EFI, Alpha-N vs Speed Density fueling Strategies

[Karl Owens]

I have found the Alpha N makes the car more consistent. The MAP sensor senses barometric pressure when the key is on and the engine is not running and makes adjustments to the fuel map accordingly, also at WOT there really isn't a difference between Alpha N and Speed Density unless you ave a really restrictive throttle body.

[Ed Wright]

Originally Posted by Karl Owens

I have found the Alpha N makes the car more consistent. The MAP sensor senses barometric pressure when the key is on and the engine is not running and makes adjustments to the fuel map accordingly, also at WOT there really isn't a difference between Alpha N and Speed Density unless you ave a really restrictive throttle body.

I have not found that at all. If you see a big change in Baro using Speed Density, as I explained earlier, it won't use the same cels in the V.E. table. If you have the V.E. Table correct, it will correct back to the same air/fuel ratio unless you tell it differently.

[Signman]

Originally Posted by Bobby Fazio

I thought Open Loop meant there was no such thing as a target A/F ratio since no correction is present? Basically it's a carburetor, no? What if it is 65 degrees and 500' DA during Stock Q1 and then 80 degrees and 2000' going into E1, wouldn't you have to make some VE changes? My stocker runs Open Loop Speed Density, Sequential fire, and was deadly to the .001 second during Q1 and Q2 but lost 1 tenth in Q3 and another tenth in E1 at the Summernationals because it got hot on Saturday.

I guess what I want to know is what method is the most consistent for bracket racing? Predictable dial-ins? And not having to hook the laptop up before or after every pass to add/subtract fuel or guess on a fuel setting before first round?

Bobby,
Cells in fueling table of FAST 2.0 are VE values for the given load and RPM. Those values are developed by achieving the optimal HP for that cell (generally done a a dyno) recording the AF ratio. That optimal AF ratio is input the closed loop AF table in the related cell and becomes the target in closed loop or your tuning target open loop when adjusting at the track. In speed density open loop the system does not adjust to the live AF input from the O2 sensor but does use air temp and manifold pressure to calculate the optimal fueling to achieve that VE value in each cell of the fueling table. In closed loop AF valued from O2 sensor is used in addition to air temp and manifold pressure.
Manifold pressure is effected by outside barometric pressure and engine vacuum with any restriction in the intake system.
Once the correct VE values are input the car should be very consistent and write time slips. In my case it does when I leave it alone.
With the FAST system you can run Alpha-N with MAP sensor open to atmosphere, I have not done it but others have been successful as XFI 2.0 has a change making it more to pressure changes seen from MAP sensor input. So you can use ALPHA-N and not need to tune over different or changing weather conditions.

See you soon!

[pbp1]

Originally Posted by Karl Owens

I have found the Alpha N makes the car more consistent. The MAP sensor senses barometric pressure when the key is on and the engine is not running and makes adjustments to the fuel map accordingly, also at WOT there really isn't a difference between Alpha N and Speed Density unless you ave a really restrictive throttle body.

Alpha-N will make your fueling more consistent, no changes, basically, an electronic carburetor. If you are using an Air Temp Sensor and a MAP sensor (or baro sensor in this case), then the ECU will make some corrections based on temp and pressure. The issue with this is that basically, every super stocker (with the exception of the new combos that come with a 4 bbl, 1000+ cfm throttle body) will actually begin to pull vacuum at high RPMs and with Alpha-N, there is no compensation for this. As Ed pointed out, in Speed Density mode, when the manifold pressure moves down into vacuum, it will not only move down a row or two in the table, but the ECU takes into account the fact that the air has become less dense in the manifold (because it is in vacuum) and fuels the engine accordingly. You are right that Alpha-N will make your fueling more consistent, but why do you want your fuel to stay the same when the air is always changing. When the system fuels according to the atmospheric conditions (inside the manifold), then your performance is consistent. The goal here is to make the car only speed up or slow down because of weather changes. That way, you can use your weather station to predict the change in performance. If your fueling stays static and the air changes, then your state of tune (actual A/F ratio) will change with the weather so you have to get your laptop out and chase the tune.
I have a perfect example of a test I saw that proved this theory. I had a customer, running in Speed Density, Open Loop, who iced his manifold to pick up some ET. This car has a near perfect calibration and the actual A/F lays right on the Target A/F even though it is not using any O2 correction. When he iced the manifold, we did not think about the fact that the Air Temp Sensor was in front of the throttle body. The thing was so lean that it died as soon as he left. This was because the air temperature actually entering the engine was much colder than the sensor was reading. We took another car with the same combination, same exact tuning strategy, but we put the Air Temp Sensor in the manifold. We iced the manifold and this time, the car picked up .080 and the actual A/F laid right on top of the target A/F again (just like it is supposed to). I pointed out to him that when we looked at a datalog from a run with no ice compared to a run with ice, everything was the same except for on the run with ice, the air temp was lower and the pulse width was higher. He asked how the ECU knew to add the perfect amount of fuel for the air temp change, I told him that the math in this thing just works! This is not some formula that we made up, this is based on the physical laws of the density of air. If this had been an Alpha-N tune, we would have had to guess how much fuel to add for the air temp. Using Alpha-N is like having a spreadsheet with 100 rows of numbers, and instead of using the auto sum function to add them together, you decide to add them with pencil and paper because you just don't trust the computer! Many guys use it with success, and more power to them. I just see a lot of benefits to Speed Density. It does take a little more work to correctly tune in Speed Density, but once you do, I am convinced it is more consistent and does not require re-tuning for different tracks.

[GUMP]

Originally Posted by pbp1

.....Once the ECU has calculated the density of the air, it just needs to know the volume and your desired Air/Fuel ratio to calculate how much fuel to put into the engine.....

.....Once you have found the VE value that causes the engine to run at your desired or target Air/Fuel ratio with no O2 or other corrections, then you have discovered the accurate VE for your engine at that particular load and speed (in that particular cell in the VE table).....

.....Once your VE table is properly calibrated, you have an accurate Air Flow table for your engine.....

These three sentences speak volumes.

I can have a new combination running well in Alpha-N within 3-4 dyno pulls. I have also found that it is pretty easy to dial a car from my log book once I have a couple of runs on it. I also don't have to worry about sudden changes in performance due to too much fuel correction.

[GUMP]

Originally Posted by pbp1

.
I have a perfect example of a test I saw that proved this theory. I had a customer, running in Speed Density, Open Loop, who iced his manifold to pick up some ET. This car has a near perfect calibration and the actual A/F lays right on the Target A/F even though it is not using any O2 correction. When he iced the manifold, we did not think about the fact that the Air Temp Sensor was in front of the throttle body. The thing was so lean that it died as soon as he left. This was because the air temperature actually entering the engine was much colder than the sensor was reading. We took another car with the same combination, same exact tuning strategy, but we put the Air Temp Sensor in the manifold. We iced the manifold and this time, the car picked up .080 and the actual A/F laid right on top of the target A/F again (just like it is supposed to). I pointed out to him that when we looked at a datalog from a run with no ice compared to a run with ice, everything was the same except for on the run with ice, the air temp was lower and the pulse width was higher.

This is one of the reasons that I like to turn off any IAT corrections. This stuff is great for heads-up runs if your tune is pretty good, but it can make a car harder to dial.

[Ed Wright]

If you tune it correctly, it is easy to dial, and there will be no "sudden performance changes due to excessive fueling corrections". Non issue.

IAT correction, if you put the sensor in the manifold where it belongs, causes absolutely no issues dialing the car. I see guys putting it next to the throttle body. That is wrong. Speed Density needs it in the manifold plenum.

Patterson's COPO is Speed Density, and Closed Loop. Seen it run? It corrects it's self very well.

[pbp1]

Dear Gump, I get it that you prefer to tune in Alpha-n, but you are completely mis-understanding how speed density works. I also zero out all air temp corrections in my tuneups. I am not talking about making corrections for changes in air temperature. In speed density, the ECU uses air temperature to determine the density of the air. Please go back and read my post again. Speed Density does not make the engine richer or leaner because of changes in air temp or barometric pressure, it just calculates the fueling, taking these things into account, and gives you consistent air/fuel ratios, even as pressure and temperature change. It is just doing the same thing you do with your tune when the weather changes, or you go to a different track with a different elevation, it just does it automatically and perfectly (if setup and calibrated correctly). If you read my example about icing the manifold, I pointed out that when the air temp sensor was in the manifold where it belongs, the speed density setup produced the exact same actual A/F ratio with the manifold iced as it did with the manifold not iced. It perfectly calculated the increased density of the cooled air even in open loop and the Air/Fuel ratio stayed exactly the same. I can send you the datalogs from these two runs showing air temp. Air/Fuel ratio, and pulsewidth. If you prefer to use Alpha-n, I wouldn't try to change your mind, but I started this thread because there is so much false and incorrect information that is passed on from racer to racer, I just wanted to put out the true facts about how Speed Density works. Based on your last post, you have clearly had some of this mis-information passed on to you. The fact is, the air is always changing, if you don't change your fueling to match these changes in air density, your engine will run leaner when you get in better air and richer when you get in worse air. These changes in air fuel ratio WILL cause unpredictable changes in performance. You are correct that Alpha-n is easier or quicker to dial in your desired air fuel ratio, but the problem is, when the atmosphere or elevation change, you have to manually change your fueling to match, and if you are really experienced at it, you can do a very good job. At the end of the day, the engine doesn't know or care what strategy you use as long as it is getting the amount of fuel it wants. But if your experience showed you that Alpha-n was more consistent than Speed Density, then you were doing something wrong. It definitely is a completely different process and takes a different approach. Anyway, I'm not trying to down your tuning, just correct the mis-information.

[pbp1]

Originally Posted by GUMP

These three sentences speak volumes.

I can have a new combination running well in Alpha-N within 3-4 dyno pulls. I have also found that it is pretty easy to dial a car from my log book once I have a couple of runs on it. I also don't have to worry about sudden changes in performance due to too much fuel correction.

You completely mis-read my statements, Speed Density does not make "sudden changes", unless the air suddenly changes, in which case you need corresponding changes in the fueling. This is a perfect example of the mis-information I hear over and over. What I have found when I discuss this with different racers and tuners is that if someone doesn't fully understand how speed density works, they don't trust it to calculate the changes in air density. The interesting thing is that it is using the exact same data that your weather station uses to predict performance.

[GUMP]

Take it easy. I am pretty sure that I don't have a learning disorder!

FYI. I am currently running two COPOs. One is running in Alpha-N. The other is running in speed density and closed loop. I believe that both tunes are pretty good. Both cars are extremely consistent. In the past I have had Stock computers, Accell Gen 6 and Gen 7, FAST, and Holley. I have always done my own tuning. I currently run the Holley HP system and find that it is far superior to anything that I have worked with in the past.

The reason for my previous comments was to make the point that Alpha-N with the corrections turned off is an extremely quick way to get a very consistent tune that will show good results.

The bottom line is that if you are going to run speed density, you need to know what you are doing. It takes much longer to define the cells to optimize the tune in all conditions. You corrections need to be spot on or the car will do dumb stuff. We are talking Stock Eliminator here. The MOV is normally very tight.

If it helps any, I drive Robin Lawrence at Holley nuts too!