Stupid Doubt about FMUs
 

All the FMUs Im looking at say either 8:1 or 10:1 i.e. for every 1 PSI of boost fuel flow goes up 8 or 10 right?.

Then other regulators say Adjustable from 30psi to 120 psi.

But my requirement is I need the Fuel to flow at 4 PSI when not under boost.
And then when boost starts it needs to go up like 1:1

How do I make sure the FMU I get will work for my application

Re: Stupid Doubt about FMUs
 

You get a standard pressure referenced regulator with 1:1 ratios and the right spring for 4psi.

Re: Stupid Doubt about FMUs
 

unless you're carbureted you don't want fuel to flow at 4 psi, your injector spray pattern would be ---- and the car probably wouldn't even run.

Re: Stupid Doubt about FMUs
 

It is carbed
till 16 PSI then Extra Injectors and a speprate system take over. But lets not confuse the issue for now lets just say yes its carbed.

Its working fine till arround 10-14 PSI then my home made hand built FMU takes a Dump. I can not build another one or just put some money down for something that just works.

Probalem most all the FMUs I see start at 30 PSI and are adjustable from there out.
Where as I need it to be 4-6 PSI and then 1:1

I got a brother offering me a unit for 85$ in the HMT classfied section will it work for my app.

Re: Stupid Doubt about FMUs
 

FMU's suck herpes infested dick for fuel injected apps

Re: Stupid Doubt about FMUs
 

Ron Chinoooooooyyyyy!!!! :)

If you go to Jegs or Summit (dunno if they ship to your part of the world) then you can find 1:1 ratio "FMU" under their carb section. I imagine a stock fuel pressure regulator off of any fuel injected vehicle can be made to wok for you, as they are 1:1 "FMU"

Re: Stupid Doubt about FMUs
 

Thanks Bro thats just what I did got an FMU off a regular fuel injected car. Opened it up played with the spring to get my base 4 PSI and then let the boost handle the rest.

Its working quite ok actually.
Maybe Im just thinking if I pay for a fancy looking setup it will work a little better.
Will chk the sumit catalogue.

Re: Stupid Doubt about FMUs
 

yeah you don't need an fmu per say, most aftermarket, vacuum refrenced, fuel pressure reglators will raise fuek pressure 1:1 which is what you want for a carbed setup

Re: Stupid Doubt about FMUs
 

the aeromotive fpr is like 2:1 i think ???

Re: Stupid Doubt about FMUs
 

Ok here is the problem may need to put the brain in gear to follow.

A stock FMU yes will be 1:1 but Ive gone and moded the spring to give 4 PSI when not boosted.
THis has kinda rocked the boat I suspect.

The fuel pump puts out 40 PSI whcih should be good enoughf for a carbed setup.
Non boosted is fine steady 4 PSI. Then we go to boost. The fuel pressure scales right up to 25 PSI thats fine. Because the FMU has a return line. But so does the carb so when the bowl is full the excess fuel flow returns via the carbs return line.

But whats hapening at very high boost levels i.e. we have gone upto 22 PSI with WG disconected. the car just seems to run out of gass. Give it a second to fill up the bowl and she is ready to go. So Im thinking new FMU or maybe increase the dia of the outlet pipe from the FMU the pressure will drop but the flow should go up right.
Logic is even at 24 PSI the pump only needs to be making 28 PSI to flow right.

Considering all the facors such as how pressure in the carb also effects flow thru the jets. The carb is doing a pretty decent job of keeping the a/f ratio ok.
Im using a narrow band with the LM9044V to track a/f and its showing a healthy range bwteen 12:1 to 14:1

Guess all ya young pupps are not old enoughf to have done too many Carbed setups eh! ;D