Bugermass

I agree that with certain motors with certain pistons, with certain build specs, there is a need to run richer.. But so far what I've seen with the newer 4G63, they are fine between 12-12.5 with all else being well and good.

And I agree with crispspeed on the EGT thing.. In a normal gasoline burning engine, the best use for EGT is with one in each cylinder for checking cylinder balance.. There are so many variables that affect EGTs thats its not really a good tool to use as a benchmark for anything.. I've actually seen a test where someone purposly pushed a motor into knock by adding excessive timing and the EGTs still continued to drop even well into knock.

Golden

iTrader: (1)

So you mean the 4B11T?

Bugermass

Lol, yeah thanks for the correction. Too many engine codes to remember. I tune so many different kinds of cars.

djuosnteisn

I think the DI guys get away with lean afr ratio's cause the directly injected fuel atomizes in the combustion chamber and cools things off significantly. With PI i wouldn't want to go leaner than 12.5 personally.
...But i am newb and this was an interesting read.

Bugermass

The reason for running rich is to provide a layer of fuel to insulate the cylinder walls pistons, and chambers basically quenching the flame front when it approaches.

Direct injection is not creating any more "insulating fuel" than port injection is. GM is just smart and says HEY, we don't have to run that rich.. The direct injection creates a much more evenly atomised mix which makes it less detonation prone. BUT detonation isn't the issue.

Detonation happens AFTER the spark event. Basically what you have is your main spark kernel and flame front. Normally this should progress outwards from the ignition source smoothly and uniformly.. But you have these pockets of un-uniformly mixed gas and air around the outskirts of the cylinder. What happens is after or during the combustion event these pockets of (end gas) will ignite/explode (un-uniformly/violently) ahead of the flamefront from heat and pressure and cause pressure spikes that resonate the cylinders (ping).. This is what cracks pistons and spark plug insulators. NOW.. If your knock is occuring because of un-uniformity then running a LEANER mixture can reduce knock by reducing these pockets.

What melts pistons is pre-ignition or too much heat with crappy cast metals, or an improperly clearanced engine. And thats a whole other topic..

Knock can also occur from too little timing.. First off when you run less timing your exhaust valves take more heat.. Secondly when you run less timing you build pressure and heat at a different point in time in relation to crank angle.. Basicaly the cylinder pressures are higher sooner with less flamefront progression elevating the possibility of end gas detonation. Its all a balancing act, and these things happen in single digits of degrees and microseconds..

An example I had a car come in yesterday (N/A) that was E-tuned.. I put it on the dyno and the E-Tune made ok power but had 33 counts of knock. This knock was mainly on cylinder 2, a little less on cyl 3, and none on 1 and 4.. I looked at the individual trims and the E-Tuner, had pulled 3 deg of timing on cylinder 2 and 3 and added 5 percent more fuel on 2 and 3.. First thing I did was put the ignition trims back at 0.. Knock count on the next pull was 16.. I went back and added 3 degrees advance to cylinder 2 and 2 degrees advance to cylinder 3. Knock count was 4.. The AFRs all this time were about 12.8 where the knock was occuring. I 0ed out the fuel trims on the 2 cylinders and the mixture went to 13.6 AFR, with 0 knock count and I picked up 10HP from about 3200 to redline..

Basically what I'm saying is yeah, flooding the engine with fuel and pulling lots of timing can lower knock at the cost of power. BUT, there are times when you can go leaner and mabey depending on the engine add a bit of timing and get rid of that same knock AND gain power at the same time.. I'm not telling anyone to go run 13.5AFRs on a boosted pump gas motor. But 12-12.5 .. Not unreasonable in most cases.

Just my $.02, take it or leave it.. I only do this everyday for a living..

tephra

iTrader: (6)

leaner or richer?

I would have thought that richer would be better?

Bugermass

The more fuel molecules in the mix, the more fuel molecules availble to create pockets.. In my own theory I think that a leaner mixture would force better distribution of fuel moecules since theres more empty space to fill.. I have no hard proof of this, its just my theory based on what I DO know and what I've seen from testing on the dyno.

