am I mistaken when I say that his A/F could also be dependent upon whether or this monitored b4 or after the cat?? I recall many other dyno's on NA G's and Z's and one large factor was whether the sensor was monitored before the cat or at the tail pipe. apparently from what I recall, when a/f is monitored after the cat its more lean?? I will dig up some posts....

 

It does not make that big of a difference, maybee .2-3 of an A/F..Something is definitly not right on his set up.

 

https://g35driver.com/forums/showthr...ght=lean+a%2Ff

some of the guys who replied to this post are very well respected and very knowledgeable when it comes to a/f and dyno's and na/fi...

many members run the mods you have, although ur motordyne spacer w/ the new gaskets is relatively knew. but ur cats and exhaust are used by many other members and although are cars are diff., before shelling out $$ to buy a piggyback or reflashing ur ECU which will VOID your warranty....I'd first take it elsewhere and run it again to be safe....and maybe ask some other members on this board. Randys_G who now has a S/C stated he had a A/F of 15.9 b4 he went FI (cats/exhaust/intake). But what do i know!!

 

After reading this post I'm afraid to install my new 1/2" Plenum Spacer. I currently have Crawford Cats and Z-Tube/k&n on my 04' G. If the addition of the spacer is going to make my G run too lean, I think I should not install it at all and save myself the trouble.

If this guys car is running lean with the said combo of mods wouldn't my G pretty much experience the same results?

 

every car is different, and no i wouldnt worry. there are plenty of NA g/z's running around and none that i know of have detonated. as mentioned id get a dyno at 2 diff. places and make sure im taking all the diff. factors into account when looking at ur a/f ratio...but thats just me. short of cats and headers I have every other mod i can think of as well...

ztube/popcharger, 3/8 plenum spacer, UR crank pulley, invidia g200 exhaust

Ive never dyno'd or know what my a/f is...but i plan on having this checked...just to be safe.

 

As I suggested before I would get another Dyno with A/F on a different dyno,then check the car out to make sure it is running properly to begin with. That A/F is one of the highest I have personally seen. And if your lossing HP whats the point of modding in the first place?The whole concept is to gain hp. What alot of people fail to understand when they mod,is that the ECU will only compensate so much when at idle and part throttle.This is the ONLY time the ECU makes any adjustments to the AF mixture and it has only to do with drivability and emmisions.When you hit wide open throttle the ECU swithches into open loop where it picks prom a pre programmed set of parameters te car should be running for A/F and timing.There may be several of these maps in the stock ECU for various driving conditions but I can assure you they do not change variables based on your mods.Therefore at WOT there is ZERO correction of your AF and timing.So if you take a stock VQ and dyno it and get a 12.5 A/F all the way across and go and add a ton of breathing mods you will pick up some HP by leaning that mixture out to say 13.5 or 14.0. But the ECU is doing nothing to compensate for it under WOT conditions..
Another thing you could have is a bad Vacume leak sucking in air AFTER the mass airflow sensor...The maf could be working properly then your sucking in air after it causing the ECU to select the improper point of reference on the A/F map or the incorrect map itself..

 

IMO, I see nothing wrong with his A/Fs. Sure, the A/F is fairly lean before 5000rpms, but that's hardly anything to worry about because lots of cars (even stock ones) and very lean in the low to midrange. It's quite common to see A/Fs in the near 16:1 range initially (sub 3000rpms) and have then taper off towards 14:1-13:1 as the motor approaches redline. The other thing to note is an A/F sniffer attached to the tailpipe will read at least .5 points higher than one upstream. I've seen a lot of VQs this lean and none of them suffered a failure. My 96 Maxima with the JWT ECU and quite a bit of NA work saw 14:1 A/F ratios at redline (7000rpms) and every other Maxima with the same mods saw the same exact A/Fs. My car ran like a top, even with 113K miles. The VQ motors are equipped with knock sensors so if the A/F gets dangerously lean, the knock sensor is going to pickup the knock and pull timing and dump in fuel. Since the motor is NA, it's not going to blow up due to a lean condition because the NA motor simply doesn't make the power or come under a quick change in cylinder pressure (ie turbo). With a turbo, I'd be worried about this VQ. In NA form, it's hardly a concern.

I think to many people look at the A/F ratios for high rev motors (ie Hondas) or forced induced motors and think that the NA VQ should follow the same A/F pattern. It's simply not true. A VTEC Honda revs to 8000-8500rpms and does so VERY quickly therefore it needs the rich A/F safeguard. Same with turbo cars, when boost hits, the draw in of air happens very quickly and the A/F needs to be rich to compensate for additional 02 and to reduce any detonation problems, which could be catastophic in an instant.

