EFI, Alpha-N vs Speed Density fueling Strategies

[pbp1]

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.

[Tony Curcio]

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?

[pbp1]

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

[kdanner]

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.

[pbp1]

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.

[Ed Wright]

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.

[ken robinson]

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 .

[SS3718]

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

[Rich Biebel]

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.....

[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.