I have been hearing this term more and more recently. However, I am not quite sure what it means. Anyone out there care to enlighten.

Thanks.

JWT Pop-Charger/Z Tube * Clear Corners
20% Tint * HyperGrounding Kit * Iforged Evo's
OEM Chin Spoiler * Kinetix Plenum (on order)

 

My understanding (which may be wrong) is...

It has something to do with not getting enough fuel in your air/fuel mixture. Fuel is sprayed onto your piston. This fuel "cools" the surface of your piston. If you don't spray enough coolant (or fuel) the piston can get a hot spot and this hot spot could eventually "blow" and at a very minimum you'd need minor engine work.

I'm sure someone can give a much more detailed explaination. Might want to check out the "how stuff works" website too.

<font color=blue>The above statements are only my take on the issue. If you disagree with anything I typed then you are 100% right!</font color=blue>

 

In theory, ideal combustion (i.e. Stoichometric) occurs when there are 14.7 parts of air to 1 part of fuel. At idle, that's the reading you'll see on an A/F gauge.

However, under wide-open throttle as the engine RPMs increase, the car needs more fuel to act as a cooling agent to prevent pinging and detonation. The more taxed the engine is, the more important this extra fuel becomes. Forced induction (turbo, supercharger) on the G35 is most safe when the A/F ratio is just below 12.0 above 5000 rpms.

On a naturally aspirated G35, even though an A/F ratio as rich as 12.0 is not necessary or even desired, if the A/F ratio becomes too lean up top (above, say, 13.5 but I'm guessing) the ECU will begin to pull timing if it senses that there is not enough fuel to cool the pistons and run safely.

So what causes the engine to run leaner than normal? Well, basically anything that increases the amount of airflow into or out of the manifold. So cold air intakes, plenums, high flow cats, test pipes, Y-pipes, open exhausts all contribute to leaning out the air-fuel ratio.

In some cases, the ECU can adapt to the increased airflow and inject more fuel. That's why resetting the ECU is what folks on this board recommend doing after every airflow-related modification. In some cases, especially with lots of these mods, the ECU needs to be reprogrammed (via Technosquare) or tricked (via a piggyback computer like the SAFC-II) into providing enough fuel.

--Steve

 

If you make changes in front of MAF the calibration can be thrown off........more or less air is flowing but the MAF does not read it correctly ..........the MAF is 3% accurate at high flow rates with oem air box/filter in front of it.

The factory software is always excessive rich at WOT to provide safety and long term durability.

Using a dyno jet causes problems because the acceleration is twice as fast as normal......the software gets confused in this unrealistic non real world situation......something that cannot happen on the road!

A Mustang Dyno with eddy brake set to real weight of car and loads emulating air resistance will accelerate at a real [highway] speed thus the AF will read correctly!!!!!!!!!!!!

 

From a A/F safety perspective, I think the advantages of a DynaPack dyno compared to a DynoJet are pretty obvious.

--Steve

 

All this talk about running lean or rich starts to get confusing. What should some expected numbers be for a G35 coupe's A/F ratio be? Here is a link to my stock dyno run on a dynojet. I dont know if referencing this chart could help explain the stock numbers to be good, bad, or on target.

My Stock G35 Dyno

someone mentioned 13.5 and higher is bad. Are they right? How my looking?

 

are there any a/f mixture electronic piggy back control systems that would work with the stock ecu? I am only wondering because i would like to keep doing more air mods exhaust in about a month or so and then plenum then either stripped out stock cats or high flow aftermarket ones.... But i have 2004.5 so the ts ecu isnt out yet for my car according to the forums, so i wouldnt want to run lean expecting tha to come out and do some type of damage or something to my car from not getting enough fuel. The ts ecu would definatly replace some kinda pigga back system eventually, but i wouldnt mind paying 300-400 dollars on a system and then selling it and losing a lot of money if that would work. Performance shouldnt be looked at in terms of dollar amount... it should only be looked at in terms of fun and seconds (maybe not in that order tho)

2004 Black on Black g coupe 6spd.... aluminum pedals, clear corners, z tube, and pop charger. soon to have 19" volk gt-c's and PIAA xtreme whites in the clearance and corners
Houston Texas

 

The Apexi AFC-II controller can certainly be used. In the dyno posted by a previous poster, you'll notice that the A/F ratio steadily declines at WOT. If there were spikes or if the A/F ratio stayed above 14 at 5500 then I would be concerned.

Unfortunately, I don't know exactly what "safe" is for an N/A car above 5000 rpms. For FI, it's below 12.0.

--Steve

 

Safe and ideal for power are far apart because the power on time is so variable lots of difference in a quarter mile run and a top speed test. The cooling system can only transport so much heat. Lots of difference between 40F and 120F in Arizona.

The factory had to assume someone would run the G35 for a few minutes WOT at max speed therefore they made the AF ratio overly rich beyond the power peak rpm and the Summer protection software starts reducing the ignition advance when the head output coolant temp goes above 195F [1 degree in 5F steps to a max of 5 degrees at 215F].
The knock sensors add to this protection by further reducing ignition advance just at first hint of knock and progressively more till the knock stops [usually long before you can hear knock].

Normally 12.2 AF at torque peak rpm and 12.5-12.75AF at HP peak rpm is ideal but that depends on the fuel knock index and combustion chamber temperature.
If the cooling system is marginal [they all are not designed to get rid of 100% of wide open power indefinitely because the rad would need to be to large and the grill opening would limit top speed]. Industry norms are to use EXCESS FUEL to help remove the WOT HEAT from heads by forcing the evaporation of fuel that never gets burned which SLOWS down the flame speed and temperature. Not unusal to see 10:1 AF ratios near redline as a way to hint to owner to back off.....make the engine boggy and unresponsive.

Going 10-20% rich [12.2>11-9.75AF] does affect power very much going 10% leaner 12.2>13.5 AF] causes a 5% drop in power and a 12% rise in combustion temperatures.

There is an IDEAL range [16-17.5 degrees ATDC] where the maximum pressure from combustion creates the maximum downward push on the pistion. By slowing down the flame speed [the time from spark to peak pressure] the peak pressure occurs LATE after the best moment.

You could either change the timing [spark advance] or change the mixture ratio to change the time when peak pressure occurs.

In NASCAR and racing where WOT fuel economy matters you set the AF ratio correctly to peak power and install a cooling system that is adequate. On a street car you use the excess fuel trick.......after all no one cares if it burns [passes out unchanged] 20% too much gasoline for 15 or even 60 seconds.

 

Your usual fine job, Q45tech.

Great explanation, and glad again for your willingness to share your knowledge and expertise!

P.S. - Remember, there are HUNDREDS of us reading these threads and learning, at any given moment, and we appreciate your efforts.

Sport Sedan Fan - 2004 6MT Sedan
Sport/Navigation/Premium/Aero; "Invisiguard" Bra, Madico Onyx Tint
Obsidian Black/Graphite & "Titanium"
SHE'S SILVER & BLACK - GO RAIDERS!

 

Are you just making this all up?
I think its time to change your name to G35tech! Good job as always and after reading this post I actually feel a little bit smarter....


Kevin
www.KPtechnologies.net
AIM: KPiersonTec
04 DG Coupe / VDC Memory
OEM Remote Window up mod
Procharged / Crawford / TS