Bugermass

All I can say is that what I have been doing has been working very well, and most of the time makes more power and runs better. I can't tell you how many customers I've had call me shortly after getting a tune saying how "smooth" their car runs..

tephra

iTrader: (6)

yeah im not doubting you - I am just trying to understand the physics

Bugermass

Me too lol... I kinda work backwards.. I try stuff, then I take the results and try to figure out why.. Somtimes its hard to nail it down because what I find is so contridictory to the "norm" but here and there I'll talk to somone or read somthing and then the peices come together and it all makes sence. I'm not claiming to be 100% correct, or know it all, I'm just putting out there what I believe at this point in time from years of tuning and trying different things and reading very interesting an indepth papers on things not directly related to the application but having the same fundamental components. I wouldn't risk my reputation as a tuner by putting out info that hasn't worked for me..

Bugermass

What I find is theres alot of GOOD info out there, but its almost never the complete story. Usually its great advice for a certain instance or within those parameters. So you kinda have to take bits and peices of contradictory information and figure out what is different between the two cases that lead to contradictory results.. Alot of times by doing that you figure out somthing that neither of the two original sources even though about.

ScottSpeed21

iTrader: (7)

Very interesting theory...

As you said, completely different from what's usually considered the "norm", but it completely makes sense the way you explain everything

E6-X

iTrader: (4)

leaner or richer ? hmmm, i think it also depends on the application of the car . . . whether using it for DD, Track or Drag. Leaner for DD & Drag and richer for Track purposes. Too lean as we know to hot but for a short period of time i think it's ok and richer it does cool things down a bit but on the other hand it creates hotspots (not always) but for track it will be alot of heat so imho a little richer.

what's the perfect number then ? hmmm who knows ... LOL i'd say between not richer than 11.5 and not leaner than 12.5 AAFR depending on usage and fuel octane rating, weather conditions, location, tuner experience, mods, particular engine & etc.

Clipse3GT

iTrader: (10)

Well I decided to test this little theory...since I just love trying new things, especially with tuning.

So basically I moved peak torque to 12's and then peak horsepower to 11.5's

Previously it was 11.5 peak TQ and 11.0 peak HP.

This is from VDR 3rd gear pull. Everything was the same on the map, except fueling changed.

Notice the gain 5000 to 7000 (green/yellow) in TQ and HP. 93 octane Shell V-Powa

Mods listed below...

UT_EvoX

x2

You'd never want to tune for 12.5 AFR on a track car. Let's completely ignore detonation. That extra fuel injected when you're running ~11.0 AFR carries away heat in the intake charge when the atomized charge phase changes from a liquid to a gas... aka evaporates. The heat that was previously present in the combustion chamber charge is now contained in the faster-moving gas-phase gasoline particles.

We all know gasoline doesn't have as high of a latent heat of vaporization as, say, methanol does.... but it's enough to keep a high HP engine from melting something. No high-output 4B11T is going to last under sustained WOT conditions @ 0.85 lambda unless you are running something other than pump ****. i.e. E85. That extra heat is going to melt something - remember, pistons are aluminum. 2618 aluminum (used in high-strength forged pistons) has a melting point of about 950 degrees F. Combustion temperature inside a high-output turbocharged engine is well over 2000 degrees. Guess what happens when that heat overcomes the boundary layer around the piston crown, and any carbon deposits that are on the surface of the piston?



CP 2618 alloy forged piston from a ~600 WHP 3.0 L V6 @ 23 psi

Granted, some detonation was occurring during that ... basically the engine was tuned for 12.2 AFR @ WOT with a huge shot of methanol, and minimal knock (count of 2, intermittent). This happened during a sustained 160 mph pull... on a closed road. Just too little fuel, but minimal knock because of the shot of methanol + water.

YMMV as always, but just remember 12.x AFR is not safe for sustained WOT operation on pump gas. Plain and simple.