Air Fuel ratio questions

[LoserbabyS13]

I know have my car running great pulls like a raped monkey. But it likes to idle best at about 11.0:1 or richer. This seems pretty rich. I have it tuned to run about 11.5-12.5 through out the rest of the rpms but the idle just wont be stable or smooth unless my LM-1 is showing 11.0 or richer. Is this normal????

[KaZ (VaBch)]

On a turbocharged car, richer is safer to a point... don't want to be washing the cylinder walls... but don't want to go lean... =) . On an NA you'd want 14.7, or a touch richer. On a turbocharged car, you want is I've been told between 11-12 or so for safety due to intake temps etc in the combustion chamber. Also, the higher the boost, the higher the intake temps... so keep that in mind while tuning.

[LoserbabyS13]

I know most of that but I am concerned with my idle being so rich.

[float_6969]

have you tried leaning it out? I'm wonder if your LM-1 is giving accurate readings. You might try taking it to a dyno and hook it up to their wideband and see what it says. To be honest, I'm suprised that it will idle at 11:1.

[LoserbabyS13]

I tried leaning it out and it wants to die. I am fairly sure its reading accurate cause I have calibrated it several times and if I take it out to the plain air it reads the content of 02 in the air to exact point 20.9% o2 in air. It will barley idle at 12:1

[float_6969]

Are you running colder plugs? I'm still baffled by this. On the stock ecu, mine actually runs so lean at idle that it falls off the edge of my A/F ratio gauge (autometer). And I don't think that is abnormal. I don't really know that this is something to be concerned about, but it does seem odd, and kinda wasteful. Maybe we can get Dee in on this one....

[LoserbabyS13]

I wonder if an old fuel pump that is not giving enough pressure couold cause the injectors to no be able to atomize the fuel so I am having to dump more in to get it the stablize and I am reading the extra fuel that could not be burnt because of a lack of fuel pressure. I mearly guessing as I dont have an fuel pressure gauge but I do know that my fuel pump is 200k or more so.

[float_6969]

I think that is a valid train of thought, but if that were the case, then you'd have problems maintaining the proper A/F ratios in the higher rpm ranges.

[LoserbabyS13]

True. I do seem to be able to have a fairly steady a/r ratio but it does fluctuate although I can attribute that to not having the SDS perfectly tuned yet. I just need to get on a dyno!

[boost_boy]

Quote »I just need to get on a dyno[/quote] You don't want to go put your car on a dyno whilst having driveability issues. Tuning a standalone is best done once you've referenced daily driveability. Your system is definitely not tuned correct because you shouldn't be smoking at all. Just because you get it to idle okay doesnt mean that you're anywhere closer to having the system somewhat dialed in. You must be able to have some fun on the street before you go spend money on dyno time.

Dee

[LoserbabyS13]

I never said I was smoking. The idle is the only thing that is not 100%. I have been driving and I am at about 11.5 12.5 range when driving under full load I tend to be on the richer side. I am running total timing of 26*. I am not really having drivablitiy issues anymore either.

[KaZ (VaBch)]

Here is something for your reading pleasure... got this from Innovate Motorsports... they're new Newsletter just came out... good read.

Quote »Application Note: You CAN be too RichBy Klaus Allmendinger, VP of Engineering, Innovate Motorsports

Many people with turbochargers believe that they need to run at very rich mixtures. The theory is that the excess fuel cools the intake charge and therefore reduces the probability of knock. It does work in reducing knock, but not because of charge cooling. The following little article shows why.

First let’s look at the science. Specific heat is the amount of energy required to raise 1 kg of material by one degree K (Kelvin, same as Celsius but with 0 point at absolute zero). Different materials have different specific heats. The energy is measured in kJ or kilojoules:

Air ~ 1 kJ/( kg * deg K)Gasoline 2.02 kJ/( kg * deg K)Water 4.18 kJ/( kg * deg K)Ethanol 2.43 kJ/( kg * deg K)Methanol 2.51 kJ/( kg * deg K)

Fuel and other liquids also have what's called latent heat. This is the heat energy required to vaporize 1 kg of the liquid. The fuel in an internal combustion engine has to be vaporized and mixed thoroughly with the incoming air to produce power. Liquid gasoline does not burn. The energy to vaporize the fuel comes partially from the incoming air, cooling it. The latent heat energy required is actually much larger than the specific heat. That the energy comes from the incoming air can be easily seen on older carbureted cars, where frost can actually form on the intake manifold from the cooling of the charge.

