Dyno Test

[Steve M]

Ahh interesting I just assumed that stoic was the same or very similar for most gas and didn't change until you got into ethanol or some other exotic fuels....

The simple work around to this is to tune by lambda instead of air/fuel ratio (AFR), which is what any tuner even remotely worth his/her salt is going to do because there is simply no way to know exactly what mix of fuel is in the tank. The stoich AFR value for gasoline is 14.7; for E10 (which is what nearly all pump gas in the US is) it is closer to 14.1. The stoich lambda value for both is 1.

Oxygen sensors are lambda sensors - always have been, always will be. The numbers people are more familiar with seeing take that lambda value and multiply it by 14.7, assuming they were using gasoline. It's been many years since you've been able to reliably find ethanol-free gas - I've usually only seen it around marinas due to the known issues with using ethanol in a high moisture content environment.

Bottom line: tuning in lambda gets you around this nonsense. You still need to find what WOT lambda value gives you the best power/torque for your application. If you are having a vehicle tuned, pick the gas you intend to run most of the time and tune to it. It's that simple.

[Nth Moto]

Stock injectors - 810bhp.

Aaron,
Have you run a H/C car on the dyno and swapped out the injectors (stock vs performance injectors)? Have you seen any performance gains or losses?

No Michael, not back to back in the instance that the car didn't need the increased fuel flow to justify the injector change itself. In that case there are gains obviously, because we can achieve our target lambda.

Steve is right on with Lambda vs AFR. Something that has to be considered if this topic stays technical is response rate of different types of sensors, and then the response and/or filtering level of the device being used to monitor it. It can get kind of interesting when that comes into play.

[Jack B]

Here is an old white paper on AF tuning versus different race gas combo's :

================================================== =========
Race Gas Stoich Rating Tuning Considerations
Well I have seen questions from time to time about adding race gas without tuning which can be a very expensive experiment. I am going to explain how stoich effects AFR. Hopefully in simple format.

I am not going to get into MAF transfer functions or other tuning functions.This is just about fuel.

First lets define a few terms:

AFR: Air Fuel Ratio

Stoich Rating: In simple terms is the AFR to have chemically complete combustion that is neither rich or lean. For Example most pump gasoline is about 14.64 to 1. Which means 14.7 parts of air to 1 part of fuel.

Lambda: Is a term that is utilized when tuning. In basic terms think of it as an adjustment to your stoich rating when tuning AFR. For example with pump gas tuning .80 lambda, 14.7 x .80 = 11.76 AFR target.

Lets assume your car blower car has a nice tune that gives a perfect 11.8 AFR under WOT with pump gas.

So now it is race day. We add some timing to our tune, drain the fuel tank, and fill up with some high octane unleaded VP109.

We go for a blast down the 1/4 mile while datalogging and see the A/F is reading 12.8 then make a quick trip to the bathroom only to find out they are out of toilet paper -lol.

There are a few factors here to consider.

The stoich rating of VP109 is 13.41.
Most wideband A/F modules are calibrated to 14.7 pump gas stoich.

So this is the formula to determine the true A/F for the run.
AFR/Wideband Stoich x Race Gas Stoich
12.8/14.7*13.41= 11.7 AFR on Race Gas

So you may think 11.7 sounds safe but we must remember the VP109 stoich is 13.41. So 11.7 AFR = .87 lambda. For the most part a safe lambda value is .80 to .82 for a forced induction mustang. I prefer .80

So we take VP109 stoich of 13.41 x .80 lambda = 10.73 AFR
This is the AFR (10.73) I am tuning for.

Keep in mind this is not what will display on your wide band as it is programmed to 14.7 stoich. You must convert the AFR.

AFR/Race Gas Stoich*Wide Band Stoich

10.73/13.41*14.7 = 11.76 AFR is what I want to see on my wideband when running VP109.

Just to reiterate 11.7 on the AFR display with VP 109 is really a 10.7 AFR.

Ok so hopefully you are not totally confused.

There is a simple solution to all of this madness. The SCT Advantage software has a Scalar for Stoichiometric Air Fuel Ratio. You simply enter the correct value for the fuel you are using and all lambda fuel calculations will be based on this value. Then just do the first formula conversion to determine what you should be reading on the AFR display. Some AFR modules may be able to be programed to the correct stoich.

Or leave the stoich in the tune and wideband at 14.64 and calcualte what AFR you need to read on the wideband for the fuel that is used. (This is how I did it in the past, but I find it easier to change the stoich scalar)

This is why you have to exercise caution when mixing race gas and pump gas as you do not know the true stoich of the mixture. The leaded race fuels have a stoich that is closest to pump gas. I always drain my tank before putting in the race gas. When I mixed fuels in the past I didn't notice a drastic change in AFR, but when I have 100% unleaded race gas it really leans out with a 14.64 stoich scalar in the tune.

The other caution is the winter (oxgenated) gas we get in Arizona. I noticed the car leaned out in the winter when it was tuned on the better summer blend. A 14.1 stoich scalar works for the AZ winter gas if your initial tune was based on the summer blend.




Race Gas Stoich Ratings

Sunoco MO2X UL – 14.5
Sunoco 260 GTX – 14.4
Sunoco 260 GT – 13.9
Sunoco 260 GT Plus – 13.7
Sunoco Standard – 14.8
Sunoco Supreme – 14.9
Sunoco MO2X – 14.5
Sunoco HCR Plus – 14.8
Sunoco Maximal – 15.0
Sunoco MaxNOS – 14.9

Turbo Blue Unleaded (100 octane) -13.9
Turbo Blue Unleaded Plus (104 octane) - 13.7
Turbo Blue 110 - 14.7
Turbo Blue Advantage - 14.9

[Steve M]

Something that has to be considered if this topic stays technical is response rate of different types of sensors, and then the response and/or filtering level of the device being used to monitor it. It can get kind of interesting when that comes into play.

Are you talking about this in regards to WOT operation, or all operating conditions?

I've always wondered why more manufacturers (or high end shops) don't go with widebands so you could do closed loop WOT operation, but when I started to think about it, it just sounds like a pain. You'd need a sensor that had a fast enough response, and you'd need to close that loop really fast too in order for it to work since things are happening so quickly under those conditions. I'm not even sure what the state-of-the-art is in the automotive world, but I'm not sure it would be worth it in the end. A static look up table is certainly sufficient - just add more fuel when needed (high IAT/ECT/etc.) and call it a day...well, provided you have a known, stable supply on the fuel side. I know some cars do come with widebands these days, but I'm not sure what it really buys you.

[Jack B]

Are you talking about this in regards to WOT operation, or all operating conditions?

I've always wondered why more manufacturers (or high end shops) don't go with widebands so you could do closed loop WOT operation, but when I started to think about it, it just sounds like a pain. You'd need a sensor that had a fast enough response, and you'd need to close that loop really fast too in order for it to work since things are happening so quickly under those conditions. I'm not even sure what the state-of-the-art is in the automotive world, but I'm not sure it would be worth it in the end. A static look up table is certainly sufficient - just add more fuel when needed (high IAT/ECT/etc.) and call it a day...well, provided you have a known, stable supply on the fuel side. I know some cars do come with widebands these days, but I'm not sure what it really buys you.

I have solstice GXP, it has a wideband but, still uses a fixed map for wot.