FMU worthless with larger injectors?
 

Here is what is it and has.
95 GT :vortech supercharger with 8psi, 155lph T-rex fuel pump, vortech FMU, pullies, X-pipe, shifter, broken vortech BTM ignition, stock motor

Here is what is happening:
12psi pulley upgrade, 30lb injectors with Mass Air meter, 75mm throttle body, Trickflow Street Intake, new ignition box with BTM, 3.73 gears.

Will this be stable for a stock bottom end and should I ditch the FMU? If so what hoses do I need to reroute and/or bypass? Thanks, any other suggestions for these kind of upgrades will be very helpfull. I am limited on funds since all of this is already bought and in the garage, I know that compression should be lowered before going higher on boost, but will I be ok with what i have for everyday driving?

I cant help you with the technical part of your question and I have "0" first hand knowledge of superchargers.

But what I can tell you is I am a member of several mustang boards and have seen this question many times. By looking at your combo I would say you would get better performance and driveability without the FMU.

Most people ditch the FMU in your situation.

Later,

Re: FMU worthless with larger injectors?
 

The 30's and the fmu work pretty well if your on a tight budget. With the upgrade in boost, I would definately ungrade the in-tank pump to a 255 (Walbro GSS340). The 155 just isn't going to keep up. Fmu's are good for people who don't have the time, money, or avaliability to a proper dyno tune. Your setup would make more power with a slightly bigger injector, no fmu, and a good tune than it would with the fmu in other words. Most guys want to optimize their setups, so they get rid of them and get bigger injectors.

As far as the 12 lbs being safe on a stock bottom end, as long as you don't have any detonation, you should be fine. I've seen more than that ran on a stock bottom end, just not for long if you know what I mean.

If you ditch the FMU, I'd also suggest the Walbro GSS340. The 30's should be ok running 12 psi.

Well, we will be putting the car on a Dyno upon completion so I assume we will see all of the air/fuel ratio's and so on and make adjustments accordingly. Looks like we will be ditching the FMU then and stepping up on the fuel pump. Thanks everyone.

Re: Re: FMU worthless with larger injectors?
 

Ditto,
get a larger intank pump, keep fmu until you decide to get larger injectors, and get a dyno tune.

Dan
95 rio red cobra #2021

It's actually an external T-rex with aftermarket lines, but I have just bought the 255 external to replace it.

another idea...
 

42 lb-ers with a aftermarket chip in lieu of a FMU.
FMU is just too inefficient.
I only run 8lbs (daily driver) so I have to keep it maintainable...
Oh yeah, a 255 internal and a T-rex will be okay too.
Good luck...

Ok

The FMU will work well with the 30's; just remember that when you go to static fuel pressure (manually set) it can be by passed.
Only if statically set it lets say for instants at 50 psi... At the track I would set it at 50 psi. Before I left I would set it back 38 with no vacuum. That was back the day using a cartech unit.....

Thanks, will test and tune and find the best settings. thanks for all the advice.

You can lose the FMU, but you must consider a few things before you do this.

1) Unless you have an aftermarket, boost compensating fuel regulator (usually the adjustable kind), you will have the equivalent of 26 psi fuel of pressure at full boost. How so? You'll have 12 psi pushing back on the fuel coming out of the injector. So:

38 psi stock minus 12 psi boost = 26 psi. That offsets the benefit of big injectors.

Boost compensating fuel regulators will add 1 lb. fuel pressure for every pound of boost. This is what you should look at if you are not going to run an FMU.

2) No FMU may work okay with a near stock motor, but if you add heads, exhaust, intake, and cam, you may want that extra fuel that the FMU delivers.


Just a few thoughts.

Russ