Originally Posted by FAQs in Stickies at the top of the 5th Gen pages

First of all, if you have a 2001 Maxima, it has California/NLEV Spec emissions. If not though, you can look under the hood for a white sticker that displays emissions information. If the sticker states anything about meeting California or NLEV emissions standards, you have a Cali/NLEV spec Maxima.

The main difference between Federal and NLEV emissions is that the latter has two precats with a total of four O2 sensors versus a single precat and three O2 sensors for Federal emissions standards. In the Federal Spec emissions Maxima, you will find a single precat built into the intermediate pipe. Two of the sensors are placed before this and the last sensor is after the main cat. The Cali spec Maxima has two precats with one in the intermediate pipe and another one built into the front exhaust manifold. Two O2 sensors are located before the precats and the other two are after each of the precats. There are no O2 sensors after the main cat in this case.

Another, way is by the number of 02-plugs you have on the front valve cover clip/rack: Refer to diagram posted above by Trance Artur

Originally Posted by 5thgen2nr

Cali-spec=slower than Fed-spec...all you need to know right there.

Originally Posted by sloppymax

i remember way back when, someone in AZ swapped all the necessaries to go from cali to fed spec. showed a gain of around 3-4whp. no torque difference if i remember correctly. cali spec has one more secondary o2 sensor, swirl control and one more precat that the additional o2 monitors.

Originally Posted by Puppetmaster

So its like adding "half a y-pipe"? Since you're removing one pre-cat going from Cali to Fed?

Originally Posted by chun

i think my car is cali spec too, so would getting a y-pipe fix the hp loss? what about getting a cat-back?

Originally Posted by Trance Artur

Originally Posted by chun

yeah ive heard about the headers, 650 is alot of money, i wish i can buy them separately... precat and then y-pipe or other way around...i used to live in raleigh, man NC roads are so nice..BTW are you from the west?

Originally Posted by Ivanhoe

This picture is not right. The 4th O2 sensor on the Cali spec is over by the strut tower and not in line with the other 3. Jusy FYI...