All,

I need some more help fighting Infiniti with my warranty issue. Peninsula Infiniti is claiming that my A/F Ratio is too rich which contributed to my "engine failure". Any STOCK sedan owners have A/F ration numbers for me to compare with. I need this info ASAP. Thanks in advance.

 

If anything your CAI and Borla exhaust leaned the engine at WOT otherwise there would be no power gain - if there was any in the first place!

Other than the dubious ground wires are you sure there is NO OTHER MODS than you mentioned in the first post?

Don't assume that dealerships know very much about engines!

When is your meeting with the Infiniti Regional Rep?

 

No other mods, just the CAI, exhaust and grounding kit. Everything else is cosmetic.

 

I got a question, if your computer was reprogrammed for those mod's would the A/F mix been different. anyone know the answer to this question

 

The WOT AF is extremely over rich compared to a 12.2AF [usual optimum for HP peak] because going super rich doesn't affect HP as much as going leaner than optimum.

Even a 10 AF may only be down 5-7%.

Louder Exhaust work by letting more of the 10% residual burned gases out of the cylinder...........1-2% less [8%]residual means 1-2% more fresh air can get into cylinder.

Most of these mods create at most 10 HP compared to stock so 3-4% leaner is insignificant like 11.0 AF > 11.4 AF

 

How are they determining A/F ratio on a dead engine? Are they looking at the plugs? Are they examing the cyl. walls for evidence of too much fuel "washing out" the cylinders? Please explain so we can assist you.

FWIW, there should be some baseline dyno results out there with A/F curves

'04 G35X Graphite/graphite, NAV, wood, premium

 

Unfortunately most AF ratios taken [reproduced] on dyno's sheets are not from precision temp corrected sensors screwed into exhaust manifolds to replace the primary O2 sensors............tail pipe test is far from accurate because of the way cats modify the exhaust stream.

 

So are you saying that 12.2 A/F ratio at WOT is what a stock G35 sedan would produce?

 

Over the last 30 years, this 12.2 [+-4%] AF ratio [in the cylinder] is pretty much the standard for creating peak HP assumming that the ignition event is timed so that the peak BMEP occurs at 15-17 degrees ATC.

As the AF changes the flame spread speed varies and thus the ignition advance needs to vary. Unfortunately each cylinder is different [the air flow varies and the injector varies] so you set the worst case to 12.2 which means some may run at 12.0 or even 11.8.

Exotics use a pressure sensor per cylinder [and a seperate fuel trim controller] to optimize each cylinder with different AF and ignition to squeeze the last HP out.

To protect the motor from WOT in Summer the factory uses less than optimum advance and richer than optimum AF to provide extra cooling for heads, piston crowns and exhaust valves to increase durability. The cooling system is not designed to run WOT for long thus the extra fuel cools things down and the unburned gasoline vapor just passes out the exhaust.

The following paper may help understand:
http://www.fs.isy.liu.se/Publication...1649_PB_AP.pdf

Even though 14.7AF is optimum for emissions and necessary for cats to work correctly, addition fuel is necessary to create a 98% probablity that every oxygen molecule will react so the oxygen must be surrounded with more.

This may help:
http://www.engr.colostate.edu/~allan...e1/page1f.html

If 500 mile engine life is acceptable you go to the ragged edge