Well, for all you folks doing prom tuning, I have a question.

It seems to me, that having fuel pressure change throughout the RPM range simply adds another variable to an already complex equation. Would it not make life easier having fuel pressure remain constant? Thus, removing one variable from the equation?

Thanks

 

Not really it's more then compensated for by increasing the dynamic range of the injector.
I've been know to use two regulators on a TBI to increase the dynamic range of them. With one being vac referenced, there is too much dynamic range, so a second one that wasn't vac referenced was added to clip the range some.

It's not really a variable anyway. The couple K/Pa difference from baro changes isn't a large change.

 

It is precisely because it alters the characteristics of the injector that I ask.

It would seem to me (and I may be way off base here, not speaking from direct experience......) that having fuel pressure remain constant throughout the RPM range would make tuning changes more predictable. It would also lessen the impact of, say, a cam change. (since the cam will also alter the engines manifold vacuum characteristics.......)

I may be talking out my a$$, but, as I am planning to get into this REAL soon. I want to make my life as easy as possible. (Yes, I am lazy......... but, I love to work on my car)

Thanks Grumpy. I note that you live in Dayton. I manage to make my way down there on occasion, perhaps if there is an event in the not-too-distant future, we could meet..... I would welcome the opportunity to talk with other folks that enjoy this passtime as much as I do.

 

Guess you've never heard of the EFI POWWOWs that I host 2x a year.

By making the FPR vac compenstaed it's actually simplier to tune.
It makes the baro correction less of an issue.
When you get to actually looking into the tables from a TBI to MAP TPI they really aren't that different.

I've tried even vac referencing none referenced systems and it makes for an interesting final result <g>

 

POWWOW? Hhhhmmm. Let me know when the next one is.... You can email me at brianp@aix.cc

Thanks

 

Also, the vacuum on an FPR helps reduce the amount of fuel that is delievered to the injectors in idle, light throttle and deceleration. There is a limit of how short the injector pulse width will go. The vacuum's lowering of the fuel pressure in these circumstances helps the ecm keep from needing too short of a pulse width.

Tuning the VE Tables is far simpler than people think.