Why 42 lb Injectors??

I finally got my ATI Procharger kit in. I ordered the 8 psi intercooled kit for my '96 Z and upon reading the instructions for it Procharger says I can get away with the stock 22 lb'ers I just have to adjust the FMU they include in the kit. From what I gather you hook it up to the return line off of the regulator and when you go up in boost it slows down the rate of fuel returned so the pressure goes up in the fuel system itself (??). Well my question is how come so many people put 42 lb's and up in their cars with the same kit? Am I missing something? I was thinking of just going with 30 lb injectors to give my self a little lee-way and not worry about the stockers maxing out. Does this sound like a plan or should I just go with 42 lb's? Thanks

Myles

FMUs are not consistent. They make the mixture very rich so the sc won't destroy the stock pos pistons, but they do it incostently at times. The proper way to tune a sc car is to ditch the FMU and use the proper size injectors and normal fuel pressure. If you don't plan to try to tune the car and are happy with how it runs, then just keep the setup you have. If you want to optimize the power you have with the new sc, then throw some more money at it and get the right size injectors. Blower cars are fuel pigs. Ooooh Ra - Semper Fi-

Actually FMU's are usually pretty consistent, but.....not optimal. The adjustment will not be optimal over the entire boosted range so some areas will be richer than required for best safe power so other areas don't end up too lean. FMU's do work your fuel system harder when under boost due to the high pressures they introduce. If you have the tuning capability go the injector route. Absolutely. The FMU is there so anybody can install a supercharger kit and enjoy the performance without the expense of injectors and electronics.
In a bit of weirdnes I recently installed a kit on an LT4 Vette and actually made a bit more power with the FMU only setup than the injector-LT1 edit tuning done afterwards (it was a safe conservative tune).The moral of the story is that you aren't leaving a bunch of power on the table with the FMU, but optimizing the tune could provide some more performance and ignition retard.

Some injectors don't perform well under elevated fuel pressures. They can lock up causing fuel issues. Many guys switch to the SVO style injector to eliminate this lock up issue.

It hasn't shown to be a problem with our kits, but I readily admit that at some point they will refuse to respond.

So what I gather then is to not even install the FMU, and just go with 42 lb injectors and have the computer reprogramed for them? If this is the case then will the stock regulator be sufficient still? Or should I get the injectors and install the FMU but set it so it only works towards the top end? Thanks for all the help and replies so far.

Myles

The stock regulator will be fine. I still run it and 42# injectors.

Bill

Email me I got a used set 50s about 10K mile on it for sale. Bruce383@Rochester.rr.com