which is a better FMU at 12-20psi. 12:1 or 6:1?

 

At 12-20 psi you really need to move on beyond FMUs and get yourself a real fuel solution. 20 psi at 6:1 would get you up to around 180 psi fuel pressure; on a 12:1 it would put you at 270 psi fuel pressure. You're not going to find a pump or injectors that can deal with that. Get some big injectors, a 1:1 fpr, and a Hondata or similar ecu replacement.

 

the set-up is:400cc injectors, vafc, vortec bdfpr,aem fuel rail and holley in-tank pump 255lph at 90psi. a good st-up?

 

I would say something closer to a 2:1 ratio would be sufficient. You should be OK with max fuel pressures under 80 psi; I'm not sure if the 400s will be enough for 20 psi though. 12-15 maybe. I sure wouldn't want to push that high without a standalone management system. The old VAFC just isn't smart enough.

 

i know someone with that set-up and he does gtreat with it but he has 440's

 

If you're going to push it out to 20 psi with those injectors, you're going to be seeing high fuel pressures one way or another... from what I've heard about the walbros you might want to invest in a better high-pressure pump. But hey, all you got to do is start low and gradually raise the boost. If you're careful, you'll be fine.

 

Umm, what's up with the Walbro's? I've heard nothing but good about them personally, but I assume you've heard different dbman? And of course I just happen to have installed one last night.. go figure this would come up now.

 

It just seems that I've heard several reports of walbros taking a nose dive after 6 months to a year of use at extremely high pressures like we see with FMU setups. Maybe these were just isolated incidents that stand out in my mind though.

 

If you look on the box of a walbro pump you can clearly see that at 90 psi it flows 0 lph. You need a high pressure pump like a Bosch if you're going to use an FMU.

 

dbman96--where can you get a 2:1 riser or regulator. I am currently running a 3:1 on my Vortch FMU and I would like to boost higher but the fuel pressures hitting 80psi are holding me back as I dont want to boost higher and have even more pressure. I run a Power FC so I can increase pulsewidth under boost to accomidate the lower fuel pressures.

 

You have a couple of options - use a vortech super FMU or Cartech FMU which has an adjustable rise rate, or you can put a bleeder valve onto the vacuum line feeding your FMU (but put a check valve on it so it only bleeds boost, not vacuum). With the bleeder you can reduce the rise rate to whatever you want.