O.K. we have one O2 sensor before and after each cat. There is only one flow path between the two sensors so both sensors would see the same higher flow rate - I don't believe that is the problem.

Here is another theory - In closed loop operation (both sensors used for feedback at partial throttle), the increased air flow due to the less restrictive exhaust path causes the sensors to produce a signal indicating a leaner condition. The ECU compensates for this by richening the a/f ratio in an attempt to maintain the ideal a/f ratio. This is how the system (ECU and O2 sensors) is supposed to work.

In open loop mode (WOT) the ECU follows a predefined a/f map based on the stock exhaust system flow characteristics - this would explain a lean condition only at WOT.

Why does it change to a richer mixture at the Higher RPM? Only speculation - but maybe the stock a/f map has a large degree of safety (richer a/f mixture) built in at the higher rpm since this would be the most dangerous area to have a very lean condition occur under high load.

What do you guys think? I just cannot believe that test pipes or other high flow cats would perform differently in this respect.

Cheers!

 

only thing I could see making a difference is the positioning of the 02 sensor with the RT cats...

is the pipe the same diamter or different than stock (or test pipes); does the 02 sensor sit at the same spot, or does it see more (or less) air flow than it does stock.

I know on my car, I have the Ultimate Racing High Flow cats and their Y pipe (eliminates the rear most cat), and the car ran quite rich pre ecu flash. Now that my flash has been done (on a dyno on my car, not via mail), I start at around 13.7 in the lower rpm's, and go to 12.7-12.9 in the upper rpm's.

 

So the new ECU flash intentionally leaned down your A/F mixture from the stock ECU? Interesting (and maybe promising). I forgot--what are the engine mods that you're running again?

How are the O2 sensors positioned on the Ultimate Racing cats vs. the RT?

 

Pardon me, but you guys who think that a cat-- any cat-- or an off-road pipe can cause an extremely lean condition are chasing ghosts. The problem with this is that while you're chasing ghosts, you're not finding the real cause and that can create REAL problems. True enough, a high flow cat allows the exhaust to pass through it quicker than a standard cat-- that's what gives you a horsepower increase. But regardless of how well a cat or an off-road pipe flows, the exhaust system is still enough of a restriction that it's impossible to have a car that runs too lean just because you installed high flow cats or an off-road pipe. Think about it-- the exhaust system runs the entire length of the car, and the pipes aren't all that large. Then, you have a muffler that the exhaust has to flow through. In order for an exhaust to have high enough flow to cause the engine to run too lean, you'd have to run open headers. At wide open throttle, most cars are on the rich side to begin with, so air/fuel ratio should still stay in range with exhaust modifications. I know of several cars (not Z's) that have headers, high flow cats and an exhaust system installed and they were still running slightly rich at wide open throttle. The Z uses the same type of fuel control system that most other newer cars use, so there's no reason for exhaust mods to be the cause of a too lean condition. Something else to think about, when "reading" spark plugs. you have to consider the brand of plug and brand of gas-- they don't all color the same. If my Z was running lean, I'd be checking the computer calibration, O2 sensors and fuel system.

 

I tend to agree with this--it seems to correlate with everything else I've read. The WOT mode apparently richens things up at the high RPM's but does not do so below 4500 RPM (approx.) at WOT. Maybe the slight lean situation is not a big deal in this case just mentioned.

Roadrocket35 is saying that it's essentially impossible to have a lean condition even with a wide open exhaust due to the ECU corrections. I don't fully believe that because I think it's all dependent on how the ECU is programmed--so that's mainly the issue, I think. I guess I'm not sure that I fully trust the programming of the ECU. Not quite yet anyway.

 

Yes..teh car runs incredibly rich from the factory, so whoel getting the flash done we leaned it out to more appropriate levels. My mods are Gruppe M intake, Ultimate cats, Ultiamte Y pipe, Apexi Hybrid Megaphone exhaust, and UR crank pulley.

If you look on our site, you can see how the 02 sensors are positioned on the Ultiamte cats. We don't sell RT so I have no idea on those.

 

I was under the impression that Tadashi had a program for the RT Cats that he ran on my car and Richard's and even the Performance Nissan car and none are lean anymore am I wrong?

They have striclty RT Cat program but it is a vanilla program, All Bark all this time I didn't know you were in CA man! Heck with all your mods you could get your own custom flash, I am 100% sure Tadashi could hook you up, he likes to see cars in person before commiting to a fix over the phone, I respect him for that, rather than just tell everyone yeah come on down he says, I would have to see it, I have logged 1600 miles to his shop and have always left happy. You would be the first Kinetix flash bro!

 

I just saw the dyno that zxsaint did. He has the Borla exhaust, Kinetix cats, CAI and added the plenum. The A/F was generally at 13, which is not bad!

 

13 at the tail pipe?

You could still show some gains from a flash but yeah I expected worse or should I say more lean conditions. Not bad at all, Tadashi tests at the cat though not the pipe. 13 is good N/A

 

Not sure, but I'm guessing that the measurement was taken at the tail pipe.

 

mine was done at the tail pipe as well

 

I wish this thread would be closed... or at the very least the subject edited....

 

Yeah me too! But I'd also like to know if a pop charger, Nismo exhaust and the RT cats necessitate an ECU reflash - or is this thread just another means of creating a false need for us to waste $500.

Cheers!

 

Check your plugs and post a pic, it's as simple as that! They will tell you what is happening inside your engine better than anything. Mine were not lean until I upped my boost and that was with headers and cats and so before spending money pull a plug and see if it is rich or lean or other signs that a plug will show. If you are unsure we will try and analyze the photo with you online!

Peas!