EFI, Alpha-N vs Speed Density fueling Strategies

[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.

[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!

[pbp1]

No worries, but now I understand why we are not on the same page. All of my information relates to VE based speed density only, not fuel flow based speed density (which is not speed density at all). As far as dialing in quickly, I think it is just a matter of what you are familiar with. I can dial in a speed density setup in 4-5 pulls, or 3-4 passes down track!

[GUMP]

Originally Posted by pbp1

No worries, but now I understand why we are not on the same page. All of my information relates to VE based speed density only, not fuel flow based speed density (which is not speed density at all). As far as dialing in quickly, I think it is just a matter of what you are familiar with. I can dial in a speed density setup in 4-5 pulls, or 3-4 passes down track!

Cool.

[Bobby Fazio]

Originally Posted by pbp1

No worries, but now I understand why we are not on the same page. All of my information relates to VE based speed density only, not fuel flow based speed density (which is not speed density at all). As far as dialing in quickly, I think it is just a matter of what you are familiar with. I can dial in a speed density setup in 4-5 pulls, or 3-4 passes down track!

I almost forgot, how about when you are on the two-step from an external ignition box? Do the TPS and map sensor think the engine is under load and start flooding the cylinders?

[pbp1]

Originally Posted by Bobby Fazio

I almost forgot, how about when you are on the two-step from an external ignition box? Do the TPS and map sensor think the engine is under load and start flooding the cylinders?

No, as long as you are not in Closed Loop while on the two step. That is a big no-no!
But whether you are in Alpha-N or Speed Density, the cylls that are not being dropped still need the fuel based on the load and RPM.
When you are on the 2 step, the engine load is still controlled by the throttle and measured by manifold vacuum. In other words, as long as you are on the floor, the engine is still under 100% or max load, the RPMs are just being limited by dropping cylls.
Now, the problem with being in closed loop while on a rev limiter (or two step) is that the dropping of cylls will cause the O2 sensor to read false lean and if you are in closed loop, this will cause a ton of un-needed fuel to be added as O2 correction.
The FAST XFI has internal rev limiters that you can use even if you are using an external ignition box. The benefit of using this feature is that closed loop is automatically turned off when any rev limiter is active, but this only works if you are using the XFI's two step feature. If you are using a different system that does not have this feature, or if you are using the rev limiter in your ignition box, you must set your closed loop activation RPM high enough to be above your two step RPM. Using the XFI's limiter is really nice because you can have closed loop active down low in the cruising around the pits areas and burnout areas. This helps the car run and drive better if you haven't had an opportunity to perfectly tune or "clean up" those driveability areas.

[Mack Reeves]

Originally Posted by pbp1

No, as long as you are not in Closed Loop while on the two step. That is a big no-no!
But whether you are in Alpha-N or Speed Density, the cylls that are not being dropped still need the fuel based on the load and RPM.
When you are on the 2 step, the engine load is still controlled by the throttle and measured by manifold vacuum. In other words, as long as you are on the floor, the engine is still under 100% or max load, the RPMs are just being limited by dropping cylls.
Now, the problem with being in closed loop while on a rev limiter (or two step) is that the dropping of cylls will cause the O2 sensor to read false lean and if you are in closed loop, this will cause a ton of un-needed fuel to be added as O2 correction.
The FAST XFI has internal rev limiters that you can use even if you are using an external ignition box. The benefit of using this feature is that closed loop is automatically turned off when any rev limiter is active, but this only works if you are using the XFI's two step feature. If you are using a different system that does not have this feature, or if you are using the rev limiter in your ignition box, you must set your closed loop activation RPM high enough to be above your two step RPM. Using the XFI's limiter is really nice because you can have closed loop active down low in the cruising around the pits areas and burnout areas. This helps the car run and drive better if you haven't had an opportunity to perfectly tune or "clean up" those driveability areas.

In your above reply you mention that FAST will turn off closed loop automatically when you are on the two step.. Is this in 2.0?? Where do you turn this on or is it totally automatic??? I have been told set your closed loop higher than your two-step RPM... But you do not get the clean driveability I the pit area and other low RPM areas... Thanks in advance for your help.....

[Rick Schillereff]

Ed I bracket race an 01 ls1 camaro and how and where are you putting the ITS sensor in the intake manifold. Thanks just trying to get better.

[Ed Wright]

Originally Posted by Rick Schillereff

Ed I bracket race an 01 ls1 camaro and how and where are you putting the ITS sensor in the intake manifold. Thanks just trying to get better.

If I am the Ed you are talking to, I had a bung made & welded into the back of the plenum of my sheet metal Hogan Intake. Screwed the IAT sensor into that bung.
The older "TPI" cars used a threaded IAT sensor, screwed into the Intake. I just bought an IAT sensor for a '90 Vette.
I just remembered this:
I originally put my air temp sensor in the tray I had in front of my throttle body (no longer used)
And was seeing large temp variations from the water box to third gear. Looked too large to me.
Moving that sensor to the rear of my manifold took much of those large changes away. Also made my air/fuel ratio more stable during a pass, and made my car more consistent, easier to dial.