EFI, Alpha-N vs Speed Density fueling Strategies
 

I’m sure this is going to bring out some strong opinions but I have been involved in some conversations lately about the Pros and Cons of Alpha-N vs Speed Density fuel tuning strategies. This prompted me to start a discussion about why I am a fan of Speed Density over Alpha-N.

For those of you that don’t know what I’m talking about, with modern EFI systems, there are two main strategies for fueling an engine, Alpha-N and Speed Density.

In Alpha-N mode, the system uses Throttle Position to measure the load on the engine. It then uses the throttle position and RPM to identify a cell in a 3D table that fuels the engine at that specific Load and RPM. In Alpha-N, the tuner puts a value in this cell that represents the amount of time they want to turn the injector on (pulsewidth) or Fuel in pounds per hour. The FAST XFI can use either Pulsewidth or Pounds of fuel per hour. In this mode, the tuner is basically using the system like electronically controlled mechanical injection. This is under utilizing the potential of modern EFI systems because it cannot make accurate corrections to engine fueling to compensate for changes in atmospheric conditions. Alpha-N is a direct way to tune an engine for a given set of conditions but if the conditions change, guess what, you have to re-calibrate or re-tune your fuel tables. The XFI offers Barometric pressure and air temperature correction tables that are capable of trimming the fueling when these conditions change but this requires the tuner to manually setup these tables, and throws another unknown variable into the tune vs Speed Density which automatically and accurately changes fueling to compensate for atmospheric changes.

Speed Density fueling strategy uses atmospheric pressure (measured by the MAP or Manifold Absolute Pressure sensor) and air temperature to calculate the density of a given volume of air in your engine at a specific set of atmospheric conditions. The ECU uses the same standard constant laws of physics about the relationship of the density of air to the Pressure and Temperature as your weather stations and all Dynos use. 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. The displacement of the engine is a constant so the VE or Volumetric Efficiency is the variable that you use to properly calibrate or “tune” your system. The VE is a measure of how well the cylinders are being filled compared to their potential volume. 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). The VE of the engine does not change unless mechanical parts are changed. Your engine will flow the same VOLUME of air in Denver as it does in Gainesville, the air is just more dense in Gainesville therefore it needs more fuel to get to the same Air/Fuel ratio. Once your VE table is properly calibrated, you have an accurate Air Flow table for your engine. The benefit to the racer is that once you have properly calibrated your VE table, you will not have to re-tune or re-calibrate your fuel table from track to track anymore. The ECU will do this for you. Just so you know this is not some un-proven theory, with his permission, I want to provide a real world example of a successful race program that relies on True Speed Density. Jeff Dona runs his SS LT1 Firebird in Speed Density, Open loop and he has run his car in 1.015 to 1.095 correction without changing anything in his tuneup and the actual Air/Fuel ratio never strayed more than 2% from the target Air/Fuel ratio. This allows a racer to focus on other aspects of his race program without worrying about his or her tuneup every time the engine goes from the dyno to the track or from track to track.

Some EFI manufacturers offer a hybrid Speed Density mode that allows the tuner to enter fuel in pounds per hour instead of Volumetric efficiency. The problem with that is that you lose the benefit of TRUE Speed Density as you have overridden the ECUs potential to accurately compensate for changes in atmospheric conditions. The tuner can set up some compensation tables but why guess at the needed changes in fueling when TRUE Speed Density uses known laws of physics to compensate accurately.

The engine does not know or care how the ECU decides how much fuel to inject into it. It is possible to have two tunes for an engine, one in Alpha-N and one in Speed Density and they both inject the exact same amount of fuel at all loads and RPMs, the only difference is, when the air gets better or worse, the Alpha-N tune will still provide the same amount of fuel while the Speed Density tune will compensate properly. I am not talking about the engine running richer or leaner, I am talking about the fact that as the air gets worse, it takes less fuel to get to the same Air/Fuel ratio!

