Removing the cat

[RallyEclipse98]

How much of an increase in mileage would I get if I switched the cat out for a straight pipe? Would it make the exhaust really loud or just a bit louder? I don't want reliability or anything to go down on the car so I won't do it if that would be affected. The car has a lot of miles so I don't want to do this and decrease the life at all. Thanks.

[MagicRat]

What year is the car? If it's pre-96, the engine controls are OBD1. Removing the cat will just make it noticeably, moderately louder, and make it emissions-illegal. At worst, the noise will attract a cop who will look, see no cat and give you a fat ticket for emissions tampering.

And you will not get any more power or mileage than you would with a properly-functioning cat.

If your car is newer ('96+) you have OBD II. You would have the same situation as above PLUS a 'Check Engine' light and a stored O2 sensor code.

[RallyEclipse98]

Originally Posted by MagicRat

What year is the car? If it's pre-96, the engine controls are OBD1. Removing the cat will just make it noticeably, moderately louder, and make it emissions-illegal. At worst, the noise will attract a cop who will look, see no cat and give you a fat ticket for emissions tampering.

And you will not get any more power or mileage than you would with a properly-functioning cat.

If your car is newer ('96+) you have OBD II. You would have the same situation as above PLUS a 'Check Engine' light and a stored O2 sensor code.

I completely forgot about the o2 sensor being there. I'm not going to get rid of the cat then. Emissions isn't anything to worry about. I live in Nebraska and the cars are never checked. What I will probably do is just throw in a K&N air filter. That will help my mileage enough.

[HotZ28]

I am certainly not here advocating altering emissions and normally the best solution is to replace the cat, but I will share my recent experience.

Several months ago, my '96 PA Series II S/C engine started losing power. This was soon after upgrading the S/C pulley & raising the boost to 14 1/2 psi. The first indications of something not being right, was when it developed KR @ 5500+ rpm. After further investigation, I found a hairline crack in the plastic return fuel line, which I immediately fixed. That helped some, but did not restore the full power that I had at first, with the S/C pulley & PCM upgrade.

Not long after that, I heard the "marbles in a coffee can" sound under the car, which revealed to me that the cat was broken. With the weekend approaching and limited time to find a cat, I elected to temporally install a straight-pipe to replace the cat. (Rear 02 sensor still in place) After welding the pipe in place and taking it for a test drive, I immediately noticed all the original power (+ some) up to 6K rpm was restored. The exhaust note changed to a mellow sound, not near as loud as a Flowmaster and hardly noticeable to the general public.

My annual emission test was due the following week & after driving several hundred miles, I still did not have any DTC's! I then checked everything with a scanner & I/M readiness passed with no pending, or stored codes. Rear 02 reading was normal! I then thought, what the heck, I will try passing the emissions test without a cat and hope the inspector was too lazy to look under the car for the cat. I was right, the inspector was lazy and the car passed all OBDII test with flying colors. That was three months ago and I am still running the straight-pipe and have never had a flicker of a CEL. See pics below of the clogged/broken cat after removal. BTW, I forgot to mention with the clogged cat removed & straight pipe installed, I noticed a 2+ mpg improvement!

[wafrederick]

It is illegal to remove it,a $10,000.00 fine if a shop is caught doing this.Do not ever take off the cat off an OBD II vehicle.Plus there wil be a catalytic converter code too when removed and a straight pipe installed.There are buyers for the old catalytic conveters although the prices are low.Junk catalytic converters from imports go for the most money.I have heard $900.00 off of a Lexus.

[HotZ28]

Originally Posted by wafrederick

.Do not ever take off the cat off an OBD II vehicle.Plus there wil be a catalytic converter code too when removed and a straight pipe installed.There are buyers for the old catalytic conveters although the prices are low.Junk catalytic converters from imports go for the most money.I have heard $900.00 off of a Lexus.

Evidently you did not read post # 4 before making these comments!

[RallyEclipse98]

Well, I live in Nebraska so emissions isn't even a word here. No testing whatsoever. Thanks for the post of actual tested information!