Fuel Pressure vs power

[CaptPhil]

I put an LBZ fpr in my truck and changed the fuel pressure tables to take advantage of the increased capability.

Say you have two tunes that are virtually identical, only one has fuel pressure at 165mpa (24kpsi) and the other is 180mpa (26kpsi).

The first tune (165mpa) holds 19.5-20kpsi through the first four gears, and a solid 21.5kpsi in 5th.
The second tune (180mpa) holds 21-22kpsi in the first four, and holds 23kpsi in 5th.

The second tune should make more power, but is this still going to be the case with a 5kpsi drop in rail pressure? Even though the actual rail pressure is higher than it was as a 165mpa tune?

Why does it lose more rail in 1-4 than it does in 5th gear? my #4 tune (2950pw) is rock solid at 26kpsi in 5th gear, but drops in 1-4 to 23kpsi.

 

[Ne-max]

Rpms are a huge factor here. 1-4 your trucks still shifting. 5th gear its rpms are going up keeping the cp3 spinning faster. Did you data log and see if you are comparing numbers at the same rpms?

 

[Muff]

What do you mean by the 5k drop in rail? Where is it dropping 5k at maybe i am just reading it wrong.

 

[CaptPhil]

What do you mean by the 5k drop in rail? Where is it dropping 5k at maybe i am just reading it wrong.

Drops to 21k in gears 1-4 when commanding 26k.

 

[CaptPhil]

Rpms are a huge factor here. 1-4 your trucks still shifting. 5th gear its rpms are going up keeping the cp3 spinning faster. Did you data log and see if you are comparing numbers at the same rpms?

yes, these are all from a log.

I understand that it is still shifting, just found it interesting that the rail pressure will lag a bit until it hits 5th, then it is solid.

 

[Muff]

Higher the actual rail = more power, Even if its commanding 26. Im no tuning expert though.

 

[JoshH]

What is the pulse width in each tune?

 

[S Phinney]

The CP3 is not a constant fuel volume. You have less fuel available at lower rpms and as it increases fuel available increases. You go through the gears faster and in fifth gear rpm increase is at a narrower range so more fuel is available to feed the system. This is called recovery when the pressure drops and then go back to commanded numbers. Almost all trucks have a time that desired and commanded are not matching.