I am not trying to put down anyone who uses Alpha-N fueling strategy as I know people who do so successfully. If you do use Alpha-N and are happy with your program, stick with it. I just wanted to provide some facts and information on how Speed Density uses modern EFI to its full potential.

I welcome comments and questions.:D
David Page
Fuel Air Spark Technology

Re: EFI, Alpha-N vs Speed Density fueling Strategies
 

I can see how using a Speed Density map would get the last bit of performance on a heads up run, or in a no-breakout index class such as Comp.

But, if the afr is changing while going down track, doesn't that make it harder to predict an accurate dial in? Whether using a weather station formula, or one's own ratio of performance loss or gain per 100 feet altitude change, don't these calculations assume the afr is not being adjusted from run to run, let alone during the run?

Re: EFI, Alpha-N vs Speed Density fueling Strategies
 

I run mine in Speed Desity. I consider AlphaN the easy button. They can tune it on the dyno, and ship it, leaving adjusting for conditions to the ownner.
Set the break points in the V.E. table right and once you see the Baro that causes it to reference a different row in the V.E. table and get the fueling right you won't have to change anything when you get in that air next time. First time I went to Great Bend KS mine was running 4th row down. Never had before (higher elevation) so dialed it in. Next time I went there it was fine. Once you get it dialed in, you seldom have to change anything for weather changes. I have never run mine in AlphaN. Been Speed Density for ever.

Tony, why do you think the air/fuel would be changing going down the track? I don't get your reasoning.

Re: EFI, Alpha-N vs Speed Density fueling Strategies
 

The above description says it's using the MAP sensor to determine conditions. Doesn't that mean it's adjusting any time the engine is running?

Re: EFI, Alpha-N vs Speed Density fueling Strategies
 

Why would that change? It changes a little in the top of the gears, but seldom to a different cel at a given RPM. My A/F stays dead nuts one end of the track to the other, unless I want it different. Mine does like it a little different at higher RPM, so I put it there.

Re: EFI, Alpha-N vs Speed Density fueling Strategies
 

Tony, if the atmospheric conditions are changing while you are going down track enough to affect performance, those conditions are to blame for you missing your dial in, not your EFI system. There is nothing an ECU can do to offset those changes, it can only provide the correct amount of fuel to maintain a consistent Air/Fuel ratio so that the change in performance is proportional to the change in air. In reality, it is doubtful that the air can change enough in the 9-10 seconds to cause you to miss your dial in.

Re: EFI, Alpha-N vs Speed Density fueling Strategies
 

Tony, the A/F ratio is not being adjusted, the fuel is being adjusted to keep the A/F consistent in spite of air changes. The MAP sensor is constantly registering changes because it is reading the "atmosphere" inside the manifold and that is what the engine sees. It's all about maintaining a consistent, or at least a desired Air/Fuel ratio.

Re: EFI, Alpha-N vs Speed Density fueling Strategies
 

Makes sense- So, if AF is being maintained more accurately, would you say it makes for more consistency, and/or more predictability vs. Alpha-N and carburetors?

Re: EFI, Alpha-N vs Speed Density fueling Strategies
 

In my opinion, yes. But this is especially true going from one track to another .

Re: EFI, Alpha-N vs Speed Density fueling Strategies
 

David, is there any particular reason aftermarket solutions aren't MAF based? These new Mustangs I've been working with that also run closed loop fueling at WOT just crank out beautiful consistent fuel curves every time. It's so easy and they look so good it makes it look like I am better at this than I really am.

Re: EFI, Alpha-N vs Speed Density fueling Strategies
 

MAF sensors do a very good job of measuring airflow but their weakness in a race application is that they are only accurate over a very narrow range so it would take a sensor/housing designed specifically for the application. In the case of stock and super stock, we are flowing much more air than a stock engine therefore we have moved out of their effective range. Also, since these classes are throttle body limited, anything in the airstream before the throttle body is undesirable. In stock or modified street vehicles, Mass Air systems do a great job. They just have no place in this type of racing in my opinion.

