren't excessive lean parts of the combustion chamber. Leaning a mixture will allow you to actually burn more fuel instead of dumping it out the exhaust on purpose. This is why I say bolt-ons are not power adders, they are power-enablers.

I don't think I totally missed it...just worded it differently.

I understand that our engines have a way to keep a stoic mix, I was just a hypothetical situation where they couldn't do that(or say back in the days before EFI). A loss in torque can also occur in the hypothetical very lean situation I started with...by adding that the exhaust is properly sized keeping the exhaust gases pulsating I took that loss of torque out of the picture. But yes you can lose low end torque by sizing the exhaust too large, slowing velocities, cooling the gases, and creating laminar flow as you've stated...

And I guess I phrased that sentence poorly...I was still in hypothetical mode assuming that the engine had no on board means of adjusting the mix, and meant that as long as the engine had some sort of way of adjusting for this rather it be the on board computer or tuner then it would be good. I had not even thought about the timing issue but thats a good point.

Jp7 · #13 04-28-2010, 10:57 AM

Quote:

Originally Posted by CUTiger

And I guess I phrased that sentence poorly...

I have that problem too!

Quote:

I was still in hypothetical mode assuming that the engine had no on board means of adjusting the mix, and meant that as long as the engine had some sort of way of adjusting for this rather it be the on board computer or tuner then it would be good. I had not even thought about the timing issue but thats a good point.

Coming from the turbo-world as I do, one of the main kiddie questions I get from teenager-customers whose parent buy them evos is "oh do I need a tune if I put a cat-back and cold air intake on". They say this like it is a chore to have to have it tuned. My advice is always that if you don't want to tune, stick to exhaust mods and cosmetic mods. I've been able to make gains on removing a catalyst when using adjustable cam gears or variable adjusted cam timing, but most of the time on a n/a engine it is disappointing.

DangerRanger007 · #14 04-28-2010, 01:59 PM

ok.....i should've probably stated that i have the 2.3L and i plan to put a Flowmaster 40 Series on.....btw i did have a Nissan 200SX SE-R with a cat-bak, headers, and a SRI.....so those of u who have been gettin technical and using science to explain this i actually do appreciate it

i may not remove the cat, but i wanted to try and get a majority opinion on that kind of a move....

DangerRanger007 · #15 04-28-2010, 02:02 PM

btw Jp7 im diggin the trifecta of Rotary powered cars....I originally wanted a FC3S (because i almost love them more than my gf [I hope she doesnt see that]) for my first car and i almost got one, but my parents didnt want me to kill myself haha