IMO, what I'm seeing is the Crawford cats don't do squat. Honestly, this is the first dyno I've seen for them too on this site or the 350Z site. The conditions, car, and dyno were the same. It looks like a solid test to me.

 

If your comfortable with a near 16:1 A/F ratio at peak TQ then thats cool, I know I would not be..The crawford cats are doing exactly what they are supposedto do,lean out the A/F mixture Lean generally makes more power,but at a certain level when you go leaner and make LESS power the motor is talking to you..Its telling you it is experiencing knock and pulling timing,causing a loss of power..He needs to add more fuel and less air to make optimal power..What this dyno chart does prove is that by leaning his A/F he made less power...

 

^^Which is prob. why he needs a UTEC??

 

Here we go again... Look I was asked by the original poster to come to this thread and give my opinions,that is what Im giving..His A/F is way to lean and something is not correct on his car.So either he can REMOVE his CRAWFORD cats and GAIN his HP back or he could look into a form of engine tuning whether it be a UTEC,EMANAGE,REFLASH whatever...Im not getting into a debate over this again..I could honestly care less what he chosses to do,What do we know..We only SPECIALIZE on the VQ motors.. Whatever advice you give him, we probably tried it two years ago already, FYI..

 

I really tried to have another reading done today but couldn’t make appointment with any DynoJet shops within 20 miles radius. First one that I have is on Thursday at Turbotrix Racing ($125!!! for 3 runs), which I will go to unless I arrange somewhere else earlier. After I have another A/F printout I will visit MRC.

Tomorrow I will see Service Manager at local dealer.
I went to work today with the car and nothing unusual did I see, hear or smell.

On DynoDay two weeks ago I have seen 4 printouts and all had 14+ AF. Dyno operator also told me last time that what he have seen is 14s on all Gs even for someone with body-kit only.

https://g35driver.com/forums/attachm...2&d=1132507215
https://g35driver.com/forums/showpos...3&postcount=67
https://g35driver.com/forums/showpos...14&postcount=1
and I think Frostydc4 was also above 14

However this one is mostly below 14
https://g35driver.com/forums/showpos...65&postcount=9

I would like to have 13.1 A/F across entire RPM but not at the cost of loosing remaining 30K miles or almost 3 years of warranty.

Peace. I have asked MRC for opinion in PM and I thank you.

 

I am almost inclined to believe that their 02 sensor was bunk...
PS call Crazy Horse Racing in south Amboy ask for Chris,tell him I reffered you.Their rate is $100 3 pulls with A/F..Thats $25 less right there..We use his dyno till ours arrives in Late February.Were getting the Dyno Dynamics load based dyno,its the same one APS uses..

 

Questions asked:
Is there safe highest A/F before ping? Can Consult-II display A/F? Will disconnecting O2 sensor from cats or header (in order to accurately measure A/F) throw CEL?Should I run diagnostics?Does ECU adjust-compensate for different air or fuel grade at WOT?What is ECU open loop at WOT?How do they fix too lean condition? Would 1 step colder spark plugs help?
Pretty much unknown

 

Trouble shooting is difficult,but can be done with a timeline principle.Look at a timeline of what you have done or changed on your car since you last dyno,and go backwards eliminating problems one at a time. For example if the cats were the only thing you changed in the equasion since you last dyno,one has to conclude the cats are a problem,are causing the problem,contributed to the problem,or are magnifying the problem...

 

I called CrawfordZ yesterday and Doug told me that my 12/3/2005 dyno had some kind of glitch. Also that ECU should not be reset but instead let few days pass before doing dyno.
Based on my experience, I can only say that their customer service is timely and very professional.

Went to Crazy Horse Racing and did 3 runs.


Below is comparison of all of my three dyno days. First two were made at TT Performance Parts on DynoJet Model 224x and third one was done yesterday at Crazy Horse Racing on DynoJet Model 424x.



Conclusion? None? Too lean to run safely? Too lean to make peak power. Just like with my three last wheel alignments where each of three different machines (2x Hunter and 1x John Bean) give me different readings. This aftermarket industry is blooming because of fools like me, but hey I am learning. In addition to learning experience, reason for my dyno threads was to post before and after dyno with CrafordZ cats because after many searches I could not find single one while everyone is saying how OEM cats are most restrictive part in exhaust chain. Maybe you will have more success.

Sorry for raping you with many bytes of my dynos (=long post).