EFI, Alpha-N vs Speed Density fueling Strategies

[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.....

[pbp1]

Yes Mack, this is a 2.0 feature and it is automatic, you don't have to do anything to turn it on.

[Mack Reeves]

Originally Posted by pbp1

Yes Mack, this is a 2.0 feature and it is automatic, you don't have to do anything to turn it on.

That is a feature I had not known about.. Another reason for updating to 2.0. Thanks for the information...