Re: EFI, Alpha-N vs Speed Density fueling Strategies
 

I think MAF is a better deal. I work with GM's factory systems every day, and the MAF system is much more forgiving for weather, elevation and engine combo changes. Different manifolds, headers, collectors, going to Denver, seldom require any tuning changes.

On many cars, (like mine) where would you put it? Going to put an air filter on it? The GM (don't know about Ford) sensors have heated wires. They glow red when running. They have to remain perfectly clean, or the calibration changes. Then you usually end up with elbows in the ducting to accommodate an air filter. You can't have dust, and who knows what else in Louisiana (Joke) cooked on those heated wires.
Speed Density done correctly compensates pretty well.

Re: EFI, Alpha-N vs Speed Density fueling Strategies
 

For odd ball combos (2.3 ford turbo)that do you do for a cal map to start with if one is not available ? Or do most of the company like FAST have a start up cal map on file you just need to call when ordering the the ecu .

Re: EFI, Alpha-N vs Speed Density fueling Strategies
 

David,

You mentioned a racer that is running in speed density open loop. If it is open loop, how is it that the ECU is compensating for air changes? I thought open loop meant that there was no compensating going on.

I run the "classic FAST" system in Alpha-N mode open loop. With that setup, closed loop would use the o2 sensor to correct the fuel. In open loop it doesn't. How is this different with speed density? Does speed density use the o2 sensor at all?

Also, I was told that even though I run in open loop Alpha-N that there are tables that I can't see that are compensating for barometric changes much like a carburetor does naturally. Is this true?

Re: EFI, Alpha-N vs Speed Density fueling Strategies
 

Ken, one of the beauties of Speed Density is that since it is really based on airflow, it is relatively easy to start with a basic VE table and run it in closed loop and tune it in based on the O2 correction that you see in your datalogs. There are a lot of baseline tuneups in our C-Com software to chose from and while none of them are specifically for a 4 cyll, it would be very simple to start with one of those and make a few changes to give you a close starting point. I would be glad to put a tune together for you, send me a message if you are interested in this.
David Page
FAST

Re: EFI, Alpha-N vs Speed Density fueling Strategies
 

Ricki, Closed loop is a separate consideration.

For those who aren't familiar with the term, Closed Loop is a process where the system compares the actual Air/Fuel ratio read by the O2 sensor to your programmed target A/F ratio and makes corrections to the fueling based on the difference. In Open Loop, the system still reads the Air/Fuel ratio from the O2 sensor but it does not make any corrections.

You can run Alpha-N in Closed Loop or Open Loop and you can run Speed Density mode in Closed Loop or Open Loop.

The compensation I am talking about is not really a correction. In speed density, the air pressure and temperature are taken into account "on the front end" of the ECUs fueling calculations. In Alpha-N mode with FAST systems, there are corrections made in the ECU behind the scenes for Air Pressure as long as you have a MAP sensor plugged into the harness with the hose barb of the sensor open to the atmosphere and an Air Temp sensor plugged in. Even in Open Loop, these corrections are going on behind the scenes without any input from you. If you do not have a MAP sensor or Air Temp sensor in your system, the ECU just assumes standard temp and pressure and you are using the system like a mechanical carburetor of mechanical injection.

Re: EFI, Alpha-N vs Speed Density fueling Strategies
 

so which would make more consistent power in a stocker combo batch fire or sequential in your opinion ?

