I'm not quite in New England, but pretty close. Lots of experience tuning centrifugal superchargers on a Dynojet. Will have my new Mustang Dyno in about 2 months.
FMU should be 6:1 and stock mass air meter isnt going to work but I would think it would be pig rich and notlean. I know with my blower at 5psi and 30# injectors was way to rich. I will find out on saturday how mine is with H/C/i but I think that is to much injector without more mods. I could be wrong on this but I would start with a recalibrated meter.
Thre is no reason you can't get that thing running good with the stock computer, but you definately need more information to tune this car right.
You said the tuner "shut it off" at 4800 rpm. Do you mean he shut it off on the dyno or he set the rev limiter on the MSD? If you hit the MSD rev limiter, thats your backfire right there.
A lot of your info is unclear. You said "MSD FMU." MSD makes the ignition boost timing control. Not the FMU. The standard FMU disc is 12:1. A/F ration might have been 14:1. Either way you've got to recalibrate the FMU to match the injectors, probably with a 6:1.
Questions that need to be answered before you can go any further:
1) What is the calibration on the stock meter? Is it stock calibration or just a stock housing?
2) What fuel pumps(s) are you running.
3) Are you sure they are 30 lb injectors?
4) What is the base timing set at?
The tuner stopped running the car on the dyno when it hit 4800 rpm's.
1) It is a stock housing for the mass air meter. he said he "tweaked" it to match the 30# injectors. i assume he meant calibrated.
2) 255 walbro fuel pump with vortech t-rex supplied in kit
3) posititve they are 30#ers
4) base timing is set at 16*
FMU should be 6:1 and stock mass air meter isnt going to work but I would think it would be pig rich and notlean. I know with my blower at 5psi and 30# injectors was way to rich. I will find out on saturday how mine is with H/C/i but I think that is to much injector without more mods. I could be wrong on this but I would start with a recalibrated meter.