VAFPR and tuning

[CDeeZ]

Got a 27 PSI marine spring to feed my SBC that I'd estimate is ~400 FWHP. I have that spring in there and I'm now wondering what the best approach is to dialing in the fuel.

I read a LOT of mixed information on whether or not a VAFPR is worthwhile on a TBI setup. Should I get a VAFPR to bring AFR closer to stoich at idle or can I tune around without it? Idling pretty rich right now at around 10 or 11 AFR with the 27 PSI spring in there. Injector flow rate is setup in the tune as 91.

If it can be tuned without using a VAFPR, can this be done entirely on the VE table or should I be looking elsewhere as well?

[dave w]

The VAFRP is challenging! Most TBI computers do not a table to compensate for Kpa vs. lbs. / hr

For example, (I make up some numbers):
100 Kpa / 108 lbs /hr
80 Kpa / 91 lbs / hr
60 Kpa / 78 lbs / hr
40 Kpa / 65 lbs / hr
20 Kpa / 52 lbs / hr

Perhaps Dynamic EFI has a TBI computer system that has a table for VAFPR?

dave w

[Fast355]

The VAFRP is challenging! Most TBI computers do not a table to compensate for Kpa vs. lbs. / hr

For example, (I make up some numbers):
100 Kpa / 108 lbs /hr
80 Kpa / 91 lbs / hr
60 Kpa / 78 lbs / hr
40 Kpa / 65 lbs / hr
20 Kpa / 52 lbs / hr

Perhaps Dynamic EFI has a TBI computer system that has a table for VAFPR?

dave w

The EBL has provisions for both Vacuum and Boost to work with a VAFPR. Worked well for me with the Weiand 177 I ran. A Weiand 177 is one of the easiest ways to make a TBI engine crank out decent power and ALOT of torque.

[CDeeZ]

Yes the EBL would do it. I have a 4l80 in this truck so I was trying to stay with the 7427 pcm to shift it. So are we saying there is absolutely no way to fuel a tbi at 30 psi with GM PCM? Without it being stupid rich at idle?

[myburb]

If I am reading the post correctly you haven’t tweaked the ve table down. If that is correct take idle table and lean it out. Try open and closed to see what you can come up with. Until your table takes you below the min open/close time of the injectors you should have adjustment.

[dave w]

Yes the EBL would do it. I have a 4l80 in this truck so I was trying to stay with the 7427 pcm to shift it. So are we saying there is absolutely no way to fuel a tbi at 30 psi with GM PCM? Without it being stupid rich at idle?

WBO2 tuning is a must have tool for tuning a 30 PSI TBI with or without a VAFPR: http://www.gearhead-efi.com/Fuel-Inj...g)-Spreadsheet

dave w

[1project2many]

The most common way to account for AFR is in the VE tables. It may be possible to use excel and an existing correct VE table and scale it based on AFPR changes to pressure. I would ensure both open and closed throttle VE tables are adjusted. But without a correct VE table this exercise may be a waste of time.

[Fast355]

WBO2 tuning is a must have tool for tuning a 30 PSI TBI with or without a VAFPR: http://www.gearhead-efi.com/Fuel-Inj...g)-Spreadsheet

dave w

Over the past 16 years I have tuned plenty of engines without a wideband. It is not a must have by any sense of the imagination. I am not arguing that it is not a valuable tool because it is, but it is also not necessary.

I usually disable BLM and tune off the integrator alone. History average off the Integrator with the BLM disabled is a quicker way to tune than it is off BLM.