Okay, got a few questions relating to fmu's that I hope someone will answer. First off I don't need the "fmu is junk" replies. Please only reply if you have answers.

I understand that my stock fuel pressure is at about 40psi. A 12:1 fmu at 3psi will only be sqeezing the lines to make 36psi. Will that mean at 3psi, my fmu won't even be doing anything, since my stock car regualator is already squeezing the lines beyond 36psi? I'm thinking that if my stock regualator is squeezing the line hard enough to make 40psi, the fmu squeezing the line somewhere else softer then 40psi, wont higher my fuel at all. (to think of it in another way, imagine someone squeezing the line really hard, now you squeeze somewhere else on the line, it wont really higher the pressure)

I hear around that people say FMU's wont kick in until 5psi or so. Is this why? Becuase it wont be squeezing the lines beyound the stock regualator?

 

wrong wrong wrong, lol

at 3psi, its bumping fuel pressure to 76psi.

in all honesty im going to say this,,, fmu's are junk. sell it and buy a chipped p28.

 

Yeah you got that wrong...a 12:1 FMU will increase the fuel pressure 12psi by every 1psi of added pressure in the intake manifold. So 10psi would be 120psi more fuel pressure then the stock 34 - so 150+psi!!

FMU's are junk. Dont bother. Read up about uberdata or something along those lines...

liam

 

fmu's are so 1990's

 

but they work for minimal amounts of boost

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by hondaeg8 &raquo;</TD></TR><TR><TD CLASS="quote">but they work for minimal amounts of boost </TD></TR></TABLE>

And work well when used correctly. They are right, you can buy a simple chipped ecu for $175 but don't think you can't use a FMU. I ran one with no problems at all at 10-11psi daily and weekly track trips running 11's. Granted I went Hondata but only to run more boost safely.

 

we have gone 10's on fmu with a street car 440's and a vafc2 also did it with 370's. after a certain point it doesnt raise the pressure on high boost. it just rips the injectors wide open. its definately a 90's thing. that was before it was easy to have a management. i think if you are running low boost i would just use a fmu. its much cheaper and works rather good on lower boost levels

 

Well theoretically it should do exactly as it says. It should raise fuel pressure by 12psi above static fuel pressure (or whatever your stock FPR is maintaining) for every 1psi of boost. But we know it's a simple - and not very accurate - mechanical device. It MAY have a threshold of 1-2psi boost before it starts functioning properly. And it may "peak" above a certain boost where it cannot raise fuel pressure anymore. These are all variables of an analog mechanical device. Each company's FMU will also be different. So there's my input. Your results may vary. Your only true answer will come from installing a fuel pressure guage and observing the results for yourself.

BTW - I've run an FMU based setup on my stock engine for over 5 years. The motor never gave out. I finally got bored and pulled the motor to build it. When I put it back together I kept the FMU setup (it's reliable) until I was ready to move up to tunable EFI.

 

So all this crap I hear about FMU's wont kick in until 5psi is complete crap? Planning on using it for a 4.5psi setup, and wondering if it will work well for me.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by goingtobefast &raquo;</TD></TR><TR><TD CLASS="quote">So all this crap I hear about FMU's wont kick in until 5psi is complete crap? Planning on using it for a 4.5psi setup, and wondering if it will work well for me.</TD></TR></TABLE>

yes as soon as you hit 0 vacuum and go into boost the fmu is working. i went 2 years on an fmu and it worked ok pig rich but ok.

 

What are the dangers of going to rich at 5PSI with a 12:1?

 

why not just run a 9:1 or something smaller than a 12:1

 

At 3 psi a turbo would be more of a restriction than anything I don`t think you could make even 20h.p. 5-6psi is about the lowest practical amount of boost you can run