The latent heat values of different liquids are shown here:

Gasoline 350 kJ/kgWater 2256 kJ/kgEthanol 904 kJ/kgMethanol 1109 kJ/kgMost engines produce maximum power (with optimized ignition timing) at an air-fuel-ratio between 12 and 13. Let's assume the optimum is in the middle at 12.5. This means that for every kg of air, 0.08 kg of fuel is mixed in and vaporized. The vaporization of the fuel extracts 28 kJ of energy from the air charge. If the mixture has an air-fuel-ratio of 11 instead, the vaporization extracts 31.8 kJ instead. A difference of 3.8 kJ. Because air has a specific heat of about 1 kJ/kg*deg K, the air charge is only 3.8 C (or K) degrees cooler for the rich mixture compared to the optimum power mixture. This small difference has very little effect on knock or power output.

If instead of the richer mixture about 10% (by mass) of water would be injected in the intake charge (0.008 kg Water/kg air), the high latent heat of the water would cool the charge by 18 degrees, about 4 times the cooling effect of the richer mixture. The added fuel for the rich mixture can't burn because there is just not enough oxygen available. So it does not matter if fuel or water is added.

So where does the knock suppression of richer mixtures come from?

If the mixture gets ignited by the spark, a flame front spreads out from the spark plug. This burning mixture increases the pressure and temperature in the cylinder. At some time in the process the pressures and temperatures peak. The speed of the flame front is dependent on mixture density and AFR. A richer or leaner AFR than about 12-13 AFR burns slower. A denser mixture burns faster.

So with a turbo under boost the mixture density raises and results in a faster burning mixture. The closer the peak pressure is to TDC, the higher that peak pressure is, resulting in a high knock probability. Also there is less leverage on the crankshaft for the pressure to produce torque, and, therefore, less power.

Richening up the mixture results in a slower burn, moving the pressure peak later where there is more leverage, hence more torque. Also the pressure peak is lower at a later crank angle and the knock probability is reduced. The same effect can be achieved with an optimum power mixture and more ignition retard.

Optimum mix with “later” ignition can produce more power because more energy is released from the combustion of gasoline. Here’s why: When hydrocarbons like gasoline combust, the burn process actually happens in multiple stages. First the gasoline molecules are broken up into hydrogen and carbon. The hydrogen combines with oxygen from the air to form H2O (water) and the carbon molecules form CO. This process happens very fast at the front edge of the flame front. The second stage converts CO to CO2. This process is relatively slow and requires water molecules (from the first stage) for completion. If there is no more oxygen available (most of it consumed in the first stage), the second stage can't happen. But about 2/3 of the energy released from the burning of the carbon is released in the second stage. Therefore a richer mixture releases less energy, lowering peak pressures and temperatures, and produces less power. A secondary side effect is of course also a lowering of knock probability. It's like closing the throttle a little. A typical engine does not knock when running on part throttle because less energy and therefore lower pressures and temperatures are in the cylinder.

This is why running overly-rich mixtures can not only increase fuel consumption, but also cost power.[/quote]

[LoserbabyS13]

Found this on SDS's website "You will probably notice that your engine idles the smoothest when the mixture is fairly rich. This is normal."

http://www.sdsefi.com/techtunesds.htm

[LoserbabyS13]

I just though of something else that could be making my idle readings artificialy rich. I am running straight off of the dumb pipe with no down pipe or exhaust it is dumping the exhaust straight off of the turbo elbow.

[boost_boy]

Quote »I just though of something else that could be making my idle readings artificialy rich. I am running straight off of the dumb pipe with no down pipe or exhaust it is dumping the exhaust straight off of the turbo elbow.[/quote] This is major. You may also need to stick an orifice in your map sensor's vacuum line to restrict some of the vacuum. I got your email and I'll respond to it as soon as possible. And I wasn't saying that you said your car was smoking, just letting you know that it shouldn't be smoking at idle either.

Dee

[LoserbabyS13]

This is major. You may also need to stick an orifice in your map sensor's vacuum line to restrict some of the vacuum. I got your email and I'll respond to it as soon as possible. And I wasn't saying that you said your car was smoking, just letting you know that it shouldn't be smoking at idle either.

Dee

Thanks. I am sorry for the somewhat deffensive reply. I appreciate your help. My map values dont appear to be fluctuating but I am willing to try anything to get it to smooth out. The rpms stay the same but the motor kinda shakes a little bit more than normal at idle once I get the revs up past 1500 or so is smooth as ever.

[float_6969]

You didn't tell me about the open exhaust man! Jeez! Hehehe, no it's alright, I think that may have something to do with it though. And I guess you're right about them saying that it should idle rich. Maybe I'm getting a false reading because the exhaust temperature drops and the sensor isn't operating in the correct temperature range.

[r34 gtr]

yeah, i know when i got my car dynoed the a/f ratio read about 13.5:1 at idle, then dropped like a rock to 6.... im not sure why but my engine was idling alright at about 10:1 at one point (when we were desperately trying to coax the engine to run normally..). i didnt think they could do that but then again my engine is really wierd in many different ways.

- tim