2001 Maxima, 163k

On these cars, is it possible to get rid of the third catalytic converter and still pass emissions tests? Three seems like overkill. My SHO has two and that's plenty for a 3.0L DOHC motor.

- Brian

 

You will fail with no main cat.

 

^^ pretty much

 

It's called floor cat.

 

I passed with a test pipe in place of the main cat.

 

If you're in a visual inspection state, you'll fail.

If you're in a "Plug into the obd port and let the computer do the work" state, you'll be fine.

 

That's good to know. Yeah, in Texas, as far as I know, they've always just plugged it in and run the test. I figured since my car doesn't have a sensor behind the main cat, the OBDII shouldn't pick up the missing cat. I'll consider trying a test pipe in place of it. Thanks for the info.

 

I believe the main cat is monitored on the 3.0 cars. Remove it and you'll get a code.
On the 3.5 cars only the precats are monitored.

You can get a simulator or anti fouler to fool the computer. If they do a visual or sniffer it most likely won't pass.

The two precats are there mostly for when the car is warming up. Cats don't work till they get up to temp and it takes a while for the main cat to heat up. The precats heat up faster.

If you're looking for a power upgrade you're better using an aftermarket Y-pipe which will eliminate the precats and improve the exhaust flow. The 3.0 cars respond well to this. It's also easier to pass emissions this way as long as the car is warmed up and the main cat is there.

 

Oh, I didn't realize they made an aftermarket Y-pipe for these with hi-flow cats. I'll look for one of those.

Is there a Y-pipe that has just a main cat and no precats? That'd be nice. I don't care if the car needs to warm up before the main cat works properly as long as it passes emissions tests.

I just looked up the emissions on my cali emissions car and sure enough, no O2 sensor after the main cat, so deleting the main cat shouldn't be a problem. But I still like the idea of a hi-flow Y-pipe. Had that on my last SHO and liked it well enough.

Thanks.

 

That hi-flow Y-pipe is cheap! I can't believe how cheap things are for this car. My SHO's parts are so damn expensive. If you're lucky enough to find suspension for them, it costs $1,700, and everything else is pricy, too. It's cheap as hell on this Maxima. Thank God for that since I've had to replace so much stuff. I'll be glad when I get it up to par finally.

 

So, how do you keep the computer from throwing codes if you remove the two pre-cats before the main cat?

 

I really thought there was a sensor after the main cat but it seems you're right.

Your best bet for power on that car is the y-pipe. The precats combined with other restrictions in the pipe really block the flow. Removing the main cat while leaving restrictions upstream won't do much.

Since it does monitor the precats you'll need some anti fowlers to fool the computer.

 

Look up the anti fowlers. They basically move the secondary o2 sensors away from the exhaust stream so they pick up fewer emissions. If they read less than the primary o2 sensors (before any cat) the computer will think there's a cat there reducing emissions.

 

I bought one of these for my 4th gen.
http://www.warpspeedperformance.com/...ti_i30_exhaust

Note that on the 3.0, the y-pipe deletes at least one cat, depending on whether you have a fed spec or cal spec. On the 3.5, the cats are part of the manifolds, so they don't get deleted. Changing the Y-pipe and main cat will not affect the CEL.

 

Yeah, that's the one I found, too. Not too bad a price. I saw that only one pre-cat is deleted, which has me confused. Why on earth would you want the imbalance of deleting only one pre-cat instead of both?? That's just odd. Seems like it would throw the motor off balance a little having the flow eased on one side and backpressure on the other side.

How did it work for you?

- Brian

 

I figured that's probably how they worked, but I wasn't certain. Thanks for the explanation.

If I didn't want the backpressure for gas mileage, I'd get a catless Y-pipe since the anti-foulers fix the problem. That's pretty cool.

- Brian

 

I don't think the cats are going to help your mileage. There will still be plenty of back pressure.

My mileage has gotten better with every mod I've done.

 

Exhaust obstruction DECREASES efficiency. Cats only waste money (the part and gas).

You want low end torque, but that's derived from high exhaust gas velocity due to smaller piping (stock diameter is good for this).
You should put on a catless Y and test pipe.

Therefore, you do not want back pressure, especially due to cats.

 

Any time I've gone with catless exhaust, my gas mileage has gone downhill, without exception, due to loss of backpressure on lowend. However, the gas mileage at high rpms has stayed about the same since the lack of backpressure helps at high rpm. Maybe Nissan have some characteristic that makes them different, I don't know, but I've never gotten better mpg without cats at low speeds. I'll have to check into it on these cars. Thanks.

- Brian

 

Perhaps you should look into the sho/mod for the max,it's expensive but we'll worth it!

 

I can't afford another SHO motor. lol

 

Are you SHO?

 

Yep.

 

why not just replace the Cat with the racammended part #?

 

Alternative route to deleting catalyst could effect the exhaust stroke in the engine pressure release thresh hold.
I think GM has a way to test exhaust pressure but I'd like some more info about this
I only know only to replace cat with correct part #

 

the sensor on my 4th Gen is before the cat. I was throwing a code for a bad cat. When I deleted it, my CEL turned off.

 

Interesting. I don't have the car anymore but thanks for the reply!

 

lmao. I didn’t notice it was from 2016….. 😮‍💨😮‍💨🤪

 

 

Has anyone done a floor cat delete on a 7th gen ? Just wanna know if any issues came up after the delete or if everything still ran fine im looking to remove mine.
Ive removed the resonator and changed the mufflers to flow master super 10 series feels like a lost a little bit of low end torque and thoughts on this?