I guess I will throw my 2 cents in here. I put most of this out there as you only mentioned the tank and ECU, but not what engine, what injectors and whether or not it is naturally aspirated or a boost application. The basic question you asaked has been answered here. I am just adding more info that will hopefully help you out as you move along. I apologize ahead of time as I may bounce around a bit as my thoughts come through.
I do a few LS engines here and there
and we are always in the 60 PSI fuel pressure area as that is what the factory is based on. You can run 45 PSI which is, as mentioned, a very common EFI pressure since the L98 days.
There are exceptions and one is fuel injector choice. Most of the common Bosch, Siemens and GM replacement injectors work great at 60 PSI and even more. If you use the RP or Rochester Products injectors from GM like those in an L98, Or the Holley RP injectors, I have seen them begin to lock up and begin to not work over 48 PSI. I found this out on John Parson II Much Nova when trying to go from 45 PSI to 60 PSI.
I personally like the higher pressures for better fuel atomization and, in most of my cases, what the injectors were designed for.
The factory ECM's as well as FAST XFI and Accel DFI, when equipped with an oxygen sensor, preferably a wideband, will adjust A/F to a specified AF ratio. The factory ECM's can adjust as much as 50% up or down and the aftermarkets usually 25% up or down. It is always best to tune any system to as little as much correction as possible for the best transitions on accel and decel throughout the RPM band. Since you mentioned you had an Accel Gen 7, hopefully you have the additional wideband for it also. Big help for sure.
Changing fuel pressure will definitely change a tune and though making the proper changes to the base calibration for the fuel pressure or injectors, it should never be assumed that that change will m ake it 100% correct. Always verify with proper equipment for sure. If it was correct before the pressure change, it should be close after the pressure and calibration change. If it very far off then something does not like the pressure change.
Now, most aftermarket systems with an oxygen sensor, again preferably a wideband, will adjust fueling on the fly up or down based on the allowed amounts set in the program, but it will not learn and constantly be changing everytime it goes though any certain RPM and load range that is not 100% correct for what is commanded.
Factory ECM's have a learning feature called long term fuel trims which over time the ECM learns these compensations over time and will adjust automatically as the comes into a learned are of the RPM and load map. This drastically helps the transitions, but still not 100% perfect.
Now there are aftermarket systems such as the new Holley packages have a very fast and effective self learning system. Accel does also, but not as effective and still takes good tuning.
It was not brought up here, and not an issue with aftermarket speed density systems, but with a factory EFI such as a late model LS engine using a MAF sensor, air intake design and tube diameter as well as MAF placement in the intake tract can drastically alter a tunes A/F base and compensation.
Mike Norris
Brian Hobaugh SCCA National Tour June 2014
First Hemi 'Cuda Convertible Ever Built
Short clips: Goodguys Pleasanton autocross and pit videos
pressure vs flow
Linear Mode