Re: EFI, Alpha-N vs Speed Density fueling Strategies
 

Sequential injector operation offers the most precise fueling. That being said, as injector duty cycle increases (meaning the injectors move closer to just being wide open), the difference between bank to bank operation and sequential operation diminishes. Now, selecting a large injector that will operate at a lower duty cycle gives you the room to "time" the injector open time in relation to the opening and closing of the intake valve. Operating in sequential mode also gives you the ability to add or subtract fuel to or from individual cylinders to find an optimum balance of Air/Fuel ratios from cyll. to cyll.
Now these are very small potential gains and there are no hard, fast rules to go by. If you have unlimited time and are willing to spend the time on the dyno testing every possible combination of injector size, injector opening timing, and individual cylinder corrections (and the XFI 2.0 system allows all of this) then I am certain you could find some power.
That being said, I have seen racers run their systems in bank to bank with great consistency and run in the 1.25 under range any time they want.
I guess the short answer is that it is likely that you can find some power gains by switching from bank to bank to sequential but there is no guarantee that the gains will be worth the investment required to properly test to find the optimum parameters.
I have not seen any evidence that sequential fueling offers any more consistency over bank to bank.
Now, sequential definitely offers better idling, drive ability, and part throttle operation so if I were running a stocker, it would definitely be in sequential mode.

Re: EFI, Alpha-N vs Speed Density fueling Strategies
 

David, I just wanted to say thanks for sharing and taking the time to post on this topic. As a current FAST customer, not only do you have a great product but the customer service that you provide is second to none and this post is yet another example of the service/tech support that your team provides.

Thank you and see you at the track in 2014,
Nick Morris
SS 3718
GT/FA

Re: EFI, Alpha-N vs Speed Density fueling Strategies
 

How do you add a cam sync sensor to a GM LT-1 from the mid '90s ?

I raced one and used bank to bank but my Accell Gen VII could run in sequential. I ran a crank trigger with a gutted optispark dist.and was not sure how to add a cam synch sensor.

I struggled to tune my car on my own and really needed a pro's help and some dyno time.....running in sequential sounded like it would make more sense.....

Re: EFI, Alpha-N vs Speed Density fueling Strategies
 

I used an Opti for a while. Not gutted. It can be done with the Opti electronics, although I nener tried it. Some of the Stocker guys are doing that. I now use an MSD dist with cam sync. I didn't find sequential to be the huge HP deal some make it out to be. Still, 5 to 7 hp is worth the effort. I had 2 cyls 9 & 10% lean, the rest were 2 & 3% off.

Re: EFI, Alpha-N vs Speed Density fueling Strategies
 

For reasons David mentioned, believe there is potential with sequential but not necessarily in the range we would assume.
Upper RPMs would be little gain unless all the legwork was done and then it may be minimal for the cost and effort. But consider what we pay for 5 HP..........
The greater benefit should be in low / mid range RPMs getting the car moving and to the 330. When foot-breaking the effort may be worth it making the car easier to drive.

Re: EFI, Alpha-N vs Speed Density fueling Strategies
 

My converter flashes to ~6200, my cylinder- to-cylinder air/fuel imbalance was a little different, but no worse, at 6000 than at 8500.

Re: EFI, Alpha-N vs Speed Density fueling Strategies
 

Thanks Nick. I am truly blessed to do what I enjoy for a living.

As for a cam sync on an LT1, there are several ways to accomplish this;
1. Use a distributor body w no cap/rotor, remove seven of the reluctor teeth and use the remaining tooth as a cam position sensor.
2. Use a distributor with a built in cam sync like Ed suggested.
3. You can use the factory Optispark as a cam sync with the following modification- use some metallic tape (the silver, aluminum stuff) and tape over all the slots in the Opti disk. Then, locate a slot in that wheel that will generate a single signal somewhere between 130BTDC and 60BTDC (for a FAST system, not sure about others) poke the tape through this single slot in the wheel. This sounds kind of hokey but it works!
4. Fabricate a custom aluminum wheel that will mount to the Opti shaft and a bracket to hold a pickup.
All of these obviously assume the use of a crank trigger for a crank signal.

To clear the air on the sequential fueling question, I do believe that there is power to be found in properly utilizing Sequential fueling, but it takes specific testing to find this power.

Re: EFI, Alpha-N vs Speed Density fueling Strategies
 

Here is a funny story...

When I first ran my LT-1 Stocker....I misunderstood how to enter the firing order when running bank to bank...

I entered the std Chevy F.O.

Engine sounded like a boat and ran worse than one....LOL

I discovered my mistake pretty quickly and moved on....

Was at my local track one day and heard an LT-1 Stocker drive by me and heard the same sound......I went over and asked the owner a few questions and told him I think he made the same mistake....firing order entered was not correct for bank to bank operation.....

I know most people go to a pro for a tune up and it is well worth the time and money to do.......I definitely regret not going that route with my LT-1

Re: EFI, Alpha-N vs Speed Density fueling Strategies
 

Don't know how many of you follow the Engine Masters contest but the 3/14 issue of Pop Hot Rod has an article on the engine Jon Kaase won with this year. After reading it I decided I was overdue for a lunch visit so I went to the shop.
The engine was a Ford 409 4valve mod motor. One cool thing was the set of 16 tube headers, but the interesting part of the FI system was the injector location. I am only going to tell what is in the article since I don't know how much of what I was told is public but the injectors are about 1/2 way up the runner and pointing toward the plenum. There were several locations tried but this was what went to the contest. Jon said it was hard to tune and lower rpm was not smooth. I think the dyno runs were from 3500 to 6500 so you can't give up bottom for top end power since they average the numbers over the range. Made over 800 on VP100 but was tuned for 720 at the contest.
Not something that can be done in a Stocker but in Superstock it could be done.

Re: EFI, Alpha-N vs Speed Density fueling Strategies
 

Have heard of and read a few articles on this.
Injecting fuel behind the valve may not be the best location for atomization and mixture. Moving injector up the intake runner may allow better fuel distribution in the air stream. Pointing the injector into the air stream would seem to force the issue.
Some high HP engines have two sets of injectors: at the valve and up in the runner.
Has anyone played with direct injection in a HP application?
Sounds like fun.

Re: EFI, Alpha-N vs Speed Density fueling Strategies
 

Direct injection is being used this year by the Chevrolet factory teams at LeMans in their GT-1 Corvettes. There is a detailed story about it Engine Technology magazine, a British publication. If anyone's interested, PM me and I'll look for the back issue.

Also, USAC midgets use 4cyl engines with a 23 degree SBC head. They use a nozzle in the intake manifold, and drill a hole from the exhaust side of the head, into the intake port pocket, and call it a "down-nozzle". Every GM powered car in the class seems to do this. Kinzler does the drilling, and provides the the injection system, which looks like old mechanical Hilborns, but are fairly sophisticated electronic controlled units.

Re: EFI, Alpha-N vs Speed Density fueling Strategies
 

I had a sprint car during the 1980s . We all ran down nozzles then. That has been around forever. Was still mechanical back then.
The big deal, we thought, was getting all that methanol out of the intake and port runners, making room for more air. Takes roughly twice the methanol as gasoline, which = less air. The nozzles were aimed to shoot fuel past/under the intake valve when open. Thing about those older mechanical systems, there was no injector pulsing, as with EFI. Constant stream of fuel meant an intake bowl full of fuel when the valve did open.
Brodix, AFR, etc, sold/sell their heads drilled for down nozzles.

Re: EFI, Alpha-N vs Speed Density fueling Strategies
 

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?

Re: EFI, Alpha-N vs Speed Density fueling Strategies
 

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.

Re: EFI, Alpha-N vs Speed Density fueling Strategies
 

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.

Re: EFI, Alpha-N vs Speed Density fueling Strategies
 

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!

Re: EFI, Alpha-N vs Speed Density fueling Strategies
 

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.

Re: EFI, Alpha-N vs Speed Density fueling Strategies
 

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.

Re: EFI, Alpha-N vs Speed Density fueling Strategies
 

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.

Re: EFI, Alpha-N vs Speed Density fueling Strategies
 

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.

Re: EFI, Alpha-N vs Speed Density fueling Strategies
 

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.

Re: EFI, Alpha-N vs Speed Density fueling Strategies
 

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.

Re: EFI, Alpha-N vs Speed Density fueling Strategies